Apodemus Speciosus Research Articles

Effects of environmental radiation on testes and spermatogenesis in wild large Japanese field mice (Apodemus speciosus) from Fukushima.

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident that occurred after the Great East Japan Earthquake in March 2011 released large quantities of radionuclides to the environment. The long-term effects of radioactive cesium (Cs) on biota are of particular concern. We investigated the accumulation of radioactive Cs derived from the FDNPP accident, and chronic effects of environmental radionuclides on male reproduction, in the large Japanese field mouse (Apodemus speciosus). In 2013 and 2014, wild mice were captured at 2 sites in Fukushima Prefecture and at 2 control sites that were distant from Fukushima. Although the median concentrations of 134Cs and 137Cs in the mice from Fukushima exceeded 4,000 Bq/kg, there were no significant differences in the apoptotic cell frequencies or the frequencies of morphologically abnormal sperm among the capture sites. Thus, we conclude that radiation did not cause substantial male subfertility in Fukushima during 2013 and 2014, and radionuclide pollution levels in the study sites would not be detrimental to spermatogenesis of the wild mice in Fukushima.

The effects of dioxin pollution on population of the large Japanese filed mouse, Apodemus speciosus: An attempt to capture the population response using a molecular indicator

The effects of dioxin pollution on population of the large Japanese filed mouse, Apodemus speciosus: An attempt to capture the population response using a molecular indicator

Molecular characterization and specific detection of Anaplasma species (AP-sd) in sika deer and its first detection in wild brown bears and rodents in Hokkaido, Japan

A previously undescribed Anaplasma species (herein referred to as AP-sd) has been detected in sika deer, cattle and ticks in Japan. Despite being highly similar to some strains of A. phagocytophilum, AP-sd has never been detected in humans. Its ambiguous epidemiology and the lack of tools for its specific detection make it difficult to understand and interpret the prevalence of this Anaplasma species. We developed a method for specific detection, and examined AP-sd prevalence in Hokkaido wildlife. Our study included 250 sika deer (Cervus nippon yesoensis), 13 brown bears (Ursus arctos yesoensis) and 252 rodents including 138 (Apodemus speciosus), 45 (Apodemus argenteus), 42 (Myodes rufocanus) and 27 (Myodes rutilus) were collected from Hokkaido island, northern Japan, collected during 2010 to 2015. A 770bp and 382bp segment of the 16S rRNA and gltA genes, respectively, were amplified by nested PCR. Results were confirmed by cloning and sequencing of the positive PCR products. A reverse line blot hybridization (RLB) based on the 16S rRNA gene was then developed for the specific detection of AP-sd. The prevalence of AP-sd by nested PCR in sika deer was 51% (128/250). We detected this Anaplasma sp. for the first time in wild brown bears and rodents with a prevalence of 15% (2/13) and 2.4% (6/252), respectively. The sequencing results of the 16S rRNA and gltA gene amplicons were divergent from the selected A. phagocytophilum sequences in GenBank. Using a newly designed AP-sd specific probe for RLB has enabled us to specifically detect this Anaplasma species. Besides sika deer and cattle, wild brown bears and rodents were identified as potential reservoir hosts for AP-sd. This study provided a high throughput molecular method that specifically detects AP-sd, and which can be used to investigate its ecology and its potential as a threat to humans in Japan.

Multiple-locus variable-number tandem repeat analysis of Leptospira interrogans and Leptospira borgpetersenii isolated from small feral and wild mammals in East Asia

