SREL Reprint #2574

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

LISA M. DAVIS, TRAVIS C. GLENN, RUTH M. ELSEY, I. LEHR BRISBIN JR, WALTER E. RHODES, HERBERT C. DESSAUER and ROGER H. SAWYER

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..I'he 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, Ap2) 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.

Key words: 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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