Meeting Abstract
In vertebrates, the androgen testosterone (T) regulates a variety of signals used to communicate, but our understanding of the relative importance of circulating T versus receptor sensitivity in predicting signal expression remains limited. This limitation is particularly relevant for females, however, considering that high T levels can be costly. Previous studies have shown that T-implanted females in dichromatic species may develop a partial, male-like plumage, stressing that while circulating T is important, in isolation, circulating T alone is not sufficient to explain patterns of phenotypic differentiation between sexes. Here, we explore the proximate mechanisms of female ornamentation in white-shouldered fairywren (Malurus alboscapulatus), a tropical passerine that varies in female, but not male, ornamentation among populations. In a population where both males and females exhibit black eumelanin feathers and white scapular patches (defined here as ‘ornamented’), we implanted both sexes with the potent antiandrogen bicalutamide, a drug that blocks androgen receptors. We found that the white scapular patch of females implanted with bicalutamide regrew feathers tipped in melanin pigments, but not in males. However, most of the ornament regrew normally, suggesting a role of T in regulating partial ornament expression. These results suggest that patterns of phenotypic divergence in ornamentation between sexes and among populations is a complex interaction between circulating T, androgen receptor sensitivity, and the resulting gene expression which warrants further exploration.
