Reproductive success is often highly skewed in animal populations. Yet the processes leading to this are not always clear. Similarly, connections in animal social networks are often nonrandomly distributed, with some individuals with many connections and others with few, yet whether there are simple explanations for this pattern has not been determined. Numerous social interactions involve dyads embedded within a wider network. As a result, it may be possible to model which individuals accumulate social interactions through a more general understanding of the social network's structure, and how this structure changes over time. We analysed fighting and mating interactions across the breeding season in a population of wild field crickets under surveillance from a network of video cameras. We fitted stochastic actor-oriented models to determine the dynamic process by which networks of cricket fighting and mating interactions form, and how they co-influence each other. We found crickets tended to fight those in close spatial proximity to them and those possessing a mutual connection in the fighting network, and heavier crickets fought more often. We also found that crickets that mated with many others tended to fight less in the following time period. This demonstrates that a mixture of spatial constraints, characteristics of individuals and characteristics of the immediate social environment are key for determining social interactions. The mating interaction network required very few parameters to understand its growth and thus its structure; only homophily by mating success was required to simulate the skew of mating interactions seen in this population. This demonstrates that relatively simple, but dynamic, processes can give highly skewed distributions of mating success.

Individuals frequently show long-term consistency in behaviour over their lifetimes, referred to as “personality.” Various models, revolving around the use of resources and how they are valued by individuals, attempt to explain the maintenance of these different behavioural types within a population, and evaluating them is the key for understanding the evolution of behavioural variation. The pace-of-life syndrome hypothesis suggests that differences in personalities result from divergent life-history strategies, with more active/risk-taking individuals reproducing rapidly but dying young. However, studies of wild animals provide only limited support for key elements of this and related hypotheses, such as a negative relationship between residual reproductive value and activity. Furthermore, alternative models make divergent predictions regarding the relationship between risk-taking behaviours and variables consistent in the short-term, such as condition. To test these predictions, we regularly measured willingness to leave a shelter and the activity level of wild adult field crickets (Gryllus campestris) at both short and long intervals over their entire adult lives. We found some support for a pace-of-life syndrome influencing personality, as lifespan was negatively related to willingness to leave the shelter and activity. Crickets did not appear to protect their “assets” however, as estimates of residual reproductive value were not related to behaviour. Although there was considerable variance attributed to the short-term consistency, neither trait was affected by phenotypic condition, failing to support either of the models we tested. Our study confirms that behaviours may covary with some life-history traits and highlights the scales of temporal consistency that are more difficult to explain.

The Cantabrian capercaillie (Tetrao urogallus cantabricus) is an endangered subspecies of the Western capercaillie, endemic of northern Spain, inhabiting the south-western limit of the species range. Assessing genetic variability and the factors that determine it is crucial in order to develop an effective conservation strategy. In this work, non-invasive samples were collected in some of the best preserved areas inhabited by Cantabrian capercaillie. Nine microsatellite loci and a sex-specific marker were analysed. We included five zones, separated by valleys with different levels of habitat modifications. No evidence of genetic clustering was found which suggests that fragmentation and development in the area do not act as barriers to gene flow. Nonetheless, significant differences among sampling zones were encountered in terms of their allelic frequencies (global FST = 0.035, p = 0.001). Pairwise FST comparisons showed differences between all sampling zones included, except between the two ones located in the South (Degaña and Alto Sil). These findings, along with the results of individual based genetic differences, indicate that gene flow among sampling zones might be at least slightly compromised, except between the two zones located in the South. Despite this, the sampling zones seem to exchange migrants at a rate that prevents genetic differentiation to the point of creating clusters. Our results show that the capercaillies in the study area constitute a single interbreeding group, which is an important piece of information that provides support to better understand the dynamics of this endangered subspecies.

Sexual selection results from variation in success at multiple stages in the mating process, including competition before and after mating. The relationship between these forms of competition, such as whether they trade-off or reinforce one another, influences the role of sexual selection in evolution. However, the relationship between these 2 forms of competition is rarely quantified in the wild. We used video cameras to observe competition among male field crickets and their matings in the wild. We characterized pre- and post-copulatory competition as 2 networks of competing individuals. Social network analysis then allowed us to determine 1) the effectiveness of precopulatory competition for avoiding postcopulatory competition, 2) the potential for divergent mating strategies, and 3) whether increased postcopulatory competition reduces the apparent reproductive benefits of male promiscuity. We found 1) limited effectiveness of precopulatory competition for avoiding postcopulatory competition; 2) males do not specifically engage in only 1 type of competition; and 3) promiscuous individuals tend to mate with each other, which will tend to reduce variance in reproductive success in the population and highlights the trade-off inherent in mate guarding. Our results provide novel insights into the works of sexual competition in the wild. Furthermore, our study demonstrates the utility of using network analyses to study competitive interactions, even in species lacking obvious social structure.

