Publications by category
Journal articles
Marshall H, Johnstone R, Thompson F, Nichols H, Wells D, Joe H, Kalema-Zikusoka G, Sanderson J, Vitikainen E, Blount J, et al (In Press). A veil of ignorance can promote fairness in a mammal society. Nature Communications
Orledge JM, Blount JD, Hoodless AN, Royle NJ (In Press). Antioxidant supplementation during early development reduces parasite load but does not
affect sexual ornament expression in adult ring-necked pheasants Phasianus colchicus.
Functional EcologyAbstract:
Antioxidant supplementation during early development reduces parasite load but does not
affect sexual ornament expression in adult ring-necked pheasants Phasianus colchicus
1. The ‘parasite-mediated sexual selection’ (PMSS) hypothesis predicts that exaggerated male ornamentation could provide a signal to females of a males ability to resist parasites.
Empirical tests of the PMSS have been largely equivocal, however, which may be because most have not considered the role of early life-history effects.
2. Many sexually-selected traits are carotenoid-based. Allocation of dietary-derived carotenoids to sexual ornaments may trade-off with allocation to pro-inflammatory immune response and/or antioxidant functions, mediated by the oxidative status of individuals. Exposure to parasites can increase oxidative stress, so under this scenario sexually-selected traits indicate ability to resist oxidative stress rather than ability to resist parasites per se. Such life-history trade-offs, mediated by oxidative status of individuals, are particularly acute during growth
and development.
3. Here we use ring-necked pheasants, Phasianus colchicus, a strongly sexually-selected
species, to test whether supplementation with dietary antioxidants (vitamin E) can mitigate the effects of early exposure to parasites (the nematode, Heterakis gallinarum), via alteration of the oxidative status of individuals, and positively affect the expression of sexual ornaments at adulthood.
4. We found that vitamin E mediated the effect of early exposure to parasites on levels of oxidative damage at 8 weeks of age and reduced the parasite load of individuals at adulthood as predicted. However, the expression of sexual ornaments, immune function, and growth
were unaffected by either early vitamin E supplementation or manipulation of parasite load.
In contrast to the predictions of the PMSS hypothesis the intensity of sexual ornament
expression was not related to either parasite load or oxidative status of individuals (current or long-term). Consequently there was no evidence that the expression of sexual ornaments
provided information on the ability of males to resist infection from parasites.
Abstract.
Author URL.
Blount J, Losdat S, Marri V, Maronde L, Richner H, Helfenstein F (In Press). Effects of an early-life paraquat exposure on adult resistance to oxidative stress, plumage colour and sperm performance in a wild bird. Journal of Animal Ecology
Blount J, Francis ML, Plummer KE, Lythgoe BA, Macallan C, Currie TE (In Press). Effects of supplementary feeding on interspecific dominance hierarchies in garden birds. PLoS ONE
Blount JD, Rowland HM, Drijfhout FP, Endler JA, Inger R, Sloggett JJ, Hurst GDD, Hodgson DJ, Speed MP (In Press). How the ladybird got its spots: effects of resource limitation on the honesty of aposematic signals. Funct. Ecol., (in press)
Blount J, Vitikainen EIK, Stott I, Cant MA (In Press). Oxidative shielding and the cost of reproduction.
Biological ReviewsAbstract:
Oxidative shielding and the cost of reproduction
Life history theory assumes that reproduction and lifespan are constrained by trade-offs which prevent their simultaneous increase. Recently, there has been considerable interest in the possibility that this cost of reproduction is mediated by oxidative stress. However, empirical tests of this theory have yielded equivocal support. We carried out a meta-analysis to examine associations between reproduction and oxidative damage across markers and tissues. We show that oxidative damage is positively associated with reproductive effort across females of various species. Yet paradoxically, categorical comparisons of breeders versus non-breeders reveal that transition to the reproductive state is associated with a step-change reduction in oxidative damage in certain tissues and markers. Developing offspring may be particularly sensitive to harm caused by oxidative damage in mothers. Therefore, such reductions could potentially function to shield reproducing mothers, gametes and developing offspring from oxidative insults that inevitably increase as a consequence of reproductive effort. According to this perspective, we hypothesise that the cost of reproduction is mediated by dual impacts of maternally-derived oxidative damage on mothers and offspring, and that mothers may be selected to diminish such damage. Such oxidative shielding may explain why many existing studies have concluded that reproduction has little or no oxidative cost. Future advance in life history theory therefore needs to take account of potential transgenerational impacts of the mechanisms underlying life history trade-offs.
Abstract.
Blount J, Paul SC, Stevens M, birkett M, Pell JK (In Press). Parental phenotype not predator cues influence egg warning coloration and defence levels. Animal Behaviour
Blount J (In Press). The price of defence: toxins, visual signals and oxidative state in an aposematic butterfly.
Proceedings of the Royal Society B: Biological SciencesAbstract:
The price of defence: toxins, visual signals and oxidative state in an aposematic butterfly
In a variety of aposematic species, the conspicuousness of an individual’s warning signal and the quantity of its chemical defence are positively correlated. This apparent honest signalling is predicted by resource competition models which assume that the production and maintenance of aposematic defences compete for access to antioxidant molecules that have dual functions as pigments and in protecting against oxidative damage. We raised monarch butterflies (Danaus plexippus) on their milkweed host-plants (Apocynaceae) with increasing quantities of cardenolides to test whether (1) the sequestration of secondary defences is associated with costs in the form of oxidative lipid damage and reduced antioxidant defences; and (2) that reduced oxidative state can decrease the capacity of individuals to produce aposematic displays. In male monarchs conspicuousness was explained by an interaction between oxidative damage and sequestration: males with high levels of oxidative damage become less conspicuous with increased sequestration of cardenolides, whereas those with low oxidative damage become more conspicuous with increased levels of cardenolides. There was no significant effect of oxidative damage or concentration of sequestered cardenolides on female conspicuousness. Our results demonstrate a physiological linkage between the production of coloration and protection from autotoxicity, and differential costs of signalling in monarch butterflies.
Abstract.
Blount J (In Press). Untangling the oxidative cost of reproduction: an analysis in wild banded mongooses. Ecology and Evolution
Melvin ZE, Dhirani H, Mitchell C, Davenport TRB, Blount JD, Georgiev AV (2022). Methodological confounds of measuring urinary oxidative stress in wild animals.
Ecol Evol,
12(7).
Abstract:
Methodological confounds of measuring urinary oxidative stress in wild animals.
Biomarkers of oxidative stress (OS) are useful in addressing a wide range of research questions, but thus far, they have had limited application to wild mammal populations due to a reliance on blood or tissue sampling. A shift toward non-invasive measurement of OS would allow field ecologists and conservationists to apply this method more readily. However, the impact of methodological confounds on urinary OS measurement under field conditions has never been explicitly investigated. We combined a cross-sectional analysis with a field experiment to assess the impact of four potential methodological confounds on OS measurements: (1) time of sampling, (2) environmental contamination from foliage; (3) delay between sample collection and flash-freezing in liquid nitrogen; and (4) sample storage of up to 15 months below -80°C. We measured DNA oxidative damage (8-hydroxy-2'-deoxyguanosine, 8-OHdG), lipid peroxidation (malondialdehyde, MDA), total antioxidant capacity (TAC), and uric acid (UA) in 167 urine samples collected from wild Zanzibar red colobus (Piliocolobus kirkii). We found that MDA was higher in samples collected in the morning than in the afternoon but there were no diurnal patterns in any of the other markers. Contamination of samples from foliage and length of time frozen at -80°C for up to 15 months did not affect OS marker concentrations. Freezing delay did not affect OS levels cross-sectionally, but OS values from individual samples showed only moderate-to-good consistency and substantial rank-order reversals when exposed to different freezing delays. We recommend that diurnal patterns of OS markers and the impact of storage time before and after freezing on OS marker concentrations be considered when designing sampling protocols. However, given the high stability we observed for four OS markers subject to a variety of putative methodological confounds, we suggest that urinary OS markers provide a valuable addition to the toolkit of field ecologists and conservationists within reasonable methodological constraints.
Abstract.
Author URL.
Blount JD, Horns JJ, Kittelberger KD, Neate-Clegg MHC, Şekercioğlu ÇH (2021). Avian Use of Agricultural Areas as Migration Stopover Sites: a Review of Crop Management Practices and Ecological Correlates.
Frontiers in Ecology and Evolution,
9Abstract:
Avian Use of Agricultural Areas as Migration Stopover Sites: a Review of Crop Management Practices and Ecological Correlates
An estimated 17% of migratory bird species are threatened or near threatened with extinction. This represents an enormous potential loss of biodiversity and cost to human societies due to the economic benefits that birds provide through ecosystem services and ecotourism. Conservation of migratory bird species presents many unique challenges, as these birds rely on multiple geographically distinct habitats, including breeding grounds, non-breeding grounds, and stopover sites during migration. In particular, stopover habitats are seldom studied relative to breeding and non-breeding habitats, despite their importance as refueling stations for migratory birds. In this study, we summarize the current research on the use of temporary primary crops by birds during migration and we assess the species characteristics and agricultural practices most often associated with the use of cropland as stopover habitat. First, we conducted a systematic review of the literature to document the effects various farming practices and crop types have on the abundance and diversity of migratory birds using agricultural areas for stopovers. Second, we analyzed the ecological correlates of bird species in the Northern Hemisphere that predict which species may use these areas while migrating. We ran a GLMM to test whether primary diet, diet breadth, primary habitat, habitat breadth, or realm predicted stopover use of agricultural areas. Our review suggests that particular crop types (principally rice, corn, and sunflower), as well as farming practices that result in higher non-cultivated plant diversity, encourage the use of agricultural areas by migrating birds. We found that cropland is used as stopover habitat by bird species that can utilize a large breadth of habitats, as well as species with preferences for habitat similar in structure to agricultural areas.
Abstract.
Neate-Clegg MHC, Blount JD, Şekercioğlu ÇH (2021). Ecological and biogeographical predictors of taxonomic discord across the world’s birds.
Global Ecology and Biogeography,
30(6), 1258-1270.
Abstract:
Ecological and biogeographical predictors of taxonomic discord across the world’s birds
Aim: Species delimitation is fundamental to biology, but disagreement in species concepts and the application of those concepts can lead to substantial variation in species lists, with important implications for conservation. For birds, there are four widely used global checklists that vary in length and application. Here, we investigate the biogeographical and ecological predictors of taxonomic disagreement between the four world bird species lists. Location: Global. Time period: Present. Major taxa studied: Birds. Methods: We determined taxonomic agreement based on whether each bird species name represented only one species (‘agreement’), that is, no authorities have split the species, or represented multiple species (‘disagreement’) including disputed splits recognised by some authorities. We examined taxonomic agreement for all birds and for each family and biogeographical region. We then modelled taxonomic agreement as a function of six biogeographical and ecological variables: latitude, island endemism, log(mass), forest dependency, primary diet, and migratory status. Results: Overall taxonomic agreement was 89.5%, and the remaining 10th of taxonomic names represented disputed splits upon which the four authorities disagreed. We found that taxonomic agreement was lowest for species in Southeast Asia/Australasia and the Southern Ocean, understudied regions where islands have driven high levels of cryptic diversification. In contrast, agreement was highest in the temperate Northern Hemisphere where diversity is lower and research is more extensive. Agreement was also higher for large, migratory species living in open habitats. Main conclusions: Taxonomic agreement was higher for species that are easier to study such as large, temperate species from open habitats. In addition, agreement was lower for lineages that are more likely to undergo cryptic divergence such as island endemics with intermediate forest dependency and mobility. Species with these traits should be the focus of taxonomic research in order to achieve reconciliation of the world's bird lists and to better conserve extant biodiversity.
Abstract.
Arunkumar R, Gorusupudi A, Li B, Blount JD, Nwagbo U, Kim HJ, Sparrow JR, Bernstein PS (2021). Lutein and zeaxanthin reduce A2E and iso-A2E levels and improve visual performance in Abca4<sup>−/−</sup>/Bco2<sup>−/−</sup> double knockout mice.
Experimental Eye Research,
209Abstract:
Lutein and zeaxanthin reduce A2E and iso-A2E levels and improve visual performance in Abca4−/−/Bco2−/− double knockout mice
Accumulation of bisretinoids such as A2E and its isomer iso-A2E is thought to mediate blue light-induced oxidative damage associated with age-related macular degeneration (AMD) and autosomal recessive Stargardt disease (STGD1). We hypothesize that increasing dietary intake of the macular carotenoids lutein and zeaxanthin in individuals at risk of AMD and STGD1 can inhibit the formation of bisretinoids A2E and iso-A2E, which can potentially ameliorate macular degenerative diseases. To study the beneficial effect of macular carotenoids in a retinal degenerative diseases model, we used ATP-binding cassette, sub-family a member 4 (Abca4−/−)/β,β-carotene-9′,10′-oxygenase 2 (Bco2−/−) double knockout (KO) mice that accumulate elevated levels of A2E and iso-A2E in the retinal pigment epithelium (RPE) and macular carotenoids in the retina. Abca4−/−/Bco2−/− and Abca4−/− mice were fed a lutein-supplemented chow, zeaxanthin-supplemented chow or placebo chow (~2.6 mg of carotenoid/mouse/day) for three months. Visual function and electroretinography (ERG) were measured after one month and three months of carotenoid supplementation. The lutein and zeaxanthin supplemented Abca4−/−/Bco2−/− mice had significantly lower levels of RPE/choroid A2E and iso-A2E compared to control mice fed with placebo chow and improved visual performance. Carotenoid supplementation in Abca4−/− mice minimally raised retinal carotenoid levels and did not show much difference in bisretinoid levels or visual function compared to the control diet group. There was a statistically significant inverse correlation between carotenoid levels in the retina and A2E and iso-A2E levels in the RPE/choroid. Supplementation with retinal carotenoids, especially zeaxanthin, effectively inhibits bisretinoid formation in a mouse model of STGD1 genetically enhanced to accumulate carotenoids in the retina. These results provide further impetus to pursue oral carotenoids as therapeutic interventions for STGD1 and AMD.
Abstract.
Jacobs PJ, Oosthuizen MK, Mitchell C, Blount JD, Bennett NC (2021). Oxidative stress in response to heat stress in wild caught Namaqua rock mice, Micaelamys namaquensis.
Journal of Thermal Biology,
98Abstract:
Oxidative stress in response to heat stress in wild caught Namaqua rock mice, Micaelamys namaquensis
Modelling of anthropogenic induced climate suggests more frequent and severe heatwaves in the future, which are likely to result in the mass die-off of several species of organisms. Oxidative stress induced by severe heat stress has previously been associated with a reduction in animal cognitive performance, depressed reproduction and lower life expectancy. Little is known about the non-lethal consequences of species should they survive extreme heat exposure. We investigated the oxidative stress experienced by the Namaqua rock mouse, a nocturnal rodent, using two experimental heat stress protocols, a 6 hour acute heat stress protocol without access to water and a 3-day heatwave simulation with ad libitum water. Oxidative stress was determined in the liver, kidney and brain using malondialdehyde (MDA) and protein carbonyl (PC) as markers of oxidative damage, and superoxide dismutase (SOD) and total antioxidant capacity (TAC) as markers of antioxidant defence. Incubator heat stress (heat and dehydration stress) was brought about by increasing the body temperatures of animals to 39–40.8 °C for 6 hours. Following incubator heat stress, significantly higher levels of MDA were observed in the liver. Dehydration did not explain the variation in oxidative markers and is likely a combined effect of thermal and dehydration stress. Individual body mass was significantly negatively correlated to kidney SOD and lipid peroxidation. A heatwave was simulated using a temperature cycle that would naturally occur during a heatwave in the species’ local habitat, with a maximal ambient temperature of 38 °C. Following the simulated heatwave, SOD activity of the kidney demonstrated significantly lowered activity suggesting oxidative stress. Current heat waves in this species have the potential of causing oxidative stress. Heat and dehydration stress following exacerbated temperatures are likely to incur significant oxidative stress in multiple tissues demonstrating the importance of water availability to allow for rehydration to prevent oxidative stress.
Abstract.
Allen SF, Ellis F, Mitchell C, Wang X, Boogert NJ, Lin C-Y, Clokey J, Thomas KV, Blount JD (2021). Phthalate diversity in eggs and associations with oxidative stress in the European herring gull (Larus argentatus). Marine Pollution Bulletin, 169, 112564-112564.
Blount JD, Chynoweth MW, Green AM, Şekercioğlu ÇH (2021). Review: COVID-19 highlights the importance of camera traps for wildlife conservation research and management.
Biological Conservation,
256Abstract:
Review: COVID-19 highlights the importance of camera traps for wildlife conservation research and management
COVID-19 has altered many aspects of everyday life. For the scientific community, the pandemic has called upon investigators to continue work in novel ways, curtailing field and lab research. However, this unprecedented situation also offers an opportunity for researchers to optimize and further develop available field methods. Camera traps are one example of a tool used in science to answer questions about wildlife ecology, conservation, and management. Camera traps have long battery lives, lasting more than a year in certain cases, and photo storage capacity, with some models capable of wirelessly transmitting images from the field. This allows researchers to deploy cameras without having to check them for up to a year or more, making them an ideal field research tool during restrictions on in-person research activities such as COVID-19 lockdowns. As technological advances allow cameras to collect increasingly greater numbers of photos and videos, the analysis techniques for large amounts of data are evolving. Here, we describe the most common research questions suitable for camera trap studies and their importance for biodiversity conservation. As COVID-19 continues to affect how people interact with the natural environment, we discuss novel questions for which camera traps can provide insights on. We conclude by summarizing the results of a systematic review of camera trap studies, providing data on target taxa, geographic distribution, publication rate, and publication venues to help researchers planning to use camera traps in response to the current changes in human activity.
Abstract.
Sauer L, Vitale AS, Milliken CM, Modersitzki NK, Blount JD, Bernstein PS (2020). Autofluorescence lifetimes measured with fluorescence lifetime imaging ophthalmoscopy (FLIO) are affected by age, but not by pigmentation or gender.
Translational Vision Science and Technology,
9(9), 1-13.
Abstract:
Autofluorescence lifetimes measured with fluorescence lifetime imaging ophthalmoscopy (FLIO) are affected by age, but not by pigmentation or gender
Purpose: Fluorescence lifetime imaging ophthalmoscopy (FLIO) is a novel modality to investigate the human retina. This study aims to characterize the effects of age, pigmen-tation, and gender in FLIO. Methods: a total of 97 eyes from 97 healthy subjects (mean age 37 ± 18 years, range 9–85 years) were investigated in this study. This study included 47 (49%) females and 50 males. The pigmentation analysis was a substudy including 64 subjects aged 18 to 40 years (mean age 29 ± 6 years). These were categorized in groups a (darkly pigmented, 8), B (medium pigmented, 20), and C (lightly pigmented, 36). Subjects received Heidelberg Engineering FLIO and optical coherence tomography imaging. Retinal autofluo-rescence lifetimes were detected in two spectral channels (short spectral channel [SSC]: 498–560 nm; long spectral channel [LSC]: 560–720 nm), and amplitude-weighted mean fluorescence lifetimes (τm) were calculated. Additionally, autofluorescence lifetimes of melanin were measured in a cuvette. Results: Age significantly affected FLIO lifetimes, and age-related FLIO changes in the SSC start at approximately age 35 years, whereas the LSC shows a consistent prolonga-tion with age from childhood. There were no gender-or pigmentation-specific significant differences of autofluorescence lifetimes. Conclusions: This study confirms age-effects in FLIO but shows that the two channels are affected differently. The LSC appears to show the lifelong accumulation of lipofuscin. Furthermore, it is important to know that neither gender nor pigmentation significantly affect FLIO lifetimes. Translational Relevance: This study helps to understand the FLIO technology better, which will aid in conducting future clinical studies.
Abstract.
Bodey TW, Cleasby IR, Blount JD, McElwaine G, Vigfusdottir F, Bearhop S (2020). Consistent measures of oxidative balance predict survival but not reproduction in a long-distance migrant.
J Anim Ecol,
89(8), 1872-1882.
Abstract:
Consistent measures of oxidative balance predict survival but not reproduction in a long-distance migrant.
Physiological processes, including those that disrupt oxidative balance, have been proposed as key to understanding fundamental life-history trade-offs. Yet, examination of changes in oxidative balance within wild animals across time, space and major life-history challenges remains uncommon. For example, migration presents substantial physiological challenges for individuals, and data on migratory individuals would provide crucial context for exposing the importance of relationships between oxidative balance and fitness outcomes. Here we examined the consistency of commonly used measures of oxidative balance in longitudinally sampled free-living individuals of a long-lived, long-distance migrant, the Brent goose Branta bernicla hrota over periods of months to years. Although inter-individual and temporal variation in measures of oxidative balance were substantial, we found high consistency in measures of lipid peroxidation and circulating non-enzymatic antioxidants in longitudinally sampled individuals. This suggests the potential for the existence of individual oxidative phenotypes. Given intra-individual consistency, we then examined how these physiological measures relate to survival and reproductive success across all sampled individuals. Surprisingly, lower survival was predicted for individuals with lower levels of damage, with no measured physiological metric associated with reproductive success. Our results demonstrate that snapshot measurements of a consistent measure of oxidative balance can inform our understanding of differences in a key demographic trait. However, the positive relationship between oxidative damage and survival emphasises the need to investigate the relationships between the oxidative system and fitness outcomes in other species undergoing similar physiologically challenging life cycles. This would highlight the extent to which variation in such traits and resource allocation trade-offs is a result of adaptation to different life-history strategies.
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Author URL.
Jacobs PJ, Oosthuizen MK, Mitchell C, Blount JD, Bennett NC (2020). Heat and dehydration induced oxidative damage and antioxidant defenses following incubator heat stress and a simulated heat wave in wild caught four-striped field mice Rhabdomys dilectus.
PLoS ONE,
15(11 November).
Abstract:
Heat and dehydration induced oxidative damage and antioxidant defenses following incubator heat stress and a simulated heat wave in wild caught four-striped field mice Rhabdomys dilectus
Heat waves are known for their disastrous mass die-off effects due to dehydration and cell damage, but little is known about the non-lethal consequences of surviving severe heat exposure. Severe heat exposure can cause oxidative stress which can have negative consequences on animal cognition, reproduction and life expectancy. We investigated the current oxidative stress experienced by a mesic mouse species, the four striped field mouse, Rhabdomys dilectus through a heat wave simulation with ad lib water and a more severe temperature exposure with minimal water. Wild four striped field mice were caught between 2017 and 2019. We predicted that wild four striped field mice in the heat wave simulation would show less susceptibility to oxidative stress as compared to a more severe heat stress which is likely to occur in the future. Oxidative stress was determined in the liver, kidney and brain using malondialdehyde (MDA) and protein carbonyl (PC) as markers for oxidative damage, and superoxide dismutase (SOD) and total antioxidant capacity (TAC) as markers of antioxidant defense. Incubator heat stress was brought about by increasing the body temperatures of animals to 39–40.8 C for 6 hours. A heat wave (one hot day, followed by a 3-day heatwave) was simulated by using temperature cycle that wild four striped field mice would experience in their local habitat (determined through weather station data using temperature and humidity), with maximal ambient temperature of 39 C. The liver and kidney demonstrated no changes in the simulated heat wave, but the liver had significantly higher SOD activity and the kidney had significantly higher lipid peroxidation in the incubator experiment. Dehydration significantly contributed to the increase of these markers, as is evident from the decrease in body mass after the experiment. The brain only showed significantly higher lipid peroxidation following the simulated heat wave with no significant changes following the incubator experiment. The significant increase in lipid peroxidation was not correlated to body mass after the experiment. The magnitude and duration of heat stress, in conjunction with dehydration, played a critical role in the oxidative stress experienced by each tissue, with the results demonstrating the importance of measuring multiple tissues to determine the physiological state of an animal. Current heat waves in this species have the potential of causing oxidative stress in the brain with future heat waves to possibly stress the kidney and liver depending on the hydration state of animals.
Abstract.
Malod K, Roets PD, Oosthuizen C, Blount JD, Archer CR, Weldon CW (2020). Selection on age of female reproduction in the marula fruit fly, Ceratitis cosyra (Walker) (Diptera: Tephritidae), decreases total antioxidant capacity and lipid peroxidation.
J Insect Physiol,
125Abstract:
Selection on age of female reproduction in the marula fruit fly, Ceratitis cosyra (Walker) (Diptera: Tephritidae), decreases total antioxidant capacity and lipid peroxidation.
The oxidative damage caused to cells by Reactive Oxygen Species (ROS) is one of several factors implicated in causing ageing. Oxidative damage may also be a proximate cost of reproductive effort that mediates the trade-off often observed between reproduction and survival. However, how the balance between oxidative damage and antioxidant protection affects life-history strategies is not fully understood. To improve our understanding, we selected on female reproductive age in the marula fruit fly, Ceratitis cosyra, and quantified the impact of selection on female and male mortality risk, female fecundity, male sperm transfer, calling and mating. Against expectations, upward-selected lines lived shorter lives and experienced some reductions in reproductive performance. Selection affected oxidative damage to lipids and total antioxidant protection, but not in the direction predicted; longer lives were associated with elevated oxidative damage, arguing against the idea that accumulated oxidative damage reduces lifespan. Greater reproductive effort was also associated with elevated oxidative damage, suggesting that oxidative damage may be a cost of reproduction, although one that did not affect survival. Our results add to a body of data showing that the relationship between lifespan, reproduction and oxidative damage is more complex than predicted by existing theories.
Abstract.
Author URL.
Bearhop S, Bodey T, Cleasby IR, Blount J, Vigfusdottir F, MacKie K (2019). Measures of oxidative state are primarily driven by extrinsic factors in a long-distance migrant. Biology Letters, 15, 1-4.
Briolat E, Zagrobelny M, Olsen C, Blount J, Stevens M (2019). No evidence of quantitative signal honesty across species of aposematic burnet moths (Lepidoptera: Zygaenidae). Journal of Evolutionary Biology, 32, 31-48.
Blount J, Plummer K, Bearhop S, leech D, chamberlain D (2018). Effects of winter food provisioning on the phenotypes of breeding blue tits. Ecology and Evolution
Paul S, Stevens M, Burton J, Pell J, Burkett M, Blount J (2018). Invasive egg predators and food availability interactively affect maternal investment in egg chemical defence.
Frontiers in Ecology and Evolution,
6Abstract:
Invasive egg predators and food availability interactively affect maternal investment in egg chemical defence
Invasive species commonly predate the offspring of native species and eggs are the life stage most vulnerable to this predation. In many species with no maternal care, females can alter the phenotype of eggs to protect them, for instance through chemical defense. In ladybirds egg alkaloids deter predators, including invasive predatory species of ladybirds, but conversely may attract cannibals who benefit from the consumption of eggs with higher alkaloid levels. Invasive predators tend to be more abundant where resources are also abundant, but in high resource environments the maternal fitness benefits of sibling cannibalism are low. Consequently this presents a conflict for female ladybirds between the different factors that influence egg alkaloid level, as protecting her eggs from predators might come with the cost of inadvertently encouraging within-clutch cannibalism under circumstances where it is not beneficial. We investigated how the ladybird Adalia bipunctata addresses this trade-off experimentally, by measuring the quantity of alkaloids in eggs laid by ladybirds in environments that differed in levels of resource availability and perceived predation risk from an invasive predator Harmonia axyridis. Females did lay eggs with higher egg alkaloid levels under poor resource conditions, but only when predator cues were absent. The resulting negative correlation between egg number and egg alkaloid level under poor resource conditions indicates a trade-off between these two attributes of maternal investment, mediated by female response to offspring predation risk. This implies that selection pressures on mothers to adaptively adjust the risk of siblicide may outweigh the need to protect offspring from interspecific predation. Our results demonstrate that maternal effects are an important aspect of species' responses to invasive predators, and highlight the value of studying maternal effects in the context of the multifaceted environments in which they occur.
Abstract.
Briolat E, Zagrobelny M, Olsen, CE, Blount J, Stevens M (2018). Sex differences but no evidence of quantitative honesty in the warning signals of six-spot burnet moths (Zygaena filipendulae L.). Evolution, 77, 1460-1474.
Hares MC, Vitikainen EIK, Marshall HH, Thompson FJ, Blount JD, Cant MA (2018). Telomere dynamics in wild banded mongooses: Evaluating longitudinal and quasi-longitudinal markers of senescence.
Exp Gerontol,
107, 67-73.
Abstract:
Telomere dynamics in wild banded mongooses: Evaluating longitudinal and quasi-longitudinal markers of senescence.
Telomere length and the rate of telomere shortening have been suggested as particularly useful physiological biomarkers of the processes involved in senescent decline of somatic and reproductive function. However, longitudinal data on changes in telomere length across the lifespan are difficult to obtain, particularly for long-lived animals. Quasi-longitudinal studies have been proposed as a method to gain insight into telomere dynamics in long-lived species. In this method, minimally replicative cells are used as the baseline telomere length against which telomere length in highly replicative cells (which represent the current state) can be compared. Here we test the assumptions and predictions of the quasi-longitudinal approach using longitudinal telomere data in a wild cooperative mammal, the banded mongoose, Mungos mungo. Contrary to our prediction, telomere length (TL) was longer in leukocytes than in ear cartilage. Longitudinally, the TL of ear cartilage shortened with age, but there was no change in the TL of leukocytes, and we also observed many individuals in which TL increased rather than decreased with age. Leukocyte TL but not cartilage TL was a predictor of total lifespan, while neither predicted post-sampling survival. Our data do not support the hypothesis that cross-tissue comparison in TL can act as a quasi-longitudinal marker of senescence. Rather, our results suggest that telomere dynamics in banded mongooses are more complex than is typically assumed, and that longitudinal studies across whole life spans are required to elucidate the link between telomere dynamics and senescence in natural populations.
Abstract.
Author URL.
Vitikainen EIK, Cant MA, Sanderson JL, Mitchell C, Nichols HJ, Marshall HH, Thompson FJ, Gilchrist JS, Hodge SJ, Johnstone RA, et al (2016). Evidence of Oxidative Shielding of Offspring in a Wild Mammal.
FRONTIERS IN ECOLOGY AND EVOLUTION,
4 Author URL.
Vitikainen EIK, Cant MA, Sanderson JL, Mitchell C, Nichols HJ, Marshall HH, Thompson FJ, Gilchrist JS, Hodge SJ, Johnstone RA, et al (2016). Evidence of oxidative shielding of offspring in a wild mammal. Frontiers in Ecology and Evolution
Christensen LL, Selman C, Blount JD, Pilkington JG, Watt KA, Pemberton JM, Reid JM, Nussey DH (2016). Marker-dependent associations among oxidative stress, growth and survival during early life in a wild mammal.
