Term of Award

Fall 2009

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

David Rostal

Committee Member 1

Lance McBrayer

Committee Member 2

Ann Pratt

Committee Member 3

John Harrison

Committee Member 3 Email



Author's Abstract: The purpose of this study was to examine differences in maternal investment by examining variation in the habitat structure and reproductive parameters for two populations of Gopherus polyphemus in Southeast GA. Both habitat structure and reproductive parameters for these populations are known from a previous study, thus this study expands upon the previous one and addresses four main questions. (1) Has habitat quality changed in the past ten years within and between population sites? (2) Could a change of habitat have affected female morphology or female reproductive parameters within or between populations? (3) Is female body size shaping egg size and/or clutch size for either population? (4) Are females providing equal resources to hatchlings and is hatchling growth potentially being modified by habitat quality affecting adult size and age to sexual maturity? Tortoises were captured by bucket trapping and hand trapping. Radio-graphs were used to obtain information about female body size, clutch size and egg size. In order to assess the effect of habitat quality on tortoises, hatchlings from both locations were reared under controlled, laboratory conditions. The hatchlings were measured bi-weekly to determine differences in growth. Results indicate that habitat quality for these two populations has not changed in the past fourteen years, indicating that this habitat is slow to change. In response to limited change in habitat quality, female body size and reproductive parameters have not changed. Female tortoises from one population produced significantly larger clutch sizes than the other, even when female body size was accounted for; this trend has been observed in many other Testudine species. When hatchling sizes were compared to other populations of G. polyphemus, the hatchling SCL seems consistent while the hatchling mass is variable. Thus, we believe that in Gopherus polyphemus female body size plays a small role in clutch size determination and no role on egg size determination. It is believed that G. polyphemus is minimizing hatchling size (SCL) in order to maximize clutch size and those females with access to more resources can supply more yolk to developing embryos. When hatchlings from both populations were provided with equal resources they grew at similar rates, indicating that the poorer quality habitat at GLS leads to a slower growth rate. Therefore, habitat quality is playing a major role in tortoise growth rates and reproduction. Based on these results, conservation efforts are needed to maintain healthy tortoise populations need to address habitat quality in development of management plans.

Research Data and Supplementary Material