Bidirectionality of hormone-behavior relationships and satellite-caller dynamics in green treefrogs

Whether hormonal differences among males that conditionally alternate between mating tactics are a cause or consequence of behavioral expression is central to understanding the mechanisms regulating alternative mating tactics. This issue is rooted in the bidirectionality of hormone-behavior relationships and is particularly relevant to alternative mating tactics in anuran amphibians because the social-acoustic environment can mediate changes in both tactic expression and hormone levels. Hence, it is not clear whether males adopt different mating tactics in response to rival male signals, changes in hormone levels, or both. Here, we address this problem in male green treefrogs, Hyla cinerea, using vocal playback experiments combined with measures of circulating hormone levels, vocal attractiveness, body size, body condition, and plasma glucose levels. Calling males in natural choruses that adopted non-calling satellite behavior in response to broadcast advertisement calls produced less attractive calls, were smaller and in poorer body condition than males that continued to call, but did not differ in circulating levels of the stress hormone corticosterone (CORT), androgens, or glucose. These results were unexpected because satellite males in natural choruses possess higher CORT levels and lower androgen levels than calling males and CORT administration increases the probability of satellite tactic expression in this species. Our results suggest that there may be no clear cause versus consequence dichotomy associated with hormonal disparities among males practicing different mating tactics because multiple intrinsic and extrinsic factors can influence tactic expression.