Meeting Abstract
Little is known about the mechanisms underlying female-female aggression, despite increasing evidence of its adaptiveness in many species. While some male vertebrates socially modulate circulating testosterone (T) levels after aggressive interactions, the same hormonal response has not been found in many female vertebrates, perhaps because selection has favored mechanisms that minimize the potentially high costs of elevated T levels in females. We hypothesize that, rather than changing systemic T levels in response to competitive interactions, females instead modulate local sex steroid sensitivity and conversion, i.e. by upregulating sex steroid receptors and steroid-modifying enzymes in behaviorally relevant tissues like the brain. Here we tested this hypothesis in tree swallows (Tachycineta bicolor), a species in which females compete for limited nesting sites and aggression is at least partially mediated by androgens. We found that females do not rapidly increase, and actually decrease, T levels after both real and simulated social challenges. In light of this result, we further explored whether social challenges induce changes in local steroid processing and binding within the brain. To test this, we exposed females to simulated territorial intrusions and collected neural tissue 2-3 hours later. We used qPCR to measure the expression of genes involved in steroid binding and processing in brain regions thought to mediate aggression, including nodes of the vertebrate social behavior network. These findings will provide novel insight into mechanisms by which individuals can respond to social challenges without increasing T production.
