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

A propos de la réactivation du virus de l hépatite B

CHATENAY M.-PARIS 11-BU Pharma. (920192101) / SudocSudocFranceF

Élargissement des titres exécutoires par le nouveau régime de la médiation

Rubrique ZoomNational audienc

Régime applicable aux accords auxquels le juge accord force exécutoire

Rubrique ZoomNational audienc

Régime applicable aux accords auxquels le juge accord force exécutoire

Rubrique ZoomNational audienc

Le règlement « Bruxelles I bis » est entré en application le 10 janvier 2015

Rubrique ZoomNational audienc

Le règlement « Bruxelles I bis » est entré en application le 10 janvier 2015

Rubrique ZoomNational audienc

Rapport d'analyse - Projet FORCCAST

L’acronyme FORCCAST signifie: Formation par la cartographie de controverse à l’analyse des sciences et des techniques. Ce rapport fait état des observations, remarques et recommandations qui découlent de la lecture des documents qui ont été mis à disposition des évaluateurs externes par les responsables du projet, mais aussi des échanges qui ont eu lieu avec plusieurs des acteurs de l’équipe FORCCAST au cours de la journée du vendredi 3 juillet 2015. Dans un premier temps, le rapport aborde le projet dans son ensemble puis, dans un deuxième temps et de façon plus spécifique, traite du travail et des développements réalisés par chacun des groupes de travail, en particulier au cours de la dernière année.FORCCAS

Density-dependent immunity and parasitism risk in experimental populations of lizards naturally infested by ixodid ticks

International audienceWhen effective immune defenses against parasites are costly and resources limited, individuals are expected to alter their investment in immunity in response to the risk of infection. As an ecological factor that can affect both food abundance and parasite exposure, host density can play an important role in host immunity and host-parasite interactions. High levels of intraspecific competition for food and social stress at high host density may diminish immune defenses and increase host susceptibility to parasites. At the same time, for contagious and environmentally transmitted parasites, parasite exposure often increases with host density, whereas in mobile parasites that actively search for hosts, parasite exposure can decrease with host density due to the encounter-dilution effect. To unravel these multiple and potentially opposing effects of host density on immunity, we manipulated density of the common lizard Zootoca vivipara and measured local inflammation in response to PHA injection and levels of infestation by the tick Ixodes ricinus, a mobile ectoparasite for which we expected an encounter-dilution effect to occur. Local inflammation strongly decreased with lizard density in adults, but not in yearlings. Tick infestation (abundance and prevalence) was negatively correlated with lizard density in both age classes. Using path analyses, we found independent, direct negative density feedbacks on immunity and parasite exposure in adults, supporting the hypothesis of energy constraints and/or physiological stress acting on immunity at high density. In contrast, for yearlings, the best path model showed that density diluted exposure to parasites, which themselves down-regulated immune defenses in lizards. These results highlight the importance of investigating the pathways among host density, host immunity, and parasite infestation, while accounting for relevant individual traits such as age

StressResponseData_Mugabo-etal2017_oik.03701

This excel file contains one data sheet for each of the 4 experiments presented in the publication and 2 extra data sheets including the data used to estimate the intra-plate and inter-plate repeatabilities of plasma corticosterone measurements