Conventionally and Differentially Stained Karyotypes of the Dark Red-Backed Vole, Myodes rex

The dark red-backed vole, Myodes rex, is distributed in Rishiri Island, Rebun Is., Shikotan Is., Kunashiri Is., mountainous areas of the Hokkaido mainland, and probably Sakhalin Is. (Ohdachi et al. 2009). This species was first described for specimens from Kanrosen, Rishiri Is. by Imaizumi (1971), based on the morphological characteristics that differed from those of the gray red-backed vole, Myodes (= Clethrionomys) rufocanus in Hokkaido, Japan. Subsequently, M. montanus was also described for specimens from mountainous areas of the Hidaka region, Hokkaido mainland, as a new species by Imaizumi (1972). However, most mammalogists recognized the validity of M. rex and ranked M. montanus as a junior synonym of M. rex (Abe 1984 ; Kaneko et al. 1998 ; Kaneko 2005 ; Musser and Carleton 2005 ; Ohdachi et al. 2009). Morphological, ecological and phylogenetic studies of M. rex have been performed (Haga et al. 1979 ; Nakata 1990, 1995, 2000 ; Kaneko and Sato 1993 ; Wakana et al. 1996 ; Iwasa et al. 2001 ; Lebedev et al. 2007 ; Motokawa 2008 ; Iwasa and Nakata 2011 ; Kawai et al. 2013 ; Kohli et al. 2014), but only a few cytogenetic findings for M. rex were reported (Tsuchiya 1981 ; Kashiwabara and Onoyama 1988 ; Yoshida et al. 1989).