Publications by year
In Press
Walker LA, Tschirren L, York JE, Sharp PJ, Meddle SL, Young AJ (In Press). Prolactin and the shared regulation of parental care and cooperative helping in white-browed sparrow weaver societies.
Abstract:
Prolactin and the shared regulation of parental care and cooperative helping in white-browed sparrow weaver societies
ABSTRACTIn many cooperatively breeding species non-breeding individuals help to rear the offspring of breeders. The physiological mechanisms that regulate such cooperative helping behavior are poorly understood, but may have been co-opted, during the evolution of cooperative breeding, from pre-existing mechanisms that regulated parental care. Key among these may be a role for prolactin. Here we investigate whether natural variation in circulating prolactin levels predicts both parental and helper contributions to nestling provisioning in cooperatively breeding white-browed sparrow weavers,Plocepasser mahali. In sparrow weaver groups, a single dominant pair monopolize reproduction and non-breeding subordinates help with nestling feeding. We show that: (i) among parents, dominant females feed nestlings at higher rates, make longer provisioning visits, and have higher prolactin levels than dominant males; and (ii) among subordinates, engaged in cooperative helping behavior, those within their natal groups feed nestlings at higher rates and have higher prolactin levels than immigrants. Accordingly, continuous variation in prolactin levels positively predicts nestling-provisioning rates and mean provisioning visit durations when all bird classes are combined. These relationships are principally driven by differences among bird classes in both circulating prolactin levels and provisioning traits. The more limited within-class variation in prolactin and provisioning traits were not evidently correlated, highlighting a likely role for additional mechanisms in the fine-scale regulation of care. Our findings broadly support the hypothesis that parental care and cooperative helping behavior are regulated by a common underlying mechanism and highlight the need for experimentation to now establish the causality of any role for prolactin.
Abstract.
2023
Price TN (2023). Caste plasticity and task allocation in a primitively eusocial insect.
Abstract:
Caste plasticity and task allocation in a primitively eusocial insect
Phenotypic plasticity is the ability of a given genotype to express different phenotypes in response to different environmental conditions. Plasticity is a key trait when an individual’s role in the social environment, and hence its optimum phenotype, fluctuates unpredictably. Extensive evidence exists for the capacity of individuals to be sensitive to their environments and exhibit phenotypic plasticity as a response. The selective advantage this can bring has been explored in a range of taxa. Plasticity is especially important in primitively eusocial insects where small colony sizes and little morphological caste differentiation mean that individuals can readily adopt and change specialised behavioural or physiological roles within their lifetimes. In this thesis, I examine the extent of within lifetime plasticity and task specialisation using a remarkable nest aggregation of the ground nesting primitively eusocial sweat bee, Lasioglossum malachurum. In Chapter 2, I perform a queen removal experiment and present evidence of workers taking on a reproductive role (worker queen). I find that they produce no fewer offspring than an original queen (foundress queen), but their social control of the group is likely constrained since workers from worker queen nests forage less than those in foundress queen nests. In order to quantify differences between these nest types, in Chapter 3, I use RNA-seq to explore the gene expression of worker queens, foundress queens and their workers examined in Chapter 2. I find that worker queens show extensive plasticity at the gene expression level but this does not perfectly match foundress queens in key caste differentiating genes. Furthermore, workers in worker queen nests show a generalised response to queen removal even after a new reproductive is established suggesting that all individuals respond to queen removal even if observable behavioural traits, such as foraging, continue to be carried out. Finally in Chapter 4, I present evidence of task specialisation within the worker caste of L. malachurum for foraging behaviour but not for guarding behaviour. I also discuss why there might be inactive workers within the nest, including the possibility that they prioritise direct fitness over helping behaviour. Together, this work provides novel evidence for the extent of phenotypic plasticity in primitively eusocial species, and highlights the importance of the ecology of L. malachurum for understanding the level of complexity in its behaviour.
Abstract.
Capilla-Lasheras P, Bircher N, Brown AM, Harrison X, Reed T, York JE, Cram DL, Rutz C, Walker L, Naguib M, et al (2023). Evolution of sex differences in cooperation: the role of trade-offs with dispersal.
Abstract:
Evolution of sex differences in cooperation: the role of trade-offs with dispersal
AbstractExplaining the evolution of sex differences in cooperation remains a major challenge. Comparative studies highlight that offspring of the more philopatric sex tend to be more cooperative within their family groups than those of the more dispersive sex but we do not understand why. The leading ‘Philopatry hypothesis’ proposes that the more philopatric sex cooperates more because their higher likelihood of natal breeding increases the direct fitness benefits of natal cooperation. However, the ‘Dispersal trade-off hypothesis’ proposes that the more dispersive sex cooperates less because preparations for dispersal, such as extra-territorial prospecting, trade-off against natal cooperation. Here, we test both hypotheses in cooperatively breeding white-browed sparrow weavers (Plocepasser mahali), using a novel high-resolution automated radio-tracking method. First, we show that males are the more dispersive sex (a rare reversal of the typical avian sex-difference in dispersal) and that, consistent with the predictions of both hypotheses, females contribute substantially more than males to cooperative care while within the natal group. However, the Philopatry hypothesis cannot readily explain this female-biased cooperation, as females are not more likely than males to breed within their natal group. Instead, our radio-tracking findings support the Dispersal trade-off hypothesis: males conduct pre-dispersal extra-territorial prospecting forays at higher rates than females and prospecting appears to trade-off against natal cooperation. Our findings thus highlight that the evolution of sex differences in cooperation could be widely attributable to trade-offs between cooperation and dispersal; a potentially general explanation that does not demand that cooperation yields direct fitness benefits.
Abstract.
Capilla-Lasheras P, Wilson AJ, Young AJ (2023). Mothers in a cooperatively breeding bird increase investment per offspring at the pre-natal stage when they will have more help with post-natal care.
PLoS Biol,
21(11).
Abstract:
Mothers in a cooperatively breeding bird increase investment per offspring at the pre-natal stage when they will have more help with post-natal care.
In many cooperative societies, including our own, helpers assist with the post-natal care of breeders' young and may thereby benefit the post-natal development of offspring. Here, we present evidence of a novel mechanism by which such post-natal helping could also have beneficial effects on pre-natal development: By lightening post-natal maternal workloads, helpers may allow mothers to increase their pre-natal investment per offspring. We present the findings of a decade-long study of cooperatively breeding white-browed sparrow-weaver, Plocepasser mahali, societies. Within each social group, reproduction is monopolized by a dominant breeding pair, and non-breeding helpers assist with nestling feeding. Using a within-mother reaction norm approach to formally identify maternal plasticity, we demonstrate that when mothers have more female helpers, they decrease their own post-natal investment per offspring (feed their nestlings at lower rates) but increase their pre-natal investment per offspring (lay larger eggs, which yield heavier hatchlings). That these plastic maternal responses are predicted by female helper number, and not male helper number, implicates the availability of post-natal helping per se as the likely driver (rather than correlated effects of group size), because female helpers feed nestlings at substantially higher rates than males. We term this novel maternal strategy "maternal front-loading" and hypothesize that the expected availability of post-natal help either allows or incentivizes helped mothers to focus maternal investment on the pre-natal phase, to which helpers cannot contribute directly. The potential for post-natal helping to promote pre-natal development further complicates attempts to identify and quantify the fitness consequences of helping.
Abstract.
Author URL.
Weedon M (2023). Senescence in wild European badgers: the roles of parental age effects and immunosenescence.
