Geographic Pattern of the Microsatellite DNA Polymorphism in two species of Sorex shrew in Hokkaido

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The biogeographic history of six soricine shrew species inhabiting the Japan archipelago and neighboring regions has been studied based on intra- and interspecific phylogeny of nucleotide sequences of mitochondrial cytochrome b gene.To infer biogeographic histories of S. caecutiens and S. unguiculatus in more detail, phylogenetic relationships between species or populations were investigated by restriction fragment length polymorphism (RFLP) for the nuclear ribosomal RNA genes (rDNA). Genetic population structures were examined using microsatellite DNA markers.From the rDNA-RFLP analysis, it was suggested in S. caecutiens that Hokkaido population is genetically distant from Eurasian ones and Sakhalin population originated from hybridization between the continent and Hokkaido populations.High genetic variations in microsatellite loci were observed among Hokkaido mainland populations of both species. The allelic richness and heterozygosity were proportional to the island size and positiv … More e correlation between genetic and geographic distances was detected in S. unguiculatus, while S. caecutiens showed no positive correlation between genetic and geographic distances among local populations in Hokkaido mainland. This implies that the final population expansion in Hokkaido occurred in S. unguiculatus earlier than in S. caecutiens.Combining the information from rDNA-RFLP, microsatellite DNA and mtDNA cyt-b, biogeographic histories of S. unguiculatus and S. caecutiens in Hokkaido were inferred as follows: Sorex caecutiens, which invaded Hokkaido before the last glacial age, was restricted to the forest refuge in southern Hokkaido because of its sylvicolous nature, at the maximum stage of last glacial age, where grassland vegetation prevailed in Hokkaido. However, it expanded its range with recovery of forest vegetation all over Hokkaido in post glacial age. S. unguiculatus invaded Hokkaido later than S. caecutiens, probably at the maximum stage of last gracial age, and soon came distributed throughout Hokkaido inhabiting not only the southern forest refuge but also grasslands prevaily under the cold climate. Less