Proc Biol Sci,
283(1840).
Abstract:
Marker-dependent associations among oxidative stress, growth and survival during early life in a wild mammal.
Oxidative stress (OS) is hypothesized to be a key physiological mechanism mediating life-history trade-offs, but evidence from wild populations experiencing natural environmental variation is limited. We tested the hypotheses that increased early life growth rate increases OS, and that increased OS reduces first-winter survival, in wild Soay sheep (Ovis aries) lambs. We measured growth rate and first-winter survival for four consecutive cohorts, and measured two markers of oxidative damage (malondialdehyde (MDA), protein carbonyls (PC)) and two markers of antioxidant (AOX) protection (total AOX capacity (TAC), superoxide dismutase (SOD)) from blood samples. Faster lamb growth was weakly associated with increased MDA, but not associated with variation in the other three markers. Lambs with higher SOD activity were more likely to survive their first winter, as were male but not female lambs with lower PC concentrations. Survival did not vary with MDA or total TAC. Key predictions relating OS to growth and survival were therefore supported in some OS markers, but not others. This suggests that different markers capture different aspects of the complex relationships between individual oxidative state, physiology and fitness, and that overarching hypotheses relating OS to life-history variation cannot be supported or refuted by studying individual markers.
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Author URL.
Summers K, Speed MP, Blount JD, Stuckert AMM (2015). Are aposematic signals honest? a review.
Journal of Evolutionary Biology,
28(9), 1583-1599.
Abstract:
Are aposematic signals honest? a review
We explore the relevance of honest signalling theory to the evolution of aposematism. We begin with a general consideration of models of signal stability, with a focus on the Zahavian costly signalling framework. Next, we review early models of signalling in the context of aposematism (some that are consistent and some inconsistent with costly honest signalling). We focus on controversies surrounding the idea that aposematic signals are handicaps in a Zahavian framework. Then, we discuss how the alignment of interests between signaller and predator influences the evolution of aposematism, highlight the distinction between qualitative and quantitative honesty and review theory and research relevant to these categories. We also review recent theoretical treatments of the evolution of aposematism that have focused on honest signalling as well as empirical research on a variety of organisms, including invertebrates and frogs. Finally, we discuss future directions for empirical and theoretical research in this area.
Abstract.
Summers K, Speed MP, Blount JD, Stuckert AMM (2015). Are aposematic signals honest? a review.
J Evol Biol,
28(9), 1583-1599.
Abstract:
Are aposematic signals honest? a review.
We explore the relevance of honest signalling theory to the evolution of aposematism. We begin with a general consideration of models of signal stability, with a focus on the Zahavian costly signalling framework. Next, we review early models of signalling in the context of aposematism (some that are consistent and some inconsistent with costly honest signalling). We focus on controversies surrounding the idea that aposematic signals are handicaps in a Zahavian framework. Then, we discuss how the alignment of interests between signaller and predator influences the evolution of aposematism, highlight the distinction between qualitative and quantitative honesty and review theory and research relevant to these categories. We also review recent theoretical treatments of the evolution of aposematism that have focused on honest signalling as well as empirical research on a variety of organisms, including invertebrates and frogs. Finally, we discuss future directions for empirical and theoretical research in this area.
Abstract.
Author URL.
Flores EE, Stevens M, Moore AJ, Rowland HM, Blount JD (2015). Body size but not warning signal luminance influences predation risk in recently metamorphosed poison frogs.
Ecology and Evolution,
5(20), 4603-4616.
Abstract:
Body size but not warning signal luminance influences predation risk in recently metamorphosed poison frogs
During early development, many aposematic species have bright and conspicuous warning appearance, but have yet to acquire chemical defenses, a phenotypic state which presumably makes them vulnerable to predation. Body size and signal luminance in particular are known to be sensitive to variation in early nutrition. However, the relative importance of these traits as determinants of predation risk in juveniles is not known. To address this question, we utilized computer-assisted design (CAD) and information on putative predator visual sensitivities to produce artificial models of postmetamorphic froglets that varied in terms of body size and signal luminance. We then deployed the artificial models in the field and measured rates of attack by birds and unknown predators. Our results indicate that body size was a significant predictor of artificial prey survival. Rates of attack by bird predators were significantly higher on smaller models. However, predation by birds did not differ between artificial models of varying signal luminance. This suggests that at the completion of metamorphosis, smaller froglets may be at a selective disadvantage, potentially because predators can discern they have relatively low levels of chemical defense compared to larger froglets. There is likely to be a premium on efficient foraging, giving rise to rapid growth and the acquisition of toxins from dietary sources in juvenile poison frogs.
Abstract.
Siitari H, Alatalo R, Pihlaja M, Hämäläinen J, Blount JD, Groothuis TG, Hytönen VP, Surai P, Soulsbury CD (2015). Food supplementation reveals constraints and adaptability of egg quality in the magpie Pica pica.
Avian Biology Research,
8(4), 244-253.
Abstract:
Food supplementation reveals constraints and adaptability of egg quality in the magpie Pica pica
Differences in the deposition of limited maternal resources to eggs can reflect the optimal allocation to manipulate offspring phenotype, or constraints caused by maternal condition. We examined multiple maternal substances transferred to eggs in the magpie Pica pica to test the hypothesis that certain substances represent constraint and some optimal allocation. We did this by supplementary feeding magpies prior to egg-laying and then comparing the effect of food on maternal substances in conjunction with laying order relative to a control group. Certain substances such as carotenoids, immunoglobulins and avidin responded positively to food supplementation, whereas others, such as testosterone and total protein content of eggs, did not. Immunoglobulin allocation increased with laying order in fed but not in unfed groups. Our results suggest that patterns of optimal allocation and constraint in maternally-provisioned substances co-occur within clutches. Furthermore, constraint and optimal allocation may co-occur within the same substance i.e. immunoglobulins, highlighting the complexities of maternal resource allocation.
Abstract.
Cram DL, Blount JD, York JE, Young AJ (2015). Immune response in a wild bird is predicted by oxidative status but does not cause oxidative stress. PLoS One
Blount JD, Vitikainen EIK, Stott I, Cant MA (2015). Oxidative shielding and the cost of reproduction. Biological Reviews
Cram DL, Blount JD, Young AJ (2015). Oxidative status and social dominance in a wild cooperative breeder.
Functional Ecology,
29(2), 229-238.
Abstract:
Oxidative status and social dominance in a wild cooperative breeder
© 2014 British Ecological Society. Oxidative stress has been proposed as a key mediator of life-history trade-offs, yet the social factors that affect patterns of oxidative status amongst individuals in animal societies remain virtually unexplored. This is important, as rank-related differences in reproductive effort in many social species have the potential to generate, or indeed arise from, differences in oxidative status across dominance classes. Here, we examine rank-related variation in oxidative status before and after a lengthy breeding season in a wild cooperatively breeding bird with high reproductive skew, in the semi-arid zone of Southern Africa; the white-browed sparrow weaver (Plocepasser mahali). Our findings reveal that prior to breeding, neither sex showed rank-related differences in markers of oxidative damage or antioxidant protection, suggesting that dominants' reproductive monopolies do not arise from superior pre-breeding oxidative status. After breeding, however, females (who provision young at higher rates than males) suffered elevated oxidative damage, and dominant females (the only birds to lay and incubate eggs, and the primary nestling provisioners) experienced differential declines in antioxidant protection. While males als o showed reduced antioxidant capacity after breeding, this decline was not dependent on rank and not associated with elevated oxidative damage. Our findings suggest that divisions of labour in animal societies can leave the hardest-working classes differentially exposed to oxidative stress, raising the possibility of hitherto unexplored impacts on health and ageing in social species.
Abstract.
Speakman JR, Speakman JR, Blount JD, Bronikowski AM, Buffenstein R, Isaksson C, Kirkwood TBL, Monaghan P, Ozanne SE, Beaulieu M, et al (2015). Oxidative stress and life histories: Unresolved issues and current needs.
Ecology and EvolutionAbstract:
Oxidative stress and life histories: Unresolved issues and current needs
© 2015 Published by John Wiley & Sons Ltd. Life-history theory concerns the trade-offs that mold the patterns of investment by animals between reproduction, growth, and survival. It is widely recognized that physiology plays a role in the mediation of life-history trade-offs, but the details remain obscure. As life-history theory concerns aspects of investment in the soma that influence survival, understanding the physiological basis of life histories is related, but not identical, to understanding the process of aging. One idea from the field of aging that has gained considerable traction in the area of life histories is that life-history trade-offs may be mediated by free radical production and oxidative stress. We outline here developments in this field and summarize a number of important unresolved issues that may guide future research efforts. The issues are as follows. First, different tissues and macromolecular targets of oxidative stress respond differently during reproduction. The functional significance of these changes, however, remains uncertain. Consequently there is a need for studies that link oxidative stress measurements to functional outcomes, such as survival. Second, measurements of oxidative stress are often highly invasive or terminal. Terminal studies of oxidative stress in wild animals, where detailed life-history information is available, cannot generally be performed without compromising the aims of the studies that generated the life-history data. There is a need therefore for novel non-invasive measurements of multi-tissue oxidative stress. Third, laboratory studies provide unrivaled opportunities for experimental manipulation but may fail to expose the physiology underpinning life-history effects, because of the benign laboratory environment. Fourth, the idea that oxidative stress might underlie life-history trade-offs does not make specific enough predictions that are amenable to testing. Moreover, there is a paucity of good alternative theoretical models on which contrasting predictions might be based. Fifth, there is an enormous diversity of life-history variation to test the idea that oxidative stress may be a key mediator. So far we have only scratched the surface. Broadening the scope may reveal new strategies linked to the processes of oxidative damage and repair. Finally, understanding the trade-offs in life histories and understanding the process of aging are related but not identical questions. Scientists inhabiting these two spheres of activity seldom collide, yet they have much to learn from each other.
Abstract.
Christensen LL, Selman C, Blount JD, Pilkington JG, Watt KA, Pemberton JM, Reid JM, Nussey DH (2015). Plasma markers of oxidative stress are uncorrelated in a wild mammal.
Ecology and Evolution,
5(21), 5096-5108.
Abstract:
Plasma markers of oxidative stress are uncorrelated in a wild mammal
Oxidative stress, which results from an imbalance between the production of potentially damaging reactive oxygen species versus antioxidant defenses and repair mechanisms, has been proposed as an important mediator of life-history trade-offs. A plethora of biomarkers associated with oxidative stress exist, but few ecological studies have examined the relationships among different markers in organisms experiencing natural conditions or tested whether those relationships are stable across different environments and demographic groups. It is therefore not clear to what extent studies of different markers can be compared, or whether studies that focus on a single marker can draw general conclusions regarding oxidative stress. We measured widely used markers of oxidative damage (protein carbonyls and malondialdehyde) and antioxidant defense (superoxide dismutase and total antioxidant capacity) from 706 plasma samples collected over a 4-year period in a wild population of Soay sheep on St Kilda. We quantified the correlation structure among these four markers across the entire sample set and also within separate years, age groups (lambs and adults), and sexes. We found some moderately strong correlations between some pairs of markers when data from all 4 years were pooled. However, these correlations were caused by considerable among-year variation in mean marker values; correlation coefficients were small and not significantly different from zero after accounting for among-year variation. Furthermore, within each year, age, and sex subgroup, the pairwise correlation coefficients among the four markers were weak, nonsignificant, and distributed around zero. In addition, principal component analysis confirmed that the four markers represented four independent axes of variation. Our results suggest that plasma markers of oxidative stress may vary dramatically among years, presumably due to environmental conditions, and that this variation can induce population-level correlations among markers even in the absence of any correlations within contemporaneous subgroups. The absence of any consistent correlations within years or demographic subgroups implies that care must be taken when generalizing from observed relationships with oxidative stress markers, as each marker may reflect different and potentially uncoupled biochemical processes. © 2015 Published by John Wiley
Abstract.
Christensen LL, Selman C, Blount JD, Pilkington JG, Watt KA, Pemberton JM, Reid JM, Nussey DH (2015). Plasma markers of oxidative stress are uncorrelated in a wild mammal.
Ecology and EvolutionAbstract:
Plasma markers of oxidative stress are uncorrelated in a wild mammal
Oxidative stress, which results from an imbalance between the production of potentially damaging reactive oxygen species versus antioxidant defenses and repair mechanisms, has been proposed as an important mediator of life-history trade-offs. A plethora of biomarkers associated with oxidative stress exist, but few ecological studies have examined the relationships among different markers in organisms experiencing natural conditions or tested whether those relationships are stable across different environments and demographic groups. It is therefore not clear to what extent studies of different markers can be compared, or whether studies that focus on a single marker can draw general conclusions regarding oxidative stress. We measured widely used markers of oxidative damage (protein carbonyls and malondialdehyde) and antioxidant defense (superoxide dismutase and total antioxidant capacity) from 706 plasma samples collected over a 4-year period in a wild population of Soay sheep on St Kilda. We quantified the correlation structure among these four markers across the entire sample set and also within separate years, age groups (lambs and adults), and sexes. We found some moderately strong correlations between some pairs of markers when data from all 4 years were pooled. However, these correlations were caused by considerable among-year variation in mean marker values; correlation coefficients were small and not significantly different from zero after accounting for among-year variation. Furthermore, within each year, age, and sex subgroup, the pairwise correlation coefficients among the four markers were weak, nonsignificant, and distributed around zero. In addition, principal component analysis confirmed that the four markers represented four independent axes of variation. Our results suggest that plasma markers of oxidative stress may vary dramatically among years, presumably due to environmental conditions, and that this variation can induce population-level correlations among markers even in the absence of any correlations within contemporaneous subgroups. The absence of any consistent correlations within years or demographic subgroups implies that care must be taken when generalizing from observed relationships with oxidative stress markers, as each marker may reflect different and potentially uncoupled biochemical processes.
Abstract.
Paul SC, Pell JK, Blount JD (2015). Reproduction in Risky Environments: the Role of Invasive Egg Predators in Ladybird Laying Strategies.
PLoS One,
10(10).
Abstract:
Reproduction in Risky Environments: the Role of Invasive Egg Predators in Ladybird Laying Strategies.
Reproductive environments are variable and the resources available for reproduction are finite. If reliable cues about the environment exist, mothers can alter offspring phenotype in a way that increases both offspring and maternal fitness ('anticipatory maternal effects'-AMEs). Strategic use of AMEs is likely to be important in chemically defended species, where the risk of offspring predation may be modulated by maternal investment in offspring toxin level, albeit at some cost to mothers. Whether mothers adjust offspring toxin levels in response to variation in predation risk is, however, unknown, but is likely to be important when assessing the response of chemically defended species to the recent and pervasive changes in the global predator landscape, driven by the spread of invasive species. Using the chemically defended two-spot ladybird, Adalia bipunctata, we investigated reproductive investment, including egg toxin level, under conditions that varied in the degree of simulated offspring predation risk from larval harlequin ladybirds, Harmonia axyridis. H. axyridis is a highly voracious alien invasive species in the UK and a significant intraguild predator of A. bipunctata. Females laid fewer, larger egg clusters, under conditions of simulated predation risk (P+) than when predator cues were absent (P-), but there was no difference in toxin level between the two treatments. Among P- females, when mean cluster size increased there were concomitant increases in both the mass and toxin concentration of eggs, however when P+ females increased cluster size there was no corresponding increase in egg toxin level. We conclude that, in the face of offspring predation risk, females either withheld toxins or were physiologically constrained, leading to a trade-off between cluster size and egg toxin level. Our results provide the first demonstration that the risk of offspring predation by a novel invasive predator can influence maternal investment in toxins within their offspring.
Abstract.
Author URL.
Lane SM, Solino JH, Mitchell C, Blount JD, Okada K, Hunt J, House CM (2015). Rival male chemical cues evoke changes in male pre- and post-copulatory investment in a flour beetle.
Behav Ecol,
26(4), 1021-1029.
Abstract:
Rival male chemical cues evoke changes in male pre- and post-copulatory investment in a flour beetle.
Males can gather information on the risk and intensity of sperm competition from their social environment. Recent studies have implicated chemosensory cues, for instance cuticular hydrocarbons (CHCs) in insects, as a key source of this information. Here, using the broad-horned flour beetle (Gnatocerus cornutus), we investigated the importance of contact-derived rival male CHCs in informing male perception of sperm competition risk and intensity. We experimentally perfumed virgin females with male CHCs via direct intersexual contact and measured male pre- and post-copulatory investment in response to this manipulation. Using chemical analysis, we verified that this treatment engendered changes to perfumed female CHC profiles, but did not make perfumed females "smell" mated. Despite this, males responded to these chemical changes. Males increased courtship effort under low levels of perceived competition (from 1-3 rivals), but significantly decreased courtship effort as perceived competition rose (from 3-5 rivals). Furthermore, our measurement of ejaculate investment showed that males allocated significantly more sperm to perfumed females than to control females. Together, these results suggest that changes in female chemical profile elicited by contact with rival males do not provide males with information on female mating status, but rather inform males of the presence of rivals within the population and thus provide a means for males to indirectly assess the risk of sperm competition.
Abstract.
Author URL.
Archer CR, Hempenstall S, Royle NJ, Selman C, Willis S, Rapkin J, Blount JD, Hunt J (2015). Testing the Effects of DL-Alpha-Tocopherol Supplementation on Oxidative Damage, Total Antioxidant Protection and the Sex-Specific Responses of Reproductive Effort and Lifespan to Dietary Manipulation in Australian Field Crickets (Teleogryllus commodus).
Antioxidants (Basel),
4(4), 768-792.
Abstract:
Testing the Effects of DL-Alpha-Tocopherol Supplementation on Oxidative Damage, Total Antioxidant Protection and the Sex-Specific Responses of Reproductive Effort and Lifespan to Dietary Manipulation in Australian Field Crickets (Teleogryllus commodus).
The oxidative stress theory predicts that the accumulation of oxidative damage causes aging. More generally, oxidative damage could be a cost of reproduction that reduces survival. Both of these hypotheses have mixed empirical support. To better understand the life-history consequences of oxidative damage, we fed male and female Australian field crickets (Teleogryllus commodus) four diets differing in their protein and carbohydrate content, which have sex-specific effects on reproductive effort and lifespan. We supplemented half of these crickets with the vitamin E isoform DL-alpha-tocopherol and measured the effects of nutrient intake on lifespan, reproduction, oxidative damage and antioxidant protection. We found a clear trade-off between reproductive effort and lifespan in females but not in males. In direct contrast to the oxidative stress theory, crickets fed diets that improved their lifespan had high levels of oxidative damage to proteins. Supplementation with DL-alpha-tocopherol did not significantly improve lifespan or reproductive effort. However, males fed diets that increased their reproductive investment experienced high oxidative damage to proteins. While this suggests that male reproductive effort could elevate oxidative damage, this was not associated with reduced male survival. Overall, these results provide little evidence that oxidative damage plays a central role in mediating life-history trade-offs in T. commodus.
Abstract.
Author URL.
Cram DL, Blount JD, Young AJ (2015). The oxidative costs of reproduction are group-size dependent in a wild cooperative breeder. Proceedings of the Royal Society of London. Series B
Winters AE, Stevens M, Mitchell C, Blomberg SP, Blount JD (2014). Maternal effects and warning signal honesty in eggs and offspring of an aposematic ladybird beetle. Functional Ecology
Cram DL, Blount JB, Young AJ (2014). Oxidative state and social dominance in a wild cooperative breeder. Functional Ecology
Schmidt CM, Blount JD, Bennett NC (2014). Reproduction is associated with a tissue-dependent reduction of oxidative stress in eusocial female Damaraland mole-rats (Fukomys damarensis).
PLoS One,
9(7).
Abstract:
Reproduction is associated with a tissue-dependent reduction of oxidative stress in eusocial female Damaraland mole-rats (Fukomys damarensis).
Oxidative stress has been implicated as both a physiological cost of reproduction and a driving force on an animal's lifespan. Since increased reproductive effort is generally linked with a reduction in survival, it has been proposed that oxidative stress may influence this relationship. Support for this hypothesis is inconsistent, but this may, in part, be due to the type of tissues that have been analyzed. In Damaraland mole-rats the sole reproducing female in the colony is also the longest lived. Therefore, if oxidative stress does impact the trade-off between reproduction and survival in general, this species may possess some form of enhanced defense. We assessed this relationship by comparing markers of oxidative damage (malondialdehyde, MDA; protein carbonyls, PC) and antioxidants (total antioxidant capacity, TAC; superoxide dismutase, SOD) in various tissues including plasma, erythrocytes, heart, liver, kidney and skeletal muscle between wild-caught reproductive and non-reproductive female Damaraland mole-rats. Reproductive females exhibited significantly lower levels of PC across all tissues, and lower levels of MDA in heart, kidney and liver relative to non-reproductive females. Levels of TAC and SOD did not differ significantly according to reproductive state. The reduction in oxidative damage in breeding females may be attributable to the unusual social structure of this species, as similar relationships have been observed between reproductive and non-reproductive eusocial insects.
Abstract.
Author URL.
Losdat S, Helfenstein F, Blount JD, Richner H (2014). Resistance to oxidative stress shows low heritability and high common environmental variance in a wild bird.
Journal of Evolutionary Biology,
27(9), 1990-2000.
Abstract:
Resistance to oxidative stress shows low heritability and high common environmental variance in a wild bird
Oxidative stress was recently demonstrated to affect several fitness-related traits and is now well recognized to shape animal life-history evolution. However, very little is known about how much resistance to oxidative stress is determined by genetic and environmental effects and hence about its potential for evolution, especially in wild populations. In addition, our knowledge of phenotypic sexual dimorphism and cross-sex genetic correlations in resistance to oxidative stress remains extremely limited despite important evolutionary implications. In free-living great tits (Parus major), we quantified heritability, common environmental effect, sexual dimorphism and cross-sex genetic correlation in offspring resistance to oxidative stress by performing a split-nest cross-fostering experiment where 155 broods were split, and all siblings (n = 791) translocated and raised in two other nests. Resistance to oxidative stress was measured as both oxidative damage to lipids and erythrocyte resistance to a controlled free-radical attack. Both measurements of oxidative stress showed low additive genetic variances, high common environmental effects and phenotypic sexual dimorphism with males showing a higher resistance to oxidative stress. Cross-sex genetic correlations were not different from unity, and we found no substantial heritability in resistance to oxidative stress at adult age measured on 39 individuals that recruited the subsequent year. Our study shows that individual ability to resist to oxidative stress is primarily influenced by the common environment and has a low heritability with a consequent low potential for evolution, at least at an early stage of life. © 2014 European Society for Evolutionary Biology.
Abstract.
Losdat S, Helfenstein F, Blount JD, Richner H (2014). Resistance to oxidative stress shows low heritability and high common environmental variance in a wild bird. Journal of Evolutionary Biology
Newcombe D, Blount JD, Mitchell C, Moore AJ (2013). Chemical egg defence in the large milkweed bug, Oncopeltus fasciatus, derives from maternal but not paternal diet.
Entomologia Experimentalis et Applicata,
149(3), 197-205.
Abstract:
Chemical egg defence in the large milkweed bug, Oncopeltus fasciatus, derives from maternal but not paternal diet
Many herbivorous insects sequester defensive compounds from their host-plants and incorporate them into their eggs to protect them against predation. Here, we investigate whether transmission of cardenolides from the host-diet to the eggs is maternal, paternal, or biparental in the large milkweed bug, Oncopeltus fasciatus (Dallas) (Hemiptera: Lygaeidae). We reared individual bugs on either milkweed seeds [MW; Asclepias syriaca L. (Apocynaceae)] that contain cardenolides, or on sunflower seeds [SF; Helianthus annuus L. (Asteraceae)] that do not contain cardenolides. We mated females and males so that all four maternal/paternal diet combinations were represented: MW/MW, MW/SF, SF/MW, and SF/SF. Using larvae of the common green lacewing, Chrysoperla (Chrysopa) carnea (Stevens) (Neuroptera: Chrysopidae), we conducted two-choice predation trials to assess whether maternal, paternal, or biparental transmission of cardenolides into the eggs of O. fasciatus increased protection against predation. Furthermore, we used high performance liquid chromatography (HPLC) to assess putative cardenolide content of eggs from the various parental diet treatment groups. The predation trials suggested that regardless of male diet, eggs were afforded better protection when females had been raised on milkweed. However, many eggs were at least partially consumed. This suggests that although chemical defence of eggs does not guarantee protection to eggs on an individual basis, they may increase the probability that some eggs in a clutch are left intact thereby potentially conferring a fitness advantage to more offspring than if eggs are left unprotected. Based on HPLC analysis we found that maternal contribution of cardenolides was significantly greater than paternal contribution of cardenolides to the eggs, supporting the results of our predation trials that a maternal diet of milkweed makes eggs more distasteful than a paternal diet of milkweed. © 2013 the Netherlands Entomological Society.
Abstract.
Newcombe D, Blount JD, Mitchell C, Moore AJ (2013). Chemical egg defence in the large milkweed bug, Oncopeltus fasciatus, derives from maternal but not paternal diet. Entomologia Experimentalis et Applicata
Flores EE, Stevens M, Moore AJ, Blount JD (2013). Diet, development and the optimization of warning signals in post-metamorphic green and black poison frogs.
Functional Ecology,
27(3), 816-829.
Abstract:
Diet, development and the optimization of warning signals in post-metamorphic green and black poison frogs
Many prey species are chemically defended and have conspicuous appearance to deter predators (i.e. aposematism). Such warning signals work because predators pay attention to the colour and size of signals, which they associate with unprofitability. Paradoxically, in early life stages, aposematic species are often warningly coloured, but their chemical defences are lacking because they have yet to be acquired through the diet or synthesized endogenously. This state of being conspicuous yet poorly defended must place individuals at increased risk of predation, but how they minimize this risk during development is unclear. We reared larval green and black poison frogs (Dendrobates auratus) on a relatively low or a higher food supply and tested the hypothesis that individuals with more resources should grow larger while reducing their investment in warning signals at metamorphic completion. We also assayed markers of oxidative balance (malondialdehyde, superoxide dismutase and total antioxidant capacity) to ascertain whether there were resource-allocation trade-offs that differed with diet treatments. Low-food froglets were relatively small, and their body size and signal luminance (perceived brightness) were positively correlated. In contrast, in high-food froglets body size and warning signal luminance were negatively correlated, suggesting either a resource-allocation trade-off or alternatively a facultative reduction in luminance exhibited by larger froglets. The reduction in luminance in relatively large, high-food froglets did not appear to arise because of oxidative stress: signal luminance and markers of oxidative stress were positively correlated in high-food froglets, but were negatively correlated in low-food froglets suggesting a trade-off. Our results highlight developmental plasticity in body size and coloration as affected by resource (i.e. food) supply. Such plasticity seems likely to minimize predation risk during the vulnerable period early in life when individuals are warningly coloured and must make the transition from an undefended phenotype to a mature aposematic state. © 2013 the Authors. Functional Ecology © 2013 British Ecological Society.
Abstract.
Flores EE, Stevens M, Moore AJ, Blount JD (2013). Diet, development and the optimization of warning signals in post-metamorphic green and black poison frogs. Functional Ecology
Plummer KE, Bearhop S, Leech DI, Chamberlain DE, Blount JD (2013). Fat provisioning in winter impairs egg production during the following spring: a landscape-scale study of blue tits.
Journal of Animal Ecology,
82(3), 673-682.
Abstract:
Fat provisioning in winter impairs egg production during the following spring: a landscape-scale study of blue tits
Summary: Provisioning of garden birds is a growing phenomenon, particularly during winter, but there is little empirical evidence of its true ecological impacts. One possibility is that winter provisioning could enhance subsequent breeding performance, but this seems likely to depend on the types of nutrients provided. For example, whereas effects of macronutrients such as fat are unlikely to be carried over to influence breeding in small passerines, micronutrients such as dietary vitamin E (an antioxidant) may be stored or have lasting health benefits. Here, we examine the carry-over effects of winter food supplements on egg production in wild populations of blue tits (Cyanistes caeruleus). Over three consecutive years, birds were provisioned with fat, fat plus vitamin E or remained unfed (controls). The provision of fat in winter resulted in smaller relative yolk mass in larger eggs and reduced yolk carotenoid concentrations in early breeders. However, these effects were not seen in birds provisioned with fat plus vitamin E. Lay date, clutch size, egg mass and yolk vitamin E concentrations were not significantly affected by winter provisioning treatment. Our results indicate that winter provisioning can have important downstream consequences, in particular affecting investment in egg production several weeks or months later. Provisioning is widely applied to support garden bird populations and for the conservation management of endangered species. However, our results challenge the assumption that such practices are always beneficial at the population level and emphasize how the ecological impacts can depend on the specific nutritional profile of provisioned foods. © 2013 British Ecological Society.
Abstract.
Plummer KE, Bearhop S, Leech DI, Chamberlain DE, Blount JD (2013). Fat provisioning in winter impairs egg production during the following spring: a landscape-scale study of blue tits.
J Anim Ecol,
82(3), 673-682.
Abstract:
Fat provisioning in winter impairs egg production during the following spring: a landscape-scale study of blue tits.
1. Provisioning of garden birds is a growing phenomenon, particularly during winter, but there is little empirical evidence of its true ecological impacts. One possibility is that winter provisioning could enhance subsequent breeding performance, but this seems likely to depend on the types of nutrients provided. For example, whereas effects of macronutrients such as fat are unlikely to be carried over to influence breeding in small passerines, micronutrients such as dietary vitamin E (an antioxidant) may be stored or have lasting health benefits. 2. Here, we examine the carry-over effects of winter food supplements on egg production in wild populations of blue tits (Cyanistes caeruleus). Over three consecutive years, birds were provisioned with fat, fat plus vitamin E or remained unfed (controls). 3. The provision of fat in winter resulted in smaller relative yolk mass in larger eggs and reduced yolk carotenoid concentrations in early breeders. However, these effects were not seen in birds provisioned with fat plus vitamin E. Lay date, clutch size, egg mass and yolk vitamin E concentrations were not significantly affected by winter provisioning treatment. 4. Our results indicate that winter provisioning can have important downstream consequences, in particular affecting investment in egg production several weeks or months later. 5. Provisioning is widely applied to support garden bird populations and for the conservation management of endangered species. However, our results challenge the assumption that such practices are always beneficial at the population level and emphasize how the ecological impacts can depend on the specific nutritional profile of provisioned foods.