Abstract:
Senescence in wild European badgers: the roles of parental age effects and immunosenescence
Extensive evidence now exists for senescence (within-individual age-related declines in components of fitness) in natural animal populations. Research has now expanded to investigate the inter-generational effects of senescence (‘parental age effects’) and the underlying mechanisms that give rise to senescent declines. In this thesis I use a remarkable long-term longitudinal dataset collected from wild European badgers (Meles meles) to examine the inter-generational fitness consequences of senescence, and the role that immunological changes may play in senescence. In Chapter 2, I present evidence of a deleterious maternal age effect on offspring lifetime reproductive success (LRS) that appears to arise principally from effects on offspring survival rather than annual reproductive success. Furthermore, I find that the timing of onset of this maternal senescence in offspring performance precedes that of maternal senescence in fecundity, and thereby compounds and advances the onset of the deleterious fitness consequences of senescence for mothers. In Chapter 3, I find evidence of deleterious paternal age effects on offspring LRS, which appear to arise principally from a deleterious paternal terminal effect; a decrease in offspring LRS in the father’s terminal reproductive episode. In Chapter 4, I present rare evidence from a natural animal population of a biomedically significant form of immune system ageing termed ‘inflammageing’. My findings reveal a within-individual age-related increase in a baseline inflammatory marker; haptoglobin, and a within-individual age-related decrease in the strength of the pro-inflammatory IFN-γ cytokine response to immune stimulation; both consistent with inflammageing. My analyses also suggest that the high levels of baseline inflammation experienced in late-life may entail fitness costs. In Chapter 5, I explore the effects of population density and intra-sexual competition on immunity. I find no clear evidence of population density effects on four humoral immune parameters, but do find evidence of sex differences in immunity consistent with the expectation of costs to immunity arising from higher mean levels of investment in intra-sexual mate competition among males than females in this polygynous species. Together this work provides novel evidence of the inter-generational effects of senescence and highlights the potential for inflammageing to play a key role in age-related declines in components of fitness in natural animal populations.
Abstract.
Medel JA (2023). Testing the mechanism and function of avian plumage camouflage.
Abstract:
Testing the mechanism and function of avian plumage camouflage
The overall aim of my PhD was to investigate the plumage coloration and patterns of birds to determine how their camouflage matches the biome background in which they live. Animals in a wide variety of biomes rely on phenotype-environment matching to avoid detection by predators in their specific biomes. A key prediction regarding the function of phenotype-environment matching rests on the idea that camouflage should match not only to the specific background conditions but also involve matching characteristics of the habitat. However, this has rarely been tested in animal species with fixed camouflage appearance. In this thesis, I explored the plumage attributes and the camouflage function used by specialist ground-nesting bird species of tropical rainforest, taiga forest, dry forest, grassland, desert and tundra biomes. Digital photography and image analysis were used to quantify colour patterns to models of predator vision to gain an ecologically valid assessment of camouflage. With this information I created bird models that were tested in different biomes. I found that the plumage of ground-nesting bird species have a phenotype-environment association to their respective biome, likely driven by selection for camouflage (Chapter 2). I also show that specialist bird species have a phenotype-environment matching that matches predominant background characteristics across large spatial scales of their biome backgrounds (Chapter 3). Finally, I tested how camouflage match relates to the detection of bird models in their own and different biomes (Chapter 4). In this predation experiment I found that the match for luminance, marking luminance and marking size were the main predictor of survival probability (detection times) of forest and grassland birds. However, unexpectedly, I found that the matching degree to predominant biome background structures increased bird survival probability against a different biome. This thesis chapter demonstrates that specialist birds match their phenotype to the predominant substrate composition and vegetation structure of their specific biome. However, in my experiments, these differences did not translate into a reduced detection time.
Abstract.
2022
Sharman P, Young AJ, Wilson AJ (2022). Evidence of maternal and paternal age effects on speed in thoroughbred racehorses.
R Soc Open Sci,
9(10).
Abstract:
Evidence of maternal and paternal age effects on speed in thoroughbred racehorses.
Effects of parental age on offspring viability have been reported in a wide range of species. However, to what extent parental age influences offspring traits beyond viability remains unclear. Moreover, previous research has primarily focused on maternal age effects. The purpose of this study was to test for paternal and maternal age effects on offspring speed in thoroughbred racehorses. We analysed over 900 000 race performances by over 100 000 horses on British racecourses between 1996 and 2019. With knowledge of the age of all 41 107 dams and 2 887 sires at offspring conception, we jointly modelled maternal and paternal age effects using a 'within-individual centring' approach. Within-parents, we identified a significant effect of maternal age on offspring speed of -0.017 yards s-1 yr-1 and a corresponding paternal age effect of -0.011 yards s-1 yr-1. Although maternal age effects were stronger (more negative), the existence and magnitude of paternal effects is particularly noteworthy, given thoroughbred sires have no involvement in parental care. Our results also suggest that the selective disappearance of both sires and dams is ongoing. These findings could potentially be used to optimize thoroughbred racehorse breeding decisions, and more generally, add to the increasing body of evidence that both maternal and paternal age affect a range of offspring characteristics.
Abstract.
Author URL.
Houslay TM, Earley RL, White SJ, Lammers W, Grimmer AJ, Travers LM, Johnson EL, Young AJ, Wilson A (2022). Genetic integration of behavioural and endocrine components of the stress response.
Elife,
11Abstract:
Genetic integration of behavioural and endocrine components of the stress response.
The vertebrate stress response comprises a suite of behavioural and physiological traits that must be functionally integrated to ensure organisms cope adaptively with acute stressors. Natural selection should favour functional integration, leading to a prediction of genetic integration of these traits. Despite the implications of such genetic integration for our understanding of human and animal health, as well as evolutionary responses to natural and anthropogenic stressors, formal quantitative genetic tests of this prediction are lacking. Here, we demonstrate that acute stress response components in Trinidadian guppies are both heritable and integrated on the major axis of genetic covariation. This integration could either facilitate or constrain evolutionary responses to selection, depending upon the alignment of selection with this axis. Such integration also suggests artificial selection on the genetically correlated behavioural responses to stress could offer a viable non-invasive route to the improvement of health and welfare in captive animal populations.
Abstract.
Author URL.
Brown A (2022). Mechanisms of age-related change in performance in a wild social bird: parental age effects, cellular senescence, and dominance acquisition.
Abstract:
Mechanisms of age-related change in performance in a wild social bird: parental age effects, cellular senescence, and dominance acquisition
Age-related changes in performance (reproduction and survival) are widespread in nature. In vertebrates, age-related performance trajectories are typically characterised by early-life improvements followed by late-life declines (termed ‘senescence’). However, the mechanisms that underpin such age-related changes in performance are still poorly understood. In this thesis, I combine molecular, cellular, long-term life history, and radio-telemetry data from a population of a cooperatively breeding bird, the white-browed sparrow weaver Plocepasser mahali, to investigate some key shortfalls in our understanding of the mechanistic origins of age-related changes in organismal performance. In Chapter 2, I present the first longitudinal evidence that within-parent changes in age positively predict offspring telomere lengths, an effect that has the potential to positively impact parent and offspring fitness. Then, in Chapter 3, I present the first evidence for within-individual accumulation of senescent cells with advancing age in a natural population. I also demonstrate that these within-individual increases in senescent cell frequency over the short term are not reflected at the population level, suggestive of the selective disappearance of either individuals with high incidences of senescent cells from the population, or of senescent cells within individuals. In Chapter 4, I investigate the effects of age on dominance acquisition, and provide evidence that individuals that are older relative to other potential competitors are more likely to win dominance turnovers. This finding highlights a potentially widespread mechanism by which the costs of cooperation (in terms of increased competition for breeding positions) could be mitigated in cooperatively breeding species. Finally, in Chapter 5, I investigate whether within-group social circumstances influence subordinate dispersal behaviour. Despite finding that individuals do not seem to adjust their dispersal behaviour in response to the expected payoffs of remaining in their current group versus dispersing, I show that individuals tend to disperse to subordinate positions in smaller groups and with fewer same age or older individuals. As living in a larger group entails survival costs, and individuals are more likely to win dominance in groups where they are the oldest subordinate of their sex, these results suggests individuals may ‘trade up’ their social circumstances when they disperse. Together, my findings elucidate some key shortfalls in our understanding of the mechanisms underlying age-related changes in performance.
Abstract.
Wood EM, Capilla-Lasheras P, Cram DL, Walker LA, York JE, Lange A, Hamilton PB, Tyler CR, Young AJ (2022). Social dominance and rainfall predict telomere dynamics in a cooperative arid-zone bird.
Mol Ecol,
31(23), 6141-6154.
Abstract:
Social dominance and rainfall predict telomere dynamics in a cooperative arid-zone bird.
