Olivier Chastel

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The evolution of parasite resistance has often been assumed to be governed by antagonistic selection pressures. Defense against pathogens, by mounting an immune response, confers evident benefits but may also incur costs, so that the optimal level of defense is expected to depend on the balance between benefits and costs. Although the benefits of immune(More)
Secondary sexual traits (SST) are usually thought to have evolved as honest signals of individual quality during mate choice. Honesty of SST is guaranteed by the cost of producing/maintaining them. In males, the expression of many SST is testosterone-dependent. The immunocompetence handicap hypothesis has been proposed as a possible mechanism ensuring(More)
In vertebrates, stressors such as starvation or predator attacks stimulate the rapid elevation of circulating glucocorticoid hormones, triggering physiological and behavioral responses that aid immediate survival but simultaneously inhibit reproduction. This stress response has been proposed to serve as a physiological mediator of life-history trade-offs:(More)
The oxidation handicap hypothesis proposes that testosterone mediates the trade-off between the expression of secondary sexual traits and the fight against free radicals. Coloured traits controlled by testosterone can be produced by carotenoid pigments (yellow-orange-red traits), but carotenoids also help to quench free radicals. Recently, it has been shown(More)
Optimal investment into life-history traits depends on the environmental conditions that organisms are likely to experience during their life. Evolutionary theory tells us that optimal investment in reproduction versus maintenance is likely to shape the pattern of age-associated decline in performance, also known as aging. The currency that is traded(More)
Genes of the major histocompatibility complex (MHC) are the most polymorphic loci known in vertebrates. Two main hypotheses have been put forward to explain the maintenance of MHC diversity: pathogen-mediated selection and MHC-based mate choice. Host-parasite interactions can maintain MHC diversity via frequency-dependent selection, heterozygote advantage,(More)
The stress response is highly variable among individuals, but the causes of this variation remain largely unknown. In response to stressors, vertebrates secrete elevated levels of glucocorticoids which enhance survival, but concurrently interfere with reproduction. We tested the hypothesis that individuals flexibly modulate their stress response with(More)
In vertebrates, the well established increase in plasma corticosterone in response to food shortage is thought to mediate adjustments of foraging behavior and energy allocation to environmental conditions. However, investigating the functional role of corticosterone is often constrained by the difficulty to track time-activity budget of free-ranging(More)
Malaria parasites are a major cause of human mortality in tropical countries and a potential threat for wildlife, as witnessed by the malaria-induced extinction of naive Hawaiian avifauna. Identifying resistance mechanisms is therefore crucial both for human health and wildlife conservation. Patterns of malaria resistance are known to be highly polygenic in(More)
Plasma levels of luteinizing hormone, prolactin, testosterone, and progesterone were measured throughout breeding in masked boobies, red-footed boobies, and red-tailed tropicbirds at Europa and Tromelin Islands (Indian Ocean). LH secretion showed a dampened pattern in the three species, particularly in tropicbirds. Such specific differences may be related(More)