Sex-specific density-dependent secretion of glucocorticoids in lizards: insights from laboratory and field experiments

Negative density feedbacks have been extensively described in animal species and involve both consumptive (i.e. trophic interactions) and non-consumptive (i.e. social interactions) mechanisms. Glucocorticoids are a major component of the physiological stress response and homeostasis, and therefore make a good candidate for proximate determinants of negative density feedbacks. Here, we combined laboratory and field experiments with enclosed populations to investigate the relationship between density, social stress and plasma corticosterone levels in the common lizard Zootoca vivipara. This species exhibits strong negative density feedbacks that affect females more than males, and its life history is sensitive to experimentally-induced chronic elevation of corticosterone plasma levels. We found that prolonged crowding in the laboratory can trigger a chronic secretion of corticosterone independent from food restriction. In the field experiments, corticosterone levels of females were not affected by population density. Corticosterone levels of males increased with population density but only during the late activity season in a first field experiment where we manipulated density. They also increased with density during the mating season but only in populations with a female-biased sex ratio in a second field experiment where we crossed manipulated density and adult sex ratio. Altogether, our results provide limited evidence for a role of basal corticosterone secretion in density feedbacks in this species. Context and density-dependent effects in males may arise from changes in behavior caused by competition for resources, male–male competition, and mating

Cloacal Bacterial Diversity Increases with Multiple Mates: Evidence of Sexual Transmission in Female Common Lizards

Sexually transmitted diseases have often been suggested as a potential cost of multiple mating and as playing a major role in the evolution of mating systems. Yet there is little empirical data relating mating strategies to sexually transmitted microorganisms in wild populations. We investigated whether mating behaviour influences the diversity and composition of cloacal assemblages by comparing bacterial communities in the cloaca of monandrous and polyandrous female common lizards Zootoca vivipara sampled after the mating period. We found that polyandrous females harboured more diverse communities and differed more in community composition than did monandrous females. Furthermore, cloacal diversity and variability were found to decrease with age in polyandrous females. Our results suggest that the higher bacterial diversity found in polyandrous females is due to the sexual transmission of bacteria by multiple mates. The impact of mating behaviour on the cloacal microbiota may have fitness consequences for females and may comprise a selective pressure shaping the evolution of mating systems

Carotenoid-Based Colours Reflect the Stress Response in the Common Lizard

Under chronic stress, carotenoid-based colouration has often been shown to fade. However, the ecological and physiological mechanisms that govern colouration still remain largely unknown. Colour changes may be directly induced by the stressor (for example through reduced carotenoid intake) or due to the activation of the physiological stress response (PSR, e.g. due to increased blood corticosterone concentrations). Here, we tested whether blood corticosterone concentration affected carotenoid-based colouration, and whether a trade-off between colouration and PSR existed. Using the common lizard (Lacerta vivipara), we correlatively and experimentally showed that elevated blood corticosterone levels are associated with increased redness of the lizard's belly. In this study, the effects of corticosterone did not depend on carotenoid ingestion, indicating the absence of a trade-off between colouration and PSR for carotenoids. While carotenoid ingestion increased blood carotenoid concentration, colouration was not modified. This suggests that carotenoid-based colouration of common lizards is not severely limited by dietary carotenoid intake. Together with earlier studies, these findings suggest that the common lizard's carotenoid-based colouration may be a composite trait, consisting of fixed (e.g. genetic) and environmentally elements, the latter reflecting the lizard's PSR

Plasticité phénotypique, corticostérone et traits d'histoire de vie chez le lézard vivipare (Lacerta vivipara)

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Etude expérimentale et intégrative des coûts et bénéfices de la viviparité chez le lézard vivipare