In many vertebrate societies dominant individuals breed at substantially higher rates than subordinates, but whether this hastens ageing remains poorly understood. While frequent reproduction may trade off against somatic maintenance, the extraordinary fecundity and longevity of some social insect queens highlight that breeders need not always suffer more rapid somatic deterioration than their nonbreeding subordinates. Here, we used extensive longitudinal assessments of telomere dynamics to investigate the impact of dominance status on within-individual age-related changes in somatic integrity in a wild social bird, the white-browed sparrow-weaver (Plocepasser mahali). Dominant birds, who monopolise reproduction, had neither shorter telomeres nor faster telomere attrition rates over the long-term (1-5 years) than their subordinates. However, over shorter (half-year) time intervals dominants with shorter telomeres showed lower rates of telomere attrition (and evidence suggestive of telomere lengthening), while the same was not true among subordinates. Dominants may therefore invest more heavily in telomere length regulation (and/or somatic maintenance more broadly); a strategy that could mitigate the long-term costs of reproductive effort, leaving their long-term telomere dynamics comparable to those of subordinates. Consistent with the expectation that reproduction entails short-term costs to somatic integrity, telomere attrition rates were most severe for all birds during the breeding seasons of wetter years (rainfall is the key driver of reproductive activity in this arid-zone species). Our findings suggest that, even in vertebrate societies in which dominants monopolise reproduction, dominants may experience long-term somatic integrity trajectories indistinguishable from those of their nonreproductive subordinates.
Abstract.
Author URL.
O'Callaghan O (2022). Social effects on adult survival in a wild cooperative bird.
Abstract:
Social effects on adult survival in a wild cooperative bird
Explaining the evolution of cooperation is a key challenge in evolutionary biology. It is widely recognised that cooperation often yields indirect benefits to helpers through their effects on offspring survival, however less well known are the effects of helping on breeder survival, partly as studies often struggle to disentangle helping behaviour from associated effects of group size. It is also possible that cooperation could yield direct benefits to helpers. One potentially widespread mechanism by which this could happen is ‘group augmentation’: where cooperation increases group size (by increasing the recruitment or survival of group members), co-operators will benefit directly from their actions if living in a larger group enhances their survival or future reproduction. Using long-term field data on white-browed sparrow-weavers, I investigated these two mechanisms by which helping behaviour could yield fitness benefits for helpers. Specifically, does helping yield (i) indirect fitness benefits by improving the survival of related breeders and (ii) direct fitness benefits via group augmentation. I present evidence that helping behaviour (not group size) can improve dominant female survival, most likely as a result of load-lightening, and that this should yield indirect fitness benefits to helpers. I then present evidence that living in a larger group actually has negative effects on helper survival. The results suggest that this may be a consequence of foraging competition, as group size also negatively predicted territory size per capita and helper body condition. Thus, group augmentation mechanisms could lead to selection against cooperation, rather than for it. Unlike the results of many studies on these topics, my findings cannot be readily attributed to differences among territories, as they hold when we examine the effects of within-territory variation in group size and/or helper number over time. Together, my results are particularly interesting as they show opposing effects of helping on the indirect and direct fitness of helpers.
Abstract.
Sharman P (2022). Understanding the Genetics of Thoroughbred Racehorse Speed.
Abstract:
Understanding the Genetics of Thoroughbred Racehorse Speed
Long before the publication of Darwin’s theory of evolution by natural selection and Mendel’s work on genes, horses were being selectively bred for improved racing performance. This resulted in the creation of a highly specialised breed of racing horse, known as the thoroughbred. Throughout the 19th century the winning times of the most elite thoroughbred races in Great Britain declined, suggesting genetic evolution of faster speed was ongoing in response to selective breeding. However, several studies have reported a slowing of the rate of improvement since early in the 20th century, leading to a consensus amongst scientists and industry experts that thoroughbred speed has reached a selection limit. The broad aims of my PhD thesis are to understand the genetic basis of variation in racehorse speed, and in doing so, to determine if thoroughbreds have indeed reached a genetic limit for how fast they can run. If so, what is constraining further improvement? Moreover, can a better understanding of the factors that determine the rate of improvement in thoroughbred speed allow us to design breeding programmes that would overcome this supposed limit? to do this, I apply quantitative genetic tools, developed for improving livestock since the mid-19th century but largely passed over by thoroughbred breeders, to a vast pedigreed dataset of thoroughbred performances in Great Britain. Firstly, addressing limitations of previous studies, I set out to characterise more accurately the current and historical rate of phenotypic improvement in thoroughbred speed. Secondly, I apply quantitative genetic analysis to determine the extent of heritable variation for this trait and assess whether phenotypic rates of improvement in speed - if still ongoing - are underpinned by a genetic response to selection. Next, I investigate the possibility that maternal and/or paternal age at conception may affect offspring racehorse speed and examine whether parental identity is an important source of variation in offspring performance. If so, is there any genetic basis of maternal or paternal variation identified, and what are the implications for selection response? Finally, in an essay I explore the history of equine (and jockey) welfare concerns in the sport, and consider the role quantitative genetics could play in reducing equine injury susceptibility alongside improving performance. Lastly, I discuss my findings and consider future directions for this research.
Abstract.
2021
Capilla-Lasheras P, Harrison X, Wood EM, Wilson AJ, Young AJ (2021). Altruistic bet-hedging and the evolution of cooperation in a Kalahari bird.
Science Advances,
7(39).
Abstract:
Altruistic bet-hedging and the evolution of cooperation in a Kalahari bird
Striking effects of cooperation on the reproductive variance of relatives help to explain the global biogeography of altruism.
Abstract.
Brown AM, Wood EM, Capilla-Lasheras P, Harrison XA, Young AJ (2021). Longitudinal evidence that older parents produce offspring with longer telomeres in a wild social bird.
Biology Letters,
17(10).
Abstract:
Longitudinal evidence that older parents produce offspring with longer telomeres in a wild social bird
. As telomere length (TL) often predicts survival and lifespan, there is considerable interest in the origins of inter-individual variation in TL. Cross-generational effects of parental age on offspring TL are thought to be a key source of variation, but the rarity of longitudinal studies that examine the telomeres of successive offspring born throughout the lives of parents leaves such effects poorly understood. Here, we exploit TL measures of successive offspring produced throughout the long breeding tenures of parents in wild white-browed sparrow weaver (
. Plocepasser mahali
. ) societies, to isolate the effects of within-parent changes in age on offspring TLs. Our analyses reveal the first evidence to date of a positive within-parent effect of advancing age on offspring TL: as individual parents age, they produce offspring with longer telomeres (a modest effect that persists into offspring adulthood). We consider the potential for pre- and post-natal mechanisms to explain our findings. As telomere attrition predicts offspring survival to adulthood in this species, this positive parental age effect could impact parent and offspring fitness if it arose via differential telomere attrition during offspring development. Our findings support the view that cross-generational effects of parental age can be a source of inter-individual variation in TL.
.
Abstract.
Capilla-Lasheras P, Wilson AJ, Young AJ (2021). Mothers front-load their investment to the egg stage when helped in a wild cooperative bird.
Abstract:
Mothers front-load their investment to the egg stage when helped in a wild cooperative bird
AbstractIn many cooperative societies, including our own, helpers assist with the post-natal care of breeders’ young, and may thereby benefit thepost-nataldevelopment of offspring. Here we present evidence of a novel mechanism by which such post-natal helping could also have hitherto unexplored beneficial effects onpre-nataldevelopment: by lightening post-natal maternal workloads, helpers may allow mothers to increase their pre-natal investment per offspring. We present the findings of a decade-long study of cooperatively breeding white-browed sparrow weaver,Plocepasser mahali, societies. Within each social group, reproduction is monopolized by a dominant breeding pair, and non-breeding helpers assist with nestling feeding. Using a within-mother reaction norm approach to formally identify maternal plasticity, we demonstrate that when mothers have more female helpers they decrease their ownpost-natalinvestment per offspring (feed their nestlings at lower rates) but increase theirpre-natalinvestment per offspring (lay larger eggs, which yield heavier hatchlings). That these plastic maternal responses are predicted by female helper number, and not male helper number, implicates the availability of post-natal helpingper seas the likely driver (rather than correlated effects of group size), because female helpers feed nestlings at substantially higher rates than males. We term this novel maternal strategy “maternal front-loading” and hypothesize that the expected availability ofpost-natalhelp allows helped mothers to focus maternal investment on thepre-natalphase, to which helpers cannot contribute directly. Such cryptic maternally mediated helper effects on pre-natal development may markedly complicate attempts to identify and quantify the fitness consequences of helping.
Abstract.
2020
Mathison K (2020). Comparing social dynamics and telomere attrition between high promiscuity and low promiscuity flocks of zebra finches (Taeniopygia guttata).
