Genetic and conchological variation in Littorina sitkana Philippi (Mollusca, Gastropoda) on northern Japanese coasts

A periwinkle, Littorina sitkana Philippi, 1846, does direct development and exhibits three types of shell sculpture. Lacking pelagic larval stages, th is species is expected to be genetically differentiated among populations. In the present study, genetic variation of 19 populations along northern Ja panese coasts was examined using protein electrophoresis. The relative abun dance of shell types was also investigated at each locality. The analyzed p opulations were significantly differentiated genetically from one another. However, no significant genetic difference was detected between shell types within localities where two types were nearly equally frequent. When clust ered genetically using UPGMA, the populations were divided into four geogra phic groups. The UPGMA tree also showed that the Japanese population of L. sitkana is clearly divided into two groups, which may have been derived fro m two mother populations with different genetic structures. On the other ha nd, allozymic and anatomical analyses of the present samples have refuted p ossible occurrence of sibling species of L. sitkana on the coasts of northe rn Japan.