Meeting Abstract
According to the honest signaling hypothesis, signal reliability depends on cost such that only high quality individuals can afford to signal. To assess cost, the mechanisms that link ornaments and individual quality must be understood. Bird feathers are one of the most striking examples of variation in nature. Importantly, some of the variation in ornaments have been shown to act as signals of the quality of an individual and enhance fitness by increasing the probability of attracting a mate. In some instances feather size and color are mediated by the steroid hormones testosterone and corticosterone, which can bind directly to feather follicles and have been associated with immune competence. We examined whether the size of a specific melanin-based feather ornament used in attracting mates and signaling status – the white outer tail feathers of Dark-eyed junco (Junco hyemalis) – is mediated by hormonal signaling. In particular, we investigated the abundance of androgen receptor (AR) and estrogen receptor (ER) in feathers, and compared receptor abundance among males of varied ornament size and between different feathers from the same individual. We hypothesized that white tail feathers would be more sensitive to hormonal regulation than white-black or black tail feathers. Preliminary results indicate that dark inner tail feathers have higher expression of AR than white outer feathers. However, feathers show a negative relationship between AR expression and percent-dark area. We found no significant relationship between ER expression and feather color. Future directions for study include investigating the location of AR in the developing feather tissue to further elucidate the role of testosterone in mediating ornament size.