Abstract:
Comparing social dynamics and telomere attrition between high promiscuity and low promiscuity flocks of zebra finches (Taeniopygia guttata)
Extra-pair paternity (EPP) is now recognised as a widespread phenomenon among socially monogamous avian systems, but the factors driving intraspecific variation in extra-pair mating behaviours are still poorly understood. Here, I quantified EPP in two promiscuity breeding lines of the zebra finch (Taeniopygia guttata), which had been selected to have high or low breeding values of male sex drive. I found that the majority of birds were involved in extra-pair mating behaviour, and the prevalence of EPP did not differ between the two breeding lines. I present evidence that males can benefit from an increased reproductive output by engaging in extra-pair mating strategies. However, I found no evidence that males reproduced with a larger number of different mates as compared to the females in the population. I also tested the hypothesis that extra-pair mating behaviour could be stressful due to its potential to compromise social pair bonds. To do so, I conducted a within-individual repeated-measures study of telomere attrition across an experimentally-controlled breeding season. Telomere dynamics have become widely regarded as a long-term indicator of cumulative stress and biological age. I found no conclusive evidence that receiving infidelity or experiencing weaker pair bonds induces sufficient physiological stress in zebra finches for it to affect telomere dynamics. I present evidence that in this species, some individuals experienced telomere lengthening while others experienced shortening, with the longest telomeres shortening the fastest. I demonstrate that individuals with stronger social associations produced more eggs together, both within and outside the social pairs (i.e. through EPP). For this reason, I suggest that future research investigating extra-pair mating behaviours should consider the role that the social environment plays in extra-pair reproduction. This could help us gain a further understanding of how social associations influence extra-pair mate selection and the prevalence of EPP within socially monogamous species.
Abstract.
Brown AM, Wood EM, Capilla-Lasheras P, Harrison XA, Young AJ (2020). Older mothers produce offspring with longer telomeres: a longitudinal within-parent analysis.
Capilla-Lasheras P (2020). The evolution of cooperation in an arid-zone bird:. bet-hedging, plasticity and constraints.
Abstract:
The evolution of cooperation in an arid-zone bird:. bet-hedging, plasticity and constraints
The evolution of cooperation represents a long-standing puzzle in evolutionary biology. From insects to mammals, this behaviour has evolved multiple times in separate lineages. Even though inclusive fitness theory provides a solid theoretical framework to understand the evolution of cooperation, there are still many research challenges in the evolutionary study of cooperation. First, most of the evidence for the effects of cooperation on the reproductive success of beneficiaries in vertebrate societies is based on correlational studies, which can be confounded by several environmental factors. Second, there are recent theoretical formulations to explain the evolution of cooperation that have not been empirically tested yet but could shed new light on the selective pressures that facilitate the evolution of cooperation. Third, we still have a poor understanding of the sources of among individual variation in cooperative behaviours. In particular, few studies have investigated whether the level of cooperation expressed by individuals is heritable and, therefore, could respond to natural selection. In this thesis, I combine nine years of life-history and behavioural information with field experiments and genomics to investigate (i) the routes for non-breeding individuals to acquire indirect fitness benefits and (ii) the sources of among-individual variation in cooperation in white-browed sparrow-weavers (Plocepasser mahali), an arid-zone cooperative breeder. After a general introduction to the subject of cooperative breeding, in Chapter 2 I test a novel hypothesis for the evolution of cooperation, the ‘altruistic bet-hedging’ hypothesis. There, I show that non-breeding helpers reduce variation in the reproductive success of breeders without affecting their arithmetic mean reproductive success. Furthermore, I show that this reproductive variance compression appears to arise because helpers specifically reduce unpredictable rainfall-induced variation in reproductive success, just as hypothesised by global comparative studies of the evolution of cooperative breeding in birds. Then, I investigate alternative routes through which helpers may gain indirect fitness benefits. Specifically, in Chapter 3 I investigate the effects of helpers on pre- and post-natal maternal investment in reproduction. The findings in Chapter 3 provide clear evidence for maternal plasticity in pre-natal investment in reproduction (egg volume) in response to the number of helpers. Moreover, the helper effect of increased pre-natal maternal investment is associated with a decrease in post-natal maternal investment. In Chapter 4, I test the philopatry hypothesis for the evolution of sex differences in cooperation within animal societies and find strong support for this hypothesis in white-browed sparrow-weavers. Furthermore, Chapter 4 highlights the need to consider both sex differences in direct fitness benefits and costs when trying to understand sex differences in cooperation. Finally, in Chapter 5 I investigate among-helper variation in cooperative generosity, finding consistent individual differences and providing evidence for heritable variation in this trait. To conclude, in Chapter 6 I discuss the implications of these results for our general understanding of the evolution of cooperation in animal societies and highlight methodological approaches for future empirical studies of cooperation in the wild.
Abstract.
2019
Łapińska U, Glover G, Capilla-Lasheras P, Young AJ, Pagliara S (2019). Bacterial ageing in the absence of external stressors.
Philosophical Transactions of the Royal Society B: Biological Sciences,
374(1786), 20180442-20180442.
Abstract:
Bacterial ageing in the absence of external stressors
. Evidence of ageing in the bacterium
. Escherichia coli
. was a landmark finding in senescence research, as it suggested that even organisms with morphologically symmetrical fission may have evolved strategies to permit damage accumulation. However, recent work has suggested that ageing is only detectable in this organism in the presence of extrinsic stressors, such as the fluorescent proteins and strong light sources typically used to excite them. Here we combine microfluidics with brightfield microscopy to provide evidence of ageing in
. E. coli
. in the absence of these stressors. We report (i) that the doubling time of the lineage of cells that consistently inherits the ‘maternal old pole’ progressively increases with successive rounds of cell division until it reaches an apparent asymptote, and (ii) that the parental cell divides asymmetrically, with the old pole daughter showing a longer doubling time and slower glucose accumulation than the new pole daughter. Notably, these patterns arise without the progressive accumulation or asymmetric partitioning of observable misfolded-protein aggregates, phenomena previously hypothesized to cause the ageing phenotype. Our findings suggest that ageing is part of the naturally occurring ecologically-relevant phenotype of this bacterium and highlight the importance of alternative mechanisms of damage accumulation in this context.
.
. This article is part of a discussion meeting issue ‘Single cell ecology’.
Abstract.
York JE, Wells KJ, Young AJ (2019). Dominance-related contributions to collective territory defence are adjusted according to the threat.
Animal Behaviour,
158, 25-34.
Abstract:
Dominance-related contributions to collective territory defence are adjusted according to the threat
Across diverse societies, group members benefit from the cooperative maintenance of a shared territory (a public good). How such public goods are maintained has received extensive interest, yet individual contributions to cooperative territory defence remain poorly understood. Recent theory predicts that, in groups with social hierarchies, privileged individuals will contribute most to competition with rival groups as they benefit most from defence of the territory. Here, we investigated whether dominant individuals contribute more to territory defence in a group-territorial bird in which dominants monopolize within-group reproduction: the white-browed sparrow-weaver, Plocepasser mahali. Using simulated territorial intrusions, we demonstrate that dominants contributed significantly more than subordinates to territory defence. We also found that individual contributions were adjusted according to threat: males of both social classes significantly and similarly increased their contributions to defence in response to a high threat (playback of an unfamiliar pair's duet, rather than that of a neighbouring pair), which was associated with a stronger collective response by the group. Thus, while dominants contributed most as predicted by the asymmetry in benefits, subordinates did increase contributions when they were needed most (in small groups and under greater threat). Contributions by subordinates when needed most also highlights that dominants could still benefit substantially from tolerating the presence of subordinates despite their overall lower contributions. Our results show that public goods can be maintained despite unequal contributions and highlight the potential importance of context-dependent behavioural flexibility in mitigating collective action problems.
Abstract.
Houslay TM, Earley RL, White SJ, Lammers W, Grimmer AJ, Travers LM, Johnson EL, Young AJ, Wilson AJ (2019). Genetic integration of behavioural and endocrine components of the stress response.
Abstract:
Genetic integration of behavioural and endocrine components of the stress response
AbstractThe vertebrate stress response comprises a suite of behavioural and physiological traits that must be functionally integrated to ensure organisms cope adaptively with acute stressors. Natural selection should favour functional integration, leading to a prediction of genetic integration of these traits. Despite the implications of such genetic integration for our understanding of human and animal health, as well as evolutionary responses to natural and anthropogenic stressors, formal quantitative genetic tests of this prediction are lacking. Here we demonstrate that acute stress response components in Trinidadian guppies are both heritable and integrated on the major axis of genetic covariation. This integration could either facilitate or constrain evolutionary responses to selection, depending upon the alignment of selection with this axis. Such integration also suggests artificial selection on the genetically correlated behavioural responses to stress could offer a viable non-invasive route to the improvement of health and welfare in captive animal populations.