Abstract.
Author URL.
Losdat S, Helfenstein F, Blount JD, Marri V, Maronde L, Richner H (2013). Nestling erythrocyte resistance to oxidative stress predicts fledging success but not local recruitment in a wild bird.
Biology Letters,
9(1).
Abstract:
Nestling erythrocyte resistance to oxidative stress predicts fledging success but not local recruitment in a wild bird
Stressful conditions experienced by individuals during their early development have long-term consequences on various life-history traits such as survival until first reproduction. Oxidative stress has been shown to affect various fitness-related traits and to influence key evolutionary trade-offs but whether an individual's ability to resist oxidative stress in early life affects its survival has rarely been tested. In the present study, we used four years of data obtained from a free-living great tit population (Parus major; n = 1658 offspring) to test whether pre-fledging resistance to oxidative stress, measured as erythrocyte resistance to oxidative stress and oxidative damage to lipids, predicted fledging success and local recruitment. Fledging success and local recruitment, both major correlates of survival, were primarily influenced by offspring body mass prior to fledging. We found that prefledging erythrocyte resistance to oxidative stress predicted fledging success, suggesting that individual resistance to oxidative stress is related to shortterm survival. However, local recruitment was not influenced by pre-fledging erythrocyte resistance to oxidative stress or oxidative damage. Our results suggest that an individual ability to resist oxidative stress at the offspring stage predicts short-term survival but does not influence survival later in life. © 2012 the Author(s) Published by the Royal Society. All rights reserved.
Abstract.
Plummer KE, Bearhop S, Leech DI, Chamberlain DE, Blount JD (2013). Winter food provisioning reduces future breeding performance in a wild bird.
Sci Rep,
3Abstract:
Winter food provisioning reduces future breeding performance in a wild bird.
Supplementation of food to wild birds occurs on an enormous scale worldwide, and is often cited as an exemplar of beneficial human-wildlife interaction. Recently it has been speculated that winter feeding could have negative consequences for future reproduction, for example by enabling low quality individuals to recruit into breeding populations. However, evidence that winter feeding has deleterious impacts on reproductive success is lacking. Here, in a landscape-scale study of blue tits (Cyanistes caeruleus) across multiple years, we show that winter food supplementation reduced breeding performance the following spring. Compared to unfed populations, winter-fed birds produced offspring that weighed less, were smaller, and had lower survival. This impairment was observed in parents that had received fat only, or in combination with vitamin E, suggesting some generality in the mechanism by which supplementary feeding affected reproduction. Our results highlight the potential for deleterious population-level consequences of winter food supplementation on wild birds.
Abstract.
Author URL.
Orledge JM, Blount JD, Hoodless AN, Royle NJ (2012). Antioxidant supplementation during early development reduces parasite load but does not affect sexual ornament expression in adult ring-necked pheasants.
Functional Ecology,
26(3), 688-700.
Abstract:
Antioxidant supplementation during early development reduces parasite load but does not affect sexual ornament expression in adult ring-necked pheasants
The 'parasite-mediated sexual selection' (PMSS) hypothesis predicts that exaggerated male ornamentation could provide a signal to females of a male's ability to resist parasites. Empirical tests of the PMSS have been largely equivocal, however, which may be because most have not considered the role of early life-history effects. 2.Many sexually selected traits are carotenoid-based. Allocation of dietary-derived carotenoids to sexual ornaments may trade-off with allocation to pro-inflammatory immune response and/or antioxidant functions, mediated by the oxidative status of individuals. Exposure to parasites can increase oxidative stress, so under this scenario, sexually selected traits indicate ability to resist oxidative stress rather than ability to resist parasites per se. Such life-history trade-offs, mediated by oxidative status of individuals, are particularly acute during growth and development. 3.Here, we use ring-necked pheasants, Phasianus colchicus, a strongly sexually selected species, to test whether supplementation with dietary antioxidants (vitamin E) can mitigate the effects of early exposure to parasites (the nematode, Heterakis gallinarum), via alteration of the oxidative status of individuals, and positively affect the expression of sexual ornaments at adulthood. 4.We found that vitamin E mediated the effect of early exposure to parasites on levels of oxidative damage at 8weeks of age and reduced the parasite load of individuals at adulthood as predicted. However, the expression of sexual ornaments, immune function and growth were unaffected by either early vitamin E supplementation or manipulation of parasite load. In contrast to the predictions of the PMSS hypothesis, the intensity of sexual ornament expression was not related to either parasite load or oxidative status of individuals (current or long-term). Consequently, there was no evidence that the expression of sexual ornaments provided information on the ability of males to resist infection from parasites. © 2012 the Authors. Functional Ecology © 2012 British Ecological Society.
Abstract.
Sepp T, Karu U, Blount JD, Sild E, Maenniste M, Horak P (2012). Coccidian Infection Causes Oxidative Damage in Greenfinches.
PLOS ONE,
7(5).
Author URL.
Müller W, Vergauwen J, Eens M, Blount JD (2012). Environmental effects shape the maternal transfer of carotenoids and vitamin E to the yolk.
Frontiers in Zoology,
9Abstract:
Environmental effects shape the maternal transfer of carotenoids and vitamin E to the yolk
Introduction: Maternal effects occur when the phenotype of the offspring is influenced by the phenotype of the mother, which in turn depends on her heritable state as well as on influences from the current and past environmental conditions. All of these pathways may, therefore, form significant sources of variation in maternal effects. Here, we focused on the maternal transfer of carotenoids and vitamin E to the egg yolk, using canaries as a model species. Maternal yolk carotenoids and vitamin E are known to generate significant phenotypic variation in offspring, representing examples of maternal effects. We studied the intra-individual consistency in deposition patterns across two years and the mother-daughter resemblance across two generations in order to estimate the level of heritable variation. The effects of the current environmental conditions were studied via a food supplementation experiment, while the consequences of past environmental conditions were estimated on the basis of the early growth trajectories.Results: There was a significant effect of the current environmental conditions on the yolk carotenoid and vitamin E deposition, but this effect varied between antioxidant components. The deposition of yolk carotenoids and vitamin E were linked to the process of yolk formation. Past environmental conditions did not contribute to the variation in yolk carotenoid and vitamin E levels nor did we find significant heritable variation.Conclusions: the transfer of carotenoids or vitamin E may be an example where current environmental variation is largely passed from the mother to the offspring, despite the numerous intermediate physiological steps that are involved. Differences in the effect of the environmental conditions as experienced by the mother during laying may be due to differences in availability as well as physiological processes such as competitive exclusion or selective absorption. © 2012 Müller et al.; licensee BioMed Central Ltd.
Abstract.
Weber SB, Broderick AC, Groothuis TGG, Ellick J, Godley BJ, Blount JD (2012). Fine-scale thermal adaptation in a green turtle nesting population.
Proc Biol Sci,
279(1731), 1077-1084.
Abstract:
Fine-scale thermal adaptation in a green turtle nesting population.
The effect of climate warming on the reproductive success of ectothermic animals is currently a subject of major conservation concern. However, for many threatened species, we still know surprisingly little about the extent of naturally occurring adaptive variation in heat-tolerance. Here, we show that the thermal tolerances of green turtle (Chelonia mydas) embryos in a single, island-breeding population have diverged in response to the contrasting incubation temperatures of nesting beaches just a few kilometres apart. In natural nests and in a common-garden rearing experiment, the offspring of females nesting on a naturally hot (black sand) beach survived better and grew larger at hot incubation temperatures compared with the offspring of females nesting on a cooler (pale sand) beach nearby. These differences were owing to shallower thermal reaction norms in the hot beach population, rather than shifts in thermal optima, and could not be explained by egg-mediated maternal effects. Our results suggest that marine turtle nesting behaviour can drive adaptive differentiation at remarkably fine spatial scales, and have important implications for how we define conservation units for protection. In particular, previous studies may have underestimated the extent of adaptive structuring in marine turtle populations that may significantly affect their capacity to respond to environmental change.
Abstract.
Author URL.
Mainwaring MC, Blount JD, Hartley IR (2012). Hatching asynchrony can have long-term consequences for offspring fitness in zebra finches under captive conditions.
Biological Journal of the Linnean Society,
106(2), 430-438.
Abstract:
Hatching asynchrony can have long-term consequences for offspring fitness in zebra finches under captive conditions
Hatching asynchrony can have profound short-term consequences for offspring, although the long-term consequences are less well understood. The purpose of this study was to examine the long-term consequences of hatching asynchrony for offspring fitness in birds. Specifically, we aimed to test the hypothesis that hatching asynchrony increases the sexual attractiveness and fecundity, respectively, of early-hatched male and female zebra finch, Taeniopygia guttata (Vieillot, 1817) offspring. Mate-choice trials comparing male nestlings with the same parents, but that were reared in asynchronous or experimentally synchronous broods, revealed no female preference in relation to hatching regime. We did however find strong evidence that, as adults, late-hatched males were more attractive to females than siblings that had hatched earlier. Meanwhile, we found a weak trend towards early-hatched females depositing more carotenoids and retinol in the egg yolk than late-hatched or synchronously hatched females, although there were no differences in terms of clutch characteristics or the deposition of α-tocopherol or γ-tocopherol in the egg yolk. Therefore, we found that the beneficial long-term consequences of hatching asynchrony were sex specific, being accrued by late-hatched male nestlings and by early-hatched female nestlings. Consequently, we conclude that the long-term consequences of hatching asynchrony are more complex than previously realised. © 2012 the Linnean Society of London.
Abstract.
Blount JD, Rowland HM, Drijfhout FP, Endler JA, Inger R, Sloggett JJ, Hurst GDD, Hodgson DJ, Speed MP (2012). How the ladybird got its spots: Effects of resource limitation on the honesty of aposematic signals.
Functional Ecology,
26(2), 334-342.
Abstract:
How the ladybird got its spots: Effects of resource limitation on the honesty of aposematic signals
Prey species often possess defences (e.g. toxins) coupled with warning signals (i.e. aposematism). There is growing evidence that the expression of aposematic signals often varies within species and correlates with the strength of chemical defences. This has led to the speculation that such signals may be 'honest', with signal reliability ensured by the costliness of producing or maintaining aposematic traits. We reared larval seven-spot ladybirds (Coccinella septempunctata) on a Low or High aphid diet and measured the effects on warning signal expression (elytral carotenoid pigmentation, conspicuousness, spot size), levels of defensive alkaloids (precoccinelline, coccinelline), and relationships between these traits. High-diet individuals had greater total precoccinelline levels, and elytra carotenoid concentrations at adulthood which was detectable to a typical avian predator. However, larval diet did not significantly affect adult body mass or size, spot size or coccinelline levels. Elytra carotenoid concentrations correlated positively with total precoccinelline levels in both diet groups and sexes. However, the relationship between elytra carotenoid concentrations and total levels of coccinelline depended on sex: in both diet groups, elytra carotenoids and coccinelline levels were positively correlated in females, but negatively correlated in males. Spot size and coccinelline levels correlated positively in Low-diet individuals, but negatively in High-diet individuals. These results point to physiological linkages between components of aposematism, which are modulated by resource (i.e. food) availability and affect the honesty of signals. Developmental diet, but also sex, influenced the relationships between signals and toxin levels. Ladybirds are sexually size dimorphic, and thus in comparison with males, females may be more susceptible to resource limitation and more likely to be honest signallers. © 2012 the Authors. Functional Ecology © 2012 British Ecological Society.
Abstract.
Sepp T, Sild E, Blount JD, Männiste M, Karu U, Hõrak P (2012). Individual consistency and covariation of measures of oxidative status in greenfinches.
Physiol Biochem Zool,
85(3), 299-307.
Abstract:
Individual consistency and covariation of measures of oxidative status in greenfinches.
Oxidative stress results from a mismatch between production of reactive oxygen species (ROS) and the organism's capacity to mitigate their damaging effects by building up sufficient antioxidant protection and/or repair mechanisms. Because ROS production is a universal consequence of cellular metabolism and immune responses, evolutionary animal ecologists have become increasingly interested in involvement of oxidative stress as a proximate mechanism responsible for the emergence of trade-offs related to the evolution of life-history and signal traits. Among the most practical problems pertinent to ecological research on oxidative stress is finding a combination of biomarkers of oxidative status that can be applied to typical wild animal models such as small birds, mammals, and reptiles. This study describes covariation and individual consistency of eight parameters of oxidative status in a small passerine bird, wild-caught captive greenfinch (Carduelis chloris). We measured two markers of plasma antioxidant potential--total antioxidant capacity (TAC) and oxygen radical absorbance (OXY)--and concentrations of one lipophilic (carotenoids) and two hydrophilic (uric acid and ascorbate) antioxidants in plasma. We also measured total glutathione (GSH) concentration and superoxide dismutase (SOD) activity in erythrocytes. Oxidative damage was assessed on the basis of plasma malondialdehyde (MDA) levels, measured by high-performance liquid chromatography. Plasma carotenoids, TAC, and erythrocyte GSH showed significant individual consistency over an 8-d period, indicating that those variables reflected more persistent differences between individuals than plasma OXY, MDA, and uric acid. We did not detect any strong or moderate correlations between the studied parameters, which suggests that all of these biomarkers contain potentially unique information. Injection of a synthetic mimetic of SOD and catalase--EUK-134--did not affect any of the parameters of oxidative status. Capability of phagocytes to produce oxidative burst was not associated with MDA, indicating that under our experimental conditions, ROS production by phagocytes was not a strong determinant of oxidative damage. Altogether these findings suggest that attempts to characterize oxidative balance should use a wide range of biomarkers, and further studies of oxidative status in wild animals may benefit from the experimental induction of oxidative stress.
Abstract.
Author URL.
Selman C, Blount JD, Nussey DH, Speakman JR (2012). Oxidative damage, ageing, and life-history evolution: Where now?.
Trends in Ecology and Evolution,
27(10), 570-577.
Abstract:
Oxidative damage, ageing, and life-history evolution: Where now?
The idea that resources are limited and animals can maximise fitness by trading costly activities off against one another forms the basis of life-history theory. Although investment in reproduction or growth negatively affects survival, the mechanisms underlying such trade-offs remain obscure. One plausible mechanism is oxidative damage to proteins, lipids, and nucleic acids caused by reactive oxygen species (ROS). Here, we critically evaluate the premise that ROS-induced oxidative damage shapes life history, focussing on birds and mammals, and highlight the importance of ecological studies examining free-living animals within this experimental framework. We conclude by emphasising the value of using multiple assays to determine oxidative protection and damage. We also highlight the importance of using standardised and appropriate protocols, and discuss future research directions. © 2012 Elsevier Ltd.
Abstract.
Selman C, Blount JD, Nussey DH, Speakman JR (2012). Oxidative damage, ageing, and life-history evolution: where now?. Trends in Ecology and Evolution
Orledge JM, ROYLE NJ, BLOUNT JD, PIKE TW, HOODLESS AN (2012). Synergistic effects of supplementation of dietary antioxidants during growth on adult phenotype in ring-necked pheasants, Phasianus colchicus.
Heidinger BJ, Blount JD, Boner W, Griffiths K, Metcalfe NB, Monaghan P (2012). Telomere Length in Early Life Predicts Life Span EDITORIAL COMMENT.
OBSTETRICAL & GYNECOLOGICAL SURVEY,
67(5), 283-284.
Author URL.
Heidinger BJ, Blount JD, Boner W, Griffiths K, Metcalfe NB, Monaghan P (2012). Telomere length in early life predicts life span. Obstetrical and Gynecological Survey, 67(5), 283-284.
Heidinger BJ, Blount JD, Boner W, Griffiths K, Metcalfe NB, Monaghan P (2012). Telomere length in early life predicts lifespan. Proc. Nat. Acad. Sci. USA
Flores EE, Moore AJ, Blount JD (2012). Unusual whitish eggs in the poison frog Dendrobates auratus Girard, 1855.
Tropical Zoology,
25(2), 67-73.
Abstract:
Unusual whitish eggs in the poison frog Dendrobates auratus Girard, 1855
Poison frogs in the genus Dendrobates (sensu Grant et al. 2006) are known to lay black pigmented eggs. During a field study in May 2010 in central Panama, a captive pair of wild-caught adult Dendrobates auratus laid a clutch of whitish eggs. The eggs developed and metamorphic froglets were similar in size and color to that of age-matched normal-colored tadpoles produced by different parents and reared in exactly the same conditions. The observation of a pale pigmented tadpole in the wild suggests that polymorphism in the degree of melanism is not simply an artifact of laboratory rearing. Our study is the first to report the production of viable whitish eggs by any species in the genus Dendrobates. Whether this coloration arises due to constraint or is a polymorphism that has adaptive significance awaits further study. © Istituto per lo Studio degli Ecosistemi of the Consiglio Nazionale delle Ricerche, Firenze 2012.
Abstract.
Blount JD, Speed MP, Ruxton GD, Stephens PA (2012). Warning displays may function as honest signals of toxicity.
Proceedings of the Royal Society B: Biological Sciences,
276(1658), 871-877.
Abstract:
Warning displays may function as honest signals of toxicity
Many prey species use colourful 'aposematic' signalling to advertise the fact that they are toxic. Some recent studies have shown that the brightness of aposematic displays correlates positively with the strength of toxicity, suggesting that aposematic displays are a form of handicap signal, the conspicuousness of which reliably indicates the level of toxicity. The theoretical consensus in the literature is, however, at odds with this finding. It is commonly assumed that the most toxic prey should have less bright advertisements because they have better chances of surviving attacks and can therefore reduce the costs incurred by signalling. Using a novel theoretical model, we show that aposematic signals can indeed function as handicaps. To generate this prediction, we make a key assumption that the expression of bright displays and the storage of anti-predator toxins compete for resources within prey individuals. One shared currency is energy. However, competition for antioxidant molecules, which serve dual roles as pigments and in protecting prey against oxidative stress when they accumulate toxins, provides a specific candidate resource that could explain signal honesty. Thus, contrary to the prevailing theoretical orthodoxy, warning displays may in fact be honest signals of the level of (rather than simply the existence of) toxicity. © 2008 the Royal Society.
Abstract.
Blount JD, Pike TW (2011). Deleterious effects of light exposure on immunity and sexual colouration in birds.
Functional EcologyAbstract:
Deleterious effects of light exposure on immunity and sexual colouration in birds
1. Sunlight ultraviolet (UV) exposure can be highly damaging to biological tissues, being known to cause cellular damage and immunosuppression in humans and rodents, and depletion of carotenoid-based sexual plumage colouration in birds (i.e. photobleaching). However, it remains unknown whether sunlight may cause photobleaching in living tissues that comprise sexual signals such as bare parts in birds. It seems possible that any carotenoids depleted from bare parts by sunlight could be replenished, but if so, this could impact the availability of carotenoids for other functions such as immunity and antioxidant defence. Such trade-offs seem particularly likely in individuals that have a low dietary intake of carotenoids, or small amounts of carotenoids in body storage.
2. We investigated the effects of exposure to simulated sunlight UV (UV+) on bill colouration, blood plasma and liver (i.e. body storage) carotenoids, and pro-inflammatory immune responses in male zebra finches (Taeniopygia guttata) in vivo, compared to individuals maintained in an identical environment but with the UV wavelengths removed by a filter (UV-). We also investigated whether any deleterious effects of UV exposure were mitigated by dietary carotenoid supplementation (UV+ Car+).
3. Exposure to simulated sunlight UV was associated with low levels of carotenoids in liver, and elevated levels of carotenoids in blood plasma, suggesting mobilisation of stored carotenoids. Simulated sunlight UV also caused impaired pro-inflammatory immune responses, whereas this was not seen in carotenoid-supplemented birds. We found no effects of simulated sunlight UV or carotenoid supplementation on oxidative damage in blood plasma or bill.
4. Bill ‘carotenoid chroma’ diminished, and bill ‘UV chroma’ correspondingly increased, in all groups during the experiment (i.e. even in UV+ Car+ birds, and in UV- birds). This likely arose because the illuminance in the experimental cages was far higher than in standard laboratory housing conditions, and suggests that carotenoid pigmentation is highly susceptible to photobleaching even under exposure to human-visible wavelengths.
5. These results highlight the potential for sunlight exposure to invoke a range of deleterious consequences for birds, including photobleaching and depression of immunity via pathways mediated by carotenoid allocation trade-offs. The expression of carotenoid-based sexual signals may therefore reveal an individual’s history of sunlight exposure and its deleterious effects on immunity.
Abstract.
Pike TW, Bjerkeng B, Blount JD, Lindström J, Metcalfe NB (2011). How integument colour reflects its carotenoid content: a stickleback's perspective.
Functional Ecology,
25(1), 297-304.
Abstract:
How integument colour reflects its carotenoid content: a stickleback's perspective
1.Carotenoid-based signals typically vary in both the total concentration of carotenoids deposited and the relative quantities of different constituent carotenoids. As these constituents often have differing spectral properties, the relative and absolute concentrations of different carotenoids deposited in a signal can significantly affect the spectrum of light reflected. A critical but rarely tested assumption of hypotheses concerning the information content of carotenoid-based signals is that their colour directly reveals the concentration and composition of constituent carotenoids to intended recipients. Most previous studies have attempted to address this question using either photographic techniques or by analysing recorded reflectance spectra, neither of which take into account the specific properties of the receiver's visual system. 2.Here, we use psychophysical models of the visual system of three-spined sticklebacks (Gasterosteus aculeatus) to estimate their sensitivity to variation in the concentration and relative abundance of constituent carotenoids of males' carotenoid-based sexual signals. 3.We demonstrate that sticklebacks are acutely sensitive to variation in both the total concentration of carotenoids in the signal and the relative proportion of its constituents, and that the accuracy of these assessments is largely unaffected by the presence or absence of ultraviolet radiation in the illuminant. We discuss these findings in relation to the evolution, maintenance and information content of carotenoid-based sexual signals. © 2010 the Authors. Functional Ecology © 2010 British Ecological Society.
Abstract.
Losdat S, Richner H, Blount JD, Helfenstein F (2011). Immune activation reduces sperm quality in the great tit.
PLoS ONE,
6(7).
Abstract:
Immune activation reduces sperm quality in the great tit
Mounting an immune response against pathogens incurs costs to organisms by its effects on important life-history traits, such as reproductive investment and survival. As shown recently, immune activation produces large amounts of reactive species and is suggested to induce oxidative stress. Sperm are highly susceptible to oxidative stress, which can negatively impact sperm function and ultimately male fertilizing efficiency. Here we address the question as to whether mounting an immune response affects sperm quality through the damaging effects of oxidative stress. It has been demonstrated recently in birds that carotenoid-based ornaments can be reliable signals of a male's ability to protect sperm from oxidative damage. In a full-factorial design, we immune-challenged great tit males while simultaneously increasing their vitamin E availability, and assessed the effect on sperm quality and oxidative damage. We conducted this experiment in a natural population and tested the males' response to the experimental treatment in relation to their carotenoid-based breast coloration, a condition-dependent trait. Immune activation induced a steeper decline in sperm swimming velocity, thus highlighting the potential costs of an induced immune response on sperm competitive ability and fertilizing efficiency. We found sperm oxidative damage to be negatively correlated with sperm swimming velocity. However, blood resistance to a free-radical attack (a measure of somatic antioxidant capacity) as well as plasma and sperm levels of oxidative damage (lipid peroxidation) remained unaffected, thus suggesting that the observed effect did not arise through oxidative stress. Towards the end of their breeding cycle, swimming velocity of sperm of more intensely colored males was higher, which has important implications for the evolution of mate choice and multiple mating in females because females may accrue both direct and indirect benefits by mating with males having better quality sperm. © 2011 Losdat et al.
Abstract.
Losdat S, Richner H, Blount JD, Helfenstein F (2011). Immune activation reduces sperm quality in the great tit.
PLoS ONE,
6(7), 1-10.
Abstract:
Immune activation reduces sperm quality in the great tit.
Mounting an immune response against pathogens incurs costs to organisms by its effects on important life-history traits, such as reproductive investment and survival. As shown recently, immune activation produces large amounts of reactive species and is suggested to induce oxidative stress. Sperm are highly susceptible to oxidative stress, which can negatively impact sperm function and ultimately male fertilizing efficiency. Here we address the question as to whether mounting an immune response affects sperm quality through the damaging effects of oxidative stress. It has been demonstrated recently in birds that carotenoid-based ornaments can be reliable signals of a male's ability to protect sperm from oxidative damage. In a full-factorial design, we immune-challenged great tit males while simultaneously increasing their vitamin E availability, and assessed the effect on sperm quality and oxidative damage. We conducted this experiment in a natural population and tested the males' response to the experimental treatment in relation to their carotenoid-based breast coloration, a condition-dependent trait. Immune activation induced a steeper decline in sperm swimming velocity, thus highlighting the potential costs of an induced immune response on sperm competitive ability and fertilizing efficiency. We found sperm oxidative damage to be negatively correlated with sperm swimming velocity. However, blood resistance to a free-radical attack (a measure of somatic antioxidant capacity) as well as plasma and sperm levels of oxidative damage (lipid peroxidation) remained unaffected, thus suggesting that the observed effect did not arise through oxidative stress. Towards the end of their breeding cycle, swimming velocity of sperm of more intensely colored males was higher, which has important implications for the evolution of mate choice and multiple mating in females because females may accrue both direct and indirect benefits by mating with males having better quality sperm.
Abstract.
Teuber K, Schiller J, Jakop U, Lüpold S, Orledge JM, Blount JD, Royle NJ, Hoodless A, Müller K (2011). MALDI-TOF mass spectrometry as a simple tool to determine the phospholipid/glycolipid composition of sperm: pheasant spermatozoa as one selected example.
Anim Reprod Sci,
123(3-4), 270-278.
Abstract:
MALDI-TOF mass spectrometry as a simple tool to determine the phospholipid/glycolipid composition of sperm: pheasant spermatozoa as one selected example.
Cellular membranes are composed of highly variable lipid molecules, mainly cholesterol and phospholipids (PLs). The cholesterol moiety and the saturation degree of the fatty acyl residues of PL determine the fluidity of the membrane, which is particularly important for sperm because they have to undergo characteristic membrane-dependent processes (acrosomal exocytosis and fusion with the oocyte). Glycolipids are an essential part of the membrane surface acting as key mediators in the interactions of sperm with components of the female genital tract. Although the lipid composition of many mammalian spermatozoa has already been determined, the lipid composition of avian spermatozoa has scarcely been investigated. Using spermatozoa extracts of the ring-necked pheasant (Phasianus colchicus) as a selected example, this work demonstrates that matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a simple and fast method to determine spermatozoal lipid compositions. The lipid compositions of pheasant spermatozoa have not yet been investigated. In addition to common membrane (primarily diacyl) PL (sphingomyelin, phosphatidylcholine, phosphatidylinositol and phosphatidylethanolamine), remarkable variation of different sulfoglycolipids (sulfogalactocerebrosides) was identified. This is in strong contrast to all other animal species investigated so far which nearly exclusively contain the sulfoglycolipid seminolipid (sulfogalactoalkylacylglycerol). We emphasize that the MALDI MS approach allows the characterization of sulfoglycolipids of sperm within a few minutes without the necessity for previous chromatographic separation.
Abstract.
Okada K, Blount JD, Sharma MD, Snook RR, Hosken DJ (2011). Male attractiveness, fertility and susceptibility to oxidative stress are influenced by inbreeding in Drosophila simulans.
J Evol Biol,
24(2), 363-371.
Abstract:
Male attractiveness, fertility and susceptibility to oxidative stress are influenced by inbreeding in Drosophila simulans.
Inbreeding frequently leads to inbreeding depression, a reduction in the trait values of inbred individuals. Inbreeding depression has been documented in sexually selected characters in several taxa, and while there is correlational evidence that male fertility is especially susceptible to inbreeding depression, there have been few direct experimental examinations of this. Here, we assessed inbreeding depression in male fertility and a range of other male fitness correlates in Drosophila simulans. We found that male fertility and attractiveness were especially susceptible to inbreeding depression. Additionally, levels of testicular oxidative stress were significantly elevated in inbred males, although sperm viability did not differ between inbred and outbred males. Copulation duration, induction of oviposition, and the proportion of eggs hatching did not differ for females mated to inbred or outbred males. Nevertheless, our results clearly show that key male fitness components are impaired by inbreeding and provide evidence that aspects of male fertility are especially susceptible to inbreeding depression.
Abstract.
Author URL.
Royle NJ, Hall ME, Blount JD, Forbes S (2011). Patterns of egg yolk antioxidant co-variation in an avian brood parasite-host system.
Behavioral Ecology and Sociobiology,
65(2), 313-323.
Abstract:
Patterns of egg yolk antioxidant co-variation in an avian brood parasite-host system
Despite their importance to offspring fitness outcomes, there has been little previous work on egg-mediated maternal effects in avian brood parasites which lay their eggs in the nests of other species. Here, we examine patterns of egg yolk antioxidant deposition in an avian host (red-winged blackbird, Agelaius phoeniceus) and their brood parasite (brown-headed cowbird, Molothrus ater). Cowbird nestlings compete directly for food with host blackbird chicks and succeed, despite hatching from a smaller egg, by begging more intensely and growing as or more rapidly than their hosts. Dietary-derived antioxidants, such as carotenoids and vitamins E and A, deposited in egg yolk, may enhance growth rate and reduce oxidative stress, and therefore provide a potential mechanism by which female cowbirds could enhance the competitiveness of their young in host nests. However, provision of antioxidants to eggs is costly so we predicted that female cowbirds should adjust the amount of antioxidants in response to variation in host quality. We found that whilst red-winged blackbird clutches parasitised by cowbirds did not differ in the pattern of antioxidant deposition compared to non-parasitised clutches, levels of vitamin E deposited in cowbird eggs were closely matched to that of the individual host clutch in which cowbirds laid their egg. This supports the prediction that female cowbirds adjust the antioxidant concentration of their eggs to increase the likely competitiveness of their offspring in the host nest into which they are laid and may help explain the success of cowbirds in competing with larger host young. © 2010 Springer-Verlag.
Abstract.
Weber SB, Blount JD, Godley BJ, Witt MJ, Broderick AC (2011). Rate of egg maturation in marine turtles exhibits 'universal temperature dependence'.
J Anim Ecol,
80(5), 1034-1041.
Abstract:
Rate of egg maturation in marine turtles exhibits 'universal temperature dependence'.