Examining the relevance of 'animal personality' involves linking consistent among- and within-individual behavioural variation to fitness in the wild. Studies aiming to do this typically assay personality in captivity and rely on the assumption that measures of traits in the laboratory reflect their expression in nature. We examined this rarely tested assumption by comparing laboratory and field measurements of the behaviour of wild field crickets (Gryllus campestris) by continuously monitoring individual behaviour in nature, and repeatedly capturing the same individuals and measuring their behaviour in captivity. We focused on three traits that are frequently examined in personality studies: shyness, activity and exploration. All of them showed repeatability in the laboratory. Laboratory activity and exploration predicted the expression of their equivalent behaviours in the wild, but shyness did not. Traits in the wild were predictably influenced by environmental factors such as temperature and sunlight, but only activity showed appreciable within-individual repeatability. This suggests that some behaviours typically studied as personality traits can be accurately assayed in captivity, but the expression of others may be highly context-specific. Our results highlight the importance of validating the relevance of laboratory behavioural assays to analogous traits measured in the wild.

Investigating patterns of among and within-individual trait variation in populations is essential to understanding how selection shapes phenotypes. Behavior is often the most flexible aspect of the phenotype, and to understand how it is affected by selection, we need to examine how consistent individuals are. However, it is not well understood whether among-individual differences tend to remain consistent over lifetimes, or whether the behavior of individuals relative to one another varies over time. We examined the dynamics of 4 behavioral traits (tendency to leave a refuge, shyness, activity, and exploration) in a wild population of field crickets (Gryllus campestris). We tagged individuals and then temporarily removed them from their natural environment and tested them under laboratory conditions. All 4 traits showed among-individual variance in mean levels of expression across the adult lifespan, but no significant differences in how rapidly expression changed with age. For all traits, among-individual variance increased as individuals got older. Our findings reveal seldom examined changes in variance components over the adult lifetime of wild individuals. Such changes will have important implications for the relationship between behavioral traits, life-histories, and fitness and the consequences of selection on wild individuals.

In organisms such as fish, where body size is considered an important state variable for the study of their population dynamics, size-specific growth and survival rates can be influenced by local variation in both biotic and abiotic factors, but few studies have evaluated the complex relationships between environmental variability and size-dependent processes. We analysed a 6-year capture-recapture dataset of brown trout (Salmo trutta) collected at 3 neighbouring but heterogeneous mountain streams in northern Spain with the aim of investigating the factors shaping the dynamics of local populations. The influence of body size and water temperature on survival and individual growth was assessed under a multi-state modelling framework, an extension of classical capture-recapture models that considers the state (i.e. body size) of the individual in each capture occasion and allows us to obtain state-specific demographic rates and link them to continuous environmental variables. Individual survival and growth patterns varied over space and time, and evidence of size-dependent survival was found in all but the smallest stream. At this stream, the probability of reaching larger sizes was lower compared to the other wider and deeper streams. Water temperature variables performed better in the modelling of the highest-altitude population, explaining over a 99 % of the variability in maturation transitions and survival of large fish. The relationships between body size, temperature and fitness components found in this study highlight the utility of multi-state approaches to investigate small-scale demographic processes in heterogeneous environments, and to provide reliable ecological knowledge for management purposes.