Abstract.
Houslay TM, Earley RL, Young AJ, Wilson AJ (2019). Habituation and individual variation in the endocrine stress response in the Trinidadian guppy (Poecilia reticulata).
General and Comparative Endocrinology,
270, 113-122.
Abstract:
Habituation and individual variation in the endocrine stress response in the Trinidadian guppy (Poecilia reticulata)
The vertebrate stress response enables individuals to react to and cope with environmental challenges. A crucial aspect of the stress response is the elevation of circulating glucocorticoids. However, continued activation of the stress response under repeated exposure to stressors can be damaging to fitness. Under certain circumstances it may therefore be adaptive to habituate to repeated exposures to a particular stressor by reducing the magnitude of any associated release of glucocorticoids. Here, we investigate whether Trinidadian guppies (Poecilia reticulata) habituate to repeated exposure to a mild stressor, using a waterborne hormone sampling approach that has previously been shown to elicit a stress response in small fish. We also test for individual variation in the extent of habituation to this stressor. Concentrating on freely circulating cortisol, we found that the first exposure to the assay induced high cortisol release rates but that guppies tended to habituate quickly to subsequent exposures. There were consistent differences among individuals in their average cortisol release rate (after accounting for effects of variables such as body size) over repeated exposures. Our analyses did not find evidence of individual differences in habituation rate, although limitations in statistical power could account for this finding. We repeated the analysis for free 11-ketotestosterone, which can also respond to stressors, but found no obvious habituation pattern and no among-individual variation. We also present data on conjugated forms of both hormones, which were repeatable but did not show the expected time-lagged habituation effect. We discuss consistent individual differences around the general pattern of habituation in the flexible stress response, and highlight the potential for individual variation in habituation to facilitate selection against the deleterious effects of chronic stress.
Abstract.
Williams A (2019). Modelling the evolution of socio-political complexity.
Abstract:
Modelling the evolution of socio-political complexity
The level of organisation required to maintain cohesion in the vast societies we live in today is unprecedented in our past. In this thesis I look into why human societies began to shift from the small-scale groups which characterises the vast majority of human past, into the large-scale entities most of us currently live in. Several ideas have been proposed to explain why many different features of social complexity began to coalesce together in some areas of the world before others, each with some level of support from the archaeological record. In this thesis I have taken a different approach. I rigorously test one hypothesis for its logical consistency before applying it to archaeological data by formalising it as an agent-based model. The hypothesis described by Robert Carneiro (1970, 2012a) suggests that the more limited population movement is through environmental, resource, or social circumscription, the more likely complex societies are to form. By constructing agent-based models from this hypothesis I can show the conditions under which this statement is true, and have identified several areas where assumptions were not made explicit in the original hypothesis. By adapting the models to correspond with the conditions of the Valley of Oaxaca in highland Mexico, I show the extent to which the circumscription theory may explain the emergence of social complexity there and where the gaps in our knowledge lie. In creating and testing an agent-based model of the circumscription hypothesis I have shown how agent-based models may be used in archaeology to deepen our understanding of verbal theories and identified conditions which could have intensified the emergence of complex societies around the world.
Abstract.
Wood EM, Young AJ (2019). Telomere attrition predicts reduced survival in a wild social bird, but short telomeres do not.
Mol Ecol,
28(16), 3669-3680.
Abstract:
Telomere attrition predicts reduced survival in a wild social bird, but short telomeres do not.
Attempts to understand the causes of variation in senescence trajectories would benefit greatly from biomarkers that reflect the progressive declines in somatic integrity (SI) that lead to senescence. While telomere length has attracted considerable interest in this regard, sources of variation in telomere length potentially unrelated to declines in SI could, in some contexts, leave telomere attrition rates a more effective biomarker than telomere length alone. Here, we investigate whether telomere length and telomere attrition rates predict the survival of wild white-browed sparrow-weaver nestlings (Plocepasser mahali). Our analyses of telomere length reveal counterintuitive patterns: telomere length soon after hatching negatively predicted nestling survival to fledging, a pattern that appears to be driven by differentially high in-nest predation of broods with longer telomeres. Telomere length did not predict survival outside this period: neither hatchling telomere length nor telomere length in the mid-nestling period predicted survival from fledging to adulthood. Our analyses using within-individual telomere attrition rates, by contrast, revealed the expected relationships: nestlings that experienced a higher rate of telomere attrition were less likely to survive to adulthood, regardless of their initial telomere length and independent of effects of body mass. Our findings support the growing use of telomeric traits as biomarkers of SI, but lend strength to the view that longitudinal assessments of within-individual telomere attrition since early life may be a more effective biomarker in some contexts than telomere length alone.
Abstract.
Author URL.
2018
Houslay TM, Earley RL, Young AJ, Wilson AJ (2018). Habituation and individual variation in the endocrine stress response in the Trinidadian guppy (<i>Poecilia reticulata</i>).
Abstract:
Habituation and individual variation in the endocrine stress response in the Trinidadian guppy (Poecilia reticulata)
AbstractThe vertebrate stress response enables individuals to react to and cope with environmental challenges. A crucial aspect of the stress response is the elevation of circulating glucocorticoids. However, continued activation of the stress response under repeated (or chronic) stress can be damaging to fitness. Under certain circumstances it may therefore be adaptive to habituate to repeated exposures to a particular stressor by reducing the magnitude of any associated release of glucocorticoids. Here, we investigate whether Trinidadian guppies (Poecilia reticulata) habituate to repeated exposure to a mild stressor, using a waterborne hormone sampling approach that has previously been shown to elicit a stress response in small fish. We also test for individual variation in the extent of habituation to this stressor. Concentrating on freely circulating cortisol, we found that the first exposure to the assay induced high cortisol release rates but that guppies tended to habituate quickly to subsequent exposures. There were consistent differences among individuals in their average cortisol release rate (after accounting for effects of variables such as body size) over repeated exposures. Our analyses did not find evidence of individual differences in habituation rate, although limitations in statistical power could account for this finding. We also present data on free 11-ketotestosterone, in addition to conjugated forms of both hormones. We discuss consistent individual differences around the general pattern of habituation in the flexible stress response, and highlight the potential for individual variation in habituation to facilitate selection against the deleterious effects of chronic stress.Summary statementTrinidadian guppies habituate quickly to repeated stress exposure, and exhibit consistent differences in their endocrine stress response. We provide a framework for analysing individual variation in habituation rate.
Abstract.
Benton CH, Delahay RJ, Smith FAP, Robertson A, McDonald RA, Young AJ, Burke TA, Hodgson D (2018). Inbreeding intensifies sex- and age-dependent disease in a wild mammal.
J Anim Ecol,
87(6), 1500-1511.
Abstract:
Inbreeding intensifies sex- and age-dependent disease in a wild mammal.
The mutation accumulation theory of senescence predicts that age-related deterioration of fitness can be exaggerated when inbreeding causes homozygosity for deleterious alleles. A vital component of fitness, in natural populations, is the incidence and progression of disease. Evidence is growing for natural links between inbreeding and ageing; between inbreeding and disease; between sex and ageing; and between sex and disease. However, there is scant evidence, to date, for links among age, disease, inbreeding and sex in a single natural population. Using ecological and epidemiological data from a long-term longitudinal field study, we show that in wild European badgers (Meles meles) exposed naturally to bovine tuberculosis (bTB), inbreeding (measured as multilocus homozygosity) intensifies a positive correlation between age and evidence of progressed infection (measured as an antibody response to bTB), but only among females. Male badgers suffer a steeper relationship between age and progressed infection than females, with no influence of inbred status. We found no link between inbreeding and the incidence of progressed infection during early life in either sex. Our findings highlight an age-related increase in the impact of inbreeding on a fitness-relevant trait (disease state) among females. This relationship is consistent with the predictions of the mutation accumulation theory of senescence, but other mechanisms could also play a role. For example, late-life declines in condition, arising through mechanisms other than mutation accumulation might have increased the magnitude of inbreeding depression in late life. Whichever mechanism causes the observed patterns, we have shown that inbreeding can influence age-dependent patterns of disease and, by extension, is likely to affect the magnitude and timing of the late-life declines in components of fitness that characterise senescence. Better understanding of sex-specific links between inbreeding, disease and ageing provides insights into population-level pathogen dynamics and could influence management strategies for wildlife reservoirs of zoonotic disease.
