Meeting Abstract
Glucocorticoids (GCs) are central coordinators of metabolic processes and responses to challenges. Because of the diversity of adaptive traits they mediate, it is predicted that individual variation in the regulation of glucocorticoid signaling systems could influence the ability to survive or reproduce. Thus, many studies have investigated the relationship between circulating glucocorticoids and fitness proxies. However, because the downstream effects of GCs depend on the receptors to which they bind, understanding variation in receptor expression may be crucial for understanding hormone-fitness relationships. GCs bind to two primary receptors, the high affinity low capacity mineralocorticoid receptor (MR) and the low affinity high capacity glucocorticoid receptor (GR). We determined if patterns of MR and GR gene expression in the hippocampus, hypothalamus, and pituitary gland predict individual differences in baseline and stress-induced GC levels, and the efficacy of negative feedback in breeding female tree swallows (Tachycineta bicolor). MR gene expression in the hypothalamus was positively correlated with baseline and stress-induced GC levels. Birds with higher GR expression in the hypothalamus and higher MR expression in the pituitary gland were characterized by having both high stress-induced GC levels and strong negative feedback. This GC profile has been previously shown to confer greater stress resilience. These patterns therefore highlight important neuroendocrine mechanisms that may influence the degree to which challenges affect organismal phenotypes.
