Term of Award

Fall 2008

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (open access)

Copyright Statement / License for Reuse

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


Department of Biology

Committee Chair

Lance D. McBrayer

Committee Member 1

David C. Rostal

Committee Member 2

Bruce A. Schulte


The ability to perform key behaviors associated with reproduction, such as biting and locomotion in male lizards, has been linked to social dominance and reproductive success. The underlying mechanisms that govern variation in performance capacity, however, remain unclear. The steroid hormone testosterone mediates numerous traits associated with reproduction in male vertebrates and has been hypothesized to mediate variation in performance. This study examined seasonal patterns of circulating testosterone, morphology, bite force, and locomotor performance in a non-territorial lizard species to address this hypothesis. Male Aspidoscelis sexlineata (n=133) were collected throughout the active season, and testosterone levels and performance capacities were measured. Performance capacities were greatest during the breeding season when testosterone levels were elevated. The results of this study support the hypothesis that testosterone levels are related to variation in performance and suggest that seasonal changes in testosterone and performance are timed in a way to maximize reproductive success.

Research Data and Supplementary Material