Demographic models accounting for operational sex ratio (OSR) show that male numbers can have a substantial influence on the dynamics of wild populations. We used the Cantabrian capercaillie, a forest bird, as a model to assess the effects of the reduction in the number of breeding males (increased OSR) associated to male-biased hunting, on the genetics of the population. We based our assessment in the comparison of the dynamics of neutral markers transmitted by both parents (microsatellites) versus markers transmitted only by females (mitochondrial DNA—mtDNA). Parallel to the analysis of field data, we ran computer simulations to explore how different levels of OSR and two other important demographic factors, population size and connectivity, might influence the dynamics of genetic variation of microsatellites and mtDNA. We found evidence of a genetic bottleneck and low genetic variability affecting microsatellites but not mtDNA early in our study period, when male-biased hunting was more intense. This was followed by a decline in mtDNA variation around 10–20 years later. Simulations suggested that changes in genetic variation associated with high OSR had the closest similarity to those observed at the beginning of our study, whereas a combination of reduced size and migration rate better resembled the patterns found later on. Our findings indicate that male-biased hunting might have triggered the ongoing decline of the Cantabrian capercaillie, on its own or in combination with habitat configuration, and support the need to incorporate OSR into decision making for the management and conservation of exploited populations.

Counting rare and elusive animals and evaluating their demographic status, are fundamental yet challenging aspects of population ecology and conservation biology. We set out to estimate population size (Nc), genetic effective population size (Ne gen), sex ratio, and movements based on genetic tagging for the threatened Cantabrian capercaillie. We used 9 microsatellite loci to genotype 134 droppings collected at 34 display areas during the breeding season. Using genetic capture-mark-recapture, we estimated 93 individuals (Nc, 95% CI: 70-116) in an area of about 500 km2, with sex ratio biased towards males (1∶1.6). Estimated Ne gen (35.5) was 38% of Nc, notably higher than the published average in wild populations. This capercaillie population is small and well within concern in terms of population viability. By genetic tagging, we detected mostly short movements; just a few males were recaptured between contiguous display areas. Non-invasive surveys of endangered populations have a great potential, yet adequate sample size and location are key to obtain reliable information on conservation status.

BACKGROUND: Post-mating interactions between the reproductive traits and gametes of mating individuals and among their genes within zygotes are invariably complex, providing multiple opportunities for reproduction to go awry. These interactions have the potential to act as barriers to gene flow between species, and may be important in the process of speciation. There are multiple post-mating barriers to interbreeding between the hybridising field crickets Gryllus bimaculatus and G. campestris. Female G. bimaculatus preferentially store sperm from conspecific males when mated to both conspecific and heterospecific partners. Additionally, conspecific males sire an even greater proportion of offspring than would be predicted from their sperm's representation in the spermatheca. The nature of these post-sperm-storage barriers to hybridisation are unknown. We use a fluorescent staining technique to determine whether barriers occur prior to, or during embryo development. RESULTS: We show that eggs laid by G. bimaculatus females mated to G. campestris males are less likely to begin embryogenesis than eggs from conspecific mating pairs. of the eggs that are successfully fertilised and start to develop, those from heterospecific mating pairs are more likely to arrest early, prior to blastoderm formation. We find evidence for bimodal variation among egg clutches in the number of developing embryos that subsequently arrest, indicating that there is genetic variation for incompatibility between mating individuals. In contrast to the pattern of early embryonic mortality, those hybrids reaching advanced stages of embryogenesis have survival rates equal to that of embryos from conspecific mating pairs. CONCLUSIONS: Post-sperm-storage barriers to hybridisation show evidence of genetic polymorphism. They are sufficiently large, that if the species interbreed where they are sympatric, these barriers could play a role in the maintenance of reproductive isolation between them. The number of eggs that fail to develop represents a substantial cost of hybridization to G. bimaculatus females, and this cost could reinforce the evolution of barriers occurring earlier in the reproductive process.

Mechanisms that prevent different species from interbreeding are fundamental to the maintenance of biodiversity. Barriers to interspecific matings, such as failure to recognize a potential mate, are often relatively easy to identify. Those occurring after mating, such as differences in the how successful sperm are in competition for fertilisations, are cryptic and have the potential to create selection on females to mate multiply as a defence against maladaptive hybridization. Cryptic advantages to conspecific sperm may be very widespread and have been identified based on the observations of higher paternity of conspecifics in several species. However, a relationship between the fate of sperm from two species within the female and paternity has never been demonstrated. We use competitive microsatellite PCR to show that in two hybridising cricket species, Gryllus bimaculatus and G. campestris, sequential cryptic reproductive barriers are present. In competition with heterospecifics, more sperm from conspecific males is stored by females. Additionally, sperm from conspecific males has a higher fertilisation probability. This reveals that conspecific sperm precedence can occur through processes fundamentally under the control of females, providing avenues for females to evolve multiple mating as a defence against hybridization, with the counterintuitive outcome that promiscuity reinforces isolation and may promote speciation. © 2013 Blackwell Publishing Ltd.

