ZYSLING, D.A.; GREIVES, T.J.; DEMAS, G.E.; KETTERSON, E.D.; Indiana University; Indiana University; Indiana University; Indiana University: Effects of Testosterone on Female Aggression and Immune Function: Possible Evidence of Intersexual Conflict in Dark-Eyed Juncos (Junco hyemalis)

Intersexual conflict occurs when a trait that is beneficial to one sex is costly to the other. Conflict can be resolved through the evolution of sex-limited expression, and, in vertebrates, testosterone (T) often mediates traits in males that may fail to be expressed in females or be expressed to a lesser degree. Surprisingly little is known, however, about the role of testosterone in female vertebrates, and whether effects of T in females might constrain the evolution of T-mediated traits in males. We sought to evaluate the potential for intersexual conflict by examining the impact of experimental elevation of T on the behavior and physiology of female dark-eyed juncos. Using a wild-caught captive population, we implanted birds with silastic capsules that were either empty (C-females) or filled with testosterone (T-females). Birds were housed individually in an outdoor aviary and were injected with the antigen SRBC, bled, and observed. Using a standard resident-intruder model, we placed a novel female intruder into the compartment of an experimental female and observed behavior. We then quantified the frequency of kews (aggressive vocalizations), approaches (chases and active displacements), and flutter-ups performed by the experimental female. We found that T-females displayed significantly more kews and approaches as compared to C-females and tended towards more flutter-ups. Our results suggest that, similarly to males, females display increased aggression when treated with T. We are currently examining the effects of T on humoral immune function and corticosterone release, and these results will be discussed.