Microtus Montebelli Research Articles

Impact of late Quaternary climate change on the demographic history of Japanese field voles and hares revealed by mitochondrial cytochrome b sequences.

The mitochondrial cytochrome b gene of the Japanese field vole (Microtus montebelli), an herbivorous rodent, was subjected to an analysis of sequence variation with the objective of elucidating the population histories of this species. Construction of a phylogenetic tree revealed the existence of several region-specific lineages in Honshu and Kyushu, which were evenly separated from each other. In consideration of the documented time-dependent evolutionary rates of rodents, the estimated divergence times indicate that the region-specific lineages of M. montebelli emerged 160,000-300,000 years ago. In a haplotype network, the region-specific lineages from northern and central Honshu tended to show star-shaped clusters, with additional internal star-shaped clusters, indicative of two periods of population expansion. The onsets of the expansions were estimated to have occurred 15,000 and 10,000 years ago, respectively, suggestive of association with the two periods of rapid warming following the Last Glacial Maximum (LGM). In contrast, such predicted post-LGM expansion events were less pronounced in the southern lineages, implying latitudinal dependence of the effect of the LGM on population dynamics. Sado Island haplotypes exhibited a network with a star-shaped pattern and a 10,000-year-old expansion signal, surrounded by a Honshu haplotype cluster with a 15,000-year-old expansion signal, suggesting contribution of the post-LGM expansion events in the formation of the Sado population. A reanalysis of Cytb sequence of the Japanese hare (Lepus brachyurus), which has a similar geographic range to the voles, yielded results that were consistent with those of the vole analysis, confirming that the characteristics of the post-LGM expansion event were dependent on latitude, involved two successive expansion events, and enabled migration across deep straits. It seems reasonable to infer that the environmental changes that occurred during the warm periods following the LGM were a contributing factor in the expansion of the distribution range of newly emerged haplotype groups.

Unique population dynamics of Japanese field vole: Winter breeding and summer population decline

AbstractIt is common knowledge that winter temperatures influence the life history of small mammals. Cold temperatures necessitate increased energy requirements for survival, and recent studies indicate that snow cover can have both negative and positive influences. With each new observation, we develop a more comprehensive understanding of the mechanisms that influence small mammal populations. Here we report on our recent study on Japanese field vole Microtus montebelli, which reaches its peak in population during the early spring and its low during the autumn. To understand the population dynamics of these voles, we conducted a capture‐mark‐recapture survey, then estimated the seasonal abundance, recruit, capture probabilities, and survival probabilities using the Bayesian hierarchical model. We also analyzed the impact of mammalian generalist predator visits on the survival probabilities. Our data indicates that the early spring peak in population is due to intensive winter breeding and the highest survival probabilities during the periods of deep snow cover. When snow cover reaches a certain depth, the circumstances can combine to raise survival probability and favor breeding. During the breeding season in May and June, on the contrary, the survival probability reached its lowest, resulting in a decrease in population despite breeding. The low survival probability between spring and autumn could be attributed to the impact of generalist predators, and low vegetation may have amplified the effect. In summary, the deep snow cover and generalist predators were considered to be the key factors shaping this unique population dynamics in this orchard area.

Complete mitochondrial genome of the Japanese field vole microtus montebelli (Milne-Edwards, 1872) (Rodentia: Arvicolinae)

The complete mitochondrial DNA sequence of the Japanese field vole Microtus montebelli was determined using Illumina MiSeq platform. The assembled genome was 16,307 bp in length and contained 13 protein-coding genes, two ribosomal RNA genes, 22 transfer RNA genes. According to phylogenetic analysis of 13 protein-coding genes, M. montebelli and other Microtus species consist of paraphyletic clades and M. montebelli is most closely related to M. kikuchii, a species endemic to Taiwan.

