GENETIC DIFFERENTIATION OF SETTLEMENTS OF LITTORINA-BREVICULA (MOLLUSCA, GASTROPODA) IN PETER-THE-GREAT-BAY (SEA OF JAPAN)

Genetic differentiation among eight samples of Littorina brevicula fro m Peter the Great Bay was estimated using five highly polymorphic loci as genetic markers. The coefficient of relative genetic differentiati on was low (G(ST) = 1.6%). This is probably caused by intense gene flo w be tween snail setflements because L. brevicula has a planktonic lar val stage, which lasts at least 10 days. Despite the low level of gene tic differentiation, heterogeneity of allele frequencies among samples was statistically significant at three loci. Also, microgeographic di fferentiation (within several dozen meters) among samples within conti nuous settlements was found to be significant, Natural selection is su ggested as a possible explanation.