Molecular phylogeny of Lethenteron species from the Far East, with their taxonomic problems

Abstract

Allozyme analyses were performed to disclose the phylogenetic relationships among Lethenteron species occurring in the Far East. As a result, several complete allele substitutions were found between all sympatric pairs of four Lethenteron taxa, strongly suggesting the existence of reproductive isolation among them. Therefore, these four taxa, L. japonicum, L. kessleri, and the northern and southern forms of L. reissneri, should be regarded as discrete species. Lethenteron japonicum appeared to be closely related to L. kessled and the northern form of L. reissneri, whereas the southern form of L. reissned was greatly divergent from the other three Lethenteron species, suggesting that the former three species are monophyletic. In the monophyletic group, the two nonparasitic (and fluvial) species, L. kessleri and the northern form of L. reissnen, are supposed to have speciated from the ancestral stocks of parasitic (and anadromous) L. japonicum in different geological times. The present study also indicates that some taxonomic problems are comprised in fluvial, nonparasitic lamprey species from the Far East. At present, some fluvial lamprey species and local populations are faced with endangered situation in Japan and Korea.