Leptospira spp. are the causative agents of a worldwide zoonosis, leptospirosis, maintained by various mammals. Each Leptospira serovar is frequently associated with a particular maintenance host, and recently, Leptospira genotype–host association has also been suggested to limit serovars to restricted areas. We investigated the molecular characteristics of L. interrogans and L. borgpetersenii which were isolated from small feral and wild animals in four East Asian states using multiple-locus variable-number tandem repeat analysis (MLVA).MLVA using 11 loci was performed on 110 L. interrogans serogroups from Japan (79 strains of 5 serogroups from 3 animal species), Philippines (21; 3; 2), Taiwan (7; 2; 3), and Vietnam (3; 1; 1). A MLVA method using 4 loci for L. borgpetersenii was established and performed on 52 isolates from Japan (26; 3; 7), Philippines (13; 1; 2), and Taiwan (13; 1; 3). In L. interrogans, serogroups Autumnalis and Hebdomadis appeared more genetically diverse than serogroups Bataviae, Grippotyphosa, Icterohaemorrhagiae, Pomona, or Pyrogenes. The former serogroup strains with the exception of one Hebdomadis strain were isolated from Apodemus speciosus while all the latter serogroup strains with the exception of Grippotyphosa were isolated from Rattus norvegicus. L. borgpetersenii was isolated from at least 11 animal species while L. interrogans was isolated from five species, which might suggest a wider host range for L. borgpetersenii. Broad host preference in a single genotype was also observed, which colonized not only different species of the same genera but also multiple animal genera.This study demonstrates that there may be variability in the range of genetic diversity among different Leptospira serogroups, which may be attributed to maintenance host animals and environmental factors.

Effects of within‐plant variability in seed weight and tannin content on foraging behaviour of seed consumers

Summary Individual plants provide a habitat patch for foragers where the sought‐after resources (e.g. leaves, fruits and seeds) are clustered in locally dense aggregations. Characteristics of these resources often vary greatly even within individual plants, which is known as within‐plant or subindividual variation. To best describe properties of the patch (individual plants), the higher moments of trait‐value distributions must be included in addition to the mean values. However, the question whether differences in within‐plant variability of a given trait influence the foraging behaviours of consumers has been mostly untested. To test the hypothesis that differences in within‐plant variation of traits can influence the patch selection behaviour of seed consumers, we used the mean, coefficient of variation (CV) and skewness of within‐plant distributions of two Quercus serrata (Thunb) seed traits (weight and tannin content) as descriptors of plant phenotypes. We then examined the relationships between these descriptors and patch selection by the wood mouse Apodemus speciosus, where individual Quercus trees formed a foraging patch for seed removal. We collected 8594 seeds from 26 individual trees in a forest in northern Japan. We then measured their weight and tannin content, marked and returned them to the locations where they were found, and traced their fates in relation to seed removal by the wood mouse. Tannin content was nondestructively estimated using near‐infrared spectroscopy (NIRS). There was notable within‐plant variation in seed weight and tannin content. Generalized additive modelling revealed that trees with a large mean and CV of seed weight and those with a small CV and skewness of tannin content had a high frequency of seed removal. These results highlight the importance of considering the within‐plant distribution of seed trait values, in addition to the mean trait values of individual seeds, when describing plant phenotypes. The inclusion of these data is essential to understand the ecological and evolutionary processes at work in plant–animal interactions.

The effects of maternal presence on natal dispersal are seasonally flexible in an asocial rodent

In mammals, social tolerance among females, the philopatric sex, is formed through continued physical proximity between kin after offspring are weaned. However, the benefits of continued close association may be outweighed by costs such as local resource competition and risk of inbreeding. We hypothesized that for ‘philopatric females’, a flexible tendency towards either natal dispersal or philopatry is an important behavioral response to changes in social conditions. We examined this using an asocial rodent, Apodemus speciosus, which exhibits two discrete breeding seasons, one in spring and the second in autumn. Daughters and mothers were shown to recognize each other as kin at the time of weaning in both seasons. In spring, some mothers reproduced twice, and some first-litter daughters matured and reproduced in the same season. In autumn, however, only mothers reproduced, and there were no second litters. In spring, the proportion of natal dispersers was higher among weaned offspring whose mother remained present than those whose mother was absent, while in autumn, natal dispersal was more frequent when the mother was absent than when she remained. Sons dispersed earlier than their female littermates. Population density alone is insufficient to explain these patterns. We suggest that variable levels of reproductive competition between female kin result in seasonal differences in female natal dispersal. Breeding condition can be modulated by environmental factors, and the promotion of reproductive activity of females in spring may cause natal dispersal of daughters, while the inhibition of reproductive activity in autumn may permit philopatry.

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).

Classification of the spermatogenic cycle, seasonal changes of seminiferous tubule morphology and estimation of the breeding season of the large Japanese field mouse (Apodemus speciosus) in Toyama and Aomori prefectures, Japan.

