Meeting Abstract
In many vertebrate species, males respond to competitive interactions by rapidly elevating testosterone (T) levels in circulation. Though there is growing evidence that aggression can also be adaptive for females, and that females can synthesize and respond to T, we still lack a full understanding of how females hormonally respond to social challenges. Tree swallows (Tachycineta bicolor) are an ideal system in which to explore this issue because females compete for limited nesting cavities, and their aggression is at least partly mediated by T. Here, we measured circulating T levels in pre-laying females that were exposed to 30 min simulated territorial intrusions, compared to stage-matched controls. In a separate experiment conducted after initial territory establishment, we experimentally reduced the availability of nesting cavities, allowing us to compare T levels in females experiencing real social instability to those of controls. Results suggest that female tree swallows do not elevate T levels in circulation after behaving aggressively toward real or simulated competitors. This apparent lack of T elevation stands in sharp contrast to prior work showing that females are physiologically capable of elevating T (i.e. to GnRH) during this same breeding stage. Collectively, these results provide new insight into how females do (or do not) respond to social competition, raising new questions as to whether females socially modulate other hormones as an adaptive response to social challenges.
