We conducted univariate and multivariate statistical analyses of the morphometry of five island populations of the house mouse Mus musculus, from the Izu Islands (Oshima, Nijima, Kozushima, Miyakejima, Hachijojima), and compared them with three populations from the Japanese mainland of Honshu (from Kamogawa, Yokosuka, and Kawazu). Analyses were based on bodies, mandibles and molars. According to the analyses based on the mandible and molar measurements, the island samples differed from each other, and many of them also differed from the Honshu samples, although there was no evidence of positive directional variation, such as gigantism, in the insular samples. Cluster analyses of morphological distance, based on mandible and molar measurements, indicated that the island populations, with the exception of that on Oshima, were closely related to those on Honshu, while the Oshima population was slightly more distantly related. These results indicate that the divergence of the island populations is mainly attributable to the genetic variation of the initial founders and to subsequent isolation. The differentiation of the island populations may have taken place as recently as within the past 1,200 years.

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The morphometric relationships among five operational taxonomic units of the Sorex caecutiens/shinto group (Soricidae) (S. caecutiens of Hokkaido, S. shinto shinto of Honshu including the S. chouei holotype, S. s. shikokensis of Shikoku, and S. s. sadonis of Sado) in the Japanese Islands, were examined using uni- and multivariate analyses of 15 cranial, dental, and external characters. The morphological analyses showed that the shrew from Hokkaido (S. caecutiens) and those from Honshu, Shikoku, and Sado (S. shinto) were exclusively differentiated. In particular, the surface structure of the fourth upper premolar completely separated the two taxa. In contrast, S. s. sadonis from Sado could not be completely distinguished from related taxa from Honshu and Shikoku. Thus these morphometric analyses re-confirm that S. caecutiens of Hokkaido, and S. shinto from Honshu, Shikoku, and Sado, should be treated as two separate species, as has previously been proposed on the basis of a molecular phylogenetical study.

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Ruminants were categorized into three feeding types: grazers, mixed feeders and browsers based on their food habits. We studied how phylogeny constrains the feeding types, the morphology of digestive organs, and their relationships in Cervidae and Bovidae. It is shown that species with different feeding types occur in the same phylogenetic group of the family, subfamily, and tribe. This suggests that phylogeny does not always reflect feeding type. Comparisons of three morphological indices of digestive organs (parotid gland size, rumino-reticulum capacity, and rumino-reticulum contents weight) among feeding types found that trends along the grazer-browser continuum were similar in both families. The index values of the same feeding types were similar in the two families. These results suggest that the morphology of digestive organs is closely related to feeding types, and that phylogenetic characteristics are less important. The species in the same feeding type also share other morphological characteristics of digestive organs, irrespective of phylogeny.

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The diet of the Japanese serow (Capricornis crispus) was analyzed quantitatively in a high density (14.8±3.0 individuals/km²) population throughout the year by direct observation of feeding behavior on the Shimokita Peninsula, northern Japan, during two survey periods, 1978-1980 and 1994-1996. Serows fed on 114 plants species and one species of fungus. Analyses of 16,686 bites indicated that serows fed mainly on leaves and twigs of deciduous broad-leaved trees, which formed 54.8-58.3% of the diet in autumn and 94.5-95.0% in winter, followed by forbs (16.5-39.1% from spring to autumn). The results suggest that the Japanese serow is a browser throughout the year, and is mainly a folivore. There was no significant difference in the dietary composition at the food category level, nor was there any change in the diversity index of the diet between the two study periods. The four top-ranking food species were identical in the both periods. Browsing by Japanese serows may have only limited impacts on vegetation because of low population densities related to territoriality.

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The XY chromosomes of bone marrow metaphases and the XY-synapses of pachytene spermatocytes of six taxa of Clethrionomys and Eothenomys from Japan were examined using C-banding and surface-spreading techniques. Light, and electron, microscopy revealed that in the red-backed vole, the XY size ratios of the metaphase sex chromosomes and the SC-axes of pachytene XY-synapses show a similar pattern of variation. The X chromosomes of these vole taxa were classified, on the basis of their size and morphology, as one of two types, that is they were either acrocentric or sub-telocentric. Similarly, two types of Y chromosome, small and medium, were recorded. According to these criteria, C. rufocanus, C. rutilus and Eothenomys andersoni carry an acrocentric X chromosome and a small Y chromosome, whereas the two local forms of E. smithii, the so-called “smithii-type” and “kageus-type”, carry a subtelocentric X chromosome and a medium Y chromosome. In contrast to these XY combinations, E. imaizumii showed a composite combination, with a subtelocentric X chromosome and a small Y chromosome. In view of earlier findings on the genetic background of E. imaizumii (Suzuki 1994; Suzuki et al. 1999), such a composite combination of the sex chromosomes suggests that E. imaizumii may have inherited an X chromosome from a female E. smithii and a Y chromosome from a male E. andersoni during the course of speciation through hybridisation.

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