1. The metabolic theory of ecology (MTE) predicts that, after correcting for body mass variation among organisms, the rates of most biological processes will vary as a universal function of temperature. However, empirical support for 'universal temperature dependence' (UTD) is currently equivocal and based on studies of a limited number of traits. 2. In many ectothermic animals, the rate at which females produce mature eggs is temperature dependent and may be an important factor in determining the costs of reproduction. 3. We tested whether the rate of egg maturation in marine turtles varies with environmental temperature as predicted by MTE, using the time separating successive clutches of individual females to estimate the rate at which eggs are formed. We also assessed the phenotypic contribution to this rate, by using radio telemetry to make repeated measurements of interclutch intervals for individual green turtles (Chelonia mydas). 4. Rates of egg maturation increased with seasonally increasing water temperatures in radio-tracked green turtles, but were not repeatable for individual females, and did not vary according to maternal body size or reproductive investment (number and size of eggs produced). 5. Using a collated data set from several different populations and species of marine turtles, we then show that a single relationship with water temperature explains most of the variation in egg maturation rates, with a slope that is statistically indistinguishable from the UTD predicted by MTE. However, several alternative statistical models also described the relationship between temperature and egg maturation rates equally parsimoniously. 6. Our results offer novel support for the MTE's predicted UTD of biological rates, although the underlying mechanisms require further study. The strong temperature dependence of egg maturation combined with the apparently weak phenotypic contribution to this rate has interesting behavioural implications in ectothermic animals. We suggest that maternal thermoregulatory behaviour in marine turtles, and many other reptiles, is consistent with a strategy of adaptively increasing body temperatures to accelerate egg maturation.
Abstract.
Author URL.
Harrison XA, Blount J, Inger R, Bearhop S (2010). Carry-over Effects as Drivers of Fitness in Animals. Journal of Animal Ecology, 79, 974-982.
Pike TW, Blount JD, Metcalfe NB, Lindström J (2010). Dietary carotenoid availability and reproductive effort influence the age-related decline in performance.
Behavioral Ecology,
21(5), 1048-1053.
Abstract:
Dietary carotenoid availability and reproductive effort influence the age-related decline in performance
Elevated breeding effort is known to increase an individual's rate of senescence, although the underlying mechanisms are not well understood. One possibility is that the ability to resist senescence is limited by the availability of antioxidants, which are necessary to mitigate the deleterious effects of oxidative stress thought to underlie the aging process. Susceptibility to oxidative stress is likely to be particularly high during reproduction, and so for a given level of reproductive effort, the rate of senescence should be fastest in those individuals with the poorest antioxidant capacity. We tested this hypothesis in an experimental study of breeding male three-spined sticklebacks (Gasterosteus aculeatus) held under a high or low reproduction regime and fed on either high or low levels of carotenoids (potentially limiting dietary compounds with antioxidant properties). Fish on the high reproduction regime and those on the low-carotenoid diet both showed an accelerated decline in sustained swimming performance (an indicator of locomotor senescence) compared with males on the low reproduction regime and high-carotenoid diet, respectively. The swimming performance of fish subjected to the high rate of reproduction, but fed a low-carotenoid diet, appeared to decline most rapidly, perhaps because of the additive effects of increased levels of reproduction-induced oxidative stress and lower antioxidant availability. These findings show that both dietary carotenoid intake and breeding effort can impact on the age-related decline in swimming performance and have important implications for female choice and the capacity of males with insufficient antioxidant defenses to adequately perform paternal care. © 2010 the Author.
Abstract.
Pike TW, Blount JD, Lindström J, Metcalfe NB (2010). Dietary carotenoid availability, sexual signalling and functional fertility in sticklebacks.
Biol Lett,
6(2), 191-193.
Abstract:
Dietary carotenoid availability, sexual signalling and functional fertility in sticklebacks.
In species where males express carotenoid-based sexual signals, more intensely coloured males may be signalling their enhanced ability to combat oxidative stress. This may include mitigating deleterious oxidative damage to their sperm, and so be directly related to their functional fertility. Using a split-clutch in vitro fertilization technique and dietary carotenoid manipulation, we demonstrate that in non-competitive fertilization assays, male three-spined sticklebacks (Gasterosteus aculeatus) that are fed higher (but biologically relevant) levels of carotenoids had a significantly increased fertilization success, irrespective of maternal carotenoid intake. Furthermore, within diet groups, a male's fertilization success was positively related to the expression of his carotenoid-based nuptial coloration, with more intensely coloured males having higher functional fertility. These data provide, to our knowledge, the first demonstration that dietary access to carotenoids influences fertilization success, and suggest that females could use a male's nuptial coloration as an indicator of his functional fertility.
Abstract.
Author URL.
Speed MP, Ruxton GD, Blount JD, Stephens PA (2010). Diversification of honest signals in a predator-prey system.
Ecology Letters,
13(6), 744-753.
Abstract:
Diversification of honest signals in a predator-prey system
Many animals use bright colouration to advertise their toxicity to predators. It is now well established that both toxicity and colouration are often variable within prey populations, yet it is an open question whether or not brighter signals should be used by the more toxic members of the population. We therefore describe a model in which signal honesty can easily be explained. We assumed that prey toxicity is environmentally conferred and variable between individuals, and that signalling bears a cost through attracting the attention of predators. A key assumption is that predators know the mean toxicity associated with each signalling level, so that the probability of attack for each signal value declines as mean toxicity associated with that signal increases. The probability of death given attack for each individual, however, declines with the precise value of its own toxicity, and prey must evolve the optimal level of signal to match the toxicity level that they acquire from their environments. At the start of our simulations there is no signalling system, as neither prey nor predators have biases that favour signal diversification. Over evolutionary time, however, a positive correlation emerges between signal strength and the mean toxicity associated with each signal level. When stability is reached, predators change their behaviour so that they now tend to avoid prey that signal conspicuously. In addition to predicting within-species signal reliability, our model can explain the initial evolution of aposematic displays without the need to assume special biases in predators. © 2010 Blackwell Publishing Ltd/CNRS.
Abstract.
Hall ME, Blount JD, Forbes S, Royle NJ (2010). Does oxidative stress mediate the trade-off between growth and self-maintenance in structured families?.
Functional Ecology,
24(2), 365-373.
Abstract:
Does oxidative stress mediate the trade-off between growth and self-maintenance in structured families?
Life-history theory predicts a trade-off between growth and self-maintenance. However, little is known about the underlying mechanisms. Oxidative stress, the imbalance between the production of reactive oxygen species (ROS) during normal metabolic processes and the level of antioxidant defences, is a potential mechanism. In many altricial birds asynchronous hatching creates different castes of progeny as a hedge against developmental and environmental uncertainty (a 'structured' family). Older, 'core' offspring and later hatched 'marginal' offspring consequently experience contrasting levels of resource availability during development. To be adaptive the phenotypic handicap incurred by marginal offspring must be reversible when conditions allow. Dietary-derived antioxidants are an important component of antioxidant defences, which modulate oxidative damage arising from normal metabolic processes such as growth. Dietary antioxidants could therefore be important determinants of trade-offs during growth, with the balance of these trade-offs differing between core and marginal offspring. To investigate this, we manipulated brood size and structure as well as antioxidant availability (by vitamin and mineral supplementation), then measured growth and oxidative damage in nestling red-winged blackbirds Agelaius phoeniceus. We found that individuals supplemented with dietary antioxidants allocated these extra resources to increasing growth rate, rather than reducing oxidative damage. Irrespective of hatch rank, nestlings that received supplementary antioxidants grew faster than controls, despite no difference in their begging behaviour or parental provisioning rates. There was no overall difference in the level of lipid peroxidation (malondialdehyde; MDA) in the blood plasma of supplemented and control chicks, but among marginal offspring those that received an antioxidant supplement had lower plasma MDA. Antioxidant supplementation did not affect nestling survival to fledging age. These novel results support the idea that oxidative stress may play a central role in the trade-off between growth and self-maintenance. Moreover, they further highlight the importance of physiological costs in the evolution of life-histories and propose a role for oxidative stress in the adaptive basis of the structured family. © 2009 the Authors. Journal compilation © 2009 British Ecological Society.
Abstract.
Mougeot F, Martínez-Padilla J, Blount JD, Pérez-Rodríguez L, Webster LMI, Piertney SB (2010). Oxidative stress and the effect of parasites on a carotenoid-based ornament. Journal of Experimental Biology, 213(10), 1796-1796.
Mougeot F, Martínez-Padilla J, Blount JD, Pérez-Rodríguez L, Webster LMI, Piertney SB (2010). Oxidative stress and the effect of parasites on a carotenoid-based ornament.
Journal of Experimental Biology,
213(3), 400-407.
Abstract:
Oxidative stress and the effect of parasites on a carotenoid-based ornament
Oxidative stress, the physiological condition whereby the production of reactive oxygen and nitrogen species overwhelms the capacity of antioxidant defences, causes damage to key bio-molecules. It has been implicated in many diseases, and is proposed as a reliable currency in the trade-off between individual health and ornamentation. Whether oxidative stress mediates the expression of carotenoid-based signals, which are among the commonest signals of many birds, fish and reptiles, remains controversial. In the present study, we explored interactions between parasites, oxidative stress and the carotenoid-based ornamentation of red grouse Lagopus lagopus scoticus. We tested whether removing nematode parasites influenced both oxidative balance (levels of oxidative damage and circulating antioxidant defences) and carotenoid-based ornamentation. At the treatment group level, parasite purging enhanced the size and colouration of ornaments but did not significantly affect circulating carotenoids, antioxidant defences or oxidative damage. However, relative changes in these traits among individuals indicated that males with a greater number of parasites prior to treatment (parasite purging) showed a greater increase in the levels of circulating carotenoids and antioxidants, and a greater decrease in oxidative damage, than those with initially fewer parasites. At the individual level, a greater increase in carotenoid pigmentation was associated with a greater reduction in oxidative damage. Therefore, an individual's ability to express a carotenoid-based ornament appeared to be linked to its current oxidative balance and susceptibility to oxidative stress. Our experimental results suggest that oxidative stress can mediate the impact of parasites on carotenoid-based signals, and we discuss possible mechanisms linking carotenoid-based ornaments to oxidative stress. ©2010. Published by the Company of Biologists Ltd.
Abstract.
Helfenstein F, Losdat S, Møller AP, Blount JD, Richner H (2010). Sperm of colourful males are better protected against oxidative stress.
Ecology Letters,
13(2), 213-222.
Abstract:
Sperm of colourful males are better protected against oxidative stress
Sperm cells are highly vulnerable to free radicals, and sperm quality and male fertility are critically affected by oxidative stress. Recently, sexual ornaments, particularly carotenoid-based colourful traits, have been proposed to depend on a male's capacity to resist oxidative stress, and thus to signal sperm quality. We conducted an experimental test of this hypothesis on great tits Parus major, in which adults are sexually dichromatic in carotenoid-based breast plumage. We report the first evidence that ornaments and sperm quality may be linked through oxidative stress. When experimentally subjected to oxidative stress resulting from increased workload, less colourful males suffered a greater reduction in sperm motility and swimming ability, and increased levels of sperm lipid peroxidation compared to more colourful males. Moreover, the level of sperm lipid peroxidation was negatively correlated with sperm quality. Finally, carotenoid supplementation increased sperm quality of less colourful males, suggesting that pale males are deficient in carotenoid antioxidants. © 2009 Blackwell Publishing Ltd/CNRS.
Abstract.
Svensson PA, Blount JD, Forsgren E, Amundsen T (2009). Female ornamentation and egg carotenoids of six sympatric gobies.
Journal of Fish Biology,
75(10), 2777-2787.
Abstract:
Female ornamentation and egg carotenoids of six sympatric gobies
Belly colouration, gonad carotenoid concentration and skin transparency were quantified in gravid Gobiusculus flavescens, as well as in females of five sympatric gobies where belly ornamentation has not been described. Although G. flavescens females did, indeed, have far more colourful bellies than the other species, this could only in part be explained by a high concentration of total gonad carotenoids. Comparable, or occasionally higher, carotenoid levels were found in the gonads of other species. Instead, the unusual ornamentation of G. flavescens arises from a unique combination of carotenoid-rich gonads and a highly transparent abdominal skin. © 2009 the Fisheries Society of the British Isles.
Abstract.
Mougeot F, Martínez-Padilla J, Webster LMI, Blount JD, Pérez-Rodríguez L, Piertney SB (2009). Honest sexual signalling mediated by parasite and testosterone effects on oxidative balance.
Proceedings of the Royal Society B: Biological Sciences,
276(1659), 1093-1100.
Abstract:
Honest sexual signalling mediated by parasite and testosterone effects on oxidative balance
Extravagant ornaments evolved to advertise their bearers' quality, the honesty of the signal being ensured by the cost paid to produce or maintain it. The oxidation handicap hypothesis (OHH) proposes that a main cost of testosterone-dependent ornamentation is oxidative stress, a condition whereby the production of reactive oxygen and nitrogen species (ROS/RNS) overwhelms the capacity of antioxidant defences. ROS/RNS are unstable, very reactive by-products of normal metabolic processes that can cause extensive damage to key biomolecules (cellular proteins, lipids and DNA). Oxidative stress has been implicated in the aetiology of many diseases and could link ornamentation and genetic variation in fitness-related traits. We tested the OHH in a free-living bird, the red grouse. We show that elevated testosterone enhanced ornamentation and increased circulating antioxidant levels, but caused oxidative damage. Males with smaller ornaments suffered more oxidative damage than those with larger ornaments when forced to increase testosterone levels, consistent with a handicap mechanism. Parasites depleted antioxidant defences, caused oxidative damage and reduced ornament expression. Oxidative damage extent and the ability of males to increase antioxidant defences also explained the impacts of testosterone and parasites on ornamentation within treatment groups. Because oxidative stress is intimately linked to immune function, parasite resistance and fitness, it provides a reliable currency in the trade-off between individual health and ornamentation. The costs induced by oxidative stress can apply to a wide range of signals, which are testosterone-dependent or coloured by pigments with antioxidant properties. © 2008 the Royal Society.
Abstract.
Nussey DH, Pemberton JM, Pilkington JG, Blount JD (2009). Life history correlates of oxidative damage in a free-living mammal population.
Functional Ecology,
23(4), 809-817.
Abstract:
Life history correlates of oxidative damage in a free-living mammal population
Reactive oxygen species, produced as a by-product of normal metabolism, can cause intracellular damage and negatively impact on cell function. Such oxidative damage has been proposed as an evolutionarily important cost of growth and reproduction and as a mechanistic explanation for organismal senescence, although few tests of these ideas have occurred outside the laboratory.2. Here, we examined correlations between a measure of phospholipid oxidative damage in plasma samples and age, growth rates, parasite burden and investment in reproduction in a population of wild Soay sheep on St. Kilda, Scotland.3. We found that, amongst females of different ages, lambs had significantly elevated levels of oxidative damage compared to all other age classes and there was no evidence of increasing damage with age amongst adult sheep.4. Amongst lambs, levels of oxidative damage increased significantly with increasing growth rates over the first 4 months of life. Neither mean damage nor the effect of growth rate on damage differed between male and female lambs.5. Amongst adult female sheep, there was no evidence that body mass, current parasite burden or metrics of recent and past reproductive effort significantly predicted oxidative damage levels.6.This study is the first to examine age variation in an assay of oxidative damage and correlations between oxidative damage, growth and reproduction in a wild mammal. Our results suggest strong links between early conditions and oxidative damage in lambs, but also serve to highlight the limitations of cross-sectional data for studies examining associations between oxidative stress, ageing and life history in free-living populations. © 2009 British Ecological Society.
Abstract.
Lindström J, Pike TW, Blount JD, Metcalfe NB (2009). Optimization of resource allocation can explain the temporal dynamics and honesty of sexual signals.
Am Nat,
174(4), 515-525.
Abstract:
Optimization of resource allocation can explain the temporal dynamics and honesty of sexual signals.
In species in which males are free to dynamically alter their allocation to sexual signaling over the breeding season, the optimal investment in signaling should depend on both a male's state and the level of competition he faces at any given time. We developed a dynamic optimization model within a game-theoretical framework to explore the resulting signaling dynamics at both individual and population levels and tested two key model predictions with empirical data on three-spined stickleback (Gasterosteus aculeatus) males subjected to dietary manipulation (carotenoid availability): (1) fish in better nutritional condition should be able to maintain their signal for longer over the breeding season, resulting in an increasingly positive correlation between nutritional status and signal (i.e. increasing signal honesty), and (2) female preference for more ornamented males should thus increase over the breeding season. Both predictions were supported by the experimental data. Our model shows how such patterns can emerge from the optimization of resource allocation to signaling in a competitive situation. The key determinants of the honesty and dynamics of sexual signaling are the condition dependency of male survival, the initial frequency distribution of nutritional condition in the male population, and the cost of signaling.
Abstract.
Author URL.
Gasparini J, Bize P, Piault R, Wakamatsu K, Blount JD, Ducrest AL, Roulin A (2009). Strength and cost of an induced immune response are associated with a heritable melanin-based colour trait in female tawny owls.
Journal of Animal Ecology,
78(3), 608-616.
Abstract:
Strength and cost of an induced immune response are associated with a heritable melanin-based colour trait in female tawny owls
Melanin pigments provide the most widespread source of coloration in vertebrates, but the adaptive function of such traits remains poorly known. 2. In a wild population of tawny owls (Strix aluco), we investigated the relationships between plumage coloration, which varies continuously from dark to pale reddish, and the strength and cost of an induced immune response. 3. The degree of reddishness in tawny owl feather colour was positively correlated with the concentration of phaeomelanin and eumelanin pigments, and plumage coloration was highly heritable (h2 = 0·93). No carotenoids were detected in the feathers. 4. In mothers, the degree of melanin-based coloration was associated with antibody production against a vaccine, with dark reddish females maintaining a stronger level of antibody for a longer period of time compared to pale reddish females, but at a cost in terms of greater loss of body mass. 5. A cross-fostering experiment showed that, independent of maternal coloration, foster chicks reared by vaccinated mothers were lighter than those reared by nonvaccinated mothers. Hence, even though dark reddish mothers suffered a stronger immune cost than pale reddish mothers, this asymmetric cost was not translated to offspring growth. 6. Our study suggests that different heritable melanin-based colorations are associated with alternative strategies to resist parasite attacks, with dark reddish individuals investing more resources towards the humoral immune response than lightly reddish conspecifics. © 2009 British Ecological Society.
Abstract.
Svensson PA, Pélabon C, Blount JD, Forsgren E, Bjerkeng B, Amundsen T (2009). Temporal variability in a multicomponent trait: Nuptial coloration of female two-spotted gobies.
Behavioral Ecology,
20(2), 346-353.
Abstract:
Temporal variability in a multicomponent trait: Nuptial coloration of female two-spotted gobies
Animals that breed more than once may face different environmental and physiological conditions at each reproductive event. Costs and benefits of sexual ornaments could therefore vary both within and between breeding seasons. Despite this, the ornaments are often assumed to be fixed, and temporal changes in ornamentation have rarely been investigated. Female two-spotted gobies (Gobiusculus flavescens) have colorful orange bellies when sexually mature and nest-holding males prefer females with more colorful bellies. This nuptial coloration is caused both by the carotenoids-rich gonads being directly visible through the skin and by the chromatophore pigmentation of the abdominal skin. Toward the end of the breeding season, males become rare and females become the more competitive sex. We show that female ornamentation of G. flavescens is a complex multicomponent trait and that the separate components, as well as their interactions, are variable. As gonads matured, they became more colorful while the abdominal skin became more transparent, causing more intense belly coloration in sexually mature females. However, coloration varied greatly also among fully mature females, suggesting that it may not only be a signal of readiness to spawn. Indeed, belly coloration predicted gonad carotenoid concentration, but there were several important seasonal differences in color expression. Females sampled toward the end of the breeding season were more colorful. This was due to seasonal increases in both gonad carotenoid concentration and skin coloration. Thus, at a time when competition over males is stronger and the terminal reproductive event approaches, females appear to invest more in signaling.
Abstract.
Blount JD, Speed MP, Ruxton GD, Stephens PA (2009). Warning displays may function as honest signals of toxicity.
Proc Biol Sci,
276(1658), 871-877.
Abstract:
Warning displays may function as honest signals of toxicity.
Many prey species use colourful 'aposematic' signalling to advertise the fact that they are toxic. Some recent studies have shown that the brightness of aposematic displays correlates positively with the strength of toxicity, suggesting that aposematic displays are a form of handicap signal, the conspicuousness of which reliably indicates the level of toxicity. The theoretical consensus in the literature is, however, at odds with this finding. It is commonly assumed that the most toxic prey should have less bright advertisements because they have better chances of surviving attacks and can therefore reduce the costs incurred by signalling. Using a novel theoretical model, we show that aposematic signals can indeed function as handicaps. To generate this prediction, we make a key assumption that the expression of bright displays and the storage of anti-predator toxins compete for resources within prey individuals. One shared currency is energy. However, competition for antioxidant molecules, which serve dual roles as pigments and in protecting prey against oxidative stress when they accumulate toxins, provides a specific candidate resource that could explain signal honesty. Thus, contrary to the prevailing theoretical orthodoxy, warning displays may in fact be honest signals of the level of (rather than simply the existence of) toxicity.
Abstract.
Author URL.
Roulin A, Almasi, B. Rossi-Pedruzzi, A. Ducrest, A.L. Wakamatsu K, Miksik I, Blount JD, Jenni-Eiermann S, Jenni L (2008). Corticosterone mediates the condition-dependent component of melanin-based coloration. Animal Behaviour, 75, 1351-1358.
Pike TW, Blount, J.D. Lindström, J. Metcalfe, N.B. (2007). Availability of non-carotenoid antioxidants affects the expression of a carotenoid-based sexual ornament. Biology Letters, 3, 353-356.
Pike TW, Blount, J.D. Bjerkeng, B. Lindström, J. Metcalfe NB (2007). Carotenoids, oxidative stress and female mating preference for longer-lived males. Proceedings of the Royal Society B, 274, 1591-1596.
Pike TW, Blount, J.D. Lindström, J. Metcalfe, N.B. (2007). Dietary carotenoid availability influences a male's ability to provide parental care. Behavioral Ecology, 18, 1100-1105.
Arnold KE, Blount, J.D. Metcalfe, N.B. Orr, K.J. Adam A, Houston D, Monaghan P (2007). Sex-specific differences in compensation for poor neonatal nutrition in the zebra finch Taeniopygia guttata. Journal of Avian Biology, 38, 365-366.
Svensson PA, Pélabon, C. Blount, J.D. Surai, P.F. Amundsen T (2006). Does female nuptial coloration reflect egg carotenoids and clutch quality in the Two-Spotted Goby (Gobiusculus flavescens, Gobiidae)?. Functional Ecology, 20, 689-698.
Blount JD, Matheson, S.M. (2006). Effects of carotenoid supply on escape-flight responses in zebra finches Taeniopygia guttata. Animal Behaviour, 72, 595-601.
Blount JD, Metcalfe, N.B. Arnold, K.E. Surai, P.F. Monaghan P (2006). Effects of neonatal nutrition on adult reproduction in a passerine bird. Ibis, 148, 509-514.
Nager RG, Monaghan, P. Houston, D.C. Arnold, K.E. Blount JD, Verboven N (2006). Maternal effects through the avian egg. Acta Zoologica Sinica, 52, S658-S661.
Groothuis TGG, Eising, C.M. Blount, J.D. Surai, P. Apanius V, Dijkstra C, Müller W (2006). Multiple pathways of maternal effects in black-headed gull eggs: Constraint and mutual adjustment. Journal of Evolutionary Biology, 19, 1304-1313.
Verboven N, Evans, N.P. D'Alba, L. Nager, R.G. Blount JD, Surai PF, Monaghan P (2005). Intra-specific interactions influence egg composition in the lesser black-backed gull (<em>Larus fuscus</em>). Behavioral Ecology and Sociobiology, 57, 357-365.
Blount, J.D. (2004). Carotenolds and life-history evolution in animals. Archives of Biochemistry & Biophysics, 430, 10-15.
Blount J, Houston DC, Moller AP, Surai PF (2004). Egg-laying capacity is limited by carotenoid pigment availability in wild gulls Larus fuscus. Biology Letters, 271(0), S79-S81.
Blount JD, Birkhead TR, Metcalfe NB, Surai PF (2003). Carotenoid modulation of immune function and sexual attractiveness in zebra finches. Science, 300(5616), 125-127.
Blount JD, Houston, D.C. Møller, A.P. Wright, J. (2003). Do individual branches of immune defence correlate? a comparative case study of scavenging and non-scavenging birds. Oikos, 102, 340-350.
Blount JD, Arnold KE, Metcalfe NB, Surai PF, Devevey GL, Monaghan P (2003). Neonatal nutrition, adult antioxidant defences and sexual attractiveness in the zebra finch. Proceedings of the Royal Society B Biological Sciences, 270(1525), 1691-1696.
Blount J, Birkhead TR, Nager RG, Surai PF (2002). Carotenoids and egg quality in the lesser black-backed gull Larus fuscus: a supplemental feeding study of maternal effects. Proceedings of the Royal Society B Biological Sciences, 269(1486), 29-36.
Blount JD, Surai, P.F. Nager, R.G. Houston DC, Moller AP, Trewby ML, Kennedy MW (2002). Carotenoids and egg quality in the lesser black-backed gull Larus fuscus: a supplemental feeding study of maternal effects. Proceedings of the Royal Society B, 269(1486), 29-36.
Blount JD, Surai, P.F. Houston, D.C. Møller, A.P. (2002). Patterns of yolk enrichment with dietary carotenoids in gulls: the roles of pigment acquisition and utilization. Functional Ecology, 16, 445-453.
Ward JM, Blount, J.D. Ruxton, G.D. Houston, D.C. (2002). The adaptive significance of dark plumage for birds in desert environments. Ardea, 90, 311-323.
Blount JD, Møller, A.P. Houston, D.C. (2001). Antioxidants, showy males and sperm quality. Ecology Letters, 4, 393-396.
Surai PF, Speake, B.K. Wood, N.A.R. Blount, J.D. Bortolotti GR, Sparks NHC (2001). Carotenoid discrimination by the avian embryo: a lesson from wild birds. Comparative Biochemistry and Physiology Part B, 128, 743-750.
Surai PF, Bortolotti, G.R. Fidgett, A.L. Blount, J.D. Speake BK (2001). Effects of piscivory on the fatty acid profiles and antioxidants of avian yolk: studies on eggs of the gannet, skua, pelican and cormorant. Journal of Zoology (London), 255, 305-312.
Blount JD, Surai PF, Houston DC, Møller AP (2001). The relationship between dietary and yolk carotenoid composition in a wild bird: a supplemental feeding study of lesser black-backed gulls (Larus fuscus). British Poultry Science, 42(SUPPL. 1).
Moller AP, Biard, C. Blount, J.D. Houston, D.C. Ninni P, Saino N, Surai PF (2000). Carotenoid-dependent signals: Indicators of foraging efficiency, immunocompetence or detoxification ability?. Avian & Poultry Biology Reviews, 11, 137-159.
Blount JD, Taylor NJ (2000). The relative effectiveness of manipulable feeders and olfactory enrichment for Kinkajous.
International Zoo Yearbook,
37(1), 381-394.
Abstract:
The relative effectiveness of manipulable feeders and olfactory enrichment for Kinkajous
The Kinkajou Potos flavus (Carnivora: Procyonidae) is a nocturnal, arboreal species that feeds opportunistically, mostly on fruits and insects. The implications for the management of these aspects of the ecology of P. flavus in captivity have received little attention in the literature. Captive Kinkajous often show stereotypic behaviour, indicating sub-optimal welfare and probably reflecting insufficient opportunity to display important aspects of natural behaviour. This study assessed the individual and additive effects of complex feeders and scented cloths as enrichment for a pair of Kinkajous at Newquay Zoo. Feeding enrichment, alone and in combination with scented cloths, elicited most positive active behaviours and space utilization, and least stereotypic and inactive behaviours. Food provision requiring species-typical exploration and manipulation may improve the welfare and educational value of Kinkajous. © 2017 Wiley. All rights reserved.
Abstract.
Blount JD (2000). Why egg yolk is yellow (vol 15, pg 47, 2000).
TRENDS IN ECOLOGY & EVOLUTION,
15(4), 131-131.
Author URL.
Blount JD, Houston, D.C. Møller, A.P. (2000). Why egg yolk is yellow. Trends in Ecology & Evolution, 15, 47-49.
Blount JD (1998). Redevelopment of a disused enclosure for housing Sulawesi crested macaques Macaca Nigra at Newquay Zoo.
International Zoo Yearbook,
36(1), 56-63.
Abstract:
Redevelopment of a disused enclosure for housing Sulawesi crested macaques Macaca Nigra at Newquay Zoo
In 1995 at Newquay Zoo a bear pit was redeveloped for Sulawesi crested macaques Macaca nigra. Visual screening and foraging enrichment were used to improve tolerance between ♂♂ and to increase mating opportunities for sub-dominant ♂♂. To further improve opportunities for avoidance of of seclusion from conspecifics the outdoor area was equipped with a complex climbing apparatus and environmental enrichment, such as a puzzle feeder, sand pit and waterfall, was also provided. The indoor areas were refurbished, heated and fitted with new lighting. The circular shape of the enclosure and improved spatial complexity provides continuity of space, which may reduce the likelihood of physical harm during aggressive encounters. After the death of the dominant ♂ a new adult ♂ was introduced to the established group without difficulty and he has since adopted the dominant position. © 2017 Wiley. All rights reserved.
Abstract.
Chapters
Royle NJ, Orledge JM, Blount JD (In Press). Early life-history effects, oxidative stress and the evolution and expression of animal signals. In Irschick D, Podos J, Briffa M (Eds.) Animal Signaling: Functional and Evolutionary Perspectives (Eds. Irschick, D. Podos, J. and Briffa, M.) (In press).
McGraw KJ, Blount, J.D. (2008). Control and function of carotenoid coloration in birds: a review of case studies. In Landrum JT (Ed) Carotenoids: Physical, Chemical and Biological Functions and Properties, CRC Press Ltd.
Blount JD, McGraw, K.J. (2008). Signal functions of carotenoid colouration. In Britton G, Liaaen-Jensen S, Pfander H (Eds.) Carotenoids. Volume 4: Natural Functions.