The 3 lamprey species, sea lamprey Petromyzon marinus L. European river lamprey Lampetra fluviatilis L. and European brook lamprey L. planeri Bloch, that inhabit the Iberian Peninsula are of conservation concern. They are considered either Vulnerable, Critically Endangered, and even Extinct in different regions of this area mainly due to habitat loss and population fragmentation. Although several other factors contribute to the decline of lamprey populations in Iberian rivers, obstacles to migration (dams and weirs) are probably the most widespread and significant, causing an estimated 80% loss of accessible habitat in most river basins. We analysed historical records from all main Iberian rivers before the construction of impassable dams became widespread, and found that lampreys were consistently present in the upper reaches. The un -blocking of the lower stretches of major river basins and the restoration of former spawning sites and larval habitats should be considered as priority measures for the conservation of these species. Identification of Special Areas of Conservation to be included in the Natura 2000 European network can also be very relevant for lamprey conservation. © Inter-Research 2012.

The ecological and evolutionary importance of fine-scale genetic structure within populations is increasingly appreciated. However, available data are largely restricted to wild vertebrates and eusocial insects. In addition, there is the expectation that most insects tend to have such large- and high-density populations and are so mobile that they are unlikely to face inbreeding risks through fine-scale population structuring. This has made the growing body of evidence for inbreeding avoidance in insects and its implication in mating systems evolution somewhat enigmatic. We present a 4-year study of a natural population of field crickets. Using detailed video monitoring combined with genotyping, we track the movement of all adults within the population and investigate genetic structure at a fine scale. We find some evidence for relatives being found in closer proximity, both across generations and within a single breeding season. Whilst incestuous matings are not avoided, population inbreeding is low, suggesting that mating is close to random and the limited fine-scale structure does not create significant inbreeding risk. Hence, there is little evidence for selective pressures associated with the evolution of inbreeding avoidance mechanisms in a closely related species.

Males frequently remain in close proximity to their mate immediately postcopulation. This behavior has generally been interpreted as a guarding tactic designed to reduce the likelihood that a rival male can rapidly displace the ejaculate of the guarding male [1, 2]. Such attempts by males to control their mates represent a potential source of conflict [3-5], but guarding behaviors in species where it is difficult for males to control their mates suggest that conflict is not inevitable [6, 7]. We employed a network of infrared video cameras to study a wild population of individually marked and genotyped field crickets (Gryllus campestris). Lone females or males suffer similar rates of predation, but when a pair is attacked, the male allows the female priority access to their burrow, and in doing so dramatically increases his probability of being killed. In compensation for this increased predation risk, paired males mate more frequently and father more of the female's offspring. By staying with a male, females increase the sperm contribution of preferred males as well as reducing their predation risk. In contrast to conclusions based on previous lab studies, our field study suggests that mate guarding can evolve in a context of cooperation rather than conflict between the sexes.

Understanding speciation hinges on understanding how reproductive barriers arise between incompletely isolated populations. Despite their crucial role in speciation, prezygotic barriers are relatively poorly understood and hard to predict. We use two closely related cricket species, Gryllus bimaculatus and G. campestris, to experimentally investigate premating barriers during three sequential mate choice steps. Furthermore, we experimentally show a significant difference in polyandry levels between the two species and subsequently test the hypothesis that females of the more polyandrous species, G. bimaculatus, will be less discriminating against heterospecific males and hence hybridise more readily. During close-range mating behaviour experiments, males showed relatively weak species discrimination but females discriminated very strongly. In line with our predictions, this discrimination is asymmetric, with the more polyandrous G. bimaculatus mating heterospecifically and G. campestris females never mating heterospecifically. Our study shows clear differences in the strength of reproductive isolation during the mate choice process depending on sex and species, which may have important consequences for the evolution of reproductive barriers.

The understanding of natural and sexual selection requires both field and laboratory studies to exploit the advantages and avoid the disadvantages of each approach. However, studies have tended to be polarized among the types of organisms studied, with vertebrates studied in the field and invertebrates in the lab. We used video monitoring combined with DNA profiling of all of the members of a wild population of field crickets across two generations to capture the factors predicting the reproductive success of males and females. The factors that predict a male's success in gaining mates differ from those that predict how many offspring he has. We confirm the fundamental prediction that males vary more in their reproductive success than females, and we find that females as well as males leave more offspring when they mate with more partners.

