Genetic relationships of American alligator populations distributed across different ecological and geographic scales

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 alligator populations 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 7 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 reveal 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.