Concentration of radioactive materials in small mammals collected from a restricted area in Fukushima, Japan since 2012

AbstractFukushima Daiichi Nuclear Power Plant was struck by a huge earthquake and tsunami, which ultimately released a large amount of radioactive material owing to steam explosion in March 2011. This accident affected extensive area and resulted in soil contamination, which would prevail over a long period. The contaminants included various types of nuclear materials, among which cesium (134,137Cs) has a particularly long half‐life. Organisms living in the contaminated area are presumably exposed to radiation caused by the presence of these radioactive contaminants in their environment, in addition to internal exposure owing to the intake of these contaminants through the food web. The purpose of our data collection is to monitor accumulation of radioactive materials in small mammals for a long period and to predict its effects. Reasons for focusing on small mammals include: (a) mammals are the most sensitive to radiation, (b) small mammals have a smaller home range compared to large mammals; therefore, accumulation of radioactive materials in small mammals is considered to reflect the condition of the surrounding environment, and (c) among the small mammals, rodents are used as laboratory animals and provide a lot of information, from which we can expect to acquire much knowledge based on investigations. The dataset contains measurements of 134,137Cs and potassium (40K) concentrations in small terrestrial mammals collected in areas contaminated with radioactive contaminants from the Fukushima Daiichi Nuclear Power Plant accident. We established two fixed study sites and three temporary sites inside the zone from which humans were evacuated owing to high levels of radiation. Annual monitoring of Cs contamination in small mammals was started in 2012 at the fixed study sites. Until 2016, we collected 547 individuals of four species (Apodemus speciosus, Apodemus argenteus, Microtus montebelli and Urotrichus talpoides). Cs concentrations in each individual were measured using high‐purity germanium detectors against a ground body after removing the internal organs and the head. Our data provide valuable information about temporal changes in 134Cs and 137Cs concentrations in small mammals following the Fukushima Daiichi Nuclear Power Plant accident. The study is continuing and the present dataset will be updated in the future.

Effectiveness of vole control by owls in apple orchards

Abstract Biological pest control is gaining greater acceptance as an important part of integrated pest management for sustainable agriculture. However, knowledge regarding biological control of rodent pests is limited, and its effectiveness in temperate areas has not been quantified. In traditional Japanese apple orchards, the Ural owl Strix uralensis breeds in tree hollows and preys on the Japanese field vole Microtus montebelli, a native pest species that can harm fruit production. In this study, we hypothesised that the Ural owl, a generalist predator, can act as a biological control agent by reducing vole densities in temperate orchards. To quantify the pest control effects of breeding Ural owls, we first analysed the diet of individual owls nesting in apple tree hollows. Second, we installed nest boxes in orchards to attract breeding owl pairs and collected data on vole population changes around owl nests to compare with control areas. The population changes were analysed using a generalised linear mixed model to assess the effect of breeding owls within their breeding territory. The model considered seasonal fluctuations in vole population size as well as surrounding land‐use. We also examined vole populations around the owl nests in April, and the distance between nests and forested areas, to determine if these variables influenced nest site selection. Voles were the primary prey of Ural owls breeding in orchards and the owls reduced vole populations within their estimated breeding territories by 63% (±SE: 53%–70%) compared with the predicted density without owls. Owls preferred to nest in orchards with higher vole population densities in April. Our findings also indicate that higher occupancy rates are possible by distributing nest boxes based on Ural owl breeding territory size (306 m radius circle in our study). Synthesis and applications. As breeding Ural owls provide significant pest control effects within their breeding territories, the reintroduction of breeding Ural owl pairs within orchards would contribute to rodent pest control. Promoting the reproduction of native raptors in agricultural areas can be an option for developing integrated pest management while simultaneously maintaining regional biodiversity.

Assisted reproductive technologies in Microtus genus.

Background Microtus genus is one of the experimental animals showing unique characteristics, and some species have been used as various research models. In order to advance the utilization of Microtus genus, the development of assisted reproductive technologies (ARTs) is a key point. This review introduces recent progress in the development of ARTs for Microtus genus, especially Microtus montebelli (Japanese field vole).MethodsBased on previous and our publications, current status of the development of ARTs was summarized.ResultsIn M. montebelli, ARTs, such as superovulation, in vitro fertilization, intracytoplasmic sperm injection, embryo transfer, sperm cryopreservation, and nonsurgical artificial insemination, have considerably been established by using the procedures which were originally devised for mice and partly modified. However, when the methods for M. montebelli were applied to Microtus arvalis and Microtus rossiaemeridionalis, all protocols of ARTs except for sperm cryopreservation were technologically invalid.ConclusionAssisted reproductive technologies (ARTs) are considerably established in M. montebelli, and this fact allows this species to be potentially useful as a model animal. However, since ART protocols of M. montebelli are mostly invalid for other species of the Microtus genus, it is necessary to improve them specifically for each of other species.