Publications by year
In Press
Marshall H, Johnstone R, Thompson F, Nichols H, Wells D, Joe H, Kalema-Zikusoka G, Sanderson J, Vitikainen E, Blount J, et al (In Press). A veil of ignorance can promote fairness in a mammal society. Nature Communications
Orledge JM, Blount JD, Hoodless AN, Royle NJ (In Press). Antioxidant supplementation during early development reduces parasite load but does not
affect sexual ornament expression in adult ring-necked pheasants Phasianus colchicus.
Functional EcologyAbstract:
Antioxidant supplementation during early development reduces parasite load but does not
affect sexual ornament expression in adult ring-necked pheasants Phasianus colchicus
1. The ‘parasite-mediated sexual selection’ (PMSS) hypothesis predicts that exaggerated male ornamentation could provide a signal to females of a males ability to resist parasites.
Empirical tests of the PMSS have been largely equivocal, however, which may be because most have not considered the role of early life-history effects.
2. Many sexually-selected traits are carotenoid-based. Allocation of dietary-derived carotenoids to sexual ornaments may trade-off with allocation to pro-inflammatory immune response and/or antioxidant functions, mediated by the oxidative status of individuals. Exposure to parasites can increase oxidative stress, so under this scenario sexually-selected traits indicate ability to resist oxidative stress rather than ability to resist parasites per se. Such life-history trade-offs, mediated by oxidative status of individuals, are particularly acute during growth
and development.
3. Here we use ring-necked pheasants, Phasianus colchicus, a strongly sexually-selected
species, to test whether supplementation with dietary antioxidants (vitamin E) can mitigate the effects of early exposure to parasites (the nematode, Heterakis gallinarum), via alteration of the oxidative status of individuals, and positively affect the expression of sexual ornaments at adulthood.
4. We found that vitamin E mediated the effect of early exposure to parasites on levels of oxidative damage at 8 weeks of age and reduced the parasite load of individuals at adulthood as predicted. However, the expression of sexual ornaments, immune function, and growth
were unaffected by either early vitamin E supplementation or manipulation of parasite load.
In contrast to the predictions of the PMSS hypothesis the intensity of sexual ornament
expression was not related to either parasite load or oxidative status of individuals (current or long-term). Consequently there was no evidence that the expression of sexual ornaments
provided information on the ability of males to resist infection from parasites.
Abstract.
Author URL.
Royle NJ, Orledge JM, Blount JD (In Press). Early life-history effects, oxidative stress and the evolution and expression of animal signals. In Irschick D, Podos J, Briffa M (Eds.) Animal Signaling: Functional and Evolutionary Perspectives (Eds. Irschick, D. Podos, J. and Briffa, M.) (In press).
Blount J, Losdat S, Marri V, Maronde L, Richner H, Helfenstein F (In Press). Effects of an early-life paraquat exposure on adult resistance to oxidative stress, plumage colour and sperm performance in a wild bird. Journal of Animal Ecology
Blount J, Francis ML, Plummer KE, Lythgoe BA, Macallan C, Currie TE (In Press). Effects of supplementary feeding on interspecific dominance hierarchies in garden birds. PLoS ONE
Blount JD, Rowland HM, Drijfhout FP, Endler JA, Inger R, Sloggett JJ, Hurst GDD, Hodgson DJ, Speed MP (In Press). How the ladybird got its spots: effects of resource limitation on the honesty of aposematic signals. Funct. Ecol., (in press)
Blount J, Vitikainen EIK, Stott I, Cant MA (In Press). Oxidative shielding and the cost of reproduction.
Biological ReviewsAbstract:
Oxidative shielding and the cost of reproduction
Life history theory assumes that reproduction and lifespan are constrained by trade-offs which prevent their simultaneous increase. Recently, there has been considerable interest in the possibility that this cost of reproduction is mediated by oxidative stress. However, empirical tests of this theory have yielded equivocal support. We carried out a meta-analysis to examine associations between reproduction and oxidative damage across markers and tissues. We show that oxidative damage is positively associated with reproductive effort across females of various species. Yet paradoxically, categorical comparisons of breeders versus non-breeders reveal that transition to the reproductive state is associated with a step-change reduction in oxidative damage in certain tissues and markers. Developing offspring may be particularly sensitive to harm caused by oxidative damage in mothers. Therefore, such reductions could potentially function to shield reproducing mothers, gametes and developing offspring from oxidative insults that inevitably increase as a consequence of reproductive effort. According to this perspective, we hypothesise that the cost of reproduction is mediated by dual impacts of maternally-derived oxidative damage on mothers and offspring, and that mothers may be selected to diminish such damage. Such oxidative shielding may explain why many existing studies have concluded that reproduction has little or no oxidative cost. Future advance in life history theory therefore needs to take account of potential transgenerational impacts of the mechanisms underlying life history trade-offs.
Abstract.
Blount J, Paul SC, Stevens M, birkett M, Pell JK (In Press). Parental phenotype not predator cues influence egg warning coloration and defence levels. Animal Behaviour
Blount J (In Press). The price of defence: toxins, visual signals and oxidative state in an aposematic butterfly.
Proceedings of the Royal Society B: Biological SciencesAbstract:
The price of defence: toxins, visual signals and oxidative state in an aposematic butterfly
In a variety of aposematic species, the conspicuousness of an individual’s warning signal and the quantity of its chemical defence are positively correlated. This apparent honest signalling is predicted by resource competition models which assume that the production and maintenance of aposematic defences compete for access to antioxidant molecules that have dual functions as pigments and in protecting against oxidative damage. We raised monarch butterflies (Danaus plexippus) on their milkweed host-plants (Apocynaceae) with increasing quantities of cardenolides to test whether (1) the sequestration of secondary defences is associated with costs in the form of oxidative lipid damage and reduced antioxidant defences; and (2) that reduced oxidative state can decrease the capacity of individuals to produce aposematic displays. In male monarchs conspicuousness was explained by an interaction between oxidative damage and sequestration: males with high levels of oxidative damage become less conspicuous with increased sequestration of cardenolides, whereas those with low oxidative damage become more conspicuous with increased levels of cardenolides. There was no significant effect of oxidative damage or concentration of sequestered cardenolides on female conspicuousness. Our results demonstrate a physiological linkage between the production of coloration and protection from autotoxicity, and differential costs of signalling in monarch butterflies.
Abstract.
Blount J (In Press). Untangling the oxidative cost of reproduction: an analysis in wild banded mongooses. Ecology and Evolution
2022
Melvin ZE, Dhirani H, Mitchell C, Davenport TRB, Blount JD, Georgiev AV (2022). Methodological confounds of measuring urinary oxidative stress in wild animals.
Ecol Evol,
12(7).
Abstract:
Methodological confounds of measuring urinary oxidative stress in wild animals.
Biomarkers of oxidative stress (OS) are useful in addressing a wide range of research questions, but thus far, they have had limited application to wild mammal populations due to a reliance on blood or tissue sampling. A shift toward non-invasive measurement of OS would allow field ecologists and conservationists to apply this method more readily. However, the impact of methodological confounds on urinary OS measurement under field conditions has never been explicitly investigated. We combined a cross-sectional analysis with a field experiment to assess the impact of four potential methodological confounds on OS measurements: (1) time of sampling, (2) environmental contamination from foliage; (3) delay between sample collection and flash-freezing in liquid nitrogen; and (4) sample storage of up to 15 months below -80°C. We measured DNA oxidative damage (8-hydroxy-2'-deoxyguanosine, 8-OHdG), lipid peroxidation (malondialdehyde, MDA), total antioxidant capacity (TAC), and uric acid (UA) in 167 urine samples collected from wild Zanzibar red colobus (Piliocolobus kirkii). We found that MDA was higher in samples collected in the morning than in the afternoon but there were no diurnal patterns in any of the other markers. Contamination of samples from foliage and length of time frozen at -80°C for up to 15 months did not affect OS marker concentrations. Freezing delay did not affect OS levels cross-sectionally, but OS values from individual samples showed only moderate-to-good consistency and substantial rank-order reversals when exposed to different freezing delays. We recommend that diurnal patterns of OS markers and the impact of storage time before and after freezing on OS marker concentrations be considered when designing sampling protocols. However, given the high stability we observed for four OS markers subject to a variety of putative methodological confounds, we suggest that urinary OS markers provide a valuable addition to the toolkit of field ecologists and conservationists within reasonable methodological constraints.
Abstract.
Author URL.
2021
Blount JD, Horns JJ, Kittelberger KD, Neate-Clegg MHC, Şekercioğlu ÇH (2021). Avian Use of Agricultural Areas as Migration Stopover Sites: a Review of Crop Management Practices and Ecological Correlates.
Frontiers in Ecology and Evolution,
9Abstract:
Avian Use of Agricultural Areas as Migration Stopover Sites: a Review of Crop Management Practices and Ecological Correlates
An estimated 17% of migratory bird species are threatened or near threatened with extinction. This represents an enormous potential loss of biodiversity and cost to human societies due to the economic benefits that birds provide through ecosystem services and ecotourism. Conservation of migratory bird species presents many unique challenges, as these birds rely on multiple geographically distinct habitats, including breeding grounds, non-breeding grounds, and stopover sites during migration. In particular, stopover habitats are seldom studied relative to breeding and non-breeding habitats, despite their importance as refueling stations for migratory birds. In this study, we summarize the current research on the use of temporary primary crops by birds during migration and we assess the species characteristics and agricultural practices most often associated with the use of cropland as stopover habitat. First, we conducted a systematic review of the literature to document the effects various farming practices and crop types have on the abundance and diversity of migratory birds using agricultural areas for stopovers. Second, we analyzed the ecological correlates of bird species in the Northern Hemisphere that predict which species may use these areas while migrating. We ran a GLMM to test whether primary diet, diet breadth, primary habitat, habitat breadth, or realm predicted stopover use of agricultural areas. Our review suggests that particular crop types (principally rice, corn, and sunflower), as well as farming practices that result in higher non-cultivated plant diversity, encourage the use of agricultural areas by migrating birds. We found that cropland is used as stopover habitat by bird species that can utilize a large breadth of habitats, as well as species with preferences for habitat similar in structure to agricultural areas.
Abstract.
Neate-Clegg MHC, Blount JD, Şekercioğlu ÇH (2021). Ecological and biogeographical predictors of taxonomic discord across the world’s birds.
Global Ecology and Biogeography,
30(6), 1258-1270.
Abstract:
Ecological and biogeographical predictors of taxonomic discord across the world’s birds
Aim: Species delimitation is fundamental to biology, but disagreement in species concepts and the application of those concepts can lead to substantial variation in species lists, with important implications for conservation. For birds, there are four widely used global checklists that vary in length and application. Here, we investigate the biogeographical and ecological predictors of taxonomic disagreement between the four world bird species lists. Location: Global. Time period: Present. Major taxa studied: Birds. Methods: We determined taxonomic agreement based on whether each bird species name represented only one species (‘agreement’), that is, no authorities have split the species, or represented multiple species (‘disagreement’) including disputed splits recognised by some authorities. We examined taxonomic agreement for all birds and for each family and biogeographical region. We then modelled taxonomic agreement as a function of six biogeographical and ecological variables: latitude, island endemism, log(mass), forest dependency, primary diet, and migratory status. Results: Overall taxonomic agreement was 89.5%, and the remaining 10th of taxonomic names represented disputed splits upon which the four authorities disagreed. We found that taxonomic agreement was lowest for species in Southeast Asia/Australasia and the Southern Ocean, understudied regions where islands have driven high levels of cryptic diversification. In contrast, agreement was highest in the temperate Northern Hemisphere where diversity is lower and research is more extensive. Agreement was also higher for large, migratory species living in open habitats. Main conclusions: Taxonomic agreement was higher for species that are easier to study such as large, temperate species from open habitats. In addition, agreement was lower for lineages that are more likely to undergo cryptic divergence such as island endemics with intermediate forest dependency and mobility. Species with these traits should be the focus of taxonomic research in order to achieve reconciliation of the world's bird lists and to better conserve extant biodiversity.
Abstract.
Arunkumar R, Gorusupudi A, Li B, Blount JD, Nwagbo U, Kim HJ, Sparrow JR, Bernstein PS (2021). Lutein and zeaxanthin reduce A2E and iso-A2E levels and improve visual performance in Abca4<sup>−/−</sup>/Bco2<sup>−/−</sup> double knockout mice.
Experimental Eye Research,
209Abstract:
Lutein and zeaxanthin reduce A2E and iso-A2E levels and improve visual performance in Abca4−/−/Bco2−/− double knockout mice
Accumulation of bisretinoids such as A2E and its isomer iso-A2E is thought to mediate blue light-induced oxidative damage associated with age-related macular degeneration (AMD) and autosomal recessive Stargardt disease (STGD1). We hypothesize that increasing dietary intake of the macular carotenoids lutein and zeaxanthin in individuals at risk of AMD and STGD1 can inhibit the formation of bisretinoids A2E and iso-A2E, which can potentially ameliorate macular degenerative diseases. To study the beneficial effect of macular carotenoids in a retinal degenerative diseases model, we used ATP-binding cassette, sub-family a member 4 (Abca4−/−)/β,β-carotene-9′,10′-oxygenase 2 (Bco2−/−) double knockout (KO) mice that accumulate elevated levels of A2E and iso-A2E in the retinal pigment epithelium (RPE) and macular carotenoids in the retina. Abca4−/−/Bco2−/− and Abca4−/− mice were fed a lutein-supplemented chow, zeaxanthin-supplemented chow or placebo chow (~2.6 mg of carotenoid/mouse/day) for three months. Visual function and electroretinography (ERG) were measured after one month and three months of carotenoid supplementation. The lutein and zeaxanthin supplemented Abca4−/−/Bco2−/− mice had significantly lower levels of RPE/choroid A2E and iso-A2E compared to control mice fed with placebo chow and improved visual performance. Carotenoid supplementation in Abca4−/− mice minimally raised retinal carotenoid levels and did not show much difference in bisretinoid levels or visual function compared to the control diet group. There was a statistically significant inverse correlation between carotenoid levels in the retina and A2E and iso-A2E levels in the RPE/choroid. Supplementation with retinal carotenoids, especially zeaxanthin, effectively inhibits bisretinoid formation in a mouse model of STGD1 genetically enhanced to accumulate carotenoids in the retina. These results provide further impetus to pursue oral carotenoids as therapeutic interventions for STGD1 and AMD.
Abstract.
Jacobs PJ, Oosthuizen MK, Mitchell C, Blount JD, Bennett NC (2021). Oxidative stress in response to heat stress in wild caught Namaqua rock mice, Micaelamys namaquensis.
Journal of Thermal Biology,
98Abstract:
Oxidative stress in response to heat stress in wild caught Namaqua rock mice, Micaelamys namaquensis
Modelling of anthropogenic induced climate suggests more frequent and severe heatwaves in the future, which are likely to result in the mass die-off of several species of organisms. Oxidative stress induced by severe heat stress has previously been associated with a reduction in animal cognitive performance, depressed reproduction and lower life expectancy. Little is known about the non-lethal consequences of species should they survive extreme heat exposure. We investigated the oxidative stress experienced by the Namaqua rock mouse, a nocturnal rodent, using two experimental heat stress protocols, a 6 hour acute heat stress protocol without access to water and a 3-day heatwave simulation with ad libitum water. Oxidative stress was determined in the liver, kidney and brain using malondialdehyde (MDA) and protein carbonyl (PC) as markers of oxidative damage, and superoxide dismutase (SOD) and total antioxidant capacity (TAC) as markers of antioxidant defence. Incubator heat stress (heat and dehydration stress) was brought about by increasing the body temperatures of animals to 39–40.8 °C for 6 hours. Following incubator heat stress, significantly higher levels of MDA were observed in the liver. Dehydration did not explain the variation in oxidative markers and is likely a combined effect of thermal and dehydration stress. Individual body mass was significantly negatively correlated to kidney SOD and lipid peroxidation. A heatwave was simulated using a temperature cycle that would naturally occur during a heatwave in the species’ local habitat, with a maximal ambient temperature of 38 °C. Following the simulated heatwave, SOD activity of the kidney demonstrated significantly lowered activity suggesting oxidative stress. Current heat waves in this species have the potential of causing oxidative stress. Heat and dehydration stress following exacerbated temperatures are likely to incur significant oxidative stress in multiple tissues demonstrating the importance of water availability to allow for rehydration to prevent oxidative stress.
Abstract.
Allen SF, Ellis F, Mitchell C, Wang X, Boogert NJ, Lin C-Y, Clokey J, Thomas KV, Blount JD (2021). Phthalate diversity in eggs and associations with oxidative stress in the European herring gull (Larus argentatus). Marine Pollution Bulletin, 169, 112564-112564.
Blount JD, Chynoweth MW, Green AM, Şekercioğlu ÇH (2021). Review: COVID-19 highlights the importance of camera traps for wildlife conservation research and management.
Biological Conservation,
256Abstract:
Review: COVID-19 highlights the importance of camera traps for wildlife conservation research and management
COVID-19 has altered many aspects of everyday life. For the scientific community, the pandemic has called upon investigators to continue work in novel ways, curtailing field and lab research. However, this unprecedented situation also offers an opportunity for researchers to optimize and further develop available field methods. Camera traps are one example of a tool used in science to answer questions about wildlife ecology, conservation, and management. Camera traps have long battery lives, lasting more than a year in certain cases, and photo storage capacity, with some models capable of wirelessly transmitting images from the field. This allows researchers to deploy cameras without having to check them for up to a year or more, making them an ideal field research tool during restrictions on in-person research activities such as COVID-19 lockdowns. As technological advances allow cameras to collect increasingly greater numbers of photos and videos, the analysis techniques for large amounts of data are evolving. Here, we describe the most common research questions suitable for camera trap studies and their importance for biodiversity conservation. As COVID-19 continues to affect how people interact with the natural environment, we discuss novel questions for which camera traps can provide insights on. We conclude by summarizing the results of a systematic review of camera trap studies, providing data on target taxa, geographic distribution, publication rate, and publication venues to help researchers planning to use camera traps in response to the current changes in human activity.
Abstract.
Blount JD, Rowland HM, Mitchell C, Speed MP, Ruxton GD, Endler JA, Brower LP (2021). The price of defence: toxins, visual signals and oxidative state in an aposematic butterfly.
2020
Sauer L, Vitale AS, Milliken CM, Modersitzki NK, Blount JD, Bernstein PS (2020). Autofluorescence lifetimes measured with fluorescence lifetime imaging ophthalmoscopy (FLIO) are affected by age, but not by pigmentation or gender.
Translational Vision Science and Technology,
9(9), 1-13.
Abstract:
Autofluorescence lifetimes measured with fluorescence lifetime imaging ophthalmoscopy (FLIO) are affected by age, but not by pigmentation or gender
Purpose: Fluorescence lifetime imaging ophthalmoscopy (FLIO) is a novel modality to investigate the human retina. This study aims to characterize the effects of age, pigmen-tation, and gender in FLIO. Methods: a total of 97 eyes from 97 healthy subjects (mean age 37 ± 18 years, range 9–85 years) were investigated in this study. This study included 47 (49%) females and 50 males. The pigmentation analysis was a substudy including 64 subjects aged 18 to 40 years (mean age 29 ± 6 years). These were categorized in groups a (darkly pigmented, 8), B (medium pigmented, 20), and C (lightly pigmented, 36). Subjects received Heidelberg Engineering FLIO and optical coherence tomography imaging. Retinal autofluo-rescence lifetimes were detected in two spectral channels (short spectral channel [SSC]: 498–560 nm; long spectral channel [LSC]: 560–720 nm), and amplitude-weighted mean fluorescence lifetimes (τm) were calculated. Additionally, autofluorescence lifetimes of melanin were measured in a cuvette. Results: Age significantly affected FLIO lifetimes, and age-related FLIO changes in the SSC start at approximately age 35 years, whereas the LSC shows a consistent prolonga-tion with age from childhood. There were no gender-or pigmentation-specific significant differences of autofluorescence lifetimes. Conclusions: This study confirms age-effects in FLIO but shows that the two channels are affected differently. The LSC appears to show the lifelong accumulation of lipofuscin. Furthermore, it is important to know that neither gender nor pigmentation significantly affect FLIO lifetimes. Translational Relevance: This study helps to understand the FLIO technology better, which will aid in conducting future clinical studies.
Abstract.
Bodey TW, Cleasby IR, Blount JD, McElwaine G, Vigfusdottir F, Bearhop S (2020). Consistent measures of oxidative balance predict survival but not reproduction in a long-distance migrant.
J Anim Ecol,
89(8), 1872-1882.
Abstract:
Consistent measures of oxidative balance predict survival but not reproduction in a long-distance migrant.
Physiological processes, including those that disrupt oxidative balance, have been proposed as key to understanding fundamental life-history trade-offs. Yet, examination of changes in oxidative balance within wild animals across time, space and major life-history challenges remains uncommon. For example, migration presents substantial physiological challenges for individuals, and data on migratory individuals would provide crucial context for exposing the importance of relationships between oxidative balance and fitness outcomes. Here we examined the consistency of commonly used measures of oxidative balance in longitudinally sampled free-living individuals of a long-lived, long-distance migrant, the Brent goose Branta bernicla hrota over periods of months to years. Although inter-individual and temporal variation in measures of oxidative balance were substantial, we found high consistency in measures of lipid peroxidation and circulating non-enzymatic antioxidants in longitudinally sampled individuals. This suggests the potential for the existence of individual oxidative phenotypes. Given intra-individual consistency, we then examined how these physiological measures relate to survival and reproductive success across all sampled individuals. Surprisingly, lower survival was predicted for individuals with lower levels of damage, with no measured physiological metric associated with reproductive success. Our results demonstrate that snapshot measurements of a consistent measure of oxidative balance can inform our understanding of differences in a key demographic trait. However, the positive relationship between oxidative damage and survival emphasises the need to investigate the relationships between the oxidative system and fitness outcomes in other species undergoing similar physiologically challenging life cycles. This would highlight the extent to which variation in such traits and resource allocation trade-offs is a result of adaptation to different life-history strategies.
Abstract.
Author URL.
Jacobs PJ, Oosthuizen MK, Mitchell C, Blount JD, Bennett NC (2020). Heat and dehydration induced oxidative damage and antioxidant defenses following incubator heat stress and a simulated heat wave in wild caught four-striped field mice Rhabdomys dilectus.
PLoS ONE,
15(11 November).
Abstract:
Heat and dehydration induced oxidative damage and antioxidant defenses following incubator heat stress and a simulated heat wave in wild caught four-striped field mice Rhabdomys dilectus
Heat waves are known for their disastrous mass die-off effects due to dehydration and cell damage, but little is known about the non-lethal consequences of surviving severe heat exposure. Severe heat exposure can cause oxidative stress which can have negative consequences on animal cognition, reproduction and life expectancy. We investigated the current oxidative stress experienced by a mesic mouse species, the four striped field mouse, Rhabdomys dilectus through a heat wave simulation with ad lib water and a more severe temperature exposure with minimal water. Wild four striped field mice were caught between 2017 and 2019. We predicted that wild four striped field mice in the heat wave simulation would show less susceptibility to oxidative stress as compared to a more severe heat stress which is likely to occur in the future. Oxidative stress was determined in the liver, kidney and brain using malondialdehyde (MDA) and protein carbonyl (PC) as markers for oxidative damage, and superoxide dismutase (SOD) and total antioxidant capacity (TAC) as markers of antioxidant defense. Incubator heat stress was brought about by increasing the body temperatures of animals to 39–40.8 C for 6 hours. A heat wave (one hot day, followed by a 3-day heatwave) was simulated by using temperature cycle that wild four striped field mice would experience in their local habitat (determined through weather station data using temperature and humidity), with maximal ambient temperature of 39 C. The liver and kidney demonstrated no changes in the simulated heat wave, but the liver had significantly higher SOD activity and the kidney had significantly higher lipid peroxidation in the incubator experiment. Dehydration significantly contributed to the increase of these markers, as is evident from the decrease in body mass after the experiment. The brain only showed significantly higher lipid peroxidation following the simulated heat wave with no significant changes following the incubator experiment. The significant increase in lipid peroxidation was not correlated to body mass after the experiment. The magnitude and duration of heat stress, in conjunction with dehydration, played a critical role in the oxidative stress experienced by each tissue, with the results demonstrating the importance of measuring multiple tissues to determine the physiological state of an animal. Current heat waves in this species have the potential of causing oxidative stress in the brain with future heat waves to possibly stress the kidney and liver depending on the hydration state of animals.
Abstract.
Malod K, Roets PD, Oosthuizen C, Blount JD, Archer CR, Weldon CW (2020). Selection on age of female reproduction in the marula fruit fly, Ceratitis cosyra (Walker) (Diptera: Tephritidae), decreases total antioxidant capacity and lipid peroxidation.
J Insect Physiol,
125Abstract:
Selection on age of female reproduction in the marula fruit fly, Ceratitis cosyra (Walker) (Diptera: Tephritidae), decreases total antioxidant capacity and lipid peroxidation.
The oxidative damage caused to cells by Reactive Oxygen Species (ROS) is one of several factors implicated in causing ageing. Oxidative damage may also be a proximate cost of reproductive effort that mediates the trade-off often observed between reproduction and survival. However, how the balance between oxidative damage and antioxidant protection affects life-history strategies is not fully understood. To improve our understanding, we selected on female reproductive age in the marula fruit fly, Ceratitis cosyra, and quantified the impact of selection on female and male mortality risk, female fecundity, male sperm transfer, calling and mating. Against expectations, upward-selected lines lived shorter lives and experienced some reductions in reproductive performance. Selection affected oxidative damage to lipids and total antioxidant protection, but not in the direction predicted; longer lives were associated with elevated oxidative damage, arguing against the idea that accumulated oxidative damage reduces lifespan. Greater reproductive effort was also associated with elevated oxidative damage, suggesting that oxidative damage may be a cost of reproduction, although one that did not affect survival. Our results add to a body of data showing that the relationship between lifespan, reproduction and oxidative damage is more complex than predicted by existing theories.
Abstract.
Author URL.
2019
Bearhop S, Bodey T, Cleasby IR, Blount J, Vigfusdottir F, MacKie K (2019). Measures of oxidative state are primarily driven by extrinsic factors in a long-distance migrant. Biology Letters, 15, 1-4.
Briolat E, Zagrobelny M, Olsen C, Blount J, Stevens M (2019). No evidence of quantitative signal honesty across species of aposematic burnet moths (Lepidoptera: Zygaenidae). Journal of Evolutionary Biology, 32, 31-48.
2018
Blount J (2018). Effects of supplementary feeding on interspecific dominance hierarchies in garden birds.
Blount J, Plummer K, Bearhop S, leech D, chamberlain D (2018). Effects of winter food provisioning on the phenotypes of breeding blue tits. Ecology and Evolution
Paul S, Stevens M, Burton J, Pell J, Burkett M, Blount J (2018). Invasive egg predators and food availability interactively affect maternal investment in egg chemical defence.
Frontiers in Ecology and Evolution,
6Abstract:
Invasive egg predators and food availability interactively affect maternal investment in egg chemical defence
Invasive species commonly predate the offspring of native species and eggs are the life stage most vulnerable to this predation. In many species with no maternal care, females can alter the phenotype of eggs to protect them, for instance through chemical defense. In ladybirds egg alkaloids deter predators, including invasive predatory species of ladybirds, but conversely may attract cannibals who benefit from the consumption of eggs with higher alkaloid levels. Invasive predators tend to be more abundant where resources are also abundant, but in high resource environments the maternal fitness benefits of sibling cannibalism are low. Consequently this presents a conflict for female ladybirds between the different factors that influence egg alkaloid level, as protecting her eggs from predators might come with the cost of inadvertently encouraging within-clutch cannibalism under circumstances where it is not beneficial. We investigated how the ladybird Adalia bipunctata addresses this trade-off experimentally, by measuring the quantity of alkaloids in eggs laid by ladybirds in environments that differed in levels of resource availability and perceived predation risk from an invasive predator Harmonia axyridis. Females did lay eggs with higher egg alkaloid levels under poor resource conditions, but only when predator cues were absent. The resulting negative correlation between egg number and egg alkaloid level under poor resource conditions indicates a trade-off between these two attributes of maternal investment, mediated by female response to offspring predation risk. This implies that selection pressures on mothers to adaptively adjust the risk of siblicide may outweigh the need to protect offspring from interspecific predation. Our results demonstrate that maternal effects are an important aspect of species' responses to invasive predators, and highlight the value of studying maternal effects in the context of the multifaceted environments in which they occur.
Abstract.
Briolat E, Zagrobelny M, Olsen, CE, Blount J, Stevens M (2018). Sex differences but no evidence of quantitative honesty in the warning signals of six-spot burnet moths (Zygaena filipendulae L.). Evolution, 77, 1460-1474.
Hares MC, Vitikainen EIK, Marshall HH, Thompson FJ, Blount JD, Cant MA (2018). Telomere dynamics in wild banded mongooses: Evaluating longitudinal and quasi-longitudinal markers of senescence.
Exp Gerontol,
107, 67-73.
Abstract:
Telomere dynamics in wild banded mongooses: Evaluating longitudinal and quasi-longitudinal markers of senescence.
Telomere length and the rate of telomere shortening have been suggested as particularly useful physiological biomarkers of the processes involved in senescent decline of somatic and reproductive function. However, longitudinal data on changes in telomere length across the lifespan are difficult to obtain, particularly for long-lived animals. Quasi-longitudinal studies have been proposed as a method to gain insight into telomere dynamics in long-lived species. In this method, minimally replicative cells are used as the baseline telomere length against which telomere length in highly replicative cells (which represent the current state) can be compared. Here we test the assumptions and predictions of the quasi-longitudinal approach using longitudinal telomere data in a wild cooperative mammal, the banded mongoose, Mungos mungo. Contrary to our prediction, telomere length (TL) was longer in leukocytes than in ear cartilage. Longitudinally, the TL of ear cartilage shortened with age, but there was no change in the TL of leukocytes, and we also observed many individuals in which TL increased rather than decreased with age. Leukocyte TL but not cartilage TL was a predictor of total lifespan, while neither predicted post-sampling survival. Our data do not support the hypothesis that cross-tissue comparison in TL can act as a quasi-longitudinal marker of senescence. Rather, our results suggest that telomere dynamics in banded mongooses are more complex than is typically assumed, and that longitudinal studies across whole life spans are required to elucidate the link between telomere dynamics and senescence in natural populations.
Abstract.
Author URL.
2016
Vitikainen EIK, Cant MA, Sanderson JL, Mitchell C, Nichols HJ, Marshall HH, Thompson FJ, Gilchrist JS, Hodge SJ, Johnstone RA, et al (2016). Evidence of Oxidative Shielding of Offspring in a Wild Mammal.
