Meeting Abstract
Expression of melanin-based coloration is associated with a number of plastic physiological and behavioral traits including concentrations of sex and stress hormones, immune responses, and territorial aggression. One potential mechanism that could produce these relationships is condition-dependent signaling in which case individuals with larger or darker ornaments should be in better condition during molt or better able to bear the cost of displaying the ornament. Recently, it has been suggested that these associations could arise due to pleiotropic effects associated with melanin synthesis. We examined these relationships in male song sparrows, which possess melanin-based spotting on their breast. Specifically, we quantified (1) the size and reflectance of the spotting, (2) baseline and gonadotropin releasing hormone (GnRH) induced concentrations of testosterone (T), (3) baseline corticosterone (CORT) concentrations, (4) territorial aggression in response to playback, and (5) bacteria killing ability (BKA) as a measure of innate immunity and (6) male condition during molt using growth bars. We found that GnRH induced T concentrations were positively associated with male badge size. Additionally, males with lighter badges displayed more aggressive behavior toward the playback than males with darker badges. Neither BKA nor the rate of feather growth during molt were related to badge size or color and the latter result suggests that condition during molt does not affect the expression of this ornament. These results indicate that pleiotropic effects associated with melanin synthesis could underlie for some aspects of male phenotype in song sparrows.