Abstract.
Author URL.
Houslay TM, Vierbuchen M, Grimmer AJ, Young AJ, Wilson AJ (2018). Testing the stability of behavioural coping style across stress contexts in the Trinidadian guppy.
Functional Ecology,
32(2), 424-438.
Abstract:
Testing the stability of behavioural coping style across stress contexts in the Trinidadian guppy
Within populations, individuals can vary in stress response, a multivariate phenomenon comprising neuroendocrine, physiological and behavioural traits. Verbal models of individual stress “coping style” have proposed that the behavioural component of this variation can be described as a single axis, with each individual's coping style being consistent across time and stress contexts. Focusing on this behavioural component of stress response and combining repeated measures of multiple traits with a novel multivariate modelling framework, we test for the existence of coping style variation and assess its stability across contexts in the Trinidadian guppy (Poecilia reticulata). Specifically, we test the following hypotheses: (1) there exists repeatable among-individual behavioural (co)variation (“personality”) within a mild stress context consistent with a risk-averse–risk-prone continuum of behavioural coping style, (2) there is population-level plasticity in behaviour as a function of stressor severity, (3) there is among-individual variation in plasticity (i.e. IxE), and (4) the presence of IxE reduces cross-context stability of behavioural coping style. We found significant repeatable among-individual behavioural (co)variation in the mild stress context (open field trial), represented as an I matrix. However, I was not readily described by a simple risk-averse–risk-prone continuum as posited by the original coping style model. We also found strong evidence for population-level changes in mean behaviour with increasing stressor severity (simulated avian and piscine predation risks). Single-trait analyses did show the presence of individual-by-environment interactions (IxE), as among-individual cross-context correlations were significantly less than +1. However, multitrait analysis revealed the consequences of this plasticity variation were minimal. Specifically, we found little evidence for changes in the structure of I between mild and moderate stress contexts overall, and only minor changes between the two moderate contexts (avian vs. piscine predator). We show that a multivariate approach to assessing changes in among-individual (co)variance across contexts can prevent the over-interpretation of statistically significant, but small, individual-by-environment effects. While behavioural flexibility enables populations (and individuals) to respond rapidly to changes in the environment, multivariate personality structure can be conserved strongly across such contexts. A plain language summary is available for this article.
Abstract.
Young AJ (2018). The role of telomeres in the mechanisms and evolution of life-history trade-offs and ageing. Philosophical Transactions B: Biological Sciences
2017
Thompson FJ, Cant MA, Marshall HH, Vitikainen, Sanderson JL, Nichols HJ, Gilchrist JS, Bell MBV, Hodge SJ, Young AJ, et al (2017). Explaining negative kin discrimination in a cooperative mammal society. Proceedings of the National Academy of Sciences of the USA
Thompson FJ, Marshall HH, Vitikainen EIK, Young AJ, Cant MA (2017). Individual and demographic consequences of mass eviction in cooperative banded mongooses.
Animal Behaviour,
134, 103-112.
Abstract:
Individual and demographic consequences of mass eviction in cooperative banded mongooses
In animal societies, conflict within groups can result in eviction, where individuals are often permanently expelled from their group. To understand the evolution of eviction and its role in the resolution of within-group conflict requires information on the demographic consequences of eviction for individuals and groups. However, such information is usually difficult to obtain because of the difficulty in tracking and monitoring individuals after they are evicted from their natal groups. Here we used a 15-year data set on life history and demography to investigate the consequences of eviction in a tractable cooperatively breeding mammal, the banded mongoose, Mungos mungo. In this species, groups of individuals are periodically evicted en masse and eviction is a primary mechanism by which new groups form in the study population. Following eviction, we found sex differences in dispersal distance: some females established new groups on the study peninsula but males always dispersed away from the study peninsula. Evicted females suffered reduced reproductive success in the year after eviction. For the evicting group, eviction was associated with increased per capita reproductive success for females, suggesting that eviction is successful in reducing reproductive competition. However, eviction was also associated with increased intergroup conflict for the evicting group. Our results suggest that within-group conflict resolution strategies affect group productivity, group interactions and the structure of the population, and hence have fitness impacts that reach beyond the individual evictors and evictees involved in eviction.
Abstract.
2016
Beirne C, Waring L, Mcdonald RA, Delahay R, Young AJ (2016). Age-related declines in immune response in a wild mammal are unrelated to immune cell telomere length. Proceedings of the Royal Society of London. Series B
York JE, Radford AN, de Vries B, Groothuis TG, Young AJ (2016). Dominance-related seasonal song production is unrelated to circulating testosterone in a subtropical songbird.
General and Comparative Endocrinology,
233, 43-52.
Abstract:
Dominance-related seasonal song production is unrelated to circulating testosterone in a subtropical songbird
Circulating testosterone (T) is widely considered to play a key role in the production of sexual displays by male vertebrates. While numerous studies support a role for circulating T in promoting the production of song in male birds, this understanding is based primarily on evidence from seasonally breeding northern temperate species, leaving it unclear whether this mechanism generalizes to other regions of the world. Here we investigate whether variation in circulating levels of T can explain the marked within- and among-individual variation in male song performance observed in a subtropical population of the year-round territorial white-browed sparrow weaver (Plocepasser mahali mahali). Our findings reveal that both circulating T and male song production peaked at a similar time point, halfway through the population-level breeding season. However, while dominant males were more likely to sing and sang for longer than subordinate males, within-group paired comparisons revealed no dominance-related differences in circulating T. Moreover, comparisons both among and within individual dominant males revealed that song duration, syllable rate and proportion of time spent singing were all unrelated to circulating T. Together, our findings suggest that natural variation in male song production, at least in this population of white-browed sparrow weavers, is achieved principally through mechanisms other than variation in circulating T concentration. More widely, our results are in line with the view that male song production is not exclusively regulated by gonadally synthesized steroids.
Abstract.
York JE, Radford AN, Groothuis TG, Young AJ (2016). Dominant male song performance reflects current immune state in a cooperatively breeding songbird.
Ecol Evol,
6(4), 1008-1015.
Abstract:
Dominant male song performance reflects current immune state in a cooperatively breeding songbird.
Conspicuous displays are thought to have evolved as signals of individual "quality", though precisely what they encode remains a focus of debate. While high quality signals may be produced by high quality individuals due to "good genes" or favourable early-life conditions, whether current immune state also impacts signalling performance remains poorly understood, particularly in social species. Here, we experimentally demonstrate that male song performance is impaired by immune system activation in the cooperatively breeding white-browed sparrow weaver (Plocepasser mahali). We experimentally activated the immune system of free-living dominant males via subcutaneous injection of phytohemagglutinin (PHA) and contrasted its effects with those of a control (phosphate buffered saline) injection. PHA-challenged males showed significant reductions in both the duration and the rate of their song performance, relative to controls, and this could not be readily attributed to effects of the challenge on body mass, as no such effects were detected. Furthermore, male song performance prior to immune-challenge predicted the scale of the inflammatory response to the challenge. Our findings suggest that song performance characteristics are impacted by current immune state. This link between current state and signal performance might therefore contribute to enforcing the honesty of signal performance characteristics. Impacts of current state on signaling may be of particular importance in social species, where subordinates may benefit from an ability to identify and subsequently challenge same-sex dominants in a weakened state.
Abstract.
Author URL.
Thornton A, McAuliffe K, Dall SRX, Fernandez-Duque E, Garber PA, Young AJ (2016). Fundamental Problems with the Cooperative Breeding Hypothesis. A reply to Burkart & Van Schaik. Journal of Zoology, 299(2), 84-88.
Thompson F, Marshall HH, Sanderson JL, Vitikainen EIK, Nichols HJ, Gilchrist J, Young AJ, Hodge SJ, Cant MA (2016). Reproductive competition triggers mass eviction in cooperative banded mongooses. Proceedings of the Royal Society of London: Biological Sciences
Walker L, York JE, Young AJ (2016). Sexually-selected sentinels? Evidence of a role for intra-sexual competition in sentinel behavior. Behavioral Ecology
2015
Sanderson JL, Nichols H, Marshall HH, Vitikainen E, Thompson F, Walker S, Cant MA, Young AJ (2015). Elevated glucocorticoid concentrations during gestation predict reduced reproductive success in subordinate female banded mongooses. Biology Letters
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
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.