Preference of Japanese field voles (Microtus montebelli) for apple rootstock genotypes: Correlations with bark characteristics

Along with the expansion of dwarfing apple rootstocks in Japan, damage through bark-eating by the Japanese field vole (Microtus montebelli Milne-Edwards, 1872) in apple orchards has increased. The most prevalent cultivar, JM7, in particular, is highly susceptible to vole gnawing. Hence, it is a pressing task to reduce vole damage to apple rootstocks by developing and introducing a new dwarfing rootstock cultivar that is less susceptible to voles. In order to achieve this, it is critical to elucidate which rootstock characteristics underlie vole preference. Preferences of the Japanese field vole among seven apple rootstocks were examined by a cafeteria experiment using ten voles. Voles showed a clear preference for the JM7 cultivar. Nutrient and morphological analyses of these rootstocks revealed that voles preferred to eat rootstocks which were poor in total phenolics, rich in nitrogen, and had low edible ratios of shoots. Among the tested seven rootstocks, JM7 was richest in nitrogen, and poorest in total phenolics. Our results indicate that future breeding projects on vole-resistant dwarfing apple rootstock genotypes should aim to develop a cultivar that is rich in total phenolics and poor in nitrogen, while keeping the advantageous traits of the JM7 rootstock, such as high productivity, and ease of propagation by hardwood cutting.

Establishment of superovulation procedure in Japanese field vole, Microtus montebelli

Japanese field vole (Microtus montebelli) is a wild-derived rodent and have unique characteristic. Thus, these species have been expected as model animal. This study was performed to develop novel superovulation procedure for Japanese field vole. First, when 30 IU pregnant mare's serum gonadotropin (PMSG) and 30 IU human chorionic gonadotropin (hCG) were administrated 48 hours apart, females showed higher response to hCG compared with three concentrations of PMSG. Second, to effectively induce ovulation on females after vaginal opening, they were mated with vasectomized male instead of hCG administration. Average number of ovulated oocytes using PMSG mating (13.9 ± 1.9 oocytes) was higher than PMSG–hCG (control; 6.9 ± 2.3 oocytes) or PMSG–hCG mating (6.8 ± 0.8 oocytes). Finally, we attempted superovulation using GnRH agonist (GnRHa). With this treatment, we speculated that GnRHa might induce endogenous luteinizing hormone releasing to cause ovulation. Such superovulation was performed with 30 IU PMSG and different concentration of 20% polyvinylpyrrolidone–GnRHa (15, 30, 45, and 60 μg/kg). As results, average number of ovulated oocytes was highest with 30 μg/kg GnRHa (14.5 ± 4.1 oocytes). The numbers of ovulated oocytes of other concentrations were 5.0 ± 1.4 (15 μg/kg), 12.8 ± 2.7 (45 μg/kg), and 8.8 ± 3.7 oocytes (60 μg/kg). Nuclear status of most collected oocytes was the second meiotic division (range, 94.3%–100%). These superovulation procedures will be useful for development of in vitro culture systems and assisted reproductive technologies for not only Japanese field vole but also other voles.

Anesthetic effects of a combination of medetomidine, midazolam and butorphanol on the production of offspring in Japanese field vole, Microtus montebelli.

