Eothenomys Smithii Research Articles

How does the 120-year cycle mast seeding of dwarf bamboo affect the rodent population?

BackgroundIn 2017, large-scale flowering, seeding, and dying events of dwarf bamboo (Sasa borealis) occurred in a wide range in central Japan for the first time in 120 years. This phenomenon of S. borealis, like the mast seeding of trees, could be expected to provide a large amount of food for seed-eating rodents and gradually affect their ecology and population dynamics. We captured rodents in survey plots in a secondary broad-leaved forest with the phenomenon from 2018 to 2019 to investigate the species, the number of individuals, growing stage, sex, and body mass. In addition, we also compared the capture data for 2 years (2018–2019) with that for the mast seeding year (2017) and 6 years before it (2011–2016).ResultsThe mast seeding of S. borealis greatly increased the population size of rodents, especially Apodemus speciosus and A. argenteus. Conversely, Eothenomys smithii did not show such an increase. Most of the captured rodent individuals were already adults at the time of new capture, and the proportion of male juveniles was extremely low. These results suggest that the mast seeding of S. borealis created unusually rich food availability for the population concentration of rodents due to their immigration. However, body mass was not significantly different before and after the mast seeding. In addition, the increased populations of the two Apodemus species did not decline 2 years after the S. borealis masting, contrary to the previously reported decrease of rodent populations after tree masting.ConclusionsOur results indicate that the mast seeding of S. borealis affected the population dynamics of Apodemus species over a long time and their individual composition of different growth stages. However, it did not affect their body mass.

Environmental Factors for the Occurrence of the Smith's Red-Backed Vole,Eothenomys smithii, in Rocky Terrains at the Foot of Mt. Fuji in Central Japan

The relationship between environmental factors and the occurrence of the Smith's redbacked vole, Eothenomys smithii, was analyzed first by principle component analysis (PCA) to select factors and suitability of fit between capturing results of the voles, and subsequently by multiple regression analysis (MRA) to identify significant environmental factors affecting the occurrence of the vole. Six research sites were established along six valleys showing rocky terrain in the Tenshi Mountains at the foot of Mt. Fuji, Shizuoka Prefecture, Honshu, Japan, where the closely related species, E. andersoni, is absent. Ten environmental factors were examined for the occurrence of the vole in three quadrats at each site. In addition, thirty traps were set at 5-m intervals along the valley (150 m long) for one night at each site, and this trapping was performed four times in one year. As a result of MRA, higher coverage of bryophytes (factor 9) was significantly chosen among the four factors primarily selected by PCA. It is concluded that E. smithii prefers a dense covering of bryophytes in the rocky terrains of small valleys with forests, suggesting conditions of higher moisture and darkness appropriate for bryophyte growth.

Reproduction in a laboratory colony of the Smith's red-backed vole, Eothenomys smithii.

Reproduction in a laboratory colony of the Smith's red-backed vole, Eothenomys smithii.

Molecular phylogeny and biogeography of Oriental voles: genus Eothenomys (Muridae, Mammalia)

Oriental voles of the genus Eothenomys are predominantly distributed along the Southeastern shoulder of the Qinghai-Tibetan Plateau. Based on phylogenetic analyses of the mitochondrial cytochrome b gene (1143 bp) obtained from 23 specimens (eight species) of Oriental voles collected from this area, together with nucleotide sequences from six specimens (two species) of Japanese red-backed voles ( Eothenomys andersoni and Eothenomys smithii) and five species of the closely related genus Clethrionomys, we revised the systematic status of Eothenomys. We also tested if vicariance could explain the observed high species diversity in this area by correlating estimated divergence times to species distribution patterns and corresponding paleo-geographic events. Our results suggest that: (1) the eight species of Oriental voles form a monophyletic group with two distinct clades, and that these two clades should be considered as valid subgenera— Eothenomys and Anteliomys; (2) Eothenomys eleusis and Eothenomys miletus are not independent species; (3) Japanese red-backed voles are more closely related to the genus Clethrionomys than to continental Asian Eothenomys taxa; and (4) the genus Clethrionomys, as presently defined, is paraphyletic. In addition, the process of speciation of Oriental voles appears to be related to the Trans-Himalayan formation via three recent uplift events of the Qinghai-Tibetan Plateau within the last 3.6 million years, as well as to the effects of the mid-Quaternary ice age.

Climatic change and body size in two species of Japanese rodents

Using museum specimens, we studied temporal changes in skull size in two species of Japanese rodents, the large Japanese field mouse (Apodemus speciosus) and Pratt's vole (Eothenomys smithii = E. kageus) during the 20th century. We used the greatest length of the skull (GTL), zygomatic breadth (ZB), narrowest width of the skull across the interorbital region (IC) and the length of the upper cheek teeth row (M) as indicators to such changes. We found that GTL and ZB (but not IC and M) increased during the study period in mice, and that IC and M (but not GTL and ZB) increased marginally in voles. We attribute these changes to elevated ambient minimal temperatures, which increased food availability and energy savings for the mice, and required diet change in the voles. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82, 263–267.

