Meeting Abstract
Bird feathers are one of the most striking examples of variation in nature. Some of the variation in feather ornaments has been shown to act as a signal of the status or quality of an individual. To understand why and how particular ornaments are used as social signals, we must understand the factors that regulate their development. Hormones, such as estrogen and testosterone, have been shown to regulate sex differences in feather color. Here we asked if feathers that form a melanin-based ornament used in attracting mates and signaling status – the white outer tail feathers of Dark-eyed junco (Junco hyemalis) – are sensitive to testosterone and estrogen, and if hormonal signaling explains variation in the extent of white in junco tails. We used qPCR to measure the expression of androgen receptor (AR) and estrogen receptor (ER), and compared receptor abundance among males that showed different amounts of tail white. Furthermore, we asked if hormone receptor expression was correlated with expression of key melanocyte signaling markers agouti signaling peptide (ASIP) and melanocortin 1 receptor (MC1R). Our results show individuals with more tail white express more MC1R and marginally more ASIP. While individual variation in feather color was not directly related to hormonal sensitivity, ASIP expression was significantly positively correlated with both AR and ER expression. Our results show that developing feathers that form social ornaments are sensitive to hormones, and provide a mechanistic hypothesis for the link between the size of the ornament and the status or quality of an individual.
