Advisory Committee Chair
Thane Wibbels
Advisory Committee Members
Larry Boots
Ken Marion
Dave Owens
Bob Thacker
Document Type
Dissertation
Date of Award
2011
Degree Name by School
Doctor of Philosophy (PhD) College of Arts and Sciences
Abstract
Various aspects of TSD were examined in two different sea turtle populations, representing two sea turtle species. Sex ratio was examined in the juvenile portion of the loggerhead sea turtle population in the southeastern U.S. Turtles were captured in the intake channel of the St. Lucie Nuclear Power plant on the central Atlantic coast of Florida. Blood samples were collected from a total of 111 juvenile turtles from May 2005 through April 2007, and the samples were analyzed in a testosterone radioimmunoassay that was validated for use as a sexing technique for sea turtles. The results suggest a significant female-biased sex ratio (2.5F:1.0M). No significant differences were detected between the sex ratios of different size classes of turtles. These data are similar to those of a study from several decades earlier, indicating that a significant female bias may be a relative stable characteristic of the juvenile portion of this sea turtle population. The presence of a female-biased sex ratio has significant implications for the ecology and conservation of the loggerhead turtle in the southeastern U.S. A second study examined nesting beach temperatures throughout the range of loggerheads nesting in the southeastern U.S. This study represented a multi-year project (2004-2009) investigating beach temperatures that were simultaneously recorded at nest depth on a range of nesting beaches used by this population. The study also included the histological evaluation of the sex of a subset of hatchlings that were found dead in nests on several of the beaches. The results indicate that temperatures vary significantly between nesting beaches. The results also indicated that the spectrum of beaches used by the loggerhead population in the southeastern U.S. include a wide variety of thermal profiles, with potential sex ratios ranging from highly female biases to male biases depending on the specific beach. In general, nesting beaches temperatures along the Atlantic coast of Florida (e.g. Melbourne Beach, Juno Beach, Hutchinson Island), where the majority of nesting occurs, were relatively warm suggesting the production of female-biased sex ratios. The histology-based hatchling sex ratio data support the hypothesis that female biases may often be produced on nesting beaches on the Atlantic coast of Florida. In contrast, a few locations (e.g. Cape San Blas on the Florida panhandle) were consistently cooler suggesting the production of a greater proportion of males. However, these locations represented minor nesting beaches compared to those on the Atlantic coast. The results also provide an initial data set for evaluating potential long-term changes in beach temperatures associated with global climate change. A third study investigated temperature-dependent sex determination in the Hawaiian green turtle. The Hawaiian green is a genetically isolated population of greens, and it primary nesting habitat is on French Frigate Shoals (FFS) located in the Northwestern Hawaiian Islands. Beach temperatures at FFS were evaluated relative to their effect on sex ratio. The study also included an experiment for characterizing the effects of specific temperatures on TSD in the Hawaiian green turtle. Beach temperature data and nest temperature data from a period ranging from 2003 - 2009 were evaluated and compared to previously published data from 1996 - 2002. Collectively, the data indicate that temperatures at FFS were relatively cool compared to those reported for other sea turtle nesting beaches. Such temperatures would not be conducive to the production of female-biases which have been reported for several other sea turtle populations. An experiment was conducted to evaluate the effects of relatively low temperatures (similar to those recorded on the nesting beach) on sex determination in the Hawaiian green turtle using eggs from captive-bred green turtles were placed into laboratory incubators. The hatchlings from the three temperatures were subsequently reared in captivity for approximately one year and were sexed by laparoscopy prior to their release. Additionally, the sex of any turtle that died during late development or captive-rearing was determined by histological evaluation of the gonad. The results indicate that the pivotal temperature for the Hawaiian green is not distinctly lower than those reported for other green turtle populations. This finding together with the relatively cool temperatures recorded at FFS, indicate that the overall hatchling sex ratio of Hawaiian greens is not female-biased, rather it is predicted to be unbiased or even male-biased. The purpose of the final chapter of this dissertation was to develop an educational module for high school and college students, which exemplifies how state-of-the-art molecular genetics can be utilized for the conservation of endangered species. This chapter includes the implementation of this teaching module into local area high schools, UAB CORD Summer Science Institute, and into the summer curriculum for marine biology college students at Dauphin Island Sea Lab.
Recommended Citation
Layton, Jennifer Estes, "Biological, Ecological, and Conservational Implications of Temperature-Dependent Sex Determination in Sea Turtle Populations" (2011). All ETDs from UAB. 2234.
https://digitalcommons.library.uab.edu/etd-collection/2234