Taxonomy and molecular phylogeny of Lethenteron lampreys in eastern Eurasia

Allozyme analyses of lampreys (genus Lethenteron) in eastern Eurasia showed that samples of L. reissneri from the upper Amur River, Russia, possessed the diagnostic alleles of L. kessleri(MDH-3*-93). These samples were closely related to L. kessleri samples in the Ob, Lena and middle Amur Rivers and on Sakhalin and Hokkaido Islands. On the other hand, they were distantly related to samples of the northern and southern forms of L. reissneri in the Japanese Archipelago and the southern Korean Peninsula. The number of trunk myomeres in L. reissneri from the upper Amur (63-76) strongly overlapped the number in L. kessleri(64-73), but were markedly displaced from those of the northern (51-66) and southern forms (49-62). These results suggest that L. reissneri in the upper Amur basin is likely to be the same taxonomic entity as L. kessleri reported from eastern Eurasia. The genetic and morphological divergences from L. reissneri in the type locality make it appropriate to regard the northern and southern forms as distinct species, L. sp. N and sp. S. Despite the close relationships found among L. japonicum, the L. reissneri complex and L. sp. N, L. sp. S was highly divergent from other species of Lethenteron, Lampetra and Entosphenus. In the monophyletic group comprising L. japonicum, the L. reissneri complex and L. sp. N, the direction of life-history evolution presumed from the most parsimonious character reconstruction on the molecular tree was inconsistent with the previous hypothesis that nonparasitic species arise from parasitic species, indicating the necessity of detailed assessment of characteristics. On the other hand, L. sp. S may be a relict species of the coancestor of Lethenteron, Lampetra and Entosphenus.