Allozyme variation and behavioural dimorphism among populations of Littorina brevicula (Philippi) from Japan

Abstract

In Amakusa (Japan), an apparently homogeneous population of Littorina brevicula, divides into two groups during the reproductive season (winter). Some snails migrate to the lower intertidal zone, while the rest remain in the upper zone. This migration behaviour might be controlled genetically and the behavioural dimorphism may be maintained by assortative mating. To evaluate this hypothesis, we studied genetic variation at four polymorphic enzyme loci (Pgm, Aldh, Ipp, Gpt) in both groups, as well as in seven other samples from the coast of Japan and Vostok Bay (Russian coast of the Sea of Japan). There were no significant allele frequency differences between the two behavioural groups of snails with differing migration patterns (χ ² = 8.411, df = 12, p > 0.5). The samples from Japan belong to a panmictic population. Yet, a significant heterogeneity was found between the sample from Vostok Bay and the samples from Japan, indicating a reduced gene flow between these regions. Generally, observed genotype frequencies showed good fits to Hardy-Weinberg equilibrium expectations at three of the four loci investigated.