Microsatellite DNA Analyses Support an East-West Phylogeographic Split of American Alligator Populations

SREL Reprint #2634 Microsatellite DNA Analyses Support an East-West Phylogeographic Split of American Alligator Populations LISA M. DAVIS,^1,2 TRAVIS C. GLENN^1,2 DENISE C. STRICKLAND,¹ LOUIS J. GUILLETTE, JR.,³RUTH M. ELSEY,⁴ WALTER E. RHODES,⁵ HERBERT C. DESSAUER,⁶ AND ROGER H. SAWYER¹ ¹Department of Biological Sciences, University of South Carolina, Columbia, South Carolina 29208 ²Savannah River Ecology Laborator-y, University of Georgia, Aiken, South Carolina 29802 ³Department of Zoology, University of Florida, Gainesville, Florida 32611 ⁴Louisiana Department of Wildlife and Fisheries, Rockefeller Wildlife Refuge, Grand Chenier, Louisiana 70643 ⁵South Carolina Department of Natural Resources, Dennis Wildlife Research Center, Bonneau, South Carolina 29431 ⁶Department of Biochemistry and Molecular Biology, Louisiana State University Medical Center, New Orleans, Louisiana 70119 ABSTRACT: We examined the population genetic structure of American alligators (Alligator mississippiensis) sampled from 12 localities across the southeastern United States. The primary goal of this study was to determine the extent of population differentiation among alligators from four Florida lakes using eight microsatellite loci and compare the results to additional sites located at varying distances from them. Analyses of population structure revealed little differentiation (F_ST=0.039; Rho=0.012) among the four Florida lakes, Apopka, Griffin, Orange and Woodruff, which are all located in the St. John's River watershed in north-central Florida. Further, there was little differentiation among these samples and samples collected from the Everglades National Park (F_ST=0.044; Rho=0.009) and south Georgia (F_ST=0.045; Rho=0.032). Therefore, these six samples were pooled together as a "FL/sGA group." Similarly, samples collected in the western extent of the range, Anahuac National Wildlife Refuge in Texas and Salvador Wildlife Management Area, Marsh Island Wildlife Refuge and Rockefeller Wildlife Refuge in Louisiana, also lacked population structure (F_ST=0.024; R_ST=0.040). These four populations were pooled into the "TX/LA group." Comparisons of these two groups with samples taken from the Santee Coastal Reserve in South Carolina and Mobile, Alabama yielded three to four times more differentiation amfong groups (F_ST=0.131; Rho=0.187). These and other analyses support the hypothesis of an east-west phylogeographic split in American alligator populations and are consistent with studies of many freshwater fish and aquatic and terrestrial turtles distributed throughout this same geographic region. SREL Reprint #2634 Davis, L. M., T. C. Glenn, D. C. Strickland, L. J. Guillette, Jr., R. M. Elsey, W. E. Rhodes, H. C. Dessauer and R. H. Sawyer. 2002. Microsatellite DNA analyses support an East-West phylogeographic split of American alligator populations. Journal of Experimental Zoology/Molecular Development & Evolution 294:352-372. To request a reprint