Variation of skull characteristics of Anderson's red-backed vole Eothenomys andersoni, from Nagano City, central Honshu, Japan.

Abstract

A morphological examination of Japanese Eothenomys voles from Nagano City was carried out in order to re-evaluate the identification criteria of the taxa and to compare them with voles from north-eastern, central and western Honshu. The relationship between hind foot length and tail vertebrae length (HFL-TL) divides Japanese Eothenomys voles into two clusters, one of which has been identified as Anderson's red-backed vole E. andersoni and the other as Smith's red-backed vole E. smithii. However, four cranial and dental characteristics (the projection of the lamdoidal crest (LDC), the distance between the tympanic bullae (BTB), and the width and length of the middle lacerate (MLC-w and MLC-l)) contradict the identification based on the HFL-TL relationship. Four specimens from Nagano were clearly identified as E. andersoni on the basis of the HFL-TL relationship, but whereas three of them exhibited andersoni-type cranial and dental characteristics one showed smithii-type characteristics. Thus, cranial characteristics are necessary in order to re-examine the effectiveness of the species identification. It is possible that one of the individuals from Nagano may have resulted from hybridisation between E. andersoni and E. smithii, as has been suggested by previous genetic studies. Hybridisation may result in the ambiguity of the characteristics shown by the atypical individual from Nagano.