ROARK, A. W.; LILLYWHITE, H. B.; University of Florida; University of Florida: Genetic Variation in an Insular Population of Cottonmouth Snakes
Seahorse Key (Levy County, Florida) is an important rookery for wading birds and supports an unusually dense population of cottonmouth snakes (Agkistrodon piscivorus conanti) that are dependent on the rookery. The snakes are entirely terrestrial and scavenge on dead or rotting fish that are dropped or regurgitated by the nesting birds. Sensitivity of snakes to seawater and the apparent differentiation of character states relative to mainland populations suggest the cottonmouths on Seahorse Key comprise a relatively isolated population. DNA fingerprinting was used to study genetic divergences among the Seahorse Key and two mainland cottonmouth populations. Amplified Fragment Length Polymorphism (AFLP) analyses indicated little genetic variation (φst = 0.005 – 0.020) and small genetic distances (D = 0.003 – 0.012) between the populations, although genetic distance was least between the two mainland populations. The small differences measured suggest the population at Seahorse Key either experiences significant exchange with the mainland or has not been isolated for a long evolutionary period. It may also be that the highly conserved nature of reptilian DNA, rather than continual gene flow, accounts for the overall lack of genetic divergence. Heterozygosity estimates indicate that the Seahorse Key population has the lowest percent heterozygosity of the three populations, potentially supporting the hypothesis that this population has experienced decreased gene flow for an extended period of time. Consequently, quantitative genetic distances and variation among populations, though very small, might still be considered useful data in assessing the degree of isolation in this unusual insular population of snakes.