Recent discussion of genetic benefits of polyandry and female mate choice has distinguished between two potential factors influencing offspring quality: (i) some males carry higher quality genes and (ii) males and females differ in their degree of genetic compatibility. We examined evidence for effects of good genes and genetic compatibility on embryonic survival of sea lamprey (Petromyzon marinus), a fish species with external fertilization that spawns in North Atlantic rivers. Using in vitro fertilization, we made all possible crosses among 10 males and 5 females collected in the spawning grounds. Male identity did not have any significant effect on hatching success. However, female identity and male x female interactions had a highly significant effect on hatching success. Our results suggest that genetic compatibility between male and female genomes plays an important role in embryo survival during the early stages of development in the sea lamprey.

Donald et al. (Reports, 10 August 2007, p. 810) assessed the impact of the European Union's Birds Directive, a conservation policy enacted in 1979, and reported evidence for positive population changes in targeted species. We argue that their conclusions are overstatements based on unsuitable data and inappropriate analyses.

Despite the often dramatic negative effects of inbreeding on offspring fitness, matings between closely related individuals sometimes occur. This may be because females cannot reliably recognize related males before mating with them. As an alternative to precopulatory choice, polyandrous females may avoid inbreeding through postcopulatory mechanisms if they can assess mate relatedness during or after copulation. These mechanisms include increasing remating propensity and decreasing rate of offspring production in response to incestuous matings. Stored product pests, such as the bruchid beetle Callosobruchus maculatus, have an ecology that is likely to expose them to frequent risks of inbreeding when a small number of females found a new population on a previously uninfested store of beans. Using this species, we show that inbreeding has negative effects on offspring viability but that females do not appear to discriminate between brothers and unrelated males prior to mating. Furthermore, females that first mated with brothers did not increase their remating propensity or decrease their rate of offspring production relative to females that first mated with unrelated males. Our findings suggest that the costs of inbreeding have not been sufficient to drive the evolution of mating behaviour as a mechanism of inbreeding avoidance in C. maculatus. © 2007 the Association for the Study of Animal Behaviour.

Recent studies have suggested that females of the field cricket Gryllus bimaculatus exercise post-copulatory choice over the paternity of their offspring. There is evidence that these choices are made in relation to the genetic compatibility of mates rather than their absolute quality, but the magnitude of heritable differences in males has not been thoroughly examined. Using a half-sib breeding design we measured additive genetic variance and dam effects in a suite of reproductive and non-reproductive traits. Both components explained relatively little of the phenotypic variance across traits. The dam component in our design contains variance caused by both maternal effects and dominance. If maternal effects are negligible as suggested by previous studies, our data suggest that dominance variance is an important source of variation in these traits. The lack of additive genetic variation, but possible existence of large amounts of non-additive genetic variation is consistent with the idea that female mate choice and multiple mating may be driven by differences in genetic compatibility between potential mates rather than by differences in genetic quality.

Recent studies have suggested that females of the field cricket Gryllus bimaculatus exercise post-copulatory choice over the paternity of their offspring. There is evidence that these choices are made in relation to the genetic compatibility of mates rather than their absolute quality, but the magnitude of heritable differences in males has not been thoroughly examined. Using a half-sib breeding design we measured additive genetic variance and dam effects in a suite of reproductive and non-reproductive traits. Both components explained relatively little of the phenotypic variance across traits. The dam component in our design contains variance caused by both maternal effects and dominance. If maternal effects are negligible as suggested by previous studies, our data suggest that dominance variance is an important source of variation in these traits. The lack of additive genetic variation, but possible existence of large amounts of non-additive genetic variation is consistent with the idea that female mate choice and multiple mating may be driven by differences in genetic compatibility between potential mates rather than by differences in genetic quality.