Ce travail s intéresse à l évolution de la viviparité, mode de reproduction qui consiste à mettre au monde directement des jeunes vivants, et de l oviparité, mode de reproduction qui consiste à pondre des œufs. J ai utilisé le lézard vivipare comme espèce modèle car c est une des rares espèces au sein de laquelle on observe des femelles vivipares et ovipares. Mon étude repose sur des approches expérimentales, comparatives et corrélatives pour étudier les coûts et bénéfices de la viviparité. Tout d abord, j ai montré que l investissement dans la reproduction est contraint par la condition passée de la femelle et les conditions environnementales présentes. Cependant, le mode de reproduction vivipare ne semble pas permettre des ajustements post-ovulatoires (pendant la gestation) de cet investissement reproducteur. Selon le contexte, la gestation est associée à certains coûts, ayant des effets sur le système immunitaire, sur le comportement de thermorégulation, sur l endurance, et sur la perte de poids des femelles ; mais la gestation n a pas d effet sur la survie après la mise bas. Par ailleurs, la viviparité a aussi certains avantages. Par exemple, une comparaison intra-spécifique a montré que les coûts de la reproduction sont plus importants pour les femelles ovipares que les vivipares avant la gestation. Finalement, il existe aussi des effets maternels pendant la gestation. Afin de mettre en évidence les facteurs à l origine de ces effets maternels, j ai développé une approche expérimentale qui repose sur l incubation in vitro d embryons de lézards vivipares. Les résultats préliminaires sont prometteurs étant donné que ce processus permet d obtenir des jeunes vivants.PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Physiological actions of corticosterone and its modulation by an immune challenge in reptiles

International audienceHormones are an important interface between genome and environment, because of their ability to modulate the animal's phenotype. In particular, corticosterone, the stress hormone in lizards, is known to reallocate energy from non-essential functions to affect morphological, physiological and behavioral traits that help the organism to deal with acute or chronic stressors. However, the effects of corticosterone on life history stages are still unclear primarily because of the dependence of life history stages on both internal and external factors. Using a cross-design, we tested the effect of elevated levels of exogenous corticosterone on the physiology of pregnant females in different immune contexts in a wild population of common lizards (Lacerta vivipara). Immune challenge was induced by the injection of sheep red blood cells (SRBC) and corticosterone levels were increased using a transdermal administration of corticosterone. Thereafter, reproductive traits, metabolism and cellular immune responses were measured. The elevation of corticosterone in pregnant females significantly altered reproductive and physiological performance. The corticosterone treatment decreased clutch success, juvenile size and body condition, but enhanced measures of physiological performance, such as metabolism and catalase activity. These first results reinforce the understanding of the physiological actions of corticosterone in reptiles. The data also demonstrated different direct impacts of immune challenge by SRBC on inflammatory response and antioxidant activity. The injection of SRBC stimulated the SOD activity in larger females. Finally, we demonstrated experimentally the modulation of the corticosterone action by the immune challenge on stamina and hatching date. Copyright @ 2010 Elsevier Inc. All rights reserved

Dispersal status-dependent response to the social environment in the common lizard, Lacerta vivipara.

Peer reviewe

Grandmaternal age at reproduction affects grandoffspring body condition, reproduction and survival in a wild population of lizards

International audienceAge at reproduction can influence the survival and future reproduction of an individual as well as that of their offspring. Remarkably, it has been shown that grandmaternal age at reproduction can also affect the characteristics of grandoffspring in humans and in laboratory or semi-captive animals. However, currently we do not know whether grandmaternal age effects exist in wild populations.We gathered data on female age at reproduction, offspring and grandoffspring characteristics using a 16-year long-term survey of a natural population of the common lizard, Zootoca vivipara. The dataset contains 579 grandoffspring from 135 litters.Body size at birth was not correlated with grandmaternal age at reproduction. However, grandoffspring body condition at birth, grandoffspring survival and reproductive performance of granddaughters were dependent on grandmaternal age. These relationships were independent of maternal age.An age-structured model showed that the global effect of grandmaternal age was non linear and was largely driven by its effect on grandoffspring survival. Fitness was higher for granddaughters produced by grandmothers of intermediate ages.The study shows that age can shape life-history traits for more than one generation, documenting the importance that grandmaternal age can have in wild populations