Graduation Year

2003

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Biology

Major Professor

Karl, Stephen A.

Keywords

Biogeography, Conservation genetics, Population genetics, Simple-sequence repeats, Turtle

Abstract

Gopher tortoise (Gopherus polyphemus) population sizes have drastically declined in the past 100 years. Much of this decline has been attributed to past human predation, to habitat loss from human development, and potentially to the recently discovered upper respiratory tract disease. An understanding of the genetic structure among populations is critical for the long-term success of relocation and other management strategies. This research focuses on the development of a suite of genetic markers and the answers they provided to questions concerning present day population genetics and its use in management. In addition, this study provides inference on historical refugia and dispersal patterns of the gopher tortoise through the Pleistocene. Nine microsatellite loci were identified, optimized, and characterized from a G. polyphemus microsatellite-enriched DNA library.

These loci are applicable for population level analysis along with parentage analysis in all Gopherus species. In addition, a few of the loci also work in other Testudinies. Application of these markers to eighteen Florida and two Georgia populations of gopher tortoises reveal considerable amount of genetic diversity within the species and substantial genetic subdivision among populations, especially in the northern part of the Florida peninsula and southern Georgia. Admixture and genetic homogenization in central Florida may be attributed to past human mitigation events as much of this area has been substantially developed. These data indicate a more conservative approach to relocation is necessary if the goal is to maintain the genetic distinctiveness of these areas. Lastly, these genetic data, in conjunction with historical geological, climactic, and fossil records, were used to identify gopher tortoise refugia, and dispersal patterns during the Pleistocene.

Within Florida, four major genetic assemblages were determined that correspond to four Pleistocene ridges that would have been present at high sea levels: Lake Wales Ridge, Brooksville Ridge, Southern Atlantic Coastal Ridge, and Mt. Dora Ridge. In addition, these data indicate that tortoises that dispersed into southeastern Florida after the fall in sea level were most closely related to tortoises from the Brooksville Ridge. Likewise, tortoises in northwestern Florida and southern Georgia were most closely related to tortoises from the Mt. Dora Ridge.

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