Human babesiosis in Japan: epizootiologic survey of rodent reservoir and isolation of new type of Babesia microti-like parasite.

We have carried out epizootiologic surveys at various sites in Japan to investigate wild animals that serve as reservoirs for the agents of human babesiosis in the country. Small mammals comprising six species, Apodemus speciosus, Apodemus argenteus, Clethrionomys rufocanus, Eothenomys smithii, Crocidura dsinezumi, and Sorex unguiculatus, were trapped at various places, including Hokkaido, Chiba, Shiga, Hyogo, Shimane, and Tokushima Prefectures. Animals harboring Babesia microti-like parasites were detected in all six prefectures. Inoculation of their blood samples into hamsters gave rise to a total of 20 parasite isolates; 19 were from A. speciosus, and the other 1 was from C. rufocanus. Sequencing of the parasite small-subunit rRNA gene (rDNA) sequence revealed that 2 of the 20 isolates were classified as Kobe type because their rDNAs were identical to that of the Kobe strain (the strain from the Japanese index case). The other 18 isolates were classified as a new type, designated the Hobetsu type, because they all shared an identical rDNA sequence which differed significantly from both that of Kobe-type isolates and that of northeastern United States B. microti (U.S. type). The parasites with Kobe-, Hobetsu- and U.S.-type rDNAs were phylogenetically closely related to each other but clearly different from each other antigenically. The isolates from rodents were demonstrated to be infective for human erythrocytes by inoculation into SCID mice whose erythrocytes had been replaced with human erythrocytes. The results suggest that a new type of B. microti-like parasite, namely, the Hobetsu type, is the major one which is prevalent among Japanese wild rodents, that A. speciosus serves as a major reservoir for both Kobe- and Hobetsu-type B. microti-like parasites, and that C. rufocanus may also be an additional reservoir on Hokkaido Island.

Age determination in the Smith's red-backed vole, Eothenomys smithii, using optic lens weight.

Age determination in the Smith's red-backed vole, Eothenomys smithii, using optic lens weight.

Location and ultrastructure of Borrelia japonica in naturally infected Ixodes ovatus and small mammals.

The internal organs of Ixodes ovatus and the ears of wild rodents (Apodemus speciosus, Eothenomys smithii) and an insectivore (Crocidura dsinezumi) were cultured to isolate borreliae; positive samples were examined for the distribution and dissemination of spirochetes in the host tissues using electron microscopy. Seven isolates were derived from the unfed ticks and the three species of mammals. These isolates were identified as Borrelia japonica judging from the outer surface protein profile using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and reactivity to a B. japonica-specific monoclonal antibody. Borreliae were found only in the midgut lumen of the tick in close contact with the microvilli on the midgut epithelium; on the other hand, borreliae found in the ears of mammals existed freely in the collagenous intercellular substances of connective tissues or in close contact with fibrocytes. The ultrastructural disparities between the borreliae in ticks and mammals appeared to correspond to differences in motility. Interestingly, the borrelia which invaded through the perineurium appeared to contact the basement membrane of a Schwann cell that enclosed several nonmyelinated nerve fibers. This may offer important information regarding the involvement of the nervous system in Lyme disease.

Characterization of Borrelia spp. isolated from the tick, Ixodes tanuki and small rodents in Japan.

Spirochetes were isolated from the tick, Ixodes tanuki, as well as wood mice (Apodemus speciosus) and voles (Clethrionomys rufocanus and Eothenomys smithii), caught in Fukui, Tokushima, and Hokkaido, Japan, from 1991 to 1993. Spirochetes were characterized on the basis of protein profiles, reactivities with monoclonal antibodies (mAbs), Outer surface protein A gene (ospA) and Outer surface protein B gene (ospB) amplification analysis, rRNA gene and flagellin gene restriction fragment length polymorphism (RFLP) analysis, and DNA homology values. Protein profiles of all isolates were homologous and reacted with mAb to OspA, OspB, OspC, flagellin, and heat shock protein 60. The primer reactivity to ospA and ospB were different from those of Borrelia burgdorferi sensu stricto, B. afzelii, B. japonica, and B. garinii. Based on the DNA/DNA homology value and RFLP analysis of rRNA and flagellin gene, these Borrelia sp. isolates are a new group of B. burgdorferi sensu lato. The isolates from ticks and the host rodents were identical in these assays. We propose that these Borrelia sp. are adapted to I. tanuki and are maintained in these field rodents.

Distribution of Borrelia species associated with Lyme disease in the subalpine forests of Nagano prefecture, Japan.

