Meeting Abstract
Glucocorticoid hormones, often called “stress hormones,” mediate rapid physiological and behavioral changes that enable individuals to cope with the challenges of a fluctuating environment. Because glucocorticoids mediate the phenotypic response to immediate challenges, individual variation in the magnitude of the acute glucocorticoid stress response is often predicted to be positively associated with fitness. In contrast, individuals with higher baseline glucocorticoid concentrations are often assumed to be experiencing chronic stressors or to be less able to cope with challenges, and thus have reduced health or fitness prospects. However, these basic predictions neglect other important roles of glucocorticoids that may generate opposing hormone-fitness patterns. For example, elevations in baseline glucocorticoids are increasingly recognized to support energy acquisition during energetically demanding periods, and mounting a strong stress response may be particularly costly during some life history stages. Previous studies and reviews have found variable results; the presence and direction of glucocorticoid-fitness relationships often differ across species, sexes, and life history stages, but few clear patterns have emerged. Here, we present the first phylogenetic meta-analysis testing the relationship between glucocorticoids (baseline and stress-induced) and components of fitness (survival and reproductive success) across vertebrates. We compare this relationship across life history stages and between the sexes, separately addressing findings in observational studies and experimental hormone manipulations, and from plasma and fecal metabolites. This analysis could provide insight into the factors that influence hormonal regulation across vertebrates.