Pentobarbital sodium (Somnopentyl) can induce surgical anesthesia with a strong hypnotic effect that causes loss of consciousness. Animals have been known to die during experimental surgery under anesthesia with Somnopentyl, causing it to be declared inadequate as a general anesthetic for single treatment. An anesthetic combination of 0.3 mg/kg medetomidine, 4.0 mg/kg midazolam and 5.0 mg/kg butorphanol (M/M/B:0.3/4/5) was reported to induce anesthesia for a duration of around 40 min in ICR mice; similar anesthetic effects were reported in both male and female BALB/c and C57BL/6J strains of mice. However, the anesthetic effects of this combination in Japanese field vole, Microtus montebelli, remain to be evaluated. In the present study, we assessed the effects of Somnopentyl and different concentrations of anesthetic combination (M/M/B:0.3/4/5, 0.23/3/3.75 or 0.15/2/2.5) in Japanese field voles, by means of anesthetic scores. We also examined effect of these anesthetics on production of offspring. Death of the animals was observed only with Somnopentyl. The anesthetic score of Somnopentyl was lower than those of the other anesthetics, although there were no significant differences in duration, body weight and frequency of respiratory among the evaluated anesthetics. Abortion rate with Somnopentyl was significantly higher than that with the M/M/B:0.23/3/3.75 combination, although there was no significant difference in the number of offspring between two. In conclusion, results of this study provide basic information for achieving appropriate anesthetic concentrations in addition to indicating a new, safe and effective surgical anesthetic for Japanese field voles.

Estimation of absorbed radiation dose rates in wild rodents inhabiting a site severely contaminated by the Fukushima Dai-ichi nuclear power plant accident

The dose rates of radiation absorbed by wild rodents inhabiting a site severely contaminated by the Fukushima Dai-ichi Nuclear Power Plant accident were estimated. The large Japanese field mouse (Apodemus speciosus), also called the wood mouse, was the major rodent species captured in the sampling area, although other species of rodents, such as small field mice (Apodemus argenteus) and Japanese grass voles (Microtus montebelli), were also collected. The external exposure of rodents calculated from the activity concentrations of radiocesium (134Cs and 137Cs) in litter and soil samples using the ERICA (Environmental Risk from Ionizing Contaminants: Assessment and Management) tool under the assumption that radionuclides existed as the infinite plane isotropic source was almost the same as those measured directly with glass dosimeters embedded in rodent abdomens. Our findings suggest that the ERICA tool is useful for estimating external dose rates to small animals inhabiting forest floors; however, the estimated dose rates showed large standard deviations. This could be an indication of the inhomogeneous distribution of radionuclides in the sampled litter and soil. There was a 50-fold difference between minimum and maximum whole-body activity concentrations measured in rodents at the time of capture. The radionuclides retained in rodents after capture decreased exponentially over time. Regression equations indicated that the biological half-life of radiocesium after capture was 3.31 d. At the time of capture, the lowest activity concentration was measured in the lung and was approximately half of the highest concentration measured in the mixture of muscle and bone. The average internal absorbed dose rate was markedly smaller than the average external dose rate (<10% of the total absorbed dose rate). The average total absorbed dose rate to wild rodents inhabiting the sampling area was estimated to be approximately 52 μGy h−1 (1.2 mGy d−1), even 3 years after the accident. This dose rate exceeds 0.1–1 mGy d−1 derived consideration reference level for Reference rat proposed by the International Commission on Radiological Protection (ICRP).

Rat Damage Control to Round-Baled Silage by Modifying Storage Layout

This self-review summarizes the prevention of rat damage to wrapping film when whole-crop forage containing cereals is preserved as round-baled silage (RBS). A trapping survey at the RBS stock yards showed that Large Japanese field mice (Apodemus speciosus), Japanese grass voles (Microtus montebelli), brown rats (Rattus norvegicus), and roof rats (Rattus rattus) were species with the potential to inflict damage. The features of the damage differed for each rat species. In particular, it was observed that brown rats and roof rats tended to cause extensive film-damage. RBSs are usually stacked in close proximity because they are produced in bulk. This usual storage layout was considered to provide rats with many narrow spaces between RBS, inaccessible to most of their predators, thereby exacerbating the rat damage to RBS. When modifying the storage layout to produce open spaces between RBS by separating them, the modified layout was effective in preventing damage caused by brown rats and roof rats because the predation hazard would be increased. However, the effect was lost when the spaces between RBS were covered with snow or when species such as Large Japanese field mice damaged RBS's bottom from underground burrows. It was suggested that these problems may be resolvable by providing sufficient open space between RBS and protecting the bottom with wire netting.

