K.J. MacLeod, M.J. Sheriff, D.C. Ensminger, D.A.S. Owen, T. Langkilde

Organisms are continuously encountering both predictable and unpredictable ecological stressors within their environment. The activation of the hypothalamic-pituitary-adrenal (stress) axis is a fundamental process allowing animals to cope with and respond to such encounters. A main consequence of HPA axis activation is the release of glucocorticoid hormones. Although short-term glucocorticoid elevations lead to changes in physiological and behavioral processes that are often adaptive, our understanding of fitness consequences of repeated acute elevations in glucocorticoid hormones over a longer time period is largely lacking. This is of particular current importance as animals are facing a significant increase in exposure to stressors including those associated with human-induced rapid environmental change. Here, we test fitness-relevant consequences of repeated exposure to glucocorticoids in the absence of natural challenges, by treating wild-caught gravid female eastern fence lizards (Sceloporus undulatus) with a daily transdermal dose of a glucocorticoid hormone until laying. This treatment causes an increase in plasma glucocorticoids that mimics the natural response lizards have when they encounter a stressor in the wild, without confounding effects associated with the encounter itself. This treatment reduced females' reproductive success (hatching success) and survival. Further, glucocorticoid-induced reductions in reproductive success were greater when females had experienced higher temperatures the previous winter. This demonstrates the potential significant consequences of repeated exposure to acute elevations in glucocorticoid hormones. Additionally, the costs of repeated glucocorticoid elevation may be further exaggerated by an individual's previous experience, such as the potential compounding effects of winter warming increasing animals' vulnerability to increased glucocorticoid levels during spring breeding.