FRONTIERS IN ECOLOGY AND EVOLUTION,
4 Author URL.
Vitikainen EIK, Cant MA, Sanderson JL, Mitchell C, Nichols HJ, Marshall HH, Thompson FJ, Gilchrist JS, Hodge SJ, Johnstone RA, et al (2016). Evidence of oxidative shielding of offspring in a wild mammal. Frontiers in Ecology and Evolution
Christensen LL, Selman C, Blount JD, Pilkington JG, Watt KA, Pemberton JM, Reid JM, Nussey DH (2016). Marker-dependent associations among oxidative stress, growth and survival during early life in a wild mammal.
Proc Biol Sci,
283(1840).
Abstract:
Marker-dependent associations among oxidative stress, growth and survival during early life in a wild mammal.
Oxidative stress (OS) is hypothesized to be a key physiological mechanism mediating life-history trade-offs, but evidence from wild populations experiencing natural environmental variation is limited. We tested the hypotheses that increased early life growth rate increases OS, and that increased OS reduces first-winter survival, in wild Soay sheep (Ovis aries) lambs. We measured growth rate and first-winter survival for four consecutive cohorts, and measured two markers of oxidative damage (malondialdehyde (MDA), protein carbonyls (PC)) and two markers of antioxidant (AOX) protection (total AOX capacity (TAC), superoxide dismutase (SOD)) from blood samples. Faster lamb growth was weakly associated with increased MDA, but not associated with variation in the other three markers. Lambs with higher SOD activity were more likely to survive their first winter, as were male but not female lambs with lower PC concentrations. Survival did not vary with MDA or total TAC. Key predictions relating OS to growth and survival were therefore supported in some OS markers, but not others. This suggests that different markers capture different aspects of the complex relationships between individual oxidative state, physiology and fitness, and that overarching hypotheses relating OS to life-history variation cannot be supported or refuted by studying individual markers.
Abstract.
Author URL.
2015
Summers K, Speed MP, Blount JD, Stuckert AMM (2015). Are aposematic signals honest? a review.
Journal of Evolutionary Biology,
28(9), 1583-1599.
Abstract:
Are aposematic signals honest? a review
We explore the relevance of honest signalling theory to the evolution of aposematism. We begin with a general consideration of models of signal stability, with a focus on the Zahavian costly signalling framework. Next, we review early models of signalling in the context of aposematism (some that are consistent and some inconsistent with costly honest signalling). We focus on controversies surrounding the idea that aposematic signals are handicaps in a Zahavian framework. Then, we discuss how the alignment of interests between signaller and predator influences the evolution of aposematism, highlight the distinction between qualitative and quantitative honesty and review theory and research relevant to these categories. We also review recent theoretical treatments of the evolution of aposematism that have focused on honest signalling as well as empirical research on a variety of organisms, including invertebrates and frogs. Finally, we discuss future directions for empirical and theoretical research in this area.
Abstract.
Summers K, Speed MP, Blount JD, Stuckert AMM (2015). Are aposematic signals honest? a review.
J Evol Biol,
28(9), 1583-1599.
Abstract:
Are aposematic signals honest? a review.
We explore the relevance of honest signalling theory to the evolution of aposematism. We begin with a general consideration of models of signal stability, with a focus on the Zahavian costly signalling framework. Next, we review early models of signalling in the context of aposematism (some that are consistent and some inconsistent with costly honest signalling). We focus on controversies surrounding the idea that aposematic signals are handicaps in a Zahavian framework. Then, we discuss how the alignment of interests between signaller and predator influences the evolution of aposematism, highlight the distinction between qualitative and quantitative honesty and review theory and research relevant to these categories. We also review recent theoretical treatments of the evolution of aposematism that have focused on honest signalling as well as empirical research on a variety of organisms, including invertebrates and frogs. Finally, we discuss future directions for empirical and theoretical research in this area.
Abstract.
Author URL.
Flores EE, Stevens M, Moore AJ, Rowland HM, Blount JD (2015). Body size but not warning signal luminance influences predation risk in recently metamorphosed poison frogs.
Ecology and Evolution,
5(20), 4603-4616.
Abstract:
Body size but not warning signal luminance influences predation risk in recently metamorphosed poison frogs
During early development, many aposematic species have bright and conspicuous warning appearance, but have yet to acquire chemical defenses, a phenotypic state which presumably makes them vulnerable to predation. Body size and signal luminance in particular are known to be sensitive to variation in early nutrition. However, the relative importance of these traits as determinants of predation risk in juveniles is not known. To address this question, we utilized computer-assisted design (CAD) and information on putative predator visual sensitivities to produce artificial models of postmetamorphic froglets that varied in terms of body size and signal luminance. We then deployed the artificial models in the field and measured rates of attack by birds and unknown predators. Our results indicate that body size was a significant predictor of artificial prey survival. Rates of attack by bird predators were significantly higher on smaller models. However, predation by birds did not differ between artificial models of varying signal luminance. This suggests that at the completion of metamorphosis, smaller froglets may be at a selective disadvantage, potentially because predators can discern they have relatively low levels of chemical defense compared to larger froglets. There is likely to be a premium on efficient foraging, giving rise to rapid growth and the acquisition of toxins from dietary sources in juvenile poison frogs.
Abstract.
Siitari H, Alatalo R, Pihlaja M, Hämäläinen J, Blount JD, Groothuis TG, Hytönen VP, Surai P, Soulsbury CD (2015). Food supplementation reveals constraints and adaptability of egg quality in the magpie Pica pica.
Avian Biology Research,
8(4), 244-253.
Abstract:
Food supplementation reveals constraints and adaptability of egg quality in the magpie Pica pica
Differences in the deposition of limited maternal resources to eggs can reflect the optimal allocation to manipulate offspring phenotype, or constraints caused by maternal condition. We examined multiple maternal substances transferred to eggs in the magpie Pica pica to test the hypothesis that certain substances represent constraint and some optimal allocation. We did this by supplementary feeding magpies prior to egg-laying and then comparing the effect of food on maternal substances in conjunction with laying order relative to a control group. Certain substances such as carotenoids, immunoglobulins and avidin responded positively to food supplementation, whereas others, such as testosterone and total protein content of eggs, did not. Immunoglobulin allocation increased with laying order in fed but not in unfed groups. Our results suggest that patterns of optimal allocation and constraint in maternally-provisioned substances co-occur within clutches. Furthermore, constraint and optimal allocation may co-occur within the same substance i.e. immunoglobulins, highlighting the complexities of maternal resource allocation.
Abstract.
Cram DL, Blount JD, York JE, Young AJ (2015). Immune response in a wild bird is predicted by oxidative status but does not cause oxidative stress. PLoS One
Blount JD, Vitikainen EIK, Stott I, Cant MA (2015). Oxidative shielding and the cost of reproduction. Biological Reviews
Cram DL, Blount JD, Young AJ (2015). Oxidative status and social dominance in a wild cooperative breeder.
Functional Ecology,
29(2), 229-238.
Abstract:
Oxidative status and social dominance in a wild cooperative breeder
© 2014 British Ecological Society. Oxidative stress has been proposed as a key mediator of life-history trade-offs, yet the social factors that affect patterns of oxidative status amongst individuals in animal societies remain virtually unexplored. This is important, as rank-related differences in reproductive effort in many social species have the potential to generate, or indeed arise from, differences in oxidative status across dominance classes. Here, we examine rank-related variation in oxidative status before and after a lengthy breeding season in a wild cooperatively breeding bird with high reproductive skew, in the semi-arid zone of Southern Africa; the white-browed sparrow weaver (Plocepasser mahali). Our findings reveal that prior to breeding, neither sex showed rank-related differences in markers of oxidative damage or antioxidant protection, suggesting that dominants' reproductive monopolies do not arise from superior pre-breeding oxidative status. After breeding, however, females (who provision young at higher rates than males) suffered elevated oxidative damage, and dominant females (the only birds to lay and incubate eggs, and the primary nestling provisioners) experienced differential declines in antioxidant protection. While males als o showed reduced antioxidant capacity after breeding, this decline was not dependent on rank and not associated with elevated oxidative damage. Our findings suggest that divisions of labour in animal societies can leave the hardest-working classes differentially exposed to oxidative stress, raising the possibility of hitherto unexplored impacts on health and ageing in social species.
Abstract.
Speakman JR, Speakman JR, Blount JD, Bronikowski AM, Buffenstein R, Isaksson C, Kirkwood TBL, Monaghan P, Ozanne SE, Beaulieu M, et al (2015). Oxidative stress and life histories: Unresolved issues and current needs.
Ecology and EvolutionAbstract:
Oxidative stress and life histories: Unresolved issues and current needs
© 2015 Published by John Wiley & Sons Ltd. Life-history theory concerns the trade-offs that mold the patterns of investment by animals between reproduction, growth, and survival. It is widely recognized that physiology plays a role in the mediation of life-history trade-offs, but the details remain obscure. As life-history theory concerns aspects of investment in the soma that influence survival, understanding the physiological basis of life histories is related, but not identical, to understanding the process of aging. One idea from the field of aging that has gained considerable traction in the area of life histories is that life-history trade-offs may be mediated by free radical production and oxidative stress. We outline here developments in this field and summarize a number of important unresolved issues that may guide future research efforts. The issues are as follows. First, different tissues and macromolecular targets of oxidative stress respond differently during reproduction. The functional significance of these changes, however, remains uncertain. Consequently there is a need for studies that link oxidative stress measurements to functional outcomes, such as survival. Second, measurements of oxidative stress are often highly invasive or terminal. Terminal studies of oxidative stress in wild animals, where detailed life-history information is available, cannot generally be performed without compromising the aims of the studies that generated the life-history data. There is a need therefore for novel non-invasive measurements of multi-tissue oxidative stress. Third, laboratory studies provide unrivaled opportunities for experimental manipulation but may fail to expose the physiology underpinning life-history effects, because of the benign laboratory environment. Fourth, the idea that oxidative stress might underlie life-history trade-offs does not make specific enough predictions that are amenable to testing. Moreover, there is a paucity of good alternative theoretical models on which contrasting predictions might be based. Fifth, there is an enormous diversity of life-history variation to test the idea that oxidative stress may be a key mediator. So far we have only scratched the surface. Broadening the scope may reveal new strategies linked to the processes of oxidative damage and repair. Finally, understanding the trade-offs in life histories and understanding the process of aging are related but not identical questions. Scientists inhabiting these two spheres of activity seldom collide, yet they have much to learn from each other.
Abstract.
Christensen LL, Selman C, Blount JD, Pilkington JG, Watt KA, Pemberton JM, Reid JM, Nussey DH (2015). Plasma markers of oxidative stress are uncorrelated in a wild mammal.
Ecology and Evolution,
5(21), 5096-5108.
Abstract:
Plasma markers of oxidative stress are uncorrelated in a wild mammal
Oxidative stress, which results from an imbalance between the production of potentially damaging reactive oxygen species versus antioxidant defenses and repair mechanisms, has been proposed as an important mediator of life-history trade-offs. A plethora of biomarkers associated with oxidative stress exist, but few ecological studies have examined the relationships among different markers in organisms experiencing natural conditions or tested whether those relationships are stable across different environments and demographic groups. It is therefore not clear to what extent studies of different markers can be compared, or whether studies that focus on a single marker can draw general conclusions regarding oxidative stress. We measured widely used markers of oxidative damage (protein carbonyls and malondialdehyde) and antioxidant defense (superoxide dismutase and total antioxidant capacity) from 706 plasma samples collected over a 4-year period in a wild population of Soay sheep on St Kilda. We quantified the correlation structure among these four markers across the entire sample set and also within separate years, age groups (lambs and adults), and sexes. We found some moderately strong correlations between some pairs of markers when data from all 4 years were pooled. However, these correlations were caused by considerable among-year variation in mean marker values; correlation coefficients were small and not significantly different from zero after accounting for among-year variation. Furthermore, within each year, age, and sex subgroup, the pairwise correlation coefficients among the four markers were weak, nonsignificant, and distributed around zero. In addition, principal component analysis confirmed that the four markers represented four independent axes of variation. Our results suggest that plasma markers of oxidative stress may vary dramatically among years, presumably due to environmental conditions, and that this variation can induce population-level correlations among markers even in the absence of any correlations within contemporaneous subgroups. The absence of any consistent correlations within years or demographic subgroups implies that care must be taken when generalizing from observed relationships with oxidative stress markers, as each marker may reflect different and potentially uncoupled biochemical processes. © 2015 Published by John Wiley
Abstract.
Christensen LL, Selman C, Blount JD, Pilkington JG, Watt KA, Pemberton JM, Reid JM, Nussey DH (2015). Plasma markers of oxidative stress are uncorrelated in a wild mammal.
Ecology and EvolutionAbstract:
Plasma markers of oxidative stress are uncorrelated in a wild mammal
Oxidative stress, which results from an imbalance between the production of potentially damaging reactive oxygen species versus antioxidant defenses and repair mechanisms, has been proposed as an important mediator of life-history trade-offs. A plethora of biomarkers associated with oxidative stress exist, but few ecological studies have examined the relationships among different markers in organisms experiencing natural conditions or tested whether those relationships are stable across different environments and demographic groups. It is therefore not clear to what extent studies of different markers can be compared, or whether studies that focus on a single marker can draw general conclusions regarding oxidative stress. We measured widely used markers of oxidative damage (protein carbonyls and malondialdehyde) and antioxidant defense (superoxide dismutase and total antioxidant capacity) from 706 plasma samples collected over a 4-year period in a wild population of Soay sheep on St Kilda. We quantified the correlation structure among these four markers across the entire sample set and also within separate years, age groups (lambs and adults), and sexes. We found some moderately strong correlations between some pairs of markers when data from all 4 years were pooled. However, these correlations were caused by considerable among-year variation in mean marker values; correlation coefficients were small and not significantly different from zero after accounting for among-year variation. Furthermore, within each year, age, and sex subgroup, the pairwise correlation coefficients among the four markers were weak, nonsignificant, and distributed around zero. In addition, principal component analysis confirmed that the four markers represented four independent axes of variation. Our results suggest that plasma markers of oxidative stress may vary dramatically among years, presumably due to environmental conditions, and that this variation can induce population-level correlations among markers even in the absence of any correlations within contemporaneous subgroups. The absence of any consistent correlations within years or demographic subgroups implies that care must be taken when generalizing from observed relationships with oxidative stress markers, as each marker may reflect different and potentially uncoupled biochemical processes.
Abstract.
Paul SC, Pell JK, Blount JD (2015). Reproduction in Risky Environments: the Role of Invasive Egg Predators in Ladybird Laying Strategies.
PLoS One,
10(10).
Abstract:
Reproduction in Risky Environments: the Role of Invasive Egg Predators in Ladybird Laying Strategies.
Reproductive environments are variable and the resources available for reproduction are finite. If reliable cues about the environment exist, mothers can alter offspring phenotype in a way that increases both offspring and maternal fitness ('anticipatory maternal effects'-AMEs). Strategic use of AMEs is likely to be important in chemically defended species, where the risk of offspring predation may be modulated by maternal investment in offspring toxin level, albeit at some cost to mothers. Whether mothers adjust offspring toxin levels in response to variation in predation risk is, however, unknown, but is likely to be important when assessing the response of chemically defended species to the recent and pervasive changes in the global predator landscape, driven by the spread of invasive species. Using the chemically defended two-spot ladybird, Adalia bipunctata, we investigated reproductive investment, including egg toxin level, under conditions that varied in the degree of simulated offspring predation risk from larval harlequin ladybirds, Harmonia axyridis. H. axyridis is a highly voracious alien invasive species in the UK and a significant intraguild predator of A. bipunctata. Females laid fewer, larger egg clusters, under conditions of simulated predation risk (P+) than when predator cues were absent (P-), but there was no difference in toxin level between the two treatments. Among P- females, when mean cluster size increased there were concomitant increases in both the mass and toxin concentration of eggs, however when P+ females increased cluster size there was no corresponding increase in egg toxin level. We conclude that, in the face of offspring predation risk, females either withheld toxins or were physiologically constrained, leading to a trade-off between cluster size and egg toxin level. Our results provide the first demonstration that the risk of offspring predation by a novel invasive predator can influence maternal investment in toxins within their offspring.
Abstract.
Author URL.
Lane SM, Solino JH, Mitchell C, Blount JD, Okada K, Hunt J, House CM (2015). Rival male chemical cues evoke changes in male pre- and post-copulatory investment in a flour beetle.
Behav Ecol,
26(4), 1021-1029.
Abstract:
Rival male chemical cues evoke changes in male pre- and post-copulatory investment in a flour beetle.
Males can gather information on the risk and intensity of sperm competition from their social environment. Recent studies have implicated chemosensory cues, for instance cuticular hydrocarbons (CHCs) in insects, as a key source of this information. Here, using the broad-horned flour beetle (Gnatocerus cornutus), we investigated the importance of contact-derived rival male CHCs in informing male perception of sperm competition risk and intensity. We experimentally perfumed virgin females with male CHCs via direct intersexual contact and measured male pre- and post-copulatory investment in response to this manipulation. Using chemical analysis, we verified that this treatment engendered changes to perfumed female CHC profiles, but did not make perfumed females "smell" mated. Despite this, males responded to these chemical changes. Males increased courtship effort under low levels of perceived competition (from 1-3 rivals), but significantly decreased courtship effort as perceived competition rose (from 3-5 rivals). Furthermore, our measurement of ejaculate investment showed that males allocated significantly more sperm to perfumed females than to control females. Together, these results suggest that changes in female chemical profile elicited by contact with rival males do not provide males with information on female mating status, but rather inform males of the presence of rivals within the population and thus provide a means for males to indirectly assess the risk of sperm competition.
Abstract.
Author URL.
Archer CR, Hempenstall S, Royle NJ, Selman C, Willis S, Rapkin J, Blount JD, Hunt J (2015). Testing the Effects of DL-Alpha-Tocopherol Supplementation on Oxidative Damage, Total Antioxidant Protection and the Sex-Specific Responses of Reproductive Effort and Lifespan to Dietary Manipulation in Australian Field Crickets (Teleogryllus commodus).
Antioxidants (Basel),
4(4), 768-792.
Abstract:
Testing the Effects of DL-Alpha-Tocopherol Supplementation on Oxidative Damage, Total Antioxidant Protection and the Sex-Specific Responses of Reproductive Effort and Lifespan to Dietary Manipulation in Australian Field Crickets (Teleogryllus commodus).
The oxidative stress theory predicts that the accumulation of oxidative damage causes aging. More generally, oxidative damage could be a cost of reproduction that reduces survival. Both of these hypotheses have mixed empirical support. To better understand the life-history consequences of oxidative damage, we fed male and female Australian field crickets (Teleogryllus commodus) four diets differing in their protein and carbohydrate content, which have sex-specific effects on reproductive effort and lifespan. We supplemented half of these crickets with the vitamin E isoform DL-alpha-tocopherol and measured the effects of nutrient intake on lifespan, reproduction, oxidative damage and antioxidant protection. We found a clear trade-off between reproductive effort and lifespan in females but not in males. In direct contrast to the oxidative stress theory, crickets fed diets that improved their lifespan had high levels of oxidative damage to proteins. Supplementation with DL-alpha-tocopherol did not significantly improve lifespan or reproductive effort. However, males fed diets that increased their reproductive investment experienced high oxidative damage to proteins. While this suggests that male reproductive effort could elevate oxidative damage, this was not associated with reduced male survival. Overall, these results provide little evidence that oxidative damage plays a central role in mediating life-history trade-offs in T. commodus.
Abstract.
Author URL.
Cram DL, Blount JD, Young AJ (2015). The oxidative costs of reproduction are group-size dependent in a wild cooperative breeder. Proceedings of the Royal Society of London. Series B
2014
Winters AE, Stevens M, Mitchell C, Blomberg SP, Blount JD (2014). Maternal effects and warning signal honesty in eggs and offspring of an aposematic ladybird beetle. Functional Ecology
Cram DL, Blount JB, Young AJ (2014). Oxidative state and social dominance in a wild cooperative breeder. Functional Ecology
Schmidt CM, Blount JD, Bennett NC (2014). Reproduction is associated with a tissue-dependent reduction of oxidative stress in eusocial female Damaraland mole-rats (Fukomys damarensis).
PLoS One,
9(7).
Abstract:
Reproduction is associated with a tissue-dependent reduction of oxidative stress in eusocial female Damaraland mole-rats (Fukomys damarensis).
Oxidative stress has been implicated as both a physiological cost of reproduction and a driving force on an animal's lifespan. Since increased reproductive effort is generally linked with a reduction in survival, it has been proposed that oxidative stress may influence this relationship. Support for this hypothesis is inconsistent, but this may, in part, be due to the type of tissues that have been analyzed. In Damaraland mole-rats the sole reproducing female in the colony is also the longest lived. Therefore, if oxidative stress does impact the trade-off between reproduction and survival in general, this species may possess some form of enhanced defense. We assessed this relationship by comparing markers of oxidative damage (malondialdehyde, MDA; protein carbonyls, PC) and antioxidants (total antioxidant capacity, TAC; superoxide dismutase, SOD) in various tissues including plasma, erythrocytes, heart, liver, kidney and skeletal muscle between wild-caught reproductive and non-reproductive female Damaraland mole-rats. Reproductive females exhibited significantly lower levels of PC across all tissues, and lower levels of MDA in heart, kidney and liver relative to non-reproductive females. Levels of TAC and SOD did not differ significantly according to reproductive state. The reduction in oxidative damage in breeding females may be attributable to the unusual social structure of this species, as similar relationships have been observed between reproductive and non-reproductive eusocial insects.
Abstract.
Author URL.
Losdat S, Helfenstein F, Blount JD, Richner H (2014). Resistance to oxidative stress shows low heritability and high common environmental variance in a wild bird.
Journal of Evolutionary Biology,
27(9), 1990-2000.
Abstract:
Resistance to oxidative stress shows low heritability and high common environmental variance in a wild bird
Oxidative stress was recently demonstrated to affect several fitness-related traits and is now well recognized to shape animal life-history evolution. However, very little is known about how much resistance to oxidative stress is determined by genetic and environmental effects and hence about its potential for evolution, especially in wild populations. In addition, our knowledge of phenotypic sexual dimorphism and cross-sex genetic correlations in resistance to oxidative stress remains extremely limited despite important evolutionary implications. In free-living great tits (Parus major), we quantified heritability, common environmental effect, sexual dimorphism and cross-sex genetic correlation in offspring resistance to oxidative stress by performing a split-nest cross-fostering experiment where 155 broods were split, and all siblings (n = 791) translocated and raised in two other nests. Resistance to oxidative stress was measured as both oxidative damage to lipids and erythrocyte resistance to a controlled free-radical attack. Both measurements of oxidative stress showed low additive genetic variances, high common environmental effects and phenotypic sexual dimorphism with males showing a higher resistance to oxidative stress. Cross-sex genetic correlations were not different from unity, and we found no substantial heritability in resistance to oxidative stress at adult age measured on 39 individuals that recruited the subsequent year. Our study shows that individual ability to resist to oxidative stress is primarily influenced by the common environment and has a low heritability with a consequent low potential for evolution, at least at an early stage of life. © 2014 European Society for Evolutionary Biology.
Abstract.
Losdat S, Helfenstein F, Blount JD, Richner H (2014). Resistance to oxidative stress shows low heritability and high common environmental variance in a wild bird. Journal of Evolutionary Biology
2013
Newcombe D, Blount JD, Mitchell C, Moore AJ (2013). Chemical egg defence in the large milkweed bug, Oncopeltus fasciatus, derives from maternal but not paternal diet.
Entomologia Experimentalis et Applicata,
149(3), 197-205.
Abstract:
Chemical egg defence in the large milkweed bug, Oncopeltus fasciatus, derives from maternal but not paternal diet
Many herbivorous insects sequester defensive compounds from their host-plants and incorporate them into their eggs to protect them against predation. Here, we investigate whether transmission of cardenolides from the host-diet to the eggs is maternal, paternal, or biparental in the large milkweed bug, Oncopeltus fasciatus (Dallas) (Hemiptera: Lygaeidae). We reared individual bugs on either milkweed seeds [MW; Asclepias syriaca L. (Apocynaceae)] that contain cardenolides, or on sunflower seeds [SF; Helianthus annuus L. (Asteraceae)] that do not contain cardenolides. We mated females and males so that all four maternal/paternal diet combinations were represented: MW/MW, MW/SF, SF/MW, and SF/SF. Using larvae of the common green lacewing, Chrysoperla (Chrysopa) carnea (Stevens) (Neuroptera: Chrysopidae), we conducted two-choice predation trials to assess whether maternal, paternal, or biparental transmission of cardenolides into the eggs of O. fasciatus increased protection against predation. Furthermore, we used high performance liquid chromatography (HPLC) to assess putative cardenolide content of eggs from the various parental diet treatment groups. The predation trials suggested that regardless of male diet, eggs were afforded better protection when females had been raised on milkweed. However, many eggs were at least partially consumed. This suggests that although chemical defence of eggs does not guarantee protection to eggs on an individual basis, they may increase the probability that some eggs in a clutch are left intact thereby potentially conferring a fitness advantage to more offspring than if eggs are left unprotected. Based on HPLC analysis we found that maternal contribution of cardenolides was significantly greater than paternal contribution of cardenolides to the eggs, supporting the results of our predation trials that a maternal diet of milkweed makes eggs more distasteful than a paternal diet of milkweed. © 2013 the Netherlands Entomological Society.
Abstract.
Newcombe D, Blount JD, Mitchell C, Moore AJ (2013). Chemical egg defence in the large milkweed bug, Oncopeltus fasciatus, derives from maternal but not paternal diet. Entomologia Experimentalis et Applicata
Flores EE, Stevens M, Moore AJ, Blount JD (2013). Diet, development and the optimization of warning signals in post-metamorphic green and black poison frogs.
Functional Ecology,
27(3), 816-829.
Abstract:
Diet, development and the optimization of warning signals in post-metamorphic green and black poison frogs
Many prey species are chemically defended and have conspicuous appearance to deter predators (i.e. aposematism). Such warning signals work because predators pay attention to the colour and size of signals, which they associate with unprofitability. Paradoxically, in early life stages, aposematic species are often warningly coloured, but their chemical defences are lacking because they have yet to be acquired through the diet or synthesized endogenously. This state of being conspicuous yet poorly defended must place individuals at increased risk of predation, but how they minimize this risk during development is unclear. We reared larval green and black poison frogs (Dendrobates auratus) on a relatively low or a higher food supply and tested the hypothesis that individuals with more resources should grow larger while reducing their investment in warning signals at metamorphic completion. We also assayed markers of oxidative balance (malondialdehyde, superoxide dismutase and total antioxidant capacity) to ascertain whether there were resource-allocation trade-offs that differed with diet treatments. Low-food froglets were relatively small, and their body size and signal luminance (perceived brightness) were positively correlated. In contrast, in high-food froglets body size and warning signal luminance were negatively correlated, suggesting either a resource-allocation trade-off or alternatively a facultative reduction in luminance exhibited by larger froglets. The reduction in luminance in relatively large, high-food froglets did not appear to arise because of oxidative stress: signal luminance and markers of oxidative stress were positively correlated in high-food froglets, but were negatively correlated in low-food froglets suggesting a trade-off. Our results highlight developmental plasticity in body size and coloration as affected by resource (i.e. food) supply. Such plasticity seems likely to minimize predation risk during the vulnerable period early in life when individuals are warningly coloured and must make the transition from an undefended phenotype to a mature aposematic state. © 2013 the Authors. Functional Ecology © 2013 British Ecological Society.
Abstract.
Flores EE, Stevens M, Moore AJ, Blount JD (2013). Diet, development and the optimization of warning signals in post-metamorphic green and black poison frogs. Functional Ecology
Plummer KE, Bearhop S, Leech DI, Chamberlain DE, Blount JD (2013). Fat provisioning in winter impairs egg production during the following spring: a landscape-scale study of blue tits.
Journal of Animal Ecology,
82(3), 673-682.
Abstract:
Fat provisioning in winter impairs egg production during the following spring: a landscape-scale study of blue tits
Summary: Provisioning of garden birds is a growing phenomenon, particularly during winter, but there is little empirical evidence of its true ecological impacts. One possibility is that winter provisioning could enhance subsequent breeding performance, but this seems likely to depend on the types of nutrients provided. For example, whereas effects of macronutrients such as fat are unlikely to be carried over to influence breeding in small passerines, micronutrients such as dietary vitamin E (an antioxidant) may be stored or have lasting health benefits. Here, we examine the carry-over effects of winter food supplements on egg production in wild populations of blue tits (Cyanistes caeruleus). Over three consecutive years, birds were provisioned with fat, fat plus vitamin E or remained unfed (controls). The provision of fat in winter resulted in smaller relative yolk mass in larger eggs and reduced yolk carotenoid concentrations in early breeders. However, these effects were not seen in birds provisioned with fat plus vitamin E. Lay date, clutch size, egg mass and yolk vitamin E concentrations were not significantly affected by winter provisioning treatment. Our results indicate that winter provisioning can have important downstream consequences, in particular affecting investment in egg production several weeks or months later. Provisioning is widely applied to support garden bird populations and for the conservation management of endangered species. However, our results challenge the assumption that such practices are always beneficial at the population level and emphasize how the ecological impacts can depend on the specific nutritional profile of provisioned foods. © 2013 British Ecological Society.
Abstract.
Plummer KE, Bearhop S, Leech DI, Chamberlain DE, Blount JD (2013). Fat provisioning in winter impairs egg production during the following spring: a landscape-scale study of blue tits.
J Anim Ecol,
82(3), 673-682.
Abstract:
Fat provisioning in winter impairs egg production during the following spring: a landscape-scale study of blue tits.
1. Provisioning of garden birds is a growing phenomenon, particularly during winter, but there is little empirical evidence of its true ecological impacts. One possibility is that winter provisioning could enhance subsequent breeding performance, but this seems likely to depend on the types of nutrients provided. For example, whereas effects of macronutrients such as fat are unlikely to be carried over to influence breeding in small passerines, micronutrients such as dietary vitamin E (an antioxidant) may be stored or have lasting health benefits. 2. Here, we examine the carry-over effects of winter food supplements on egg production in wild populations of blue tits (Cyanistes caeruleus). Over three consecutive years, birds were provisioned with fat, fat plus vitamin E or remained unfed (controls). 3. The provision of fat in winter resulted in smaller relative yolk mass in larger eggs and reduced yolk carotenoid concentrations in early breeders. However, these effects were not seen in birds provisioned with fat plus vitamin E. Lay date, clutch size, egg mass and yolk vitamin E concentrations were not significantly affected by winter provisioning treatment. 4. Our results indicate that winter provisioning can have important downstream consequences, in particular affecting investment in egg production several weeks or months later. 5. Provisioning is widely applied to support garden bird populations and for the conservation management of endangered species. However, our results challenge the assumption that such practices are always beneficial at the population level and emphasize how the ecological impacts can depend on the specific nutritional profile of provisioned foods.
