Abstract
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.