A Note on the Genetic Status of the Dark Red-Backed Vole,Myodes rex, in Hokkaido, Japan

Abstract

The dark red-backed vole, Myodes (formerly Clethrionomys) rex, was first described from specimens collected on Rishiri Island, Hokkaido, northernmost Japan, by Imaizumi (1971) as a new species on the basis of the cranial characteristics, which differ from those of the gray red-backed vole, M. rufocanus, in the Hokkaido area (including Hokkaido and the peripheral islands), Japan. Myodes rex is thought to be rarer than the other Myodes voles, M. rufocanus and M. rutilus, as shown by the collection of records of M. rex, which is quite limited, according to Nakata (2000). In addition, M. rex is ranked as NT (Near Threatened) by the Ministry of the Environment of Japan (Ohdachi et al. 2009). Kaneko and Sato (1993) and Nakata (1995, 2000) reported that M. rex prefers grass fields, abandoned cultivated lands near grass fields, valley bottoms, and higher altitude forests as its habitat. In contrast, M. rufocanus prefers a habitat of Sasa dwarf bamboo, which is extensively distributed throughout Hokkaido (Toyooka et al. 1983). Such habitat preferences of the two species are more strongly observed on Rishiri Island than on Hokkaido Island. On the other hand, M. rutilus is also dominant in coniferous forests with sparse Sasa bamboo throughout Hokkaido Island, but M. rutilus and M. rufocanus show microhabitat segregation at sympatric areas, particularly in the east (Ota 1984; Abe 1986). Therefore, M. rex is not dominant and is rare in the Hokkaido area. To consider the conservation of such a rare species, fundamental biological data that include ecological and genetic information are needed. To date, Kashiwabara and Onoyama (1988) and Wakana et al. (1996) have analyzed the chromosome constitutions and genetic differentiation of M. rex interspecifically with other vole species, respectively, but the degree of intraspecifically genetic divergence in M. rex has not been analyzed and compared with those of the other Myodes voles in the Hokkaido area (Iwasa et al. 2000, 2002). In this study, to preliminarily evaluate the genetic diversity in M. rex, we analyzed the intraspecific sequence divergence of the mitochondrial cytochrome b (Cytb) gene of M. rex and compared it with that of two Myodes species, M. rufocanus and M. rutilus, in the Hokkaido area.