Cell proliferation in the forebrain and midbrain of the sea lamprey (Petromyzon marinus L.) was investigated by proliferation cell nuclear antigen (PCNA) immunocytochemistry, with BrdU labeling as a complementary technique. Correspondence between proliferation regions and areas of early neuronal differentiation was also assessed using antibodies against HNK-1 early differentiation marker. The brain of late embryos shows a homogeneously thick ventricular zone (VZ) containing PCNA-immunoreactive (PCNA-ir) nuclei. In early prolarvae, several discontinuities formed by PCNA-negative cells, and differences among regions in VZ thickness, become apparent. In late prolarvae and early larvae, these differences in VZ thickness and appearance, as well as the presence of PCNA-negative discontinuities, allowed us to correlate proliferation domains and neuroanatomical regions. In larvae, the number of PCNA-ir cells in the VZs diminish gradually, although a few PCNA-ir cells are present in the ependyma of most regions. In late larvae, proliferation becomes confined to a few ventricular areas (medial pallium, caudal habenula, ventral preoptic recess near the optic nerve, and tuberal portion of the posterior hypothalamic recess). During metamorphosis there appears to be no proliferation, but in upstream adults a few PCNA-ir cells are observed in the most caudal habenula. The characteristics of the proliferative regions revealed in lamprey with PCNA immunocytochemistry show notable differences from those observed in other vertebrates, and these differences may be related to the peculiar life cycle of lampreys.

A key prediction of theories of differential allocation and sexual conflict is that male phenotype will affect resource allocation by females. Females may adaptively increase investment in offspring when mated to high quality males to enhance the quality of their offspring, or males may vary in their ability to manipulate female investment post-mating. Males are known to be able to influence female reproductive investment, but the male traits underlying this ability have been little studied in taxa other than birds. We investigated the relationship between male dominance and female oviposition rate in two separate experiments using the field cricket, Gryllus bimaculatus. In both experiments, females mated to more dominant (but not larger) males laid more eggs. This reveals that either females allocate more effort to reproduction after mating with a dominant male or that dominance status is associated with male ability to manipulate their mates. This is the first evidence that dominance, rather than male attractiveness, has a post-copulatory effect on reproductive investment by females.

The Cantabrian capercaillie Tetrao urogallus cantabricus, a subspecies of the western capercaillie, is endemic to the Cantabrian Mountains of northwest Spain. The range is separated from its nearest neighbouring capercaillie population by a distance of more than 300 km. High genetic differentiation compared to capercaillie elsewhere qualifies the subspecies as an Evolutionarily Significant Unit. An assessment according to the IUCN Red List categories and criteria showed that the subspecies qualifies as Endangered due to rapid population declines, small population size, and severely fragmented range. The implementation of a range-wide recovery plan is vital for the survival of this subspecies. © Dt. Ornithologen-Gesellschaft e.V. 2006.

Sea lamprey Petromyzon marinus from the River Miño and Sella, Spain, showed an almost identical frequency for three observed haplotypes. None of these haplotypes were found among three North American populations. These results indicate an absence of exchange among sea lamprey populations spawning in the west and south-east Atlantic coasts. The similarity between the collections from the two Spanish rivers suggests that homing does not occur in anadromous Sea lamprey. © 2004 the Fisheries Society of the British Isles.

1. Density can influence growth through exploitation competition and behavioural or chemical interference. Negative effects of population density on the growth rate of Sea Lamprey larvae have been reported in several field and laboratory studies, but the mechanisms involved are poorly understood. 2. In this study the role of population density and waterborne-mediated interference on the growth rate of Sea Lamprey larvae was assessed in two laboratory experiments. The effects of these factors were evaluated by comparing growth of larvae reared at three different densities (27, 75 and 128 individuals m-2) or in preconditioned water (i.e. containing Sea Lamprey larvae at the same three densities). 3. Larval density had a negative effect on growth rates. Water conditioning had a negative but weaker effect on growth. Larvae reared in water preconditioned at the two higher densities showed a lower mass increase than those growing in water preconditioned at the lowest density. 4. The results are consistent with the existence of some chemical or biological agent released into the surrounding water and influencing growth in larval Sea Lampreys. However, chemical interference is not the only factor influencing density-dependent growth.

The development of neurons expressing gamma-aminobutyric acid (GABA) in the rhombencephalon and spinal cord of the sea lamprey (Petromyzon marinus) was studied for the first time with an anti-GABA antibody. The earliest GABA-immunoreactive (GABAir) neurons appear in late embryos in the basal plate of the isthmus, caudal rhombencephalon, and rostral spinal cord. In prolarvae, the GABAir neurons of the rhombencephalon appear to be distributed in spatially restricted cellular domains that, at the end of the prolarval period, form four longitudinal GABAir bands (alar dorsal, alar ventral, dorsal basal, and ventral basal). In the spinal cord, we observed only three GABAir longitudinal bands (dorsal, intermediate, and ventral). The larval pattern of GABAir neuronal populations was established by the 30-mm stage, and the same populations were observed in premetamorphic and adult lampreys. The ontogeny of GABAergic populations in the lamprey rhombencephalon and spinal cord is, in general, similar to that previously described in mouse and Xenopus.

