Genetic Variation in the Carolina Marsh Clam, Polymesoda caroliniana

Horizontal starch gel electrophoresis was used to detect genetic variation at eight enzyme loci and five general protein loci in 11 populations of Polymesoda caroliniana from the Gulf of Mexico and south Atlantic coast of the U.S. Little variability was found between four of these populations along a salinity gradient in the Cape Fear Estuary, NC, and a regional trend was not observed in other populations along a latitudinal gradient. Heterogeneity analyses and dendrograms, both based on allele frequencies, suggest populations from the Gulf coast of Florida are genetically different from both a northern Gulf population (Mississippi) and Atlantic populations. The population from Mississippi was similar to populations from the Atlantic coast, all of which were similar. Heterozygosity in the 11 populations ranged between 8.11 and 28.0%, and the percentage of loci polymorphic between 37.5 and 71.4%. Populations conformed to Hardy-Weinberg expectations at greater than 95% of all loci assayed except glucose dehydrogenase, where only the populations from Fort Myers, FL, and Sapelo Island, GA, conformed to Hardy-Weinberg expectations. Electrophoretic pattems observed suggest P. caroliniana larvae are planktonic and effective at dispersal