ホンドハタネズミ（Microtus montebelli）精子の凍結-融解後のDNA損傷レベルおよび卵活性化能

ホンドハタネズミ（Microtus montebelli）精子の凍結-融解後のDNA損傷レベルおよび卵活性化能

筑後川河原 (久留米市) に生息するハタネズミの生態

筑後川河原 (久留米市) に生息するハタネズミの生態

ホンドハタネズミ (Microtus montebelli montebelli) のG-, C-及びN-バンドパターン―大陸産ハタネズミ (M. oeconomus) との比較分析

ホンドハタネズミ (Microtus montebelli montebelli) のG-, C-及びN-バンドパターン―大陸産ハタネズミ (M. oeconomus) との比較分析

Different cross-reactivity of human and rodent sera to Tula virus and Puumala virus

Tula virus (TULV) and Puumala virus (PUUV) are hantaviruses carried by the bank vole (Myodes glareolus) and European common vole (Microtus arvalis), respectively. PUUV is a causative agent of hemorrhagic fever with renal syndrome (HFRS), while TULV is thought to be apathogenic to humans. The N-terminal regions of the N proteins from TULV and PUUV were expressed and applied as enzyme-linked immunosorbent assay (ELISA) antigens. Colonized Japanese grass voles (Microtus montebelli) and BALB/c mice were used for experimental inoculation of the vole-borne hantaviruses TULV and PUUV. Voles and mice showed significant antibody production toward both viruses, but these antisera showed little cross-reactivity between TULV and PUUV in the immunofluorescence antibody assay and ELISA. In contrast, sera from patients with HFRS caused by PUUV exhibited high cross-reactivity against the TULV antigen, and sera from a natural rodent reservoir showed moderate cross-reactivity against the heterologous antigen, indicating that the antigenic cross-reactivity between TULV and PUUV differs in sera from rodents and humans.

Genotoxic Assessment of Small Mammals at an Illegal Dumpsite at the Aomori-Iwate Prefectural Boundary

In 2003, we examined the chromosomes of grass voles at an illegal dumpsite at the Aomori-lwate prefectural boundary. In subsequent years, from 2003-2006, we surveyed the chromosomes of four species of small mammals, namely, the Japanese grass vole (Microtus montebelli), the large Japanese field mouse (Apodemus speciosus), the small Japanese field mouse (A. argenteus), and the greater Japanese shrew mole (Urotrichus talpoides). Each annual survey revealed, both on a yearly basis and during the entire period in question, that the frequencies of breaks and gaps in chromosomes of M. montebelli were significantly higher at the dumpsite than on the outskirts and in controls, suggesting that grass voles at the dumpsite have been subject to continuous genotoxic effects since the establishment of the dumpsite. We also ascertained that grass voles are much more susceptible to chromosomal damage than field mice and shrew moles, which had very low levels of chromosomal aberrations at the dumpsite, on the outskirts of the dumpsite, and in controls. Our four-year survey revealed two variants of M. montebelli from the dumpsite with M6 fission (2n=31), two variants of A. speciosus from the outskirts with XO monosomy (2n=47, XO), and a variant of A. speciosus from the dumpsite with situs inversus. Our analysis confirms our previously proposed hypothesis that M. montebelli might be useful as an indicator species for genotoxic assessment of below-ground pollution by industrial waste at illegal dumpsites.

Eye-lens weight curve for estimation of age in the Japanese grass vole, Microtus montebelli Milne-Edwards (Rodentia: Muridae)

We established a standard curve for age estimation of the Japanese grass vole, Microtus montebelli, from eye-lens weight as a tool for analyses of ages in the vole population. Predicted age was given by the equations, x=10(Y+2.00)/3.24 for males, and x=10(Y+1.72)/2.94 for females, where Y is weight of paired lenses in mg and x is predicted age in days. Indices of predictive accuracy of the technique (Syx/Y: the standard error of estimate divided by the mean of Y) were 0.059 and 0.073 for males and females, respectively.

