Meeting Abstract
Seasonally breeding animals commonly display peak aggression early in the breeding season during periods of social instability, with declining aggression during later parental stages. Decades of research suggest that seasonal changes in systemic testosterone (T) levels may influence this behavioral pattern in males, but it is unclear if similar mechanisms apply to females. Tree swallows (Tachycineta bicolor) are an emerging model organism for understanding female aggression because females fiercely compete for limited nesting cavities. Aggression in these females is partly mediated by T, and T levels decline sharply in later breeding stages (i.e., during incubation), when elevated T can reduce maternal care. Nevertheless, females retain the ability for robust aggression during incubation, suggesting a seasonal shift in the mechanisms regulating aggression. Here, we begin to address this issue using RNA-seq to explore seasonal patterns of gene expression in the female brain. We found hundreds of genes that were differentially expressed between territory establishment and incubation in the medial amygdala and hypothalamus. During territory establishment, we found greater expression of steroid-related genes, such as 5alpha-reductase, which converts T to the potent androgen dihydrotestosterone, whereas incubating females had greater expression of genes involved in nonapeptide-related signaling. These findings are consistent with a seasonal shift in mechanisms of aggression, a view that is further supported by gene network analyses. Collectively, these data highlight important gene regulatory mechanisms that may underlie behavioral plasticity in females, while also accommodating their maternal roles.
