Apodemus Argenteus Research Articles

Chromosomal Aberrations in Wild Mice Captured in Areas Differentially Contaminated by the Fukushima Dai-Ichi Nuclear Power Plant Accident.

Following the Fukushima Dai-ichi Nuclear Power Plant accident, radiation effects on nonhuman biota in the contaminated areas have been a great concern. The induction of chromosomal aberrations in splenic lymphocytes of small Japanese field mice (Apodemus argenteus) and house mice (Mus musculus) inhabiting Fukushima Prefecture was investigated. In mice inhabiting the slightly contaminated area, the average frequency of dicentric chromosomes was similar to that seen in mice inhabiting a noncontaminated control area. In contrast, mice inhabiting the moderately and heavily contaminated areas showed a significant increase in the average frequencies of dicentric chromosomes. Total absorbed dose rate was estimated to be approximately 1 mGy d(-1) and 3 mGy d(-1) in the moderately and heavily contaminated areas, respectively. Chromosomal aberrations tended to roughly increase with dose rate. Although theoretically, the frequency of chromosomal aberrations was considered proportional to the absorbed dose, chromosomal aberrations in old mice (estimated median age 300 days) did not increase with radiation dose at the same rate as that observed in young mice (estimated median age 105 days).

Communal nesting of the small Japanese field mouse in tree cavities in early spring

The small Japanese field mouse, Apodemus argenteus, is a semi-arboreal rodent that breeds in tree cavities. For this study, however, we observed its cavity-nesting behavior during the non-breeding season. In urban and riparian forests in April on the island of Hokkaido, Japan, we found two nesting cavities housing five and ten adult-like mice, respectively. Dissolutions of communal nesting advanced in late April. We consider that one reason for communal nesting is heat retention while overwintering, as is common among rodent species. Our results expand knowledge of cavity use by the mice during the non-breeding season. Previous studies of cavity use by these mice were used nest boxes as artificial substitutes for tree cavities, which can provide inaccurate information of cavity use by the mice during non-breeding season since rodent species often avoid using these boxes in the cooler temperate season. Since nest boxes are used for studies for other mammals and birds, our results suggest that they should be studied in conjunction with cavity observation to accurately explain animals’ cavity use.

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).

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.

Proposal for 'Candidatus Mycoplasma haemomuris subsp. musculi' in mice, and 'Candidatus Mycoplasma haemomuris subsp. ratti' in rats.

Mycoplasma haemomuris is causative of infectious anaemia or splenomegaly in rodents. We examined the nucleotide sequences of the non-ribosomal genes, rnpB and dnaK, in strains of the species M. haemomuris detected in small field mice and black rats. rnpB nucleotide sequences in strains of the species M. haemomuris isolated from small field mice and black rats had only 89 % sequence similarity, suggesting their separation into two distinct subgroups. dnaK had a nucleotide sequence similarity of 84 % between the subgroups. These results support the classification of M. haemomuris into two genetically distinct subgroups. Here we propose the establishment of these subgroups as 'Candidatus Mycoplasma haemomuris subsp. musculi', detected in small field mice (Apodemus argenteus), and 'Candidatus Mycoplasma haemomuris subsp. ratti', detected in black rats (Rattus rattus).

A note on the presence of B chromosome in the small Japanese field mouse, Apodemus argenteus, in central Honshu, Japan

A note on the presence of B chromosome in the small Japanese field mouse, Apodemus argenteus, in central Honshu, Japan

A note on the presence of B chromosome in the small Japanese field mouse, Apodemus argenteus, in Central Honshu, Japan.

Previously, many studies have revealed the presence of B chromosomes in wild mouse taxa of the genus Apodemus (Rodentia, Muridae). In one of the Apodemus species, A. argenteus, which is endemic to