Genetic Relationships of American Alligator Populations Distributed Across Different Ecological and Geographic Scales WADE A. RYBERG, 1 n LEE A. FITZGERALD, 1 RODNEY L. HONEYCUTT, 1 and JAMES C. CATHEY 2 1 The Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, Texas 77843-2258 2 Texas Parks and Wildlife Department, Gus Engeling Wildlife Management Area, Tennessee Colony, Texas 75861 ABSTRACT Although much work has been conducted on coastal populations of the American alligator (Alligator mississippiensis), less is known about the population dynamics and genetic structure of populations of alligators confined to inland habitats. DNA microsatellite loci, derived from the American alligator, were used to investigate patterns of genetic variation within and between populations of alligators distributed at coastal and inland localities in Texas. These data were used to evaluate the genetic discreteness of different alligator stocks relative to their basic ecology at these sites. Observed mean heterozygosities across seven loci for both coastal and inland populations ranged from 0.50–0.61, with both inland and coastal populations revealing similar patterns of variation. Measures of F st revealed significant population differentiation among all populations; however, analyses of molecular variance (AMOVAs) failed to demonstrate any apparent geographic pattern relative to the population differentiation indicated by F st values. Each population contained unique alleles for at least one locus. Additionally, assignment tests based on the distribution of genotypes placed 76% of individuals to their source population. These genetic data suggest considerable subdivision among alligator populations, possibly influenced by demographic and life history differences as well as barriers to dispersal. These results have clear implications for management. Rather than managing alligators in Texas as a single panmictic population, translocation programs and harvest quotas should consider the ecological and genetic distinctiveness of local alligator populations. J. Exp. Zool. (Mol. Dev. Evol.) 294:325–333, 2002. r 2002, Wiley-Liss, Inc. Although a steady decline in populations of the American alligator was noted by naturalists as early as the 1900s, the species did not receive national attention until the late 1960s after huge population declines in response to years of excessive hunting pressure. Coupled with extreme hunting pressure, systematic exploration of oil and gas resources in the southeastern United States created a network of waterways that left remote alligator populations vulnerable to exploitation by man (McIlhenny, ’35; Joanen and McNease, ’87). The state of Louisiana was the first to pass legislation protecting the American alligator by establishing controls on seasonal harvests, and subsequent to this legislation, federal protection was added (Joanen and McNease, ’87). Today, the American alligator is the most well studied crocodilian, and its successful recovery and man- agement are the result of basic research on alligator populations. Most research programs on the American alligator have focused on coastal populations (Thompson and Gidden, ’72; Gartside et al., ’77; Adams et al., ’80; Taylor and Neal, ’84; Joanen and McNease, ’87; Taylor et al., ’91; Glenn et al., ’98). Considerably less information is available for alligators restricted to inland habi- tats. Coastal and inland habitats used by alligators are extremely different. Coastal habitats are more homogeneous, characterized by swamps, slow moving water, and marshy areas that tend to support relatively dense populations of alligators (Ross, ’89). In contrast, inland habitats are more heterogeneous, composed of streams and creeks interspersed with ponds and lakes where water n Correspondence to: Wade Ryberg, The Department of Wildlife and Fisheries Sciences, Texas A&M University, 2258 TAMU, 210 Nagle Hall, College Station, Texas 77843-2258. E-mail: wryberg@neo.tamu.edu Received 24 January 2002; Accepted 13 September 2001 Published online in Wiley InterScience (www.interscience.wiley. com). DOI:10.1002/jez.10207 r 2002 WILEY-LISS, INC. JOURNAL OF EXPERIMENTAL ZOOLOGY (MOL DEV EVOL) 294:325–333 (2002)