Lampreys have a complex life cycle, with largely differentiated larval and adult periods. Despite the considerable interest of lampreys for understanding vertebrate evolution, knowledge of the early development of their eye and pineal complex is very scarce. Here, the early immunocytochemical organization of the pineal complex and retina of the sea lamprey was studied by use of antibodies against proliferating cell nuclear antigen (PCNA), opsin, serotonin, and gamma-aminobutyric acid (GABA). Cell differentiation in the retina, pineal organ, and habenula begins in prolarvae, as shown by the appearance of PCNA-negative cells, whereas differentiation of the parapineal vesicle was delayed until the larval period. In medium-sized to large larvae, PCNA-immunoreactive (-ir) cells were numerous in regions of the lateral retina near the differentiated part of the larval retina (central retina). A late-proliferating region was observed in the right habenula. Opsin immunoreactivity appears in the pineal vesicle of early prolarvae and 3 or 4 days later in the retina. In the parapineal organ, opsin immunoreactivity was observed only in large larvae. In the pineal organ, serotonin immunoreactivity was first observed in late prolarvae in photoreceptive (photoneuroendocrine) cells, whereas only a few of these cells appeared in the parapineal organ of large larvae. No serotonin immunoreactivity was observed in the larval retina. GABA immunoreactivity appeared earlier in the retina than in the pineal complex. No GABA-ir perikaryon was observed in the retina of larval lampreys, although a few GABA-ir centrifugal fibers innervate the inner retina in late prolarvae. First GABA-ir ganglion cells occur in the pineal organ of 15-17 mm larvae, and their number increases during the larval period. The only GABA-ir structures observed in the parapineal ganglion of larvae were afferent fibers, which appeared rather late in development. The time sequence of development in these photoreceptive structures is rather different from that observed in teleosts and other vertebrates. This suggests that the unusual development of the three photoreceptive organs in lampreys reflects specialization for their different functions during the larval and adult periods.

We assessed the effect of short-term (4.7-75.3 h) storage at low temperature (approximately 1 °C) on the viability of sea lamprey (Petromyzon marinus L.) gametes. Hatching success decreased with storage time, but more than 20% eggs hatched even after 75.3 h of preservation. However, storage time drastically reduced the survival rate to the burrowing stage (i.e. the last prelarval stage), which decreased from 76% when the gametes were stored for 4.7 h to 0% after 75.3 h of storage.

Although brain organization in lampreys is of great interest for understanding evolution in vertebrates, knowledge of early development is very scarce. Here, the development of the forebrain and midbrain gamma-aminobutyric acid (GABA)-ergic systems was studied in embryos, prolarvae, and small larvae of the sea lamprey using an anti-GABA antibody. Ancillary immunochemical markers, such as proliferating cell nuclear antigen (PCNA), calretinin, and serotonin, as well as general staining methods and semithin sections were used to characterize the territories containing GABA-immunoreactive (GABAir) neurons. Differentiation of GABAir neurons in the diencephalon begins in late embryos, whereas differentiation in the telencephalon and midbrain was delayed to posthatching stages. In lamprey prolarvae, the GABAir populations appear either as compact GABAir cell groups or as neurons interspersed among GABA-negative cells. In the telencephalon of prolarvae, a band of cerebrospinal fluid-contacting (CSF-c) GABAir neurons (septum) was separated from the major GABAir telencephalic band, the striatum (ganglionic eminence) primordium. The striatal primordium appears to give rise to most GABAir neurons observed in the olfactory bulb and striatum of early larval stages. GABAir populations in the dorsal telencephalon appear later, in 15-30-mm-long larvae. In the diencephalon, GABAir neurons appear in embryos, and the larval pattern of GABAir populations is recognizable in prolarvae. A small GABAir cluster consisting mainly of CSF-c neurons was observed in the caudal preoptic area, and a wide band of scattered CSF-c GABAir neurons extended from the preoptic region to the caudal infundibular recess. A mammillary GABAir population was also distinguished. Two compact GABAir clusters, one consisting of CSF-c neurons, were observed in the rostral (ventral) thalamus. In the caudal (dorsal) thalamus, a long band extended throughout the ventral tier. The nucleus of the medial longitudinal fascicle contained an early-appearing GABAir population. The paracommissural pretectum of prolarvae and larvae contained a large group of non-CSF-c GABAir neurons, although it was less compact than those of the thalamus, and a further group was found in the dorsal pretectum. In the midbrain of larvae, several groups of GABAir neurons were observed in the dorsal and ventral tegmentum and in the torus semicircularis. The development of GABAergic populations in the lamprey forebrain was similar to that observed in teleosts and in mouse, suggesting that GABA is a very useful marker for understanding evolution of forebrain regions. The possible relation between early GABAergic cell groups and the regions of the prosomeric map of the lamprey forebrain (Pombal and Puelles [ 1999] J. Comp. Neurol. 414:391-422) is discussed in view of these results and information obtained with ancillary markers.

