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Abstract
A large increase in glucocorticoid hormones can inhibit or completely shut down breeding
in wild animals. Because of its critical role in reducing glucocorticoids after exposure
to stressors, hypothalamic-pituitary-adrenal (HPA) negative feedback could be an important
mediator of the ecological trade-off between investing limited resources into survival/self
vs. reproduction/offspring. Although assessing negative feedback in a standardized
way using injections of the synthetic glucocorticoid dexamethasone is a straightforward
procedure, we show that several different approaches are used to report negative feedback
in the literature, and then demonstrate that this can in turn affect the statistical
results and conclusions of a study. We then review six specific predictions about
adaptive within- and across-species patterns in glucocorticoids based on the relative
costs and benefits of maintaining or abandoning breeding attempts when animals are
faced with prolonged strong stressors, and examine evidence for these predictions
in the context of HPA negative feedback. Thus far, evidence supporting these predictions
for negative feedback is mixed, with the strongest evidence supporting a link between
poor body condition and weak negative feedback in breeding animals. However, more
research is necessary to assess the importance of changes in HPA negative feedback,
especially in reptile, fish, and amphibian species. Furthermore, future research would
benefit from reporting negative feedback ability in a standardized way, or at least
making raw data available for the computation of alternate measures, to more easily
compare studies in this growing area of research.