Biochemical and Morphological Evidence of Two Sympatric Forms, Interpreted as Sibling Species, in the Estuarine Grapsid Crab Hemigrapsus penicillatus (De Haan)

Abstract

Two sympatric forms (I and II) of the estuarine grapsid crab Hemigrapsus penicillatus from the Nanakita River (Sendai, Japan) were detected by starch gel electrophoresis. Form I consists of individuals possessing the allele 6Pgd^B, while Form II has the allele 6Pgd^C. Heterozygote individuals (genotype of B/C ) were not observed at the 6Pgd locus. Form I is also characterized by the alleles Aat-2^C and Pgm^A, while Form II has the alleles Aat-2^B and Pgm^B. Morphological analysis revealed that the patch of soft hairs on the male chela in Form II individuals is much larger than that in Form I. The above results suggest that the two sympatric forms are reproductively isolated and represent sibling species.