Genetic structure and differentiation of four Lethenteron taxa from the Far East, deduced from allozyme analysis

Genetic structure and differentiation among four Lethenteron taxa, L. japonicum, L. kessleri, and two groups of L. reissneri, collected from Japan and the Far Eastern region of Russia, were investigated by electrophoretic analysis. Several complete-allele substitutions were found between all possible pairs of taxa in regions of sympatry, strongly suggesting the existence of reproductive isolation between them. Therefore, four Lethenteron taxa should be regarded as discrete species, respectively. In each taxon, the genetic variability within each population (H=0.062 – 0.127 for L. japonicum, H=0.062– 0.128 for L. kessleri, H=0.026 – 0.148 for the northern group of L. reissneri, and H = 0.015 – 0.102 for the southern group of L. reissneri) was considerable, suggesting large effective sizes for most populations. The sample of L. japonicum collected from Kyiya, the basin of Amur, was somewhat divergent from the other intraspecific samples. This may have resulted mainly because it does not migrate to the sea. In contrast L. kessleri has a fluvial life style, but the genetic differentiation between populations (G_ST=0.117, D = 0.000 – 0.061) was less than that for each group of L. reissneri (G_ST = 0.493, D=0.000 – 0.226 for the northern group and G_ST=0.660, D = 0.008 – 0.422 for the southern group), probably meaning more recent dispersal of L. kessleri than the two groups of L. reissneri. The parasitic and anadromous L. japonicum appeared to be closely related to L. kessleri (D=0.042 – 0.090) and the northern group of L. reissneri (D=0.163 – 0.355), which have nonparasitic and fluvial life styles, whereas the southern group of L. reissneri was greatly divergent from the other three Lethenteron species (D=0.559 – 0.926), suggesting that the former three species might be monophyletic.