This study assesses the influence of thermal regime on the development, survival rates and early growth of embryos of sea lamprey Petromyzon marinus incubated at five constant temperatures (7, 11, 15, 19 and 23° C). The time from fertilization to 50% hatching and from hatching to 50% burrowing were inversely related to incubation temperature. All the embryos incubated at 7° C died at very early stages, while those maintained at 11° C did not attain the burrowing stage. Survival from fertilization to hatching was 61, 89, 91 and 89% at 11, 15, 19 and 23° C, decreasing to 58, 70 and 70% from hatching to burrowing at 15, 19 and 23° C, respectively. Larvae reared during the first 3 months of exogenous feeding in a common environment at constant 21° C, revealed maximum survival for an incubation temperature of 15° C (43% of burrowed larvae) decreasing strongly at 19° C (16%) and 23° C (one suvivor among 240 larvae). Body length at the burrowing stage was maximum for embryos incubated at 19° C, but body mass increased in the interval 15-23° C. Mean incubation temperatures experienced by 117 broods during the embryonic development in the source river were estimated in 15·3 ± 2·30° C and 16·7 ± 1·76° C (mean ± 1 S.D.) for the periods fertilization-to-hatching and hatching-to-burrowing, respectively. © 2001 the Fisheries Society of the British Isles.

The distribution of gamma-aminobutyric acid (GABA) immunoreactivity in the olfactory bulbs of the adult sea lamprey was studied using an antibody against this transmitter. Five types of GABA-immunoreactive (GABAir) cells were observed. Medium-sized GABAir cells (periglomerular cells) were located around the olfactory glomeruli and occasionally within them. In the inner cellular layer of the bulbs and around the olfactory ventricles, two types of GABAir perikarya were present: some medium-sized GABAir cells and numerous small GABAir cells (granules). In the walls of the olfactory ventricle, some medium-sized GABAir cells of cerebrospinal fluid-contacting type were observed. At the entrance of the olfactory nerves, medium-sized GABAir bipolar cells were present, mostly located between the olfactory nerve and the glomerular layer or close to the meninges, but some in the intracranial portion of the olfactory nerve. GABAir processes were present in all layers of the olfactory bulb. In addition there were also GABAir cells in the dorsal interbulbar commissure. The distribution of GABA observed in the olfactory system of lampreys indicates that this transmitter plays a major role in the modulation of bulbar circuits. The presence of granular and periglomerular cells in lampreys indicates that these two intrinsic GABAergic neurons of the olfactory bulbs are shared by most vertebrates, although lampreys have additional GABAir cell types.

Three embryonic stages of Atlantic salmon (Salmo salar L.) were subjected to eight constant incubation temperatures (4, 7, 10, 12, 14, 16, 19 and 22 °C) exceeding the range usually experienced in natural conditions. A change in thermal tolerance during the embryonic and larval development was registered: pre-hatching stages showed an upper thermal limit at about 16 °C, while hatched larvae survived until 22 °C. Temperature significantly affects developmental rate, resulting in a faster development and, consequently, lower yolk weight percentage at higher temperatures. We found positive relationships between incubation temperature and body size (length and weight) in the less developed stages, in which some yolk remained, but size decreased at increasing temperatures when yolk was completely exhausted.