The large Japanese field mouse, Apodemus speciosus, is a potential indicator of environmental stress, but this function has not been confirmed by histological studies. Since environmental stress affects the reproductive function of mice, we determined the reproductive characteristics of this species at two locations: Toyama (36°35ʹN, 137°24ʹE) and Aomori (40°35ʹN, 140°57ʹE). Mice were captured during May–November (n=119) and July–November (n=146) at these locations, respectively. We classified the breeding season from the numbers of pregnant females and young, in addition to the spermatogenic cycle and seasonal changes in seminiferous tubule morphology of males. Testicular weight was measured, and seminiferous tubule morphology was examined histologically. Fourteen stages were found in the seminiferous epithelium cycle based on acrosome formation and spermatid head morphology. At both locations, the breeding season peaked from late summer to early autumn and possibly in spring. Spermatogenic activity was classified into 4 periods from June to November: resting around June and October–November; resumptive around July; active around August; and degenerative around September. During the resting period, the seminiferous tubules consisted of Sertoli cells, spermatogonia and spermatocytes. Spermatogenesis began during the resumptive period, and spermatids were observed. During the active period, active spermatogenesis and a broad lumen were observed. During the degenerative period, spermatogenesis ended, and Sertoli cells, spermatogonia, spermatocytes and degenerating exfoliated round spermatids were observed. This study provides scientific information about the testicular histopathological evaluations of the large Japanese field mouse for its use as an index species of environmental pollution.

Laboratory tests for phenomenon, patterns, and processes demonstrated in the wild—the case of the endemic rodents, Apodemus speciosus and A. argenteus—

Laboratory tests for phenomenon, patterns, and processes demonstrated in the wild—the case of the endemic rodents, <i>Apodemus speciosus</i> and <i>A. argenteus</i>—

Isolation of pathogenic Yersinia enterocolitica 1B/O:8 from Apodemus mice in Japan.

Yersinia enterocolitica was isolated from 15.7% (88/560) of wild rodents captured in 15 prefectures in Japan. Prevalences by rodent species were 18.0% (70/388) in Japanese field mice (Apodemus speciosus), 20% (14/71) in small Japanese field mice (Apodemus argenteus), and 11% (4/38) in gray red-backed vole (Myodes rufocanus bedfordiae), suggesting that these rodent species are important reservoirs of Y. enterocolitica. Although most of the isolates were identified as biotype 1A, the pathogenic bioserotype 1B/O:8 was detected in one of the A. speciosus and in three of the A. argenteus captured in Aomori Prefecture. It is suggested that Apodemus mice may be an important reservoir of Y. enterocolitica, and that there are foci of the pathogenic bioserotype 1B/O:8 in Aomori Prefecture, because human sporadic cases by the serotype have been reported in this prefecture.

Magnitude of food overabundance affects expression of daily torpor

Many small mammal species use torpor as a strategy for reducing energy expenditure in winter. Some rodent hibernators also hoard food to provide reserves of energy, and individuals with large hoards express less torpor than those with smaller reserves. These facts imply that animals can recognize levels of food availability, but where food is very plentiful, it is unclear whether torpor expression is affected by temporal changes in the extent of food overabundance. Moreover, the relationship between daily torpor and excess food availability has not been clearly established. The large Japanese field mouse Apodemus speciosus caches food for use as a winter energy resource and exhibits daily torpor under artificial winter conditions. The present study examined whether individuals exposed to different magnitudes of overabundant food exhibited differences in expression of daily torpor, and secondly whether torpor expression varied in response to changes in the overall quantity of overabundant food. It was observed that while absolute quantities of overabundant food did not appear to affect daily torpor expression, the mice did respond to changes in food availability, even when food remained overabundant. This suggests that the mice respond to fluctuations in food availability, even where these changes do not place any constraint on energy budgets. Thus recognition of changing food availability cannot be a purely physiological response to shortage or plenty, and may contribute to predictions of future energy availability. The expression of torpor was inhibited in response to increasing food availability, and the mice used shallower torpor when food availability increased to superabundance. These findings suggest that daily torpor may be regulated not only physiologically in response to energy constraints but also psychologically, via recognition of food availability.

