Date of Award

2017

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

First Advisor

Dr. Cari-Ann Hickerson

Second Advisor

Dr. Carl D. Anthony

Abstract

Differences in cranial morphology among species of plethodontid salamanders have been linked to variations in diet and behavior. Individuals that consume smaller prey have larger jaw to posterior-cranium ratios. Elongation and expansion of the jaw, coupled with expansion of the posterior of the cranium (defined as robustness) are positively associated with individuals that exhibit increased levels of aggression. The bulk of previous research has focused on the effects of interspecific competition on cranial morphology; however, polymorphic populations of the Eastern Red-backed Salamander, Plethodon cinereus, represent a unique opportunity to examine the role of cranial morphology in ecological divergence among individuals of the same species. I tested for differences in cranial morphology between the striped and unstriped morphs of P. cinereus. Previous research suggests that diet and aggression differ between color morphs of this species. At the Summit Co. field site in Northeastern Ohio, the striped morph is more aggressive and maintains consistent access to high-quality territories. These territories contain numerous small-bodied prey items that are commonly consumed by the striped morph. Therefore, I hypothesized that striped salamanders would either exhibit a cranial shape consistent with increased aggression, or a morphology consistent with a diet of small prey items. We examined head shape differences between morphs (n = 1146 specimens) from 9 polymorphic sites using geometric morphometrics. Differences in head shape were significant among localities. At the Summit Co. site (i.e., the PA clade), the cranial morphology of striped morphs was significantly more robust, which is consistent with elevated aggressive and territorial behavior by this morph. 2 Within the OH clade, unstriped individuals from the Ottawa Co. locality showed an increase in the jaw:posterior-cranium ratio. Although not statistically significant, four of five remaining populations mirrored this result. I suggest that differences in head shape in the PA clade result from interference competition for territories, and those differences within the Ohio clade derive from exploitative competition for limited prey resources.

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Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

Available for download on Saturday, August 25, 2018

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