Takamichi Jogahara

Survey and capture of albino-like house musk shrews (Suncus murinus) in Okinawa, Japan, and a preliminary report regarding inheritance of the albino-like mutation

92008 ?? 33 1214 Received 2.8.2007 ; a cepted 5.5.2008 Copyright

Numerical variation of teeth in the wild house musk shrew Suncus murinus captured from Nagasaki, Japan

Wild populations of Suncus murinus from Nagasaki were thought to be extinct, although specimens from Nagasaki are kept at the National Science Museum, Tokyo. Variation in the number of teeth, including both congenital and postnatal absence, was observed in 25 of 85 individuals. All 25 abnormal individuals were checked using a micro-CT unit to document the presence or absence of embedded teeth and any traits of postnatal absence. Four of these had congenitally absent teeth, whereas the rest showed signs of postnatal absence. There was no significant difference in the ratio of length of tooth group P(4)M(3) against palatal length between individuals with congenital absent teeth and normal ones. Because S. murinus in captivity shows a high rate of periodontal disease, we suggest that the high rate of postnatal absence of teeth in the wild population is due to oral diseases such as periodontal disease or other traumatic factors.

Complex phylogeographic structuring in a continental small mammal from East Asia, the rice field mouse, Mus caroli (Rodentia, Muridae)

ABSTRACT We investigated genetic variation in mitochondrial cytochrome b within the long-tailed rice field mouse, Mus caroli Bonhote, 1902, across its entire geographic range in Southeast and East Asia with a view to: 1) assessing the pattern and causality of phylogeographic structure in a terrestrial small mammal from continental Southeast Asia; and 2) distinguishing genuine insular relics from cases of human-assisted translocation. We identified five main mtDNA lineages which show a similar level of differentiation as the subspecies of M. musculus and probably diverged during the Middle Pleistocene. Two of the lineages are restricted to large islands (Taiwan and Java) and their existence is explicable in terms of regional palaeogeographic factors including changes in sea level and climate. The remaining lineages are distributed in different regions on mainland Southeast Asia but vicariant explanations are inappropriate given the relatively short time frame. Dispersal across barriers followed by local differentiation probably explains the observed phylogeographic patterning on the mainland. A close genetic link between Okinawan M. caroli and populations in Laos confirms previous suggestions that people carried this species to the Ryukyu Archipelago. However, more intensive regional sampling is needed to identify a precise source area.

The morphological basis of the armor-like folded skin of the greater Indian rhinoceros as a thermoregulator

Abstract. The armor-like folded skin of the Indian rhinoceros (Rhinoceros unicornis) was examined by CT image analyses and microscopic observation. The three-dimensional reconstructed images demonstrate that the folded skin has the subcutaneous tissues including cutaneous muscles and connective tissues inserted to the deepest holes and grooves of 2–3 mm thickness in each fold. The cutaneous muscles are well-developed in subcutaneous tissues, in which many small blood vessels are found. We conclude that the folded skin acts as a thermoregulator, since the thin blood vessels and capillaries and cutaneous muscles in the subcutaneous tissues transmit the thermal energy from the core region of the body to the skin folds. We suggest that the greater Indian rhinoceros, Rhinoceros unicornis, has evolved the extraordinary thermoregulation mechanism in the folded skin adapted to high temperature in the tropical and subtropical regions.

Intraspecific phylogeny of the house shrews, Suncus murinus-S. montanus species complex, based on the mitochondrial cytochrome b gene

Abstract. A phylogenetic tree was reconstructed based on the mitochondrial cytochrome b gene nucleotide sequences of 169 individuals of house shrews (Suncus murinus and S. montanus) from 44 localities in East Asia, Southeast Asia, West Asia, and islands in the western Indian Ocean. Shrews from China (Zhejiang), Japan (Okinawa), Vietnam, and Indonesia (Java) formed a monophyletic group with less genetic variation. Therefore, the shrews of these regions appeared to have originated from one or a few localities. Contrary to this, shrews from Sri Lanka, Myanmar, and Pakistan consisted of several haplogroups. This finding suggests immigration movements to these areas. Fascinating findings were also obtained concerning the islands in the western Indian Ocean. First, shrews on Zanzibar Island (Tanzania) had almost the same haplotype as those in southwestern Iran. Therefore, the house shrew in Zanzibar may have immigrated from Iran (or vice versa). Second, shrews from Madagascar and Grande Comore Island shared the same haplotype, whereas the shrews on Réunion Island were clearly different from those of Madagascar and Comoros. Thus, there appears to have been several immigration routes to the islands of the western Indian Ocean.

Maxillary tooth size variability and influence of hypodontia in the Suncus murinus

Abstract Dry cranila specimens from 184 Suncus murinus from the wild Nagasaki (normal dentition) population and laboratory strains of KAT (normal dentition), NAG (missing I3) and TESS (missing P3) were examined to quantify the relationship between size variation and the influence of tooth absence in maxillary dentition. We first measured and analyzed maxillary tooth size variability in normal S. murinus based on the coefficient of variation (CV). Molariform teeth showed lower CVs, whereas unicuspid teeth showed relatively high CVs in shrews with normal dentitions. In this species, molariform teeth have complex cusps and clear ridges, whereas unicuspid teeth have no occlusal surface. In particular, I3 and P3 had relatively high CVs, and these teeth were commonly absent. We also examined the relationship between tooth size and number in this species. Individuals missing I3, namely, NAG strain, had lower P3 CVs than the normal group. However, those missing P3 had higher I3 CVs than other teeth and the normal group. These results suggest that tooth disappearance does not always lead to stability of other teeth. The variability in tooth size appears to be influenced not only by functional and developmental factors but also by phylogenetic backgrounds and factors regulating tooth formation.