Genetic Divergence Between Two Forms of the Pulmonate Limpet Siphonaria japonica (Gastropoda: Siphonariidae)

Abstract

Genetic differences between two forms (tall and short forms) of the pulmonate limpet Siphonaria japonica were examined using isozymes in order to reveal their identity. Three local samples from the tall form, two local samples from the short form, plus S. laciniosa and S. acmaeoides samples as outgroups were examined. Following the isozyme analysis, 26 loci within 17 enzymes were available commonly to the two forms. Allelic compositions between the two forms show extreme differences from each other, alleles completely or almost replacing each other at the 18 loci. The genetic distances (D values) calculated from the allelic frequencies of the samples indicated considerably high values both among the tall form samples (D = 0.0060–0.0126) and short form samples (D = 0.0181), inferring high genetic divergence in local populations. The difference in D values between the tall and short form samples were between 1.3882–1.5114, figures normally considered significant at the inter-generic level. This difference in values is considerably greater than that between the D values of the tall form samples and S. laciniosa, and the genetic divergence degree between the two forms is thus greater than that at the inter-specific level in the genus Siphonaria. The given results suggest that the tall and short forms of Siphonaria japonica are distinct species, and a taxonomic revision is required.