Abstract.
Author URL.
Losdat S, Helfenstein F, Blount JD, Marri V, Maronde L, Richner H (2013). Nestling erythrocyte resistance to oxidative stress predicts fledging success but not local recruitment in a wild bird.
Biology Letters,
9(1).
Abstract:
Nestling erythrocyte resistance to oxidative stress predicts fledging success but not local recruitment in a wild bird
Stressful conditions experienced by individuals during their early development have long-term consequences on various life-history traits such as survival until first reproduction. Oxidative stress has been shown to affect various fitness-related traits and to influence key evolutionary trade-offs but whether an individual's ability to resist oxidative stress in early life affects its survival has rarely been tested. In the present study, we used four years of data obtained from a free-living great tit population (Parus major; n = 1658 offspring) to test whether pre-fledging resistance to oxidative stress, measured as erythrocyte resistance to oxidative stress and oxidative damage to lipids, predicted fledging success and local recruitment. Fledging success and local recruitment, both major correlates of survival, were primarily influenced by offspring body mass prior to fledging. We found that prefledging erythrocyte resistance to oxidative stress predicted fledging success, suggesting that individual resistance to oxidative stress is related to shortterm survival. However, local recruitment was not influenced by pre-fledging erythrocyte resistance to oxidative stress or oxidative damage. Our results suggest that an individual ability to resist oxidative stress at the offspring stage predicts short-term survival but does not influence survival later in life. © 2012 the Author(s) Published by the Royal Society. All rights reserved.
Abstract.
Plummer KE, Bearhop S, Leech DI, Chamberlain DE, Blount JD (2013). Winter food provisioning reduces future breeding performance in a wild bird.
Sci Rep,
3Abstract:
Winter food provisioning reduces future breeding performance in a wild bird.
Supplementation of food to wild birds occurs on an enormous scale worldwide, and is often cited as an exemplar of beneficial human-wildlife interaction. Recently it has been speculated that winter feeding could have negative consequences for future reproduction, for example by enabling low quality individuals to recruit into breeding populations. However, evidence that winter feeding has deleterious impacts on reproductive success is lacking. Here, in a landscape-scale study of blue tits (Cyanistes caeruleus) across multiple years, we show that winter food supplementation reduced breeding performance the following spring. Compared to unfed populations, winter-fed birds produced offspring that weighed less, were smaller, and had lower survival. This impairment was observed in parents that had received fat only, or in combination with vitamin E, suggesting some generality in the mechanism by which supplementary feeding affected reproduction. Our results highlight the potential for deleterious population-level consequences of winter food supplementation on wild birds.
Abstract.
Author URL.
2012
Orledge JM, Blount JD, Hoodless AN, Royle NJ (2012). Antioxidant supplementation during early development reduces parasite load but does not affect sexual ornament expression in adult ring-necked pheasants.
Functional Ecology,
26(3), 688-700.
Abstract:
Antioxidant supplementation during early development reduces parasite load but does not affect sexual ornament expression in adult ring-necked pheasants
The 'parasite-mediated sexual selection' (PMSS) hypothesis predicts that exaggerated male ornamentation could provide a signal to females of a male's ability to resist parasites. Empirical tests of the PMSS have been largely equivocal, however, which may be because most have not considered the role of early life-history effects. 2.Many sexually selected traits are carotenoid-based. Allocation of dietary-derived carotenoids to sexual ornaments may trade-off with allocation to pro-inflammatory immune response and/or antioxidant functions, mediated by the oxidative status of individuals. Exposure to parasites can increase oxidative stress, so under this scenario, sexually selected traits indicate ability to resist oxidative stress rather than ability to resist parasites per se. Such life-history trade-offs, mediated by oxidative status of individuals, are particularly acute during growth and development. 3.Here, we use ring-necked pheasants, Phasianus colchicus, a strongly sexually selected species, to test whether supplementation with dietary antioxidants (vitamin E) can mitigate the effects of early exposure to parasites (the nematode, Heterakis gallinarum), via alteration of the oxidative status of individuals, and positively affect the expression of sexual ornaments at adulthood. 4.We found that vitamin E mediated the effect of early exposure to parasites on levels of oxidative damage at 8weeks of age and reduced the parasite load of individuals at adulthood as predicted. However, the expression of sexual ornaments, immune function and growth were unaffected by either early vitamin E supplementation or manipulation of parasite load. In contrast to the predictions of the PMSS hypothesis, the intensity of sexual ornament expression was not related to either parasite load or oxidative status of individuals (current or long-term). Consequently, there was no evidence that the expression of sexual ornaments provided information on the ability of males to resist infection from parasites. © 2012 the Authors. Functional Ecology © 2012 British Ecological Society.
Abstract.
Sepp T, Karu U, Blount JD, Sild E, Maenniste M, Horak P (2012). Coccidian Infection Causes Oxidative Damage in Greenfinches.
PLOS ONE,
7(5).
Author URL.
Müller W, Vergauwen J, Eens M, Blount JD (2012). Environmental effects shape the maternal transfer of carotenoids and vitamin E to the yolk.
Frontiers in Zoology,
9Abstract:
Environmental effects shape the maternal transfer of carotenoids and vitamin E to the yolk
Introduction: Maternal effects occur when the phenotype of the offspring is influenced by the phenotype of the mother, which in turn depends on her heritable state as well as on influences from the current and past environmental conditions. All of these pathways may, therefore, form significant sources of variation in maternal effects. Here, we focused on the maternal transfer of carotenoids and vitamin E to the egg yolk, using canaries as a model species. Maternal yolk carotenoids and vitamin E are known to generate significant phenotypic variation in offspring, representing examples of maternal effects. We studied the intra-individual consistency in deposition patterns across two years and the mother-daughter resemblance across two generations in order to estimate the level of heritable variation. The effects of the current environmental conditions were studied via a food supplementation experiment, while the consequences of past environmental conditions were estimated on the basis of the early growth trajectories.Results: There was a significant effect of the current environmental conditions on the yolk carotenoid and vitamin E deposition, but this effect varied between antioxidant components. The deposition of yolk carotenoids and vitamin E were linked to the process of yolk formation. Past environmental conditions did not contribute to the variation in yolk carotenoid and vitamin E levels nor did we find significant heritable variation.Conclusions: the transfer of carotenoids or vitamin E may be an example where current environmental variation is largely passed from the mother to the offspring, despite the numerous intermediate physiological steps that are involved. Differences in the effect of the environmental conditions as experienced by the mother during laying may be due to differences in availability as well as physiological processes such as competitive exclusion or selective absorption. © 2012 Müller et al.; licensee BioMed Central Ltd.
Abstract.
Weber SB, Broderick AC, Groothuis TGG, Ellick J, Godley BJ, Blount JD (2012). Fine-scale thermal adaptation in a green turtle nesting population.
Proc Biol Sci,
279(1731), 1077-1084.
Abstract:
Fine-scale thermal adaptation in a green turtle nesting population.
The effect of climate warming on the reproductive success of ectothermic animals is currently a subject of major conservation concern. However, for many threatened species, we still know surprisingly little about the extent of naturally occurring adaptive variation in heat-tolerance. Here, we show that the thermal tolerances of green turtle (Chelonia mydas) embryos in a single, island-breeding population have diverged in response to the contrasting incubation temperatures of nesting beaches just a few kilometres apart. In natural nests and in a common-garden rearing experiment, the offspring of females nesting on a naturally hot (black sand) beach survived better and grew larger at hot incubation temperatures compared with the offspring of females nesting on a cooler (pale sand) beach nearby. These differences were owing to shallower thermal reaction norms in the hot beach population, rather than shifts in thermal optima, and could not be explained by egg-mediated maternal effects. Our results suggest that marine turtle nesting behaviour can drive adaptive differentiation at remarkably fine spatial scales, and have important implications for how we define conservation units for protection. In particular, previous studies may have underestimated the extent of adaptive structuring in marine turtle populations that may significantly affect their capacity to respond to environmental change.
Abstract.
Author URL.
Mainwaring MC, Blount JD, Hartley IR (2012). Hatching asynchrony can have long-term consequences for offspring fitness in zebra finches under captive conditions.
Biological Journal of the Linnean Society,
106(2), 430-438.
Abstract:
Hatching asynchrony can have long-term consequences for offspring fitness in zebra finches under captive conditions
Hatching asynchrony can have profound short-term consequences for offspring, although the long-term consequences are less well understood. The purpose of this study was to examine the long-term consequences of hatching asynchrony for offspring fitness in birds. Specifically, we aimed to test the hypothesis that hatching asynchrony increases the sexual attractiveness and fecundity, respectively, of early-hatched male and female zebra finch, Taeniopygia guttata (Vieillot, 1817) offspring. Mate-choice trials comparing male nestlings with the same parents, but that were reared in asynchronous or experimentally synchronous broods, revealed no female preference in relation to hatching regime. We did however find strong evidence that, as adults, late-hatched males were more attractive to females than siblings that had hatched earlier. Meanwhile, we found a weak trend towards early-hatched females depositing more carotenoids and retinol in the egg yolk than late-hatched or synchronously hatched females, although there were no differences in terms of clutch characteristics or the deposition of α-tocopherol or γ-tocopherol in the egg yolk. Therefore, we found that the beneficial long-term consequences of hatching asynchrony were sex specific, being accrued by late-hatched male nestlings and by early-hatched female nestlings. Consequently, we conclude that the long-term consequences of hatching asynchrony are more complex than previously realised. © 2012 the Linnean Society of London.
Abstract.
Blount JD, Rowland HM, Drijfhout FP, Endler JA, Inger R, Sloggett JJ, Hurst GDD, Hodgson DJ, Speed MP (2012). How the ladybird got its spots: Effects of resource limitation on the honesty of aposematic signals.
Functional Ecology,
26(2), 334-342.
Abstract:
How the ladybird got its spots: Effects of resource limitation on the honesty of aposematic signals
Prey species often possess defences (e.g. toxins) coupled with warning signals (i.e. aposematism). There is growing evidence that the expression of aposematic signals often varies within species and correlates with the strength of chemical defences. This has led to the speculation that such signals may be 'honest', with signal reliability ensured by the costliness of producing or maintaining aposematic traits. We reared larval seven-spot ladybirds (Coccinella septempunctata) on a Low or High aphid diet and measured the effects on warning signal expression (elytral carotenoid pigmentation, conspicuousness, spot size), levels of defensive alkaloids (precoccinelline, coccinelline), and relationships between these traits. High-diet individuals had greater total precoccinelline levels, and elytra carotenoid concentrations at adulthood which was detectable to a typical avian predator. However, larval diet did not significantly affect adult body mass or size, spot size or coccinelline levels. Elytra carotenoid concentrations correlated positively with total precoccinelline levels in both diet groups and sexes. However, the relationship between elytra carotenoid concentrations and total levels of coccinelline depended on sex: in both diet groups, elytra carotenoids and coccinelline levels were positively correlated in females, but negatively correlated in males. Spot size and coccinelline levels correlated positively in Low-diet individuals, but negatively in High-diet individuals. These results point to physiological linkages between components of aposematism, which are modulated by resource (i.e. food) availability and affect the honesty of signals. Developmental diet, but also sex, influenced the relationships between signals and toxin levels. Ladybirds are sexually size dimorphic, and thus in comparison with males, females may be more susceptible to resource limitation and more likely to be honest signallers. © 2012 the Authors. Functional Ecology © 2012 British Ecological Society.
Abstract.
Sepp T, Sild E, Blount JD, Männiste M, Karu U, Hõrak P (2012). Individual consistency and covariation of measures of oxidative status in greenfinches.
Physiol Biochem Zool,
85(3), 299-307.
Abstract:
Individual consistency and covariation of measures of oxidative status in greenfinches.
Oxidative stress results from a mismatch between production of reactive oxygen species (ROS) and the organism's capacity to mitigate their damaging effects by building up sufficient antioxidant protection and/or repair mechanisms. Because ROS production is a universal consequence of cellular metabolism and immune responses, evolutionary animal ecologists have become increasingly interested in involvement of oxidative stress as a proximate mechanism responsible for the emergence of trade-offs related to the evolution of life-history and signal traits. Among the most practical problems pertinent to ecological research on oxidative stress is finding a combination of biomarkers of oxidative status that can be applied to typical wild animal models such as small birds, mammals, and reptiles. This study describes covariation and individual consistency of eight parameters of oxidative status in a small passerine bird, wild-caught captive greenfinch (Carduelis chloris). We measured two markers of plasma antioxidant potential--total antioxidant capacity (TAC) and oxygen radical absorbance (OXY)--and concentrations of one lipophilic (carotenoids) and two hydrophilic (uric acid and ascorbate) antioxidants in plasma. We also measured total glutathione (GSH) concentration and superoxide dismutase (SOD) activity in erythrocytes. Oxidative damage was assessed on the basis of plasma malondialdehyde (MDA) levels, measured by high-performance liquid chromatography. Plasma carotenoids, TAC, and erythrocyte GSH showed significant individual consistency over an 8-d period, indicating that those variables reflected more persistent differences between individuals than plasma OXY, MDA, and uric acid. We did not detect any strong or moderate correlations between the studied parameters, which suggests that all of these biomarkers contain potentially unique information. Injection of a synthetic mimetic of SOD and catalase--EUK-134--did not affect any of the parameters of oxidative status. Capability of phagocytes to produce oxidative burst was not associated with MDA, indicating that under our experimental conditions, ROS production by phagocytes was not a strong determinant of oxidative damage. Altogether these findings suggest that attempts to characterize oxidative balance should use a wide range of biomarkers, and further studies of oxidative status in wild animals may benefit from the experimental induction of oxidative stress.
Abstract.
Author URL.
Selman C, Blount JD, Nussey DH, Speakman JR (2012). Oxidative damage, ageing, and life-history evolution: Where now?.
Trends in Ecology and Evolution,
27(10), 570-577.
Abstract:
Oxidative damage, ageing, and life-history evolution: Where now?
The idea that resources are limited and animals can maximise fitness by trading costly activities off against one another forms the basis of life-history theory. Although investment in reproduction or growth negatively affects survival, the mechanisms underlying such trade-offs remain obscure. One plausible mechanism is oxidative damage to proteins, lipids, and nucleic acids caused by reactive oxygen species (ROS). Here, we critically evaluate the premise that ROS-induced oxidative damage shapes life history, focussing on birds and mammals, and highlight the importance of ecological studies examining free-living animals within this experimental framework. We conclude by emphasising the value of using multiple assays to determine oxidative protection and damage. We also highlight the importance of using standardised and appropriate protocols, and discuss future research directions. © 2012 Elsevier Ltd.
Abstract.
Selman C, Blount JD, Nussey DH, Speakman JR (2012). Oxidative damage, ageing, and life-history evolution: where now?. Trends in Ecology and Evolution
Orledge JM, ROYLE NJ, BLOUNT JD, PIKE TW, HOODLESS AN (2012). Synergistic effects of supplementation of dietary antioxidants during growth on adult phenotype in ring-necked pheasants, Phasianus colchicus.
Heidinger BJ, Blount JD, Boner W, Griffiths K, Metcalfe NB, Monaghan P (2012). Telomere Length in Early Life Predicts Life Span EDITORIAL COMMENT.
OBSTETRICAL & GYNECOLOGICAL SURVEY,
67(5), 283-284.
Author URL.
Heidinger BJ, Blount JD, Boner W, Griffiths K, Metcalfe NB, Monaghan P (2012). Telomere length in early life predicts life span. Obstetrical and Gynecological Survey, 67(5), 283-284.
Heidinger BJ, Blount JD, Boner W, Griffiths K, Metcalfe NB, Monaghan P (2012). Telomere length in early life predicts lifespan. Proc. Nat. Acad. Sci. USA
Flores EE, Moore AJ, Blount JD (2012). Unusual whitish eggs in the poison frog Dendrobates auratus Girard, 1855.
Tropical Zoology,
25(2), 67-73.
Abstract:
Unusual whitish eggs in the poison frog Dendrobates auratus Girard, 1855
Poison frogs in the genus Dendrobates (sensu Grant et al. 2006) are known to lay black pigmented eggs. During a field study in May 2010 in central Panama, a captive pair of wild-caught adult Dendrobates auratus laid a clutch of whitish eggs. The eggs developed and metamorphic froglets were similar in size and color to that of age-matched normal-colored tadpoles produced by different parents and reared in exactly the same conditions. The observation of a pale pigmented tadpole in the wild suggests that polymorphism in the degree of melanism is not simply an artifact of laboratory rearing. Our study is the first to report the production of viable whitish eggs by any species in the genus Dendrobates. Whether this coloration arises due to constraint or is a polymorphism that has adaptive significance awaits further study. © Istituto per lo Studio degli Ecosistemi of the Consiglio Nazionale delle Ricerche, Firenze 2012.
Abstract.
Blount JD, Speed MP, Ruxton GD, Stephens PA (2012). Warning displays may function as honest signals of toxicity.
Proceedings of the Royal Society B: Biological Sciences,
276(1658), 871-877.
Abstract:
Warning displays may function as honest signals of toxicity
Many prey species use colourful 'aposematic' signalling to advertise the fact that they are toxic. Some recent studies have shown that the brightness of aposematic displays correlates positively with the strength of toxicity, suggesting that aposematic displays are a form of handicap signal, the conspicuousness of which reliably indicates the level of toxicity. The theoretical consensus in the literature is, however, at odds with this finding. It is commonly assumed that the most toxic prey should have less bright advertisements because they have better chances of surviving attacks and can therefore reduce the costs incurred by signalling. Using a novel theoretical model, we show that aposematic signals can indeed function as handicaps. To generate this prediction, we make a key assumption that the expression of bright displays and the storage of anti-predator toxins compete for resources within prey individuals. One shared currency is energy. However, competition for antioxidant molecules, which serve dual roles as pigments and in protecting prey against oxidative stress when they accumulate toxins, provides a specific candidate resource that could explain signal honesty. Thus, contrary to the prevailing theoretical orthodoxy, warning displays may in fact be honest signals of the level of (rather than simply the existence of) toxicity. © 2008 the Royal Society.
Abstract.
2011
Blount JD, Pike TW (2011). Deleterious effects of light exposure on immunity and sexual colouration in birds.
Functional EcologyAbstract:
Deleterious effects of light exposure on immunity and sexual colouration in birds
1. Sunlight ultraviolet (UV) exposure can be highly damaging to biological tissues, being known to cause cellular damage and immunosuppression in humans and rodents, and depletion of carotenoid-based sexual plumage colouration in birds (i.e. photobleaching). However, it remains unknown whether sunlight may cause photobleaching in living tissues that comprise sexual signals such as bare parts in birds. It seems possible that any carotenoids depleted from bare parts by sunlight could be replenished, but if so, this could impact the availability of carotenoids for other functions such as immunity and antioxidant defence. Such trade-offs seem particularly likely in individuals that have a low dietary intake of carotenoids, or small amounts of carotenoids in body storage.
2. We investigated the effects of exposure to simulated sunlight UV (UV+) on bill colouration, blood plasma and liver (i.e. body storage) carotenoids, and pro-inflammatory immune responses in male zebra finches (Taeniopygia guttata) in vivo, compared to individuals maintained in an identical environment but with the UV wavelengths removed by a filter (UV-). We also investigated whether any deleterious effects of UV exposure were mitigated by dietary carotenoid supplementation (UV+ Car+).
3. Exposure to simulated sunlight UV was associated with low levels of carotenoids in liver, and elevated levels of carotenoids in blood plasma, suggesting mobilisation of stored carotenoids. Simulated sunlight UV also caused impaired pro-inflammatory immune responses, whereas this was not seen in carotenoid-supplemented birds. We found no effects of simulated sunlight UV or carotenoid supplementation on oxidative damage in blood plasma or bill.
4. Bill ‘carotenoid chroma’ diminished, and bill ‘UV chroma’ correspondingly increased, in all groups during the experiment (i.e. even in UV+ Car+ birds, and in UV- birds). This likely arose because the illuminance in the experimental cages was far higher than in standard laboratory housing conditions, and suggests that carotenoid pigmentation is highly susceptible to photobleaching even under exposure to human-visible wavelengths.
5. These results highlight the potential for sunlight exposure to invoke a range of deleterious consequences for birds, including photobleaching and depression of immunity via pathways mediated by carotenoid allocation trade-offs. The expression of carotenoid-based sexual signals may therefore reveal an individual’s history of sunlight exposure and its deleterious effects on immunity.
Abstract.
Pike TW, Bjerkeng B, Blount JD, Lindström J, Metcalfe NB (2011). How integument colour reflects its carotenoid content: a stickleback's perspective.
Functional Ecology,
25(1), 297-304.
Abstract:
How integument colour reflects its carotenoid content: a stickleback's perspective
1.Carotenoid-based signals typically vary in both the total concentration of carotenoids deposited and the relative quantities of different constituent carotenoids. As these constituents often have differing spectral properties, the relative and absolute concentrations of different carotenoids deposited in a signal can significantly affect the spectrum of light reflected. A critical but rarely tested assumption of hypotheses concerning the information content of carotenoid-based signals is that their colour directly reveals the concentration and composition of constituent carotenoids to intended recipients. Most previous studies have attempted to address this question using either photographic techniques or by analysing recorded reflectance spectra, neither of which take into account the specific properties of the receiver's visual system. 2.Here, we use psychophysical models of the visual system of three-spined sticklebacks (Gasterosteus aculeatus) to estimate their sensitivity to variation in the concentration and relative abundance of constituent carotenoids of males' carotenoid-based sexual signals. 3.We demonstrate that sticklebacks are acutely sensitive to variation in both the total concentration of carotenoids in the signal and the relative proportion of its constituents, and that the accuracy of these assessments is largely unaffected by the presence or absence of ultraviolet radiation in the illuminant. We discuss these findings in relation to the evolution, maintenance and information content of carotenoid-based sexual signals. © 2010 the Authors. Functional Ecology © 2010 British Ecological Society.
Abstract.
Losdat S, Richner H, Blount JD, Helfenstein F (2011). Immune activation reduces sperm quality in the great tit.
PLoS ONE,
6(7).
Abstract:
Immune activation reduces sperm quality in the great tit
Mounting an immune response against pathogens incurs costs to organisms by its effects on important life-history traits, such as reproductive investment and survival. As shown recently, immune activation produces large amounts of reactive species and is suggested to induce oxidative stress. Sperm are highly susceptible to oxidative stress, which can negatively impact sperm function and ultimately male fertilizing efficiency. Here we address the question as to whether mounting an immune response affects sperm quality through the damaging effects of oxidative stress. It has been demonstrated recently in birds that carotenoid-based ornaments can be reliable signals of a male's ability to protect sperm from oxidative damage. In a full-factorial design, we immune-challenged great tit males while simultaneously increasing their vitamin E availability, and assessed the effect on sperm quality and oxidative damage. We conducted this experiment in a natural population and tested the males' response to the experimental treatment in relation to their carotenoid-based breast coloration, a condition-dependent trait. Immune activation induced a steeper decline in sperm swimming velocity, thus highlighting the potential costs of an induced immune response on sperm competitive ability and fertilizing efficiency. We found sperm oxidative damage to be negatively correlated with sperm swimming velocity. However, blood resistance to a free-radical attack (a measure of somatic antioxidant capacity) as well as plasma and sperm levels of oxidative damage (lipid peroxidation) remained unaffected, thus suggesting that the observed effect did not arise through oxidative stress. Towards the end of their breeding cycle, swimming velocity of sperm of more intensely colored males was higher, which has important implications for the evolution of mate choice and multiple mating in females because females may accrue both direct and indirect benefits by mating with males having better quality sperm. © 2011 Losdat et al.
Abstract.
Losdat S, Richner H, Blount JD, Helfenstein F (2011). Immune activation reduces sperm quality in the great tit.
PLoS ONE,
6(7), 1-10.
Abstract:
Immune activation reduces sperm quality in the great tit.
Mounting an immune response against pathogens incurs costs to organisms by its effects on important life-history traits, such as reproductive investment and survival. As shown recently, immune activation produces large amounts of reactive species and is suggested to induce oxidative stress. Sperm are highly susceptible to oxidative stress, which can negatively impact sperm function and ultimately male fertilizing efficiency. Here we address the question as to whether mounting an immune response affects sperm quality through the damaging effects of oxidative stress. It has been demonstrated recently in birds that carotenoid-based ornaments can be reliable signals of a male's ability to protect sperm from oxidative damage. In a full-factorial design, we immune-challenged great tit males while simultaneously increasing their vitamin E availability, and assessed the effect on sperm quality and oxidative damage. We conducted this experiment in a natural population and tested the males' response to the experimental treatment in relation to their carotenoid-based breast coloration, a condition-dependent trait. Immune activation induced a steeper decline in sperm swimming velocity, thus highlighting the potential costs of an induced immune response on sperm competitive ability and fertilizing efficiency. We found sperm oxidative damage to be negatively correlated with sperm swimming velocity. However, blood resistance to a free-radical attack (a measure of somatic antioxidant capacity) as well as plasma and sperm levels of oxidative damage (lipid peroxidation) remained unaffected, thus suggesting that the observed effect did not arise through oxidative stress. Towards the end of their breeding cycle, swimming velocity of sperm of more intensely colored males was higher, which has important implications for the evolution of mate choice and multiple mating in females because females may accrue both direct and indirect benefits by mating with males having better quality sperm.
Abstract.
Teuber K, Schiller J, Jakop U, Lüpold S, Orledge JM, Blount JD, Royle NJ, Hoodless A, Müller K (2011). MALDI-TOF mass spectrometry as a simple tool to determine the phospholipid/glycolipid composition of sperm: pheasant spermatozoa as one selected example.
Anim Reprod Sci,
123(3-4), 270-278.
Abstract:
MALDI-TOF mass spectrometry as a simple tool to determine the phospholipid/glycolipid composition of sperm: pheasant spermatozoa as one selected example.
Cellular membranes are composed of highly variable lipid molecules, mainly cholesterol and phospholipids (PLs). The cholesterol moiety and the saturation degree of the fatty acyl residues of PL determine the fluidity of the membrane, which is particularly important for sperm because they have to undergo characteristic membrane-dependent processes (acrosomal exocytosis and fusion with the oocyte). Glycolipids are an essential part of the membrane surface acting as key mediators in the interactions of sperm with components of the female genital tract. Although the lipid composition of many mammalian spermatozoa has already been determined, the lipid composition of avian spermatozoa has scarcely been investigated. Using spermatozoa extracts of the ring-necked pheasant (Phasianus colchicus) as a selected example, this work demonstrates that matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a simple and fast method to determine spermatozoal lipid compositions. The lipid compositions of pheasant spermatozoa have not yet been investigated. In addition to common membrane (primarily diacyl) PL (sphingomyelin, phosphatidylcholine, phosphatidylinositol and phosphatidylethanolamine), remarkable variation of different sulfoglycolipids (sulfogalactocerebrosides) was identified. This is in strong contrast to all other animal species investigated so far which nearly exclusively contain the sulfoglycolipid seminolipid (sulfogalactoalkylacylglycerol). We emphasize that the MALDI MS approach allows the characterization of sulfoglycolipids of sperm within a few minutes without the necessity for previous chromatographic separation.
Abstract.
Okada K, Blount JD, Sharma MD, Snook RR, Hosken DJ (2011). Male attractiveness, fertility and susceptibility to oxidative stress are influenced by inbreeding in Drosophila simulans.
J Evol Biol,
24(2), 363-371.
Abstract:
Male attractiveness, fertility and susceptibility to oxidative stress are influenced by inbreeding in Drosophila simulans.
Inbreeding frequently leads to inbreeding depression, a reduction in the trait values of inbred individuals. Inbreeding depression has been documented in sexually selected characters in several taxa, and while there is correlational evidence that male fertility is especially susceptible to inbreeding depression, there have been few direct experimental examinations of this. Here, we assessed inbreeding depression in male fertility and a range of other male fitness correlates in Drosophila simulans. We found that male fertility and attractiveness were especially susceptible to inbreeding depression. Additionally, levels of testicular oxidative stress were significantly elevated in inbred males, although sperm viability did not differ between inbred and outbred males. Copulation duration, induction of oviposition, and the proportion of eggs hatching did not differ for females mated to inbred or outbred males. Nevertheless, our results clearly show that key male fitness components are impaired by inbreeding and provide evidence that aspects of male fertility are especially susceptible to inbreeding depression.
Abstract.
Author URL.
Royle NJ, Hall ME, Blount JD, Forbes S (2011). Patterns of egg yolk antioxidant co-variation in an avian brood parasite-host system.
Behavioral Ecology and Sociobiology,
65(2), 313-323.
Abstract:
Patterns of egg yolk antioxidant co-variation in an avian brood parasite-host system
Despite their importance to offspring fitness outcomes, there has been little previous work on egg-mediated maternal effects in avian brood parasites which lay their eggs in the nests of other species. Here, we examine patterns of egg yolk antioxidant deposition in an avian host (red-winged blackbird, Agelaius phoeniceus) and their brood parasite (brown-headed cowbird, Molothrus ater). Cowbird nestlings compete directly for food with host blackbird chicks and succeed, despite hatching from a smaller egg, by begging more intensely and growing as or more rapidly than their hosts. Dietary-derived antioxidants, such as carotenoids and vitamins E and A, deposited in egg yolk, may enhance growth rate and reduce oxidative stress, and therefore provide a potential mechanism by which female cowbirds could enhance the competitiveness of their young in host nests. However, provision of antioxidants to eggs is costly so we predicted that female cowbirds should adjust the amount of antioxidants in response to variation in host quality. We found that whilst red-winged blackbird clutches parasitised by cowbirds did not differ in the pattern of antioxidant deposition compared to non-parasitised clutches, levels of vitamin E deposited in cowbird eggs were closely matched to that of the individual host clutch in which cowbirds laid their egg. This supports the prediction that female cowbirds adjust the antioxidant concentration of their eggs to increase the likely competitiveness of their offspring in the host nest into which they are laid and may help explain the success of cowbirds in competing with larger host young. © 2010 Springer-Verlag.