Effect of founding events on coat colour polymorphism ofApodemus speciosus(Rodentia: Muridae) on the Izu Islands

To infer the evolutionary mechanism of phenotypic variation among isolated island populations, we investigated coat colour and genetic variation in the large Japanese field mouse (Apodemus speciosus) on the Izu Islands (Ohshima, Niijima, Kouzushima, and Miyakejima). Coat colour in the most remote population (Miyakejima) was unique and significantly darker than that in the other populations. Ohshima that is closest to the source population showed variation in coat colour within its population. Phylogeographical analyses using mitochondrial and microsatellite markers suggested that the island populations (except Kouzushima) were founded sequentially from the closest Ohshima to remote Niijima and Miyakejima during or before the penultimate interglacial period. Secondary gene flow from the source population was rare and occurred only for the closest (Ohshima) population. In addition, we found that an amino acid mutation in the Agouti signalling protein gene (Asip) was associated with coat colour variation among the island populations. The mutation was rare in the source population but completely fixed in the Miyakejima population. The phenotypic and genetic variation suggested that severe reduction of genetic variation and changes in allele frequency as a result of sequential colonization (i.e. the founder effect) had significant effects on colour polymorphism. The findings of the present study suggest that the founder effect, in addition to natural selection, facilitated the morphological changes below the species level over a relatively long time scale. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113, 522–535.

Huddling facilitates expression of daily torpor in the large Japanese field mouse Apodemus speciosus

Small endotherms employ multiple adaptations to maintain energy balance in winter, including spontaneous daily torpor and simultaneous huddling. The relationships between these adaptations have been discussed in several previous studies, but it has not been well-established if huddling actually affects the expression of torpor in small endotherms. We examine whether and how huddling affects the expression of torpor in the large Japanese field mouse Apodemus speciosus, which is known to become torpid under artificial winter conditions. The mice were found to adjust expression of torpor in response to the number of cage mates. Torpor frequency and minimum torpid body temperature were both significantly elevated when the number of cage mates was increased, but there was no significant change in torpor bout length. Rewarming rate on arousal was lower when the number of cage mates was increased, suggesting reduction in endogenous rewarming due to exogenous passive rewarming. Food consumption per mouse decreased significantly with increasing number of cage mates. Thus, our study demonstrates that social thermoregulatory behaviors such as huddling can facilitate expression of spontaneous daily torpor in small rodents. These findings suggest that energy constraints, such as ambient temperature and food availability may not be the only modulating factors on the expression of daily torpor.

A Few Decades of Habitat Fragmentation has Reduced Population Genetic Diversity: A Case Study of Landscape Genetics of the Large Japanese Field Mouse,Apodemus speciosus

Abstract. The effects of a few decades of habitat fragmentation on the population genetic diversity of the large Japanese field mouse, Apodemus speciosus, in the forest region around Fukuyama University was assessed with approximate 300 bp nucleotide sequences of the mitochondrial D-loop region. Two independently isolated internal populations within the campus showed a smaller number of haplotypes and lower haplotype and nucleotide diversity indices compared to those inhabiting a wide external forest area. Based on the Hst index, significant genetic differentiation was observed between geographically closely residing external and internal populations but not between distantly residing external populations, suggesting the presence of strong physical barriers between the external and internal populations. Fine-scale changes in the landscape configuration recorded in aerial photographs of Fukuyama University revealed plausible physical barriers and a correlation between isolation time and genetic diversity. ...

금원산 자연휴양림 내 들쥐류의 종 분포 및 특성

Abstract To provide basic information for wildlife management, we investigated the distribution and ecology of wild mice in Mt. Keumwon recreational forests. The trapped wild mice were a total of 4 species such as Eothenomys regulus, Apodemus speciosus peninsulae, Apodemus agarius, and Crocidura suaveolens. A total of 79 individuals from four species were trapped. Number of Eothenomys regulus was the highest as 41 individuals followed by Apodemus speciosus peninsulaeof 31 individuals, Apodemus agarius of 4 individuals, and Crocidura suaveolens of 4 individuals. Depending on forest type, 51 individuals were captured in broad-leaved forests, whereas 28 individuals were captured in coniferous forests. Average weight of the trapped Eothenomys regulus, Apodemus speciosus peninsulae, Apodemus agarius, and Crocidura suaveolens was 37.13 g, 36.29 g, 31.25 g, and 15 g, respectively. Among the trapped wild mice, vole which has the largest head and ears were Eothenomys regulus and vole which has the longest tail was Apodemus speciosus peninsulaeand Apodemus agarius (p＜0.5). This study might be valuable to control and predict some damages related to wild mice in Mt. Keumwon for protecting forest trees.Key Words: Apodemus agarius, Apodemus speciosus peninsulae, Crocidura suaveolens, Eothenomys regulus, Mt. Keumwon Recreational Forests

