Date of Award
M.S. in Biological Science
Christopher J. Leary
This thesis examines how the endocrine stress response mediates the expression of courtship signals and alternative mating tactics in male green treefrogs, Hyla cinerea. Males of this species produce acoustic signals that stimulate production of the stress hormone corticosterone (CORT) in vocal competitors, suggesting a role of CORT in intrasexual competition. I predicted that modulation of CORT level during intraspecific contests plays a pivotal role in regulating the expression of male courtship signals and behavior. Consistent with this prediction, CORT administration to calling males, simulating CORT production during male vocal contests, decreased attractiveness by compromising energetic investment in vocalization, increasing aggression, and increasing the probability that a male adopts an alternative non-calling ‘satellite’ mating tactic. These results suggest that acoustic stimulation of CORT production functions in an armament capacity by compromising the reproductive success of rival males. Secondly, I examined the extent to which CORT and androgen levels, vocal attractiveness, body size, condition, and plasma glucose levels predicted the adoption of satellite behavior in calling males exposed to broadcast advertisement calls (simulating a challenge by another male). Males that adopted satellite behavior in response to broadcast advertisement calls were vocally less attractive, smaller, and in poorer body condition than males that called, but males did not differ in CORT or androgen levels. Lastly, I examined the role of CORT and androgens in male mating behavior by performing a satellite-host manipulation experiment in which I removed the calling host male from the satellite-caller association and observed whether satellite males began to call or continued to exhibit non-calling behavior. Results indicated that satellites were smaller and in poorer body condition and possessed higher CORT and lower androgen levels relative to host males. Moreover, satellites that did not call subsequent to removal of the calling host male had lower androgen levels relative to host males and satellite males that began to call. Together, my results indicate that circulating CORT level is a target of intra- and intersexual selection and that variation in CORT and androgens levels among males in natural choruses can be a cause or consequence of mating tactic expression.
Crocker-Buta, Sarah, "Stress, sexual signaling, and alternative mating tactics in male green treefrogs, Hyla cinerea" (2016). Electronic Theses and Dissertations. 1273.