Abstract.
Weber SB, Blount JD, Godley BJ, Witt MJ, Broderick AC (2011). Rate of egg maturation in marine turtles exhibits 'universal temperature dependence'.
J Anim Ecol,
80(5), 1034-1041.
Abstract:
Rate of egg maturation in marine turtles exhibits 'universal temperature dependence'.
1. The metabolic theory of ecology (MTE) predicts that, after correcting for body mass variation among organisms, the rates of most biological processes will vary as a universal function of temperature. However, empirical support for 'universal temperature dependence' (UTD) is currently equivocal and based on studies of a limited number of traits. 2. In many ectothermic animals, the rate at which females produce mature eggs is temperature dependent and may be an important factor in determining the costs of reproduction. 3. We tested whether the rate of egg maturation in marine turtles varies with environmental temperature as predicted by MTE, using the time separating successive clutches of individual females to estimate the rate at which eggs are formed. We also assessed the phenotypic contribution to this rate, by using radio telemetry to make repeated measurements of interclutch intervals for individual green turtles (Chelonia mydas). 4. Rates of egg maturation increased with seasonally increasing water temperatures in radio-tracked green turtles, but were not repeatable for individual females, and did not vary according to maternal body size or reproductive investment (number and size of eggs produced). 5. Using a collated data set from several different populations and species of marine turtles, we then show that a single relationship with water temperature explains most of the variation in egg maturation rates, with a slope that is statistically indistinguishable from the UTD predicted by MTE. However, several alternative statistical models also described the relationship between temperature and egg maturation rates equally parsimoniously. 6. Our results offer novel support for the MTE's predicted UTD of biological rates, although the underlying mechanisms require further study. The strong temperature dependence of egg maturation combined with the apparently weak phenotypic contribution to this rate has interesting behavioural implications in ectothermic animals. We suggest that maternal thermoregulatory behaviour in marine turtles, and many other reptiles, is consistent with a strategy of adaptively increasing body temperatures to accelerate egg maturation.
Abstract.
Author URL.
2010
Harrison XA, Blount J, Inger R, Bearhop S (2010). Carry-over Effects as Drivers of Fitness in Animals. Journal of Animal Ecology, 79, 974-982.
Pike TW, Blount JD, Metcalfe NB, Lindström J (2010). Dietary carotenoid availability and reproductive effort influence the age-related decline in performance.
Behavioral Ecology,
21(5), 1048-1053.
Abstract:
Dietary carotenoid availability and reproductive effort influence the age-related decline in performance
Elevated breeding effort is known to increase an individual's rate of senescence, although the underlying mechanisms are not well understood. One possibility is that the ability to resist senescence is limited by the availability of antioxidants, which are necessary to mitigate the deleterious effects of oxidative stress thought to underlie the aging process. Susceptibility to oxidative stress is likely to be particularly high during reproduction, and so for a given level of reproductive effort, the rate of senescence should be fastest in those individuals with the poorest antioxidant capacity. We tested this hypothesis in an experimental study of breeding male three-spined sticklebacks (Gasterosteus aculeatus) held under a high or low reproduction regime and fed on either high or low levels of carotenoids (potentially limiting dietary compounds with antioxidant properties). Fish on the high reproduction regime and those on the low-carotenoid diet both showed an accelerated decline in sustained swimming performance (an indicator of locomotor senescence) compared with males on the low reproduction regime and high-carotenoid diet, respectively. The swimming performance of fish subjected to the high rate of reproduction, but fed a low-carotenoid diet, appeared to decline most rapidly, perhaps because of the additive effects of increased levels of reproduction-induced oxidative stress and lower antioxidant availability. These findings show that both dietary carotenoid intake and breeding effort can impact on the age-related decline in swimming performance and have important implications for female choice and the capacity of males with insufficient antioxidant defenses to adequately perform paternal care. © 2010 the Author.
Abstract.
Pike TW, Blount JD, Lindström J, Metcalfe NB (2010). Dietary carotenoid availability, sexual signalling and functional fertility in sticklebacks.
Biol Lett,
6(2), 191-193.
Abstract:
Dietary carotenoid availability, sexual signalling and functional fertility in sticklebacks.
In species where males express carotenoid-based sexual signals, more intensely coloured males may be signalling their enhanced ability to combat oxidative stress. This may include mitigating deleterious oxidative damage to their sperm, and so be directly related to their functional fertility. Using a split-clutch in vitro fertilization technique and dietary carotenoid manipulation, we demonstrate that in non-competitive fertilization assays, male three-spined sticklebacks (Gasterosteus aculeatus) that are fed higher (but biologically relevant) levels of carotenoids had a significantly increased fertilization success, irrespective of maternal carotenoid intake. Furthermore, within diet groups, a male's fertilization success was positively related to the expression of his carotenoid-based nuptial coloration, with more intensely coloured males having higher functional fertility. These data provide, to our knowledge, the first demonstration that dietary access to carotenoids influences fertilization success, and suggest that females could use a male's nuptial coloration as an indicator of his functional fertility.
Abstract.
Author URL.
Speed MP, Ruxton GD, Blount JD, Stephens PA (2010). Diversification of honest signals in a predator-prey system.
Ecology Letters,
13(6), 744-753.
Abstract:
Diversification of honest signals in a predator-prey system
Many animals use bright colouration to advertise their toxicity to predators. It is now well established that both toxicity and colouration are often variable within prey populations, yet it is an open question whether or not brighter signals should be used by the more toxic members of the population. We therefore describe a model in which signal honesty can easily be explained. We assumed that prey toxicity is environmentally conferred and variable between individuals, and that signalling bears a cost through attracting the attention of predators. A key assumption is that predators know the mean toxicity associated with each signalling level, so that the probability of attack for each signal value declines as mean toxicity associated with that signal increases. The probability of death given attack for each individual, however, declines with the precise value of its own toxicity, and prey must evolve the optimal level of signal to match the toxicity level that they acquire from their environments. At the start of our simulations there is no signalling system, as neither prey nor predators have biases that favour signal diversification. Over evolutionary time, however, a positive correlation emerges between signal strength and the mean toxicity associated with each signal level. When stability is reached, predators change their behaviour so that they now tend to avoid prey that signal conspicuously. In addition to predicting within-species signal reliability, our model can explain the initial evolution of aposematic displays without the need to assume special biases in predators. © 2010 Blackwell Publishing Ltd/CNRS.
Abstract.
Hall ME, Blount JD, Forbes S, Royle NJ (2010). Does oxidative stress mediate the trade-off between growth and self-maintenance in structured families?.
Functional Ecology,
24(2), 365-373.
Abstract:
Does oxidative stress mediate the trade-off between growth and self-maintenance in structured families?
Life-history theory predicts a trade-off between growth and self-maintenance. However, little is known about the underlying mechanisms. Oxidative stress, the imbalance between the production of reactive oxygen species (ROS) during normal metabolic processes and the level of antioxidant defences, is a potential mechanism. In many altricial birds asynchronous hatching creates different castes of progeny as a hedge against developmental and environmental uncertainty (a 'structured' family). Older, 'core' offspring and later hatched 'marginal' offspring consequently experience contrasting levels of resource availability during development. To be adaptive the phenotypic handicap incurred by marginal offspring must be reversible when conditions allow. Dietary-derived antioxidants are an important component of antioxidant defences, which modulate oxidative damage arising from normal metabolic processes such as growth. Dietary antioxidants could therefore be important determinants of trade-offs during growth, with the balance of these trade-offs differing between core and marginal offspring. To investigate this, we manipulated brood size and structure as well as antioxidant availability (by vitamin and mineral supplementation), then measured growth and oxidative damage in nestling red-winged blackbirds Agelaius phoeniceus. We found that individuals supplemented with dietary antioxidants allocated these extra resources to increasing growth rate, rather than reducing oxidative damage. Irrespective of hatch rank, nestlings that received supplementary antioxidants grew faster than controls, despite no difference in their begging behaviour or parental provisioning rates. There was no overall difference in the level of lipid peroxidation (malondialdehyde; MDA) in the blood plasma of supplemented and control chicks, but among marginal offspring those that received an antioxidant supplement had lower plasma MDA. Antioxidant supplementation did not affect nestling survival to fledging age. These novel results support the idea that oxidative stress may play a central role in the trade-off between growth and self-maintenance. Moreover, they further highlight the importance of physiological costs in the evolution of life-histories and propose a role for oxidative stress in the adaptive basis of the structured family. © 2009 the Authors. Journal compilation © 2009 British Ecological Society.
Abstract.
Mougeot F, Martínez-Padilla J, Blount JD, Pérez-Rodríguez L, Webster LMI, Piertney SB (2010). Oxidative stress and the effect of parasites on a carotenoid-based ornament. Journal of Experimental Biology, 213(10), 1796-1796.
Mougeot F, Martínez-Padilla J, Blount JD, Pérez-Rodríguez L, Webster LMI, Piertney SB (2010). Oxidative stress and the effect of parasites on a carotenoid-based ornament.
Journal of Experimental Biology,
213(3), 400-407.
Abstract:
Oxidative stress and the effect of parasites on a carotenoid-based ornament
Oxidative stress, the physiological condition whereby the production of reactive oxygen and nitrogen species overwhelms the capacity of antioxidant defences, causes damage to key bio-molecules. It has been implicated in many diseases, and is proposed as a reliable currency in the trade-off between individual health and ornamentation. Whether oxidative stress mediates the expression of carotenoid-based signals, which are among the commonest signals of many birds, fish and reptiles, remains controversial. In the present study, we explored interactions between parasites, oxidative stress and the carotenoid-based ornamentation of red grouse Lagopus lagopus scoticus. We tested whether removing nematode parasites influenced both oxidative balance (levels of oxidative damage and circulating antioxidant defences) and carotenoid-based ornamentation. At the treatment group level, parasite purging enhanced the size and colouration of ornaments but did not significantly affect circulating carotenoids, antioxidant defences or oxidative damage. However, relative changes in these traits among individuals indicated that males with a greater number of parasites prior to treatment (parasite purging) showed a greater increase in the levels of circulating carotenoids and antioxidants, and a greater decrease in oxidative damage, than those with initially fewer parasites. At the individual level, a greater increase in carotenoid pigmentation was associated with a greater reduction in oxidative damage. Therefore, an individual's ability to express a carotenoid-based ornament appeared to be linked to its current oxidative balance and susceptibility to oxidative stress. Our experimental results suggest that oxidative stress can mediate the impact of parasites on carotenoid-based signals, and we discuss possible mechanisms linking carotenoid-based ornaments to oxidative stress. ©2010. Published by the Company of Biologists Ltd.
Abstract.
Helfenstein F, Losdat S, Møller AP, Blount JD, Richner H (2010). Sperm of colourful males are better protected against oxidative stress.
Ecology Letters,
13(2), 213-222.
Abstract:
Sperm of colourful males are better protected against oxidative stress
Sperm cells are highly vulnerable to free radicals, and sperm quality and male fertility are critically affected by oxidative stress. Recently, sexual ornaments, particularly carotenoid-based colourful traits, have been proposed to depend on a male's capacity to resist oxidative stress, and thus to signal sperm quality. We conducted an experimental test of this hypothesis on great tits Parus major, in which adults are sexually dichromatic in carotenoid-based breast plumage. We report the first evidence that ornaments and sperm quality may be linked through oxidative stress. When experimentally subjected to oxidative stress resulting from increased workload, less colourful males suffered a greater reduction in sperm motility and swimming ability, and increased levels of sperm lipid peroxidation compared to more colourful males. Moreover, the level of sperm lipid peroxidation was negatively correlated with sperm quality. Finally, carotenoid supplementation increased sperm quality of less colourful males, suggesting that pale males are deficient in carotenoid antioxidants. © 2009 Blackwell Publishing Ltd/CNRS.
Abstract.
2009
Svensson PA, Blount JD, Forsgren E, Amundsen T (2009). Female ornamentation and egg carotenoids of six sympatric gobies.
Journal of Fish Biology,
75(10), 2777-2787.
Abstract:
Female ornamentation and egg carotenoids of six sympatric gobies
Belly colouration, gonad carotenoid concentration and skin transparency were quantified in gravid Gobiusculus flavescens, as well as in females of five sympatric gobies where belly ornamentation has not been described. Although G. flavescens females did, indeed, have far more colourful bellies than the other species, this could only in part be explained by a high concentration of total gonad carotenoids. Comparable, or occasionally higher, carotenoid levels were found in the gonads of other species. Instead, the unusual ornamentation of G. flavescens arises from a unique combination of carotenoid-rich gonads and a highly transparent abdominal skin. © 2009 the Fisheries Society of the British Isles.
Abstract.
Mougeot F, Martínez-Padilla J, Webster LMI, Blount JD, Pérez-Rodríguez L, Piertney SB (2009). Honest sexual signalling mediated by parasite and testosterone effects on oxidative balance.
Proceedings of the Royal Society B: Biological Sciences,
276(1659), 1093-1100.
Abstract:
Honest sexual signalling mediated by parasite and testosterone effects on oxidative balance
Extravagant ornaments evolved to advertise their bearers' quality, the honesty of the signal being ensured by the cost paid to produce or maintain it. The oxidation handicap hypothesis (OHH) proposes that a main cost of testosterone-dependent ornamentation is oxidative stress, a condition whereby the production of reactive oxygen and nitrogen species (ROS/RNS) overwhelms the capacity of antioxidant defences. ROS/RNS are unstable, very reactive by-products of normal metabolic processes that can cause extensive damage to key biomolecules (cellular proteins, lipids and DNA). Oxidative stress has been implicated in the aetiology of many diseases and could link ornamentation and genetic variation in fitness-related traits. We tested the OHH in a free-living bird, the red grouse. We show that elevated testosterone enhanced ornamentation and increased circulating antioxidant levels, but caused oxidative damage. Males with smaller ornaments suffered more oxidative damage than those with larger ornaments when forced to increase testosterone levels, consistent with a handicap mechanism. Parasites depleted antioxidant defences, caused oxidative damage and reduced ornament expression. Oxidative damage extent and the ability of males to increase antioxidant defences also explained the impacts of testosterone and parasites on ornamentation within treatment groups. Because oxidative stress is intimately linked to immune function, parasite resistance and fitness, it provides a reliable currency in the trade-off between individual health and ornamentation. The costs induced by oxidative stress can apply to a wide range of signals, which are testosterone-dependent or coloured by pigments with antioxidant properties. © 2008 the Royal Society.
Abstract.
Nussey DH, Pemberton JM, Pilkington JG, Blount JD (2009). Life history correlates of oxidative damage in a free-living mammal population.
Functional Ecology,
23(4), 809-817.
Abstract:
Life history correlates of oxidative damage in a free-living mammal population
Reactive oxygen species, produced as a by-product of normal metabolism, can cause intracellular damage and negatively impact on cell function. Such oxidative damage has been proposed as an evolutionarily important cost of growth and reproduction and as a mechanistic explanation for organismal senescence, although few tests of these ideas have occurred outside the laboratory.2. Here, we examined correlations between a measure of phospholipid oxidative damage in plasma samples and age, growth rates, parasite burden and investment in reproduction in a population of wild Soay sheep on St. Kilda, Scotland.3. We found that, amongst females of different ages, lambs had significantly elevated levels of oxidative damage compared to all other age classes and there was no evidence of increasing damage with age amongst adult sheep.4. Amongst lambs, levels of oxidative damage increased significantly with increasing growth rates over the first 4 months of life. Neither mean damage nor the effect of growth rate on damage differed between male and female lambs.5. Amongst adult female sheep, there was no evidence that body mass, current parasite burden or metrics of recent and past reproductive effort significantly predicted oxidative damage levels.6.This study is the first to examine age variation in an assay of oxidative damage and correlations between oxidative damage, growth and reproduction in a wild mammal. Our results suggest strong links between early conditions and oxidative damage in lambs, but also serve to highlight the limitations of cross-sectional data for studies examining associations between oxidative stress, ageing and life history in free-living populations. © 2009 British Ecological Society.
Abstract.
Lindström J, Pike TW, Blount JD, Metcalfe NB (2009). Optimization of resource allocation can explain the temporal dynamics and honesty of sexual signals.
Am Nat,
174(4), 515-525.
Abstract:
Optimization of resource allocation can explain the temporal dynamics and honesty of sexual signals.
In species in which males are free to dynamically alter their allocation to sexual signaling over the breeding season, the optimal investment in signaling should depend on both a male's state and the level of competition he faces at any given time. We developed a dynamic optimization model within a game-theoretical framework to explore the resulting signaling dynamics at both individual and population levels and tested two key model predictions with empirical data on three-spined stickleback (Gasterosteus aculeatus) males subjected to dietary manipulation (carotenoid availability): (1) fish in better nutritional condition should be able to maintain their signal for longer over the breeding season, resulting in an increasingly positive correlation between nutritional status and signal (i.e. increasing signal honesty), and (2) female preference for more ornamented males should thus increase over the breeding season. Both predictions were supported by the experimental data. Our model shows how such patterns can emerge from the optimization of resource allocation to signaling in a competitive situation. The key determinants of the honesty and dynamics of sexual signaling are the condition dependency of male survival, the initial frequency distribution of nutritional condition in the male population, and the cost of signaling.
Abstract.
Author URL.
Gasparini J, Bize P, Piault R, Wakamatsu K, Blount JD, Ducrest AL, Roulin A (2009). Strength and cost of an induced immune response are associated with a heritable melanin-based colour trait in female tawny owls.
Journal of Animal Ecology,
78(3), 608-616.
Abstract:
Strength and cost of an induced immune response are associated with a heritable melanin-based colour trait in female tawny owls
Melanin pigments provide the most widespread source of coloration in vertebrates, but the adaptive function of such traits remains poorly known. 2. In a wild population of tawny owls (Strix aluco), we investigated the relationships between plumage coloration, which varies continuously from dark to pale reddish, and the strength and cost of an induced immune response. 3. The degree of reddishness in tawny owl feather colour was positively correlated with the concentration of phaeomelanin and eumelanin pigments, and plumage coloration was highly heritable (h2 = 0·93). No carotenoids were detected in the feathers. 4. In mothers, the degree of melanin-based coloration was associated with antibody production against a vaccine, with dark reddish females maintaining a stronger level of antibody for a longer period of time compared to pale reddish females, but at a cost in terms of greater loss of body mass. 5. A cross-fostering experiment showed that, independent of maternal coloration, foster chicks reared by vaccinated mothers were lighter than those reared by nonvaccinated mothers. Hence, even though dark reddish mothers suffered a stronger immune cost than pale reddish mothers, this asymmetric cost was not translated to offspring growth. 6. Our study suggests that different heritable melanin-based colorations are associated with alternative strategies to resist parasite attacks, with dark reddish individuals investing more resources towards the humoral immune response than lightly reddish conspecifics. © 2009 British Ecological Society.
Abstract.
Svensson PA, Pélabon C, Blount JD, Forsgren E, Bjerkeng B, Amundsen T (2009). Temporal variability in a multicomponent trait: Nuptial coloration of female two-spotted gobies.
Behavioral Ecology,
20(2), 346-353.
Abstract:
Temporal variability in a multicomponent trait: Nuptial coloration of female two-spotted gobies
Animals that breed more than once may face different environmental and physiological conditions at each reproductive event. Costs and benefits of sexual ornaments could therefore vary both within and between breeding seasons. Despite this, the ornaments are often assumed to be fixed, and temporal changes in ornamentation have rarely been investigated. Female two-spotted gobies (Gobiusculus flavescens) have colorful orange bellies when sexually mature and nest-holding males prefer females with more colorful bellies. This nuptial coloration is caused both by the carotenoids-rich gonads being directly visible through the skin and by the chromatophore pigmentation of the abdominal skin. Toward the end of the breeding season, males become rare and females become the more competitive sex. We show that female ornamentation of G. flavescens is a complex multicomponent trait and that the separate components, as well as their interactions, are variable. As gonads matured, they became more colorful while the abdominal skin became more transparent, causing more intense belly coloration in sexually mature females. However, coloration varied greatly also among fully mature females, suggesting that it may not only be a signal of readiness to spawn. Indeed, belly coloration predicted gonad carotenoid concentration, but there were several important seasonal differences in color expression. Females sampled toward the end of the breeding season were more colorful. This was due to seasonal increases in both gonad carotenoid concentration and skin coloration. Thus, at a time when competition over males is stronger and the terminal reproductive event approaches, females appear to invest more in signaling.
Abstract.
Blount JD, Speed MP, Ruxton GD, Stephens PA (2009). Warning displays may function as honest signals of toxicity.
Proc Biol Sci,
276(1658), 871-877.
Abstract:
Warning displays may function as honest signals of toxicity.
Many prey species use colourful 'aposematic' signalling to advertise the fact that they are toxic. Some recent studies have shown that the brightness of aposematic displays correlates positively with the strength of toxicity, suggesting that aposematic displays are a form of handicap signal, the conspicuousness of which reliably indicates the level of toxicity. The theoretical consensus in the literature is, however, at odds with this finding. It is commonly assumed that the most toxic prey should have less bright advertisements because they have better chances of surviving attacks and can therefore reduce the costs incurred by signalling. Using a novel theoretical model, we show that aposematic signals can indeed function as handicaps. To generate this prediction, we make a key assumption that the expression of bright displays and the storage of anti-predator toxins compete for resources within prey individuals. One shared currency is energy. However, competition for antioxidant molecules, which serve dual roles as pigments and in protecting prey against oxidative stress when they accumulate toxins, provides a specific candidate resource that could explain signal honesty. Thus, contrary to the prevailing theoretical orthodoxy, warning displays may in fact be honest signals of the level of (rather than simply the existence of) toxicity.
Abstract.
Author URL.
2008
McGraw KJ, Blount, J.D. (2008). Control and function of carotenoid coloration in birds: a review of case studies. In Landrum JT (Ed) Carotenoids: Physical, Chemical and Biological Functions and Properties, CRC Press Ltd.
Roulin A, Almasi, B. Rossi-Pedruzzi, A. Ducrest, A.L. Wakamatsu K, Miksik I, Blount JD, Jenni-Eiermann S, Jenni L (2008). Corticosterone mediates the condition-dependent component of melanin-based coloration. Animal Behaviour, 75, 1351-1358.
Blount JD, McGraw, K.J. (2008). Signal functions of carotenoid colouration. In Britton G, Liaaen-Jensen S, Pfander H (Eds.) Carotenoids. Volume 4: Natural Functions.
2007
Pike TW, Blount, J.D. Lindström, J. Metcalfe, N.B. (2007). Availability of non-carotenoid antioxidants affects the expression of a carotenoid-based sexual ornament. Biology Letters, 3, 353-356.
Pike TW, Blount, J.D. Bjerkeng, B. Lindström, J. Metcalfe NB (2007). Carotenoids, oxidative stress and female mating preference for longer-lived males. Proceedings of the Royal Society B, 274, 1591-1596.
Pike TW, Blount, J.D. Lindström, J. Metcalfe, N.B. (2007). Dietary carotenoid availability influences a male's ability to provide parental care. Behavioral Ecology, 18, 1100-1105.
Arnold KE, Blount, J.D. Metcalfe, N.B. Orr, K.J. Adam A, Houston D, Monaghan P (2007). Sex-specific differences in compensation for poor neonatal nutrition in the zebra finch Taeniopygia guttata. Journal of Avian Biology, 38, 365-366.
2006
Svensson PA, Pélabon, C. Blount, J.D. Surai, P.F. Amundsen T (2006). Does female nuptial coloration reflect egg carotenoids and clutch quality in the Two-Spotted Goby (Gobiusculus flavescens, Gobiidae)?. Functional Ecology, 20, 689-698.
Blount JD, Matheson, S.M. (2006). Effects of carotenoid supply on escape-flight responses in zebra finches Taeniopygia guttata. Animal Behaviour, 72, 595-601.
Blount JD, Metcalfe, N.B. Arnold, K.E. Surai, P.F. Monaghan P (2006). Effects of neonatal nutrition on adult reproduction in a passerine bird. Ibis, 148, 509-514.
Nager RG, Monaghan, P. Houston, D.C. Arnold, K.E. Blount JD, Verboven N (2006). Maternal effects through the avian egg. Acta Zoologica Sinica, 52, S658-S661.
Groothuis TGG, Eising, C.M. Blount, J.D. Surai, P. Apanius V, Dijkstra C, Müller W (2006). Multiple pathways of maternal effects in black-headed gull eggs: Constraint and mutual adjustment. Journal of Evolutionary Biology, 19, 1304-1313.
2005
Verboven N, Evans, N.P. D'Alba, L. Nager, R.G. Blount JD, Surai PF, Monaghan P (2005). Intra-specific interactions influence egg composition in the lesser black-backed gull (<em>Larus fuscus</em>). Behavioral Ecology and Sociobiology, 57, 357-365.
2004
Blount, J.D. (2004). Carotenolds and life-history evolution in animals. Archives of Biochemistry & Biophysics, 430, 10-15.
Blount J, Houston DC, Moller AP, Surai PF (2004). Egg-laying capacity is limited by carotenoid pigment availability in wild gulls Larus fuscus. Biology Letters, 271(0), S79-S81.
2003
Blount JD, Birkhead TR, Metcalfe NB, Surai PF (2003). Carotenoid modulation of immune function and sexual attractiveness in zebra finches. Science, 300(5616), 125-127.
Blount JD, Houston, D.C. Møller, A.P. Wright, J. (2003). Do individual branches of immune defence correlate? a comparative case study of scavenging and non-scavenging birds. Oikos, 102, 340-350.
Blount JD, Arnold KE, Metcalfe NB, Surai PF, Devevey GL, Monaghan P (2003). Neonatal nutrition, adult antioxidant defences and sexual attractiveness in the zebra finch. Proceedings of the Royal Society B Biological Sciences, 270(1525), 1691-1696.
2002
Blount J, Birkhead TR, Nager RG, Surai PF (2002). Carotenoids and egg quality in the lesser black-backed gull Larus fuscus: a supplemental feeding study of maternal effects. Proceedings of the Royal Society B Biological Sciences, 269(1486), 29-36.
Blount JD, Surai, P.F. Nager, R.G. Houston DC, Moller AP, Trewby ML, Kennedy MW (2002). Carotenoids and egg quality in the lesser black-backed gull Larus fuscus: a supplemental feeding study of maternal effects. Proceedings of the Royal Society B, 269(1486), 29-36.
Blount JD, Surai, P.F. Houston, D.C. Møller, A.P. (2002). Patterns of yolk enrichment with dietary carotenoids in gulls: the roles of pigment acquisition and utilization. Functional Ecology, 16, 445-453.
Ward JM, Blount, J.D. Ruxton, G.D. Houston, D.C. (2002). The adaptive significance of dark plumage for birds in desert environments. Ardea, 90, 311-323.
2001
Blount JD, Møller, A.P. Houston, D.C. (2001). Antioxidants, showy males and sperm quality. Ecology Letters, 4, 393-396.
Surai PF, Speake, B.K. Wood, N.A.R. Blount, J.D. Bortolotti GR, Sparks NHC (2001). Carotenoid discrimination by the avian embryo: a lesson from wild birds. Comparative Biochemistry and Physiology Part B, 128, 743-750.
Surai PF, Bortolotti, G.R. Fidgett, A.L. Blount, J.D. Speake BK (2001). Effects of piscivory on the fatty acid profiles and antioxidants of avian yolk: studies on eggs of the gannet, skua, pelican and cormorant. Journal of Zoology (London), 255, 305-312.
Blount JD, Surai PF, Houston DC, Møller AP (2001). The relationship between dietary and yolk carotenoid composition in a wild bird: a supplemental feeding study of lesser black-backed gulls (Larus fuscus). British Poultry Science, 42(SUPPL. 1).
2000
Moller AP, Biard, C. Blount, J.D. Houston, D.C. Ninni P, Saino N, Surai PF (2000). Carotenoid-dependent signals: Indicators of foraging efficiency, immunocompetence or detoxification ability?. Avian & Poultry Biology Reviews, 11, 137-159.
Blount JD, Taylor NJ (2000). The relative effectiveness of manipulable feeders and olfactory enrichment for Kinkajous.
International Zoo Yearbook,
37(1), 381-394.
Abstract:
The relative effectiveness of manipulable feeders and olfactory enrichment for Kinkajous
The Kinkajou Potos flavus (Carnivora: Procyonidae) is a nocturnal, arboreal species that feeds opportunistically, mostly on fruits and insects. The implications for the management of these aspects of the ecology of P. flavus in captivity have received little attention in the literature. Captive Kinkajous often show stereotypic behaviour, indicating sub-optimal welfare and probably reflecting insufficient opportunity to display important aspects of natural behaviour. This study assessed the individual and additive effects of complex feeders and scented cloths as enrichment for a pair of Kinkajous at Newquay Zoo. Feeding enrichment, alone and in combination with scented cloths, elicited most positive active behaviours and space utilization, and least stereotypic and inactive behaviours. Food provision requiring species-typical exploration and manipulation may improve the welfare and educational value of Kinkajous. © 2017 Wiley. All rights reserved.
Abstract.
Blount JD (2000). Why egg yolk is yellow (vol 15, pg 47, 2000).
TRENDS IN ECOLOGY & EVOLUTION,
15(4), 131-131.
Author URL.
Blount JD, Houston, D.C. Møller, A.P. (2000). Why egg yolk is yellow. Trends in Ecology & Evolution, 15, 47-49.
1998
Blount JD (1998). Redevelopment of a disused enclosure for housing Sulawesi crested macaques Macaca Nigra at Newquay Zoo.
International Zoo Yearbook,
36(1), 56-63.
Abstract:
Redevelopment of a disused enclosure for housing Sulawesi crested macaques Macaca Nigra at Newquay Zoo
In 1995 at Newquay Zoo a bear pit was redeveloped for Sulawesi crested macaques Macaca nigra. Visual screening and foraging enrichment were used to improve tolerance between ♂♂ and to increase mating opportunities for sub-dominant ♂♂. To further improve opportunities for avoidance of of seclusion from conspecifics the outdoor area was equipped with a complex climbing apparatus and environmental enrichment, such as a puzzle feeder, sand pit and waterfall, was also provided. The indoor areas were refurbished, heated and fitted with new lighting. The circular shape of the enclosure and improved spatial complexity provides continuity of space, which may reduce the likelihood of physical harm during aggressive encounters. After the death of the dominant ♂ a new adult ♂ was introduced to the established group without difficulty and he has since adopted the dominant position. © 2017 Wiley. All rights reserved.
Abstract.