Susceptibility of muridae cell lines to ecotropic murine leukemia virus and the cationic amino acid transporter 1 viral receptor sequences: implications for evolution of the viral receptor

Ecotropic murine leukemia viruses (Eco-MLVs) infect mouse and rat, but not other mammalian cells, and gain access for infection through binding the cationic amino acid transporter 1 (CAT1). Glycosylation of the rat and hamster CAT1s inhibits Eco-MLV infection, and treatment of rat and hamster cells with a glycosylation inhibitor, tunicamycin, enhances Eco-MLV infection. Although the mouse CAT1 is also glycosylated, it does not inhibit Eco-MLV infection. Comparison of amino acid sequences between the rat and mouse CAT1s shows amino acid insertions in the rat protein near the Eco-MLV-binding motif. In addition to the insertion present in the rat CAT1, the hamster CAT1 has additional amino acid insertions. In contrast, tunicamycin treatment of mink and human cells does not elevate the infection, because their CAT1s do not have the Eco-MLV-binding motif. To define the evolutionary pathway of the Eco-MLV receptor, we analyzed CAT1 sequences and susceptibility to Eco-MLV infection of other several murinae animals, including the southern vole (Microtus rossiaemeridionalis), large Japanese field mouse (Apodemus speciosus), and Eurasian harvest mouse (Micromys minutus). Eco-MLV infection was enhanced by tunicamycin in these cells, and their CAT1 sequences have the insertions like the hamster CAT1. Phylogenetic analysis of mammalian CAT1s suggested that the ancestral CAT1 does not have the Eco-MLV-binding motif, like the human CAT1, and the mouse CAT1 is thought to be generated by the amino acid deletions in the third extracellular loop of CAT1.

三春ダム貯水池湖岸における水位変動域のアカネズミ (&lt;i&gt;Apodemus speciosus&lt;/i&gt;) による利用

三春ダム貯水池湖岸における水位変動域のアカネズミ (&lt;i&gt;Apodemus speciosus&lt;/i&gt;) による利用

Identification of plant residual substances in the feces of Apodemus speciosus and A. argenteus by chloroplast rbcL gene sequences

Identification of plant residual substances in the feces of <i>Apodemus speciosus</i> and <i>A. argenteus</i> by chloroplast <i>rbcL</i> gene sequences

Dioxin pollution disrupts reproduction in male Japanese field mice

Dioxins cause various adverse effects in animals including teratogenesis, induction of drug metabolizing enzymes, tumor promotion, and endocrine disruption. Above all, endocrine disruption is known to disturb reproduction in adult animals and may, also seriously impact their offspring. However, most previous studies have quantified the species-specific accumulation of dioxins, whereas few studies have addressed the physiological impacts of dioxins on wildlife, such as reduced reproductive function. Here we clarify an effect of endocrine disruption caused by dioxins on the Japanese field mouse, Apodemus speciosus. Japanese field mice collected from various sites polluted with dioxins accumulated high concentrations of dioxins in their livers. Some dioxin congeners, especially, 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin, 3,3',4,4',5-pentachloro biphenyl, 1,2,3,4,6,7,8-heptachlorodibenzofuran, and octachlorodibenzo-p-dioxin, which showed high biota-soil accumulation factors, contributed to concentration of dioxins in mouse livers with an increase of accumulation of total dioxins. As for physiological effects on the Japanese field mouse, high levels of cytochrome P450 1A1 (CYP1A1) mRNA, a drug metabolizing enzyme induced by dioxins, were found in the livers of mice captured at polluted sites. Furthermore, at such sites polluted with dioxins, increased CYP1A1 expression coincided with reduced numbers of active spermatozoa in mice. Thus, disruption in gametogenesis observed in these mice suggests that dioxins not only negatively impact reproduction among Japanese field mice, but might also act as a kind of selection pressure in a chemically polluted environment.

アカネズミ（Apodemus speciosus）の自然交配による繁殖を誘導できる飼育交配手法

アカネズミ（Apodemus speciosus）の自然交配による繁殖を誘導できる飼育交配手法