Skulls of the three species of Ryukyu spiny rats (Tokudaia osimensis, T. tokunoshimensis and T. muenninki) were osteometrically compared. In all measurements the size tendencies in which T. tokunoshimensis was the largest, T. muenninki middle, and T. osimensis the smallest were confirmed. However, the lengths of the molar row were exceptionally the largest in T. muenninki, middle in T. tokunoshimensis and the smallest in T. osimensis. The raw measurement data obviously indicated significant differences in size among the three species. We demonstrated that the neurocranium was larger in T. osimensis than in T. muenninki from the results of the proportional analyses. The principal component analyses using the raw measurement data also pointed out that the skulls from the three species were obviously distinguished in the charts, although the plots were not completely separated by the principal component analysis using the proportional indices. The CT images showed that both maxilla and palatine bone were thinner near the greater palatine foramen area and pointed out that the characteristic palatine structure fixed the position of the greater palatine foramen in each species of Tokudaia.

Effects of cold stress on immune function and energy demand were experimentally investigated in the grey-sided vole. Laboratory-born and wild voles were divided into two groups: one maintained at 5°C (low temperature) and the control at 23°C (room temperature). The voles exposed to low temperature showed a weaker immune response to the challenge antigen than the control voles. Food intake of the voles under low temperature increased in comparison with that of the control, and fat reserves reduced in the voles under low temperature. Kidney, heart and small intestine of the voles were hypertrophied by approximately 10–20% compared with the controls. These results can be interpreted as a trade-off between thermoregulation and immunity. These physiological reactions caused by low temperature may cause higher mortality of grey-sided voles during winter (the non-breeding season) in the field.

It is still unclear whether the masked palm civet (Paguma larvata) is native to the Japanese islands or introduced from the outside via human activities. In the present study, we sequenced the whole region (1,140 base-pairs) of the mitochondrial cytochrome b gene for 29 masked palm civets from Japan and Southeast Asia, and investigated their molecular phylogeography. Nine haplotypes were identified from the animals. Five halpotypes identified from 24 animals of Japan were clustered and separated from four haplotypes from five animals of Southeast Asia, showing clear differentiation between Japanese and Southeast Asian lineages. Sequence differences within Japanese haplotypes were smaller than those within Southeast Asian haplotypes and those between Japanese and Southeast Asian haplotypes. Within Japanese animals, all haplotypes found in eastern Honshu (Kanto district) were different from those of central Honshu (Chubu district). The present study highlighted the problem whether the Japanese Paguma larvata is an introduced species showing multiple original routes, or whether it is a native species genetically differentiated from Southeast Asian populations and even within Japan.

To further understand the phylogenetic relationships among the mustelid genus Mustela, we newly determined nucleotide sequences of the mitochondrial 12S rRNA gene from 11 Eurasian species of Mustela, including the domestic ferret and the American mink. Phylogenetic relationships inferred from the 12S rRNA sequences were similar to those based on previously reported mitochondrial cytochrome b data. Combined analyses of the two genes demonstrated that species of Mustela were divided into two primary clades, named “the small weasel group” and “the large weasel group”, and others. The Japanese weasel (Mustela itatsi) formerly classified as a subspecies of the Siberian weasel (M. sibirica), was genetically well-differentiated from M. sibirica, and the two species clustered with each other. The European mink (M. lutreola) was closely related to “the ferret group” (M. furo, M. putorius, and M. eversmanii). Both the American mink of North America and the back-striped weasel (M. strigidorsa) of Southeast Asia were more closely related to each other than to other species of Mustela, indicating that M. strigidorsa originated from an independent lineage that differs from other Eurasian weasels. Based on biochemical, cytogenetic, and molecular differences as well as morphological evidence, it is proposed that the American mink be elevated to a distinct mustelid genus, Neovison.

The internal architecture of the masticatory muscles in a murine murid, Rattus rattus, was examined and compared with our previous description of Peromyscus maniculatus, which seems to have primitive jaw muscles for muroid rodents. Remarkable differences were observed mainly in the masseter muscle and corresponding aponeurosis. The anterior and posterior mandibular aponeuroses for insertion of the masseter deep layer are united as a single sheet in Rattus. In Peromyscus, both the origin and insertion of the anterior part of the masseter deep layer lie on the aponeurosis. In Rattus, however, the deep fibers of the anterior part form a muscular attachment to the bone surface at either end. This characteristic suggests that the maximum angle of gape is increased in murine murids, which allows them to ingest various-sized foods.