Date of Award
M.S. in Biological Science
Christopher J. Leary
Lainy B. Day
Ecological stressors (i.e., high predator density, low food availability) are often associated with increased variation in mate choice by females. The association between environmental stressors and variation in mate choice suggests that circulating stress hormones (i.e., glucocorticoids) may mediate such effects, but this idea remains largely unexplored. I examined how circulating glucocorticoids affect preferences for male advertisement calls in female green treefrogs, Hyla cinerea, and barking treefrogs, Hyla gratiosa. Specifically, I examined whether administration of corticosterone (CORT) decreases preferences for call rate and/or call duration - two acoustic features that are highly variable and characteristically under directional selection via mate choice by females. In H. cinerea, the probability of choosing male advertisement calls broadcast at high rates in dual speaker phonotaxis trials decreased as CORT dose and circulating CORT level increased. Neither CORT dose nor level was related to the latency of female phonotactic responses suggesting that elevated CORT does not increase the motivation to mate. Variation in acoustic preferences was not attributable to variation in circulating progesterone, estradiol, or androgen levels indicating that elevated CORT diminishes directional selection on call rate independently of changes in circulating sex steroids. Results thus suggest that CORT production, which is known to be modulated by various intrinsic and extrinsic factors, can decrease the variance in male mating success and, thus, the strength of directional selection on call rate in this species. The effects of CORT on preferences for calls in H. gratiosa were not as clear. In this species, variation in preferences for call rate was not related to circulating levels of CORT or sex steroids. Moreover neither treatment nor hormone level were related to the latency of female phonotactic responses. Results thus suggest that CORT level does not affect directional selection on call rate or the motivation to mate in this species. I also examined the effects of CORT administration on preferences for call duration in this species. While CORT administration decreased the probability that females chose calls of longer duration in phonotaxis trials, it was not clear whether these effects were related to elevated CORT or elevated sex steroid levels.
Davis, Anna Gabriell, "The effects of stress hormones on preferences for acoustic signals in female green treefrogs (Hyla cinerea) and barking treefrogs (Hyla gratiosa)" (2014). Electronic Theses and Dissertations. 1283.