A DNA marker to discriminate two types of freshwater shrimp Palaemon paucidens and the distribution of these two types in Japan

Among the palaemonid shrimp species of the genus Palaemon known from Japan, Palaemon paucidens is the only species inhabiting freshwater areas. Two genetically distinct types (designated by A and B) were found by allozyme electrophoresis analysis three decades ago. We developed a simple multiplex-PCR assay to discriminate the two types based on 18S rDNA sequences. A total of 422 individuals collected at 152 localities in Japan were analyzed by the multiplex-PCR assay. No heterozygote was observed, indicating that these two types have been reproductively isolated. Both types were distributed throughout Japan; type A was observed in ponds, lakes and rivers, while type B was observed only in rivers.