SREL Reprint #2574




Genetic structure of six populations of American alligators: a microsatellite analysis

Lisa M. Davis1, Travis C. Glenn1,2, Ruth M. Elsey3, I. Lehr Brisbin Jr.2, Walter E. Rhodes4,
Herbert C. Dessauer5, and Roger H. Sawyer1

1Department of Biological Sciences, University of South Carolina, Columbia, SC 29208 USA
2Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29802 USA
3Louisiana Department of Wildlife and Fisheries, Rockefeller Wildlife Refuge, Grand Chenier, LA 70643 USA
4South Carolina Department of Natural Resources, P.O. Drawer 190, Bonneau, SC 29431 USA
5Department of Biochemistry and Molecular Biology, Louisiana State University Medical Center,
New Orleans, LA 70119 USA

Abstract: The American alligator Alligator mississippiensis was once listed as an endangered species but now thrives in many wetland ecosystems of the southeastern United States. As a result of its present abundance, state and federal wildlife agencies must manage alligator populations in a number of ways including handling nuisance calls, overseeing controlled harvests and regulating trade in meat and hides. To date, few genetic data have been available for consideration when developing management plans for alligator populations. This study uses five microsatellite loci to examine the genetic structure of six populations of American alligators throughout their geographic range. A total of 178 individuals were analysed from 1) southwest Louisiana, 2) Marsh Island, Louisiana, 3) Mobile, Alabama, 4) Savannah River Site, South Carolina, 5) Santee Coastal Reserve, South Carolina, and 6) Everglades National Park, Florida. The amount of genetic variation detected by these microsatellite loci represents the highest found by any study of this species to date. Observed mean heterozygosity across all loci for all populations ranged from 0.52 to 0.76. Measures of genetic distance (delta mu squared, Δμ2) revealed significant population differentiation among all populations and a significant correlation between genetic and geographic distance (P = 0.01). Analyses of molecular variance (AMOVAs) failed to demonstrate higher level sub-structuring of groups of populations although there was a striking degree of among population variation (26.46%). The Savannah River Site population, the only inland population in the study, had unique genetic characteristics relative to coastal populations. Each population had distinct alleles in at least one of the five loci, some of which occurred in relatively high frequency, providing possible location-specific genetic markers. Additionally, assignment tests utilizing a variety of genetic distance measurements allowed assignment of individuals to their correct population of origin 72-83% of the time, though they were assigned to their own population of origin exclusively, only 35-45% of the time.

Keywords: Alligator, Microsatellites, Population genetic structure

SREL Reprint #2574

Davis, L.M., T.C. Glenn, R.M. Elsey, I.L. Brisbin, Jr., W.E. Rhodes, H.C. Dessauer, and R.H. Sawyer. 2000. Genetic structure of six populations of American alligators: a microsatellite analysis. Crocodilian Biology and Evolution:38-50.

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