Electronic Theses and Dissertations

Date of Award

1-1-2019

Document Type

Thesis

Degree Name

M.S. in Biological Science

First Advisor

Christopher J. Leary

Second Advisor

Stephen J. Brewer

Third Advisor

William J. Resetarits

School

University of Mississippi

Relational Format

dissertation/thesis

Abstract

Reproductive interference occurs when the mating behaviors of one species negatively impact the fitness of another species. It is of increasing interest in invasive species biology because the introduction of alien species often leads to novel sexual interactions with native taxa, which can contribute to their decline. I examined whether reproductive interference plays a role in the decline of native green treefrogs (Hyla cinerea) following invasions of Cuban treefrogs (Osteopilus septentrionalis) in the southeastern United States. The impetus for this study revolves around similarities in spectro-temporal features of Cuban treefrog courtship calls and green treefrog aggressive calls. The significance of this similarity is that the aggressive calls of green treefrogs stimulate elevations in circulating glucocorticoids in rival conspecific males, which suppresses androgen production and reproductive behavior. I thus hypothesized that introduced Cuban treefrogs negatively impact green treefrogs because the courtship calls of Cuban treefrogs stimulate chronic elevations in circulating glucocorticoid levels that suppress reproduction in native green treefrogs. This hypothesis was tested using vocal playback experiments to examine the effects of Cuban treefrog calls on the endocrine physiology of green treefrogs and by examining hormone levels and calling behavior of green treefrogs in natural choruses with and without Cuban treefrogs. Playback experiments revealed that the aggressive calls of green treefrogs stimulate glucocorticoid production in conspecific males, consistent with previous work, but that Cuban treefrog vocalizations do not stimulate glucocorticoid production in green treefrogs. In natural choruses, the density of calling male green treefrogs and the proportion of non-calling male green treefrogs were positively correlated with circulating glucocorticoids and negatively correlated with androgens, and body size was positively correlated with circulating androgen levels. After statistically controlling for these variables, there was no evidence that circulating hormone levels or behavior differed in choruses of green treefrogs in the presence and absence of Cuban treefrogs. These results suggest that interactions among competing conspecific male green treefrogs influence circulating hormone levels but that Cuban treefrogs are not altering the endocrine physiology of green treefrogs.

Available for download on Tuesday, August 31, 2021

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