Beirne C, Delahay R, Young AJ (2015). Sex differences in senescence: the role of intra-sexual competition in early adulthood. Proceedings of the Royal Society of London. Series B
Sanderson JL, Stott I, Young AJ, Vitikainen E, Hodge SJ, Cant MA (2015). The origins of consistent individual differences in cooperation in wild banded mongooses. Animal Behaviour
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
Young AJ, Jarvis JUM, Barnaville J, Bennett NC (2015). Workforce effects and the evolution of complex sociality in wild Damaraland mole-rat societies. The American Naturalist
2014
Beirne C, Delahay R, Hares M, Young AJ (2014). Age-related declines and disease-associated variation in immune cell telomere length in a wild mammal. PLoS One
Sanderson JL, Young AJ, Hodge SJ, Kyabulima S, Walker S, Cant MA (2014). Hormonal mediation of a carry-over effect in a wild cooperative mammal. Functional Ecology
Harrison XA, York JE, Young AJ (2014). Population genetic structure and direct
observations reveal sex-reversed patterns of dispersal in a cooperative bird. Molecular Ecology
York JE, Young AJ, Radford AN (2014). Singing in the moonlight: dawn song performance of a diurnal bird varies with lunar phase. Biology Letters
Mares R, Bateman AW, English S, Clutton-Brock TH, Young AJ (2014). Timing of predispersal prospecting is influenced by environmental, social and state-dependent factors in meerkats. Animal Behaviour
2013
Harrison XA, York JE, Cram DL, Hares MC, Young AJ (2013). Complete reproductive skew within white-browed sparrow weaver groups despite outbreeding opportunities for subordinates of both sexes.
Behavioral Ecology and Sociobiology,
67(12), 1915-1929.
Abstract:
Complete reproductive skew within white-browed sparrow weaver groups despite outbreeding opportunities for subordinates of both sexes
The distribution of reproductive success within societies is a key determinant of the outcomes of social evolution. Attempts to explain social diversity, therefore, require that we quantify reproductive skews and identify the mechanisms that generate them. Here, we address this priority using life history and genotypic data from >600 individuals in 40 wild groups of the cooperatively breeding white-browed sparrow weaver, Plocepasser mahali. We show that groups comprise up to six males and seven females, but within-group reproduction is completely monopolised by a single dominant male and female, while extra-group males sire 12-18 % of offspring. Strong within-group kin structure could frequently explain these monopolies, as subordinates had typically delayed dispersal from their natal groups and so frequently (1) lacked within-group outbreeding partners, and/or (2) stood to gain little from contesting dominant reproduction, being almost as related to the dominant's young as they would have been to their own. Kin structure alone cannot account entirely for these monopolies, however, as they remained complete following the immigration of unrelated males and females. That subordinate females remain reproductively quiescent despite also showing comparable body condition to dominants, overlapping them substantially in age, and showing no evidence of elevated stress hormone levels raises the possibility that they exercise reproductive restraint due instead to a threat of action by dominants and/or deficits in offspring fitness that might arise if subordinates bred. Our findings highlight the complexity of the mechanisms that generate reproductive disparities in animal societies and the challenge of identifying them when skews are complete. © 2013 Springer-Verlag Berlin Heidelberg.
Abstract.
Harrison XA, York JE, Cram DL, Young AJ (2013). Extra-group mating increases inbreeding risk in a cooperatively breeding bird.
Molecular Ecology,
22(22), 5700-5715.
Abstract:
Extra-group mating increases inbreeding risk in a cooperatively breeding bird
In many cooperatively breeding species, females mate extra-group, the adaptive value of which remains poorly understood. One hypothesis posits that females employ extra-group mating to access mates whose genotypes are more dissimilar to their own than their social mates, so as to increase offspring heterozygosity. We test this hypothesis using life history and genetic data from 36 cooperatively breeding white-browed sparrow weaver (Plocepasser mahali) groups. Contrary to prediction, a dominant female's relatedness to her social mate did not drive extra-group mating decisions and, moreover, extra-group mating females were significantly more related to their extra-group sires than their social mates. Instead, dominant females were substantially more likely to mate extra-group when paired to a dominant male of low heterozygosity, and their extra-group mates (typically dominants themselves) were significantly more heterozygous than the males they cuckolded. The combined effects of mating with extra-group males of closer relatedness, but higher heterozygosity resulted in extra-group-sired offspring that were no more heterozygous than their within-group-sired half-siblings. Our findings are consistent with a role for male-male competition in driving extra-group mating and suggest that the local kin structure typical of cooperative breeders could counter potential benefits to females of mating extra-group by exposing them to a risk of inbreeding. © 2013 John Wiley & Sons Ltd.
Abstract.
Young AJ, Bennett NC (2013). Intra-sexual selection in cooperative mammals and birds: why aren't females bigger and better armed?. Philosophical Transactions of the Royal Society of London: Biological Sciences
Lutermann H, Young AJ, Bennett NC (2013). Reproductive status and testosterone among females in cooperative mole-rat societies. General and Comparative Endocrinology
Cant MA, Young AJ (2013). Resolving social conflict among females without overt aggression. Philosophical Transactions of the Royal Society of London: Biological Sciences
2012
Mares R, Young AJ, Clutton-Brock TH (2012). Individual contributions to territory defence
in a cooperative breeder: weighing up the benefits and costs. Proceedings of the Royal Society of London: Biological Sciences
2011
Abbot P, Abe J, Alcock J, Alizon S, Alpedrinha JAC, Andersson M, Andre J-B, van Baalen M, Balloux F, Balshine S, et al (2011). Inclusive fitness theory and eusociality.
Nature,
471(7339), E1-E4.
Abstract:
Inclusive fitness theory and eusociality.
Arising from M. A. Nowak, C. E. Tarnita & E. O. Wilson 466, 1057-1062 (2010); Nowak et al. reply. Nowak et al. argue that inclusive fitness theory has been of little value in explaining the natural world, and that it has led to negligible progress in explaining the evolution of eusociality. However, we believe that their arguments are based upon a misunderstanding of evolutionary theory and a misrepresentation of the empirical literature. We will focus our comments on three general issues.
Abstract.
Author URL.
Mares R, Young AJ, Levesque DL, Harrison N, Clutton-Brock TH (2011). Responses to intruder scents in the cooperatively breeding meerkat: Sex and social status differences and temporal variation.
Behavioral Ecology,
22(3), 594-600.
Abstract:
Responses to intruder scents in the cooperatively breeding meerkat: Sex and social status differences and temporal variation
Although sex-specific responses to intruder scent marks have been described in many mammal species, less is known about variation in responses in cooperatively breeding species where differential access to breeding opportunities exists within groups. When reproductive skew is high, strong responses to extragroup breeding rivals would be expected mainly from dominant individuals, with levels of investment depending on female receptiveness. However, evidence from controlled experiments on cooperative breeders for sex and social status differences in responses to intruder scent marks is limited. Here, we investigated responses to intruder scent marks in cooperatively breeding meerkats (Suricata suricatta), where a single dominant pair largely monopolizes within-group reproduction. A series of experimental presentations using feces were used to test first, whether meerkats discriminate between resident and extragroup male scent marks; second, whether sex and social status affect the response to intruding male scents; and third, whether dominant males increase their level of response when dominant females are most receptive. Our results suggest that meerkats are able to discriminate between resident and intruding male scent marks and show that dominant males have the strongest overall response to intruder scent marks, which does not increase with female receptiveness. We suggest that, although all group members may be affected by the presence of intruders, reproductive conflict may be the main reason for the stronger response of dominant males to extragroup male scent marks in this cooperatively breeding species with high reproductive skew. © the Author 2011.
Abstract.
2010
Clutton-Brock TH, Hodge SJ, Flower TP, Spong G, Young AJ (2010). Adaptive suppression of subordinate reproduction in cooperative mammals. American Naturalist, 176, 664-673.
Young AJ, Bennett NC (2010). Morphological divergence of breeders and helpers in Damaraland mole-rat societies. Evolution, 64, 3190-3197.
Young AJ, Oosthuizen MK, Lutermann H, Bennett NC (2010). Physiological suppression eases in Damaraland mole-rat societies when ecological constraints on dispersal are relaxed.
Horm Behav,
57, 177-183.
