The Role of the Amygdala in Nonbreeding Aggression in Male Green Anole Lizards, Anolis carolinensis

Aggression is a set of hostile behaviors expressed to defend and/or obtain resources. Although a social behavior network (SBN) has been postulated to explain the neural mechanisms underlying aggression, the extent of behavioral modulation by specific brain regions remains unclear. Additionally, the regulation of the SBN during the nonbreeding season (NBS) in seasonal breeders that express territorial aggression is still unknown. Thus, we aimed to study the role of one node of the SBN, the amygdala, in green anole lizards as this species displays dynamic changes in aggression, reduced testosterone levels, and increased number of neurons in the amygdala during the NBS compared to the breeding season. Male lizards were placed in a stereotactic apparatus and injected with either a neurotoxin (staurosporine) to damage the amygdala or saline as a control. These focal male lizards were also exposed to size-matched conspecifics before and 3 days after surgery to quantify aggressive behaviors. We found that partly damaging the amygdala significantly reduced aggression levels but did not affect their latency to initiate aggressive behaviors, providing support for the idea that the amygdala mediates aggression but not motivation in this species. Additionally, there was no relationship between aggression and plasma testosterone levels, suggesting that the nonbreeding aggression we measured was independent of plasma testosterone levels. These results indicate that the amygdala might play a significant role in the SBN to regulate NBS aggression and is not dependent on plasma testosterone levels.