GENETIC-HETEROGENEITY IN POPULATIONS OF LITTORINA-BREVICULA (PHILIPPI) (MOLLUSCA, GASTROPODA) IN THE NORTHERN PART OF PETER-THE-GREAT-BAY (SEA OF JAPAN)

Genetic differences among eight samples of Littorina brevicula in Pete r the Great Bay in the far east of Russia were surveyed using five hig hly polymorphic allozyme loci as genetic markers. Geographic distances between samples ranged from a few meters to more than a hundred kilom eters. The coefficient of relative gene differentiation was quite low, G(ST) = 1.6%. Such a low level of differentiation was expected becaus e L. brevicula has a planktonic larval stage lasting more than 10 days . Despite the low level of gene differentiation, there was statistical ly significant heterogeneity in allele frequencies among samples at th ree loci. Microgeographic heterogeneity (within a few dozen meters) am ong samples within continuous settlements was found to be significant in the loci Pgi, Alpdh, and Fdh. Differential natural selection, recru itment processes, and presence of a cryptic species are discussed as p ossible explanations for this observation.