Meeting Abstract

P1.225  Friday, Jan. 4  Testosterone production in response to aggression: physiological or behavioral constraint? AMBARDAR, M.*; GRINDSTAFF, J.L.; Oklahoma State University; Oklahoma State University medhavi@okstate.edu

In many animals, the hormone testosterone (T) generally promotes territorial aggression while reducing parental care. This is not always the case, however, and in those circumstances, the physiological mechanisms that mediate these relationships are poorly understood. In male birds, for example, the response of T production following a territorial challenge is variable; some species increase T production while others do not. In species that do not elevate T in response to a social challenge, T levels may already be circulating at maximum levels. Thus, a physiological constraint may be responsible for this discrepancy. Alternatively, males that provide extensive care to young may incur a cost of elevating T because of the suppressive effects of that hormone on parental care. We used a wild population of Eastern bluebirds (Sialia sialis) to examine the response of T production following a simulated territorial intrusion (STI), and how this relates to parental care. We quantified parental care by videotaping feeding behavior by adult bluebirds when nestlings were 5-7 days old. To quantify aggression, we performed STIs using a common nest site competitor, the house sparrow (Passer domesticus) when nestlings were 7-9 days old. Following parental care and STI trials, we collected a blood sample to determine circulating levels of T. We then performed gonadotropin releasing hormone (GnRH) challenges to test the capability of bluebirds to further increase T levels. The results of this study will provide insight into T production in response to social interactions, and how this relates to the trade-off between aggressive behavior and parental care.