Abstract:
Physiological suppression eases in Damaraland mole-rat societies when ecological constraints on dispersal are relaxed
In many vertebrate societies, subordinate females exhibit down-regulated reproductive physiologies relative to those of dominants, a condition commonly termed physiological suppression. Research into the causes of physiological suppression has focused principally on the role of the subordinate’s social environment (typically the presence of the dominant female and/or an absence of unrelated males within the group), while few studies have considered the additional role that the physical environment may play. Here we present new evidence from wild Damaraland mole-rats, Fukomys damarensis, revealing that physiological suppression among subordinate females eases markedly during the annual rains (a time when ecological constraints on dispersal are relaxed), despite the continued presence of the dominant female and in groups that contain no new immigrant males. Subordinate females showed substantially higher pituitary sensitivities to GnRH challenge during the wet period than the dry, a contrast that cannot be attributed to between-female differences (as it holds for paired within-female comparisons), associated changes in body mass (as our analyses control for this), or concomitant reductions in physiological stress (as their urinary cortisol concentrations were actually higher in the wet period). We suggest that our findings reflect selection for the maintenance of reproductive readiness among subordinate females during high rainfall periods, given the increased likelihood of encountering dispersal and/or mating opportunities with extra-group males when ecological constraints on dispersal are relaxed. These findings reveal new complexity in the processes that regulate physiological suppression, suggesting a key role in some species for changes in the physical as well as social environment.
Abstract.
2009
Young AJ, Monfort SL (2009). Stress and the costs of extra-territorial movement in a social carnivore. Biology Letters
Young AJ (2009). The Causes of Physiological Suppression in Vertebrate Societies: a Synthesis. In Hager R, Jones CB (Eds.) Reproductive Skew in Vertebrates, Cambridge University Press, 397-436.
2008
Spong GF, Hodge SJ, Young AJ, Clutton-Brock TH (2008). Factors affecting the reproductive success of dominant male meerkats.
Mol Ecol,
17(9), 2287-2299.
Abstract:
Factors affecting the reproductive success of dominant male meerkats.
Identifying traits that affect the reproductive success of individuals is fundamental for our understanding of evolutionary processes. In cooperative breeders, a dominant male typically restricts mating access to the dominant female for extended periods, resulting in pronounced variation in reproductive success among males. This may result in strong selection for traits that increase the likelihood of dominance acquisition, dominance retention and reproductive rates while dominant. However, despite considerable research on reproductive skew, few studies have explored the factors that influence these three processes among males in cooperative species. Here we use genetic, behavioural and demographic data to investigate the factors affecting reproductive success in dominant male meerkats (Suricata suricatta). Our data show that dominant males sire the majority of all offspring surviving to 1 year. A male's likelihood of becoming dominant is strongly influenced by age, but not by weight. Tenure length and reproductive rate, both important components of dominant male reproductive success, are largely affected by group size and composition, rather than individual traits. Dominant males in large groups have longer tenures, but after this effect is controlled, male tenure length also correlates negatively to the number of adult females in the group. Male reproductive rate also declines as the number of intra- and extra-group competitors increases. As the time spent in the dominant position and reproductive rate while dominant explain > 80% of the total variance in reproductive success, group composition thus has major implications for male reproductive success.
Abstract.
Author URL.
Young AJ, Monfort, S.L. Clutton-Brock, T.H. (2008). The causes of physiological suppression among female meerkats: a role for subordinate restraint due to the threat of infanticide?. Hormones and Behaviour, 53
2007
Russell AF, Young AJ, Spong G, Jordan NR, Clutton-Brock TH (2007). Helpers increase the reproductive potential of offspring in cooperative meerkats. Proceedings of the Royal Society B: Biological Sciences, 274
Young AJ, Spong G, Clutton-Brock TH (2007). Subordinate male meerkats prospect for extra-group paternity: alternative reproductive tactics in a cooperative animal. Proceedings of the Royal Society B Biological Sciences, 274(1618), 1603-1609.
2006
Carlson AA, Manser, M.B. Young, A.J. Russell, A.F. Jordan N, McNeilly AS, Clutton-Brock TH (2006). Cortisol levels are positively associated with pup-feeding rates in male meerkats. Proceedings of the Royal Society B: Biological Sciences, 273
Carlson AA, Russell, A.F. Young, A.J. Jordan, N. McNeilly AS, Clutton-Brock TH (2006). Elevated prolactin levels immediately precede decisions to babysit by male meerkat helpers. Hormones and Behaviour, 50
Young AJ, Clutton-Brock TH (2006). Infanticide by subordinates influences reproductive sharing in cooperatively breeding meerkats. Biology Letters, 2(3), 385-387.
Young AJ, Carlson AA, Russell AF, Bennett NC, Monfort SL, Clutton-Brock TH (2006). Stress and the suppression of subordinate reproduction in cooperatively breeding meerkats. Proceedings of the National Academy of Sciences, 103(32), 12005-12010.
2005
Stephens PA, Russell AF, Young AJ, Sutherland WJ, Clutton-Brock TH (2005). Dispersal, eviction, and conflict in meerkats (Suricata suricatta): an evolutionarily stable strategy model.
American Naturalist,
165(1), 120-135.
Abstract:
Dispersal, eviction, and conflict in meerkats (Suricata suricatta): an evolutionarily stable strategy model
Decisions regarding immigration and emigration are crucial to understanding group dynamics in social animals, but dispersal is rarely treated in models of optimal behavior. We developed a model of evolutionarily stable dispersal and eviction strategies for a cooperative mammal, the meerkat Suricata suricatta. Using rank and group size as state variables, we determined state-specific probabilities that subordinate females would disperse and contrasted these with probabilities of eviction by the dominant female, based on the long-term fitness consequences of these behaviors but incorporating the potential for error. We examined whether long-term fitness considerations explain group size regulation in meerkats; whether long-term fitness considerations can lead to conflict between dominant and subordinate female group members; and under what circumstances those conflicts were likely to lead to stability, dispersal, or eviction. Our results indicated that long-term fitness considerations can explain group size regulation in meerkats. Group size distributions expected from predicted dispersal and eviction strategies matched empirical distributions most closely when emigrant survival was approximately that determined from the field study. Long-term fitness considerations may lead to conflicts between dominant and subordinate female meerkats, and eviction is the most likely result of these conflicts. Our model is computationally intensive but provides a general framework for incorporating future changes in the size of multimember cooperative breeding groups.
Abstract.
Young AJ, Carlson AA, Clutton-Brock TH (2005). Trade-offs between extra-territorial prospecting and helping in a cooperative mammal. Animal Behaviour, 70(4), 829-837.
2004
Carlson AA, Young AJ, Russell AF, Bennett NC, McNeilly AS, Clutton-Brock T (2004). Hormonal correlates of dominance in meerkats (Suricata suricatta).
Horm Behav,
46(2), 141-150.
Abstract:
Hormonal correlates of dominance in meerkats (Suricata suricatta).
In cooperatively breeding meerkats (Suricata suricatta), individuals typically live in extended family groups in which the dominant male and female are the primary reproductives, while their offspring delay dispersal, seldom breed, and contribute to the care of subsequent litters. Here we investigate hormonal differences between dominants and subordinates by comparing plasma levels of luteinizing hormone (LH), estradiol and cortisol in females, and testosterone and cortisol in males, while controlling for potential confounding factors. In both sexes, hormone levels are correlated with age. In females, levels of sex hormone also vary with body weight and access to unrelated breeding partners in the same group: subordinates in groups containing unrelated males have higher levels of LH and estradiol than those in groups containing related males only. When these effects are controlled, there are no rank-related differences in circulating levels of LH among females or testosterone among males. However, dominant females show higher levels of circulating estradiol than subordinates. Dominant males and females also have significantly higher cortisol levels than subordinates. Hence, we found no evidence that the lower levels of plasma estradiol in subordinate females were associated with high levels of glucocorticoids. These results indicate that future studies need to control for the potentially confounding effects of age, body weight, and access to unrelated breeding partners before concluding that there are fundamental physiological differences between dominant and subordinate group members.
Abstract.
Author URL.
2003
Carlson AA, Nicol, L. Young, A.J. Parlow, A.F. McNeilly AS (2003). Radioimmunoassay of prolactin for the meerkat (Suricata suricatta), a cooperatively breeding carnivore. General & Comparative Endocrinology, 130
2002
Clutton-Brock TH, Russell, A.F. Sharpe, L.L. Young, A.J. Balmforth Z, McIlrath GM (2002). Evolution and development of sex differences in cooperative behaviour in meerkats. Science, 297(5579).
