Meeting Abstract
Transitions in avian ornamentation have occurred more frequently in females than in males, and often in the direction of gaining elaborate coloration. Recent studies have begun to uncover the function of female ornaments, yet we know little of the mechanisms that promote their expression and the behaviors that accompany them. Androgens mediate acquisition of male ornamental plumage in several taxa and govern a suite of male-typical behaviors; whether androgens have similar effects in generating elaborate female phenotypes is debated and requires empirical tests. The White-shouldered Fairywren (Malurus alboscapulatus) is sister to a species (Malurus melanocephalus) that expresses androgen-mediated male ornamental plumage. Across populations, female M. alboscapulatus can be cryptically colored or ornamented similarly to males. Ornamented females have higher circulating androgens and are more aggressive to simulated intruders. We address two causal explanations for these correlations: 1) androgens mediate both ornament acquisition and aggression, and 2) ornament expression causes elevated androgens and aggression. We tested these hypotheses by supplementing androgens to unornamented females, causing half of these females to molt in one major component of the ornamental plumage. Androgen-implanted females did not increase aggression during simulated territorial intrusions, but females who acquire ornaments express more pair-coordinated aggressive behaviors. These results suggest that androgens are partially responsible for production of ornamental plumage, and ornament expression itself may be more important for enhancing aggression.
