Yasushi Takada

Morphological variation of large Japanese field mice, Apodemus speciosus on the Izu and Oki Islands

ABSTRACT Morphological variation was examined in large Japanese field mice, Apodemus speciosus, of five populations from the Izu Islands (from Oshima, Shikinejima, Niijima, Kozushima and Miyakejima), four from the Oki Islands (from Dogo, Nishinoshima, Nakanoshima and Chiburijima), and four from the Japanese mainland of Honshu. Univariate and multivariate (PCA) analyses were conducted on the basis of body-, mandible-, and molar-measurements. Overall, the insular mice had a tendency toward gigantism, and also showed marked morphological differentiation among the islands. The sizes of the mandible and molar were inversely correlated to island area and temperature, thus suggesting a selective effect. Although faunal diversity might be related to the morphological variation in size, there was no clear relationship between the morphological variation and biotic factors such as predation and competition. The populations from the Izu Islands underwent marked morphological divergence, suggesting founder effects. The Izu Island are oceanic and have probably never been connected with Honshu, hence mice were likely transported from Honshu. On the other hand, the Oki Islands had been connected with Honshu in the late Pleistocene. The founders of the insular mice related to the history of the islands could have likely affected the morphological variation.

Comparative anatomy of the hyoid apparatus of carnivores

Abstract. The hyoid apparatus was described in order to examine morphological differences among eight species of carnivores. Confusion in terminology of its proximal elements is corrected at first. The tympanohyal, attached to the petrosal part of the temporal bone, is a small bone inside the stylomastoid foramen in the red fox, raccoon dog (Canidae), Asiatic black bear (Ursidae), and masked palm civet (Viverridae), in contrast, it is not visible in the Japanese weasel, Siberian weasel, Japanese marten (Mustelidae) and raccoon (Procyonidae). Inter-specific structural differences of the remainder of the hyoidean elements are not distinct. The basihyal attaches to the ceratohyal and thyrohyal. The thyrohyal is also connected with the thyroid cartilage. The anterior cornu besides the tympanohyal comprises, from distal, three bones; the ceratohyal, epihyal, and stylohyal, and a band of cartilage. The tympanohyal, if present, is connected to the stylohyal via the tympano-styloid synchondrosis. Allometry between the length of the hyoidean elements and that of the skull shows isometric growth. This reflects simply the masticatory function of the hyoid apparatus. The tympanohyal of the mustelids and procyonid is possibly covered and hidden by the tympanic bulla.

Effects of Isolation by Continental Islands in the Seto Inland Sea, Japan, on Genetic Diversity of the Large Japanese Field Mouse, Apodemus speciosus (Rodentia: Muridae), Inferred from the Mitochondrial Dloop Region

To study the effects of post-glacial isolation by islands on population genetic diversity and differentiation of the large Japanese field mouse, Apodemus speciosus, we examined partial nucleotide sequences of the mitochondrial Dloop region (ca. 300 bp) in 231 individuals collected from islands in the Seto Inland Sea and adjacent regions on Honshu and Shikoku Islands in the western part of the Japanese archipelago. Molecular phylogenetic and network analyses showed that haplotypes in each island tended to form monophyletic groups, while those in Honshu and Shikoku (the major Japanese islands) showed scattered relationships and were connected with island haplotypes. These observations suggest that a set of Honshu and Shikoku haplotypes became the ancestral lineages of the island population. No gene flow was detected among island populations, indicating that independent evolution occurred on each island, without the influence of human activities, since the establishment of the islands in the Holocene. Population genetic diversities on each island were lower than those on Honshu and Shikoku. Comparison between genetic diversity and island area size showed positive correlations and supported the suggestion that genetic drift is a major factor that shaped the current haplotype constitution of the islands in the Seto Inland Sea.

Phylogeography of the Japanese White-Toothed Shrew (Eulipotyphla: Soricidae): A Clear Division of Haplogroups between Eastern and Western Japan and their Recent Introduction to Some Regions

Abstract. The Japanese white-toothed shrew (Crocidura dsinezumi) is a species endemic to Japan. For this species, only minimal phylogeographic investigations have been conducted. We obtained DNA sequences of mitochondrial cytochrome b and control region and nuclear ApoB genes for 191 individuals of C. dsinezumi from 107 locations collected throughout its known range. In the phylogenetic trees based on mitochondrial DNA sequences, two haplogroups (Eastern and Western Clades) were recognized, and the demarcation line between them was located in central Honshu without an overlapping area. The estimated divergence time between the two major clades indicated that they could have diverged prior to the final geologic division of Hondo and the Asian Continent (100–150 KYA). For the ApoB gene, Types A, G, and R (heterozygote) were recognized although there was a single site mutation. Type A mainly occurs in eastern and central Japan and Types G and R in central and western Japan. It was suggested in the present study that some shrews in Hokkaido were introduced recently from eastern Honshu (possibly the Tohoku Region) whereas others might have been distributed there naturally, and that population in Jeju (South Korea) was introduced recently from Kyushu.