Karyological analysis of the Eothenomys sp. from Nagano City, central Honshu, Japan

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Red-backed voles in low mountain areas in the vicinity of Nagano City, central Honshu, Japan, have hitherto been taxonomically treated as Eothenomys sp. since species identification has not been possible due to ambiguity in diagnostic morphological characteristics that can be used to classify voles from Honshu into one of the two Eothenomys species, E. andersoni or E. smithii. We examined the karyotypes of seven individuals of from the Nagano area (altitude : 380-800 m). The karyotype of the Eothenomys sp. consisted of 26 pairs of acrocentrics and one pair of metacentrics, and the sex chromosomes, which is also the standard karyotype of E. andersoni and E. smithii. X chromosomes were comprised of two types, acrocentrics and subtelocentrics, which are known to be frequently observed in E. andersoni and E. smithii, respectively. G-band patterns of the autosomes and the long arm of the X chromosome of the Eothenomys sp. were identical to those of E. andersoni and E. smithii. In contrast, Y chromosomes in the male specimens (n = 3) were small-sized submetacentric and totally heterochromatic, which was the type of E. andersoni, and differed from those of E. smithii, which were medium-sized subtelocentric and partially heterochromatic. Since the interspeclfic varlation of the Y chromosome was likely to be specific for each of the species, the Eothenomys sp. can be regarded as members of E. andersoni.
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