Intraspecific phylogeny and geographical variation of six species of northeastern Asiatic Sorex shrews based on the mitochondrial cytochrome b sequences

Intraspecific phylogeny and genetic variation were investigated based on nucleotide sequences of the mitochondrial cytochrome b gene in six soricine shrew species, Sorex unguiculatus, S. caecutiens, S. shinto, S. gracillimus, S. minutissimus and S. hosonoi, collected primarily from northeastern Asia. Maximum likelihood trees and a phylogenetic network were generated to estimate intraspecific phylogenies. S. minutissimus showed high congruence between phylogenetic position and geographical origin and S. gracillimus showed low congruence. In contrast, there was no congruence between phylogeny and geography in S. unguiculatus and the S. caecutiens from Sakhalin-Eurasia. Positive correlation between genetic and geographical distances was found in S. minutissimus and S. gracillimus, but not in the other species (or regional populations). The results of the phylogenetic and genetic analyses suggest that S. minutissimus and S. gracillimus have occupied their present ranges for a longer time than the other species if we assume a stepping-stone model of population structure. In addition, there was no contradiction between the present investigations and the hypotheses of multiple immigration by S. gracillimus and a single immigration by S. unguiculatus into Hokkaido Island. It is proposed that these six northeastern Asian species experienced different historical processes of range expansion and dispersal despite the fact that some of them currently show similar patterns of distribution.