Chromosomal Aberrations in Japanese Grass Voles in and Around an Illegal Dumpsite at the Aomori-Iwate Prefectural Boundary

Bone marrow chromosomes of thirty specimens of the Japanese grass vole, Microtus montebelli (2n=30), which had been caught on and near an illegal dumpsite at the Aomori-Iwate prefectural boundary, were analyzed and compared with those of fifteen grass voles from non-polluted areas as part of an effort to assess genotoxic influences on grass voles in the dumpsite area. Fifty metaphases per specimen were examined with particular attention to numerical and structural aberrations. Two specimens from the dumpsite had 2n=31, which was confirmed by G-banding analysis to have been caused by centric fission of M6 homologs, while control specimens had no such abnormality. In specimens from the polluted area, the mean number of chromosomal aberrations (breaks and/or gaps) per 50 metaphases per specimen was 2.57+/-0.41, which was significantly higher than that (0.80+/-0.14; P<0.01) in control specimens. Chromosomal aberrations were randomly distributed on chromosomes, with frequencies being proportional to the relative lengths of chromosomes. Our findings suggest that grass voles at and around the dumpsite have been seriously damaged at the chromosomal level and, moreover, that M. montebelli might be useful as an indicator species for genotoxic assessment of below-ground pollution by industrial waste at illegal dumpsites.

The Delayed Quinacrine Mustard Fluorescence from the C-blocks of Apodemus argenteus Is Due to the Introduction of Nicks into the DNA

"Delayed QM-fluorescence" refers to the unusual kinetics of fluorescence from most of the C-heterochromatic regions of the chromosomes of the small Japanese field mouse Apodemus argenteus. When stained with quinacrine mustard (QM-stained), these C-heterochromatic regions emit weak fluorescence immediately after exposure to blue light (BL); they emit bright fluorescence within a few minutes; and the intensity of the fluorescence gradually decreases after maximum fluorescence has been recorded. To elucidate the mechanism of this phenomenon, we used acridine orange staining (AO-staining) and a modified version of the in situ nick-translation method. Focusing on the large C-heterochromatic region (C-block) of the X chromosome, we noted that AO-stained C-blocks emitted greenish fluorescence, while QM-stained and BL-exposed (QM-BL-processed) C-blocks emitted reddish fluorescence upon AO-staining after removal of QM. These findings suggested that the C-block DNA of A. argenteus might undergo a structural change, such as strand breaks, during QM-BL processing. Application of the modified in situ nick-translation method revealed the generation of an appreciable number of nicks in the C-block DNA by QM-BL processing. No such nick formation was observed in the C-blocks of three other mammalian species: Apodemus peninsulae, Microtus montebelli, and Urotrichus talpoides. Our findings support the hypothesis that nick formation due to exposure to BL might play a primary role in inducing delayed QM-fluorescence in the C-blocks of A. argenteus. On the basis of the present and earlier findings, we propose a probable mechanism for delayed QM-fluorescence in A. argenteus chromosomes.

Mite vectors (Acari: Trombiculidae) of scrub typhus in a new endemic area in northern Kyoto, Japan.

Between 1983 and 1999, 27 human cases of scrub typhus (two fatal) occurred in the Nodagawa River basin of northern Kyoto, Japan, an area where no cases had been previously reported. Antibody screening of infected patients' sera showed that nine of 15 patients had high titers against the Gilliam type of Orientia tsutsugamushi (Hayashi). To determine the vector mite transmitting the disease, we studied rodent and chigger populations in and near a rice field alongside the Nodagawa River between 1996 and 1999. The most common rodent species was Microtus montebelli (Milne-Edwards), representing 73.3% (33/45) of the population. The mite index (average number of mites per infested host) was highest (190.8) in Leptotrombidium pallidum Nagayo, Mitamura & Tamiya parasitizing on M. montebelli, followed by Leptotrombidium intermedium (Nagayo, Mitamura & Tamiya) (174.9) on the same host species. Orientia tsutsugamushi was isolated from 60.5% (23/38) of rodents and from 71.2% (37/52) of pools of engorged L. pallidum. The Gilliam type of O. tsutsugamushi was most prevalent in rodents, and in engorged L. pallidum and it was the only type recovered from 10 isolates inoculated into L 929 cells for indirect immunofluorescence examination. Orientia tsutsugamushi infected 14.3% (181/1263) and 14.8% (306/2066) of engorged and unfed L. pallidum larvae, respectively, and was also detected in 0.055% (2/3634) of unfed L. intermedium, although previous studies suggest that this mite rarely bites humans. These results show that L. pallidum is the primary vector species of scrub typhus in this new endemic area in Japan.