We surveyed the natural distribution of Borrelia species associated with Lyme disease in the subalpine forests of Nagano prefecture, Japan, during 1993-94. Tick-derived isolates (n = 112) from Ixodes persulcatus and rodent-derived isolates (n = 55) from Apodemus argenteus, Apodemus speciosus, Eothenomys andersoni, Eothenomys smithii, and Microtus montebelli were classified by rRNA gene restriction fragment length polymorphism analysis (RFLP ribotyping). Ribotype group IV (an intraspecific variant of Borrelia garinii) was predominant among the tick isolates. It was also isolated repeatedly from the rodents. Ribotype group III (Borrelia afzelii) was detected in low frequencies among the tick and rodent isolates. The data suggest that humans are likely to be exposed to the group IV when they are bitten by I. persulcatus ticks.

Age variation of the third upper molar in Eothenomys smithii.

A study was made of age variation in the size and enamel patterns of the third upper molar of 99 Eothenomys smithii specimens from Japan. No significant age variation was found in either the frequency of the patterns, or the width of the dentine confluent space between the second and the third triangles. Deep lingual reentrant folds, on the posterior loop, appear in specimens where the condylobasal length (CBL) is of 22-24 mm, then the pattern with a shallow reentrant fold increases in frequency in larger CBL classes. The depth of the inner fold showed the same tendency as the changes in the patterns. A significant association, however, between five enamel patterns and age classes, depends on classification according to CBL or body weight. This proved insignificant in five CBL classes, but significant in three CBL or body weight classes. A gradual transition in the age variation of the posterior loop patterns was found among Eothenomys species which have rootless molars throughout life. The simple enamel pattern form significantly increased in frequency with advancing age in E. andersoni and E. shanseius, resembling Clethrionomys glareolus and C. rufocanus ; on the other hand, in E. regulus, E. inez, E. eva, E. chinensis, E. wardi, E. custos and E. proditor no age variation was found on the posterior loop, thus resembling Microtus pennsylvanicus. E. smithii shows a little age variation in the enamel patterns, the variation of which is of an intermediate type.

Prevalence of antibodies to Borrelia spirochetes among wild small rodents in central and western Japan.

Field rodents serve as a reservoir for Lyme disease spirochetes. To evaluate the antibody responses of rodents against different Borrelia species in relation to fauna of vector ticks feeding on them, we examined 272 sera of wild rodents, Apodemus speciosus, A. argenteus, and Eothenomys smithii, obtained in 27 locations in central and western Japan from 1981 to 1994. As to prevalences by rodent species using immunoperoxidase test, A. speciosus, A. argenteus and E. smithii showed 29.4%, 11.6% and 30.8% reactivity to Borrelia japonica, 10.7%, 7.2% and 3.8% to B. afzelii, 0.6%, 1.4% and 0% to B. garinii, and 14.7%, 7.2% and 11.5% to an unknown Borrelia species designated as It type, respectively. Each antibody to B. japonica, B. afzelii and B. sp. It type was detected widely both in central and western Japan, but the antibody to B. garinii was scarcely detectable in any area and rodent species examined. Apodemus mice in high mountain altitudes tend to have antibody to B. afzelii or B. japonica, and those in lower altitudes tend to have B. japonica or B. sp. It type. All 13 Apodemus mice from which B. japonica or B. sp. It type were isolated showed higher titers of antibodies to each homologous Borrelia species. The present results indicate that these antibody prevalences among rodents may be associated with dominant Ixodes ovatus and sporadic I. persulcatus on the mainland of Japan, and that Apodemus mice may not be an efficient reservoir for B. garinii. Such a serosurvey is a useful measure to evaluate the natural distribution of the pathogen.

Variation of the X Chromosome in the Smith's Red-backed Vole Eothenomys smithii

Variation of the X Chromosome in the Smith's Red-backed Vole Eothenomys smithii

Relative Growth of the Skull in the Laboratory-reared Smith’s Red-backed Vole, Eothenomys smithii and So-called “Kage” Red-backed Vole, E. kugeus

Relative Growth of the Skull in the Laboratory-reared Smith’s Red-backed Vole, Eothenomys smithii and So-called “Kage” Red-backed Vole, E. kugeus

日本に於ける Stenoponia montana Darskaya, 1949 に就いて : 日本産隠翅類の研究 II

Stenoponia montana Darskaya has been reported in 1949 by Darskaya as a new species in the mountain forests of northern Korea. The present article deals with the records of the species from the mountain regions of central Japan, Nagano- and Kyoto- prefectures with systematic descriptions, host relations and some ecological notes. In winter, from end of October to February, the species is found on the bodies of several species of small rodents such as Apodemus speciosus, Ap. sylvaticus, Rattus rattus, Microtus montebelli and Eothenomys smithii and in one single instance on the Japanese yellow marten, Martes melampus. Eggs, before oviposition, are observed in the abdomens of four specimens of the species. The eggs are long ovoid and occur in pairs in the abdomens. The surface of the egg is uniformly covered by beautiful network consisting of smaller pentagonal and hexagonal cells. The micropylar openings on the anterior pole are found about 60 in number, whereas the posterior apparatus is found to consist of about 30 openings.