The size of a melanin-based plumage ornament correlates with glucocorticoid receptor concentrations in the skin of that ornament

Glucocorticoid hormones such as corticosterone (CORT) play crucial roles in many physiological processes. CORT's actions are primarily mediated via binding to two receptors (glucocorticoid receptors (GR) and mineralocorticoid receptors (MR)) in different target tissues. CORT receptors can be independently regulated from circulating hormone titers, from tissue to tissue and even within different regions of the same tissue type. Increasing evidence has shown relationships between circulating CORT and melanin-based pigmentation in skin and feathers, yet to our knowledge there have been no studies of CORT receptors in the skin of melanized ornaments. Male house sparrows (Passer domesticus) have a black, melanized bib, and evidence suggests that bib size is an important intraspecific signal. We examined the relationship between bib area and tissue sensitivity to CORT by quantifying GR and MR in bib skin and in adjacent paler-feathered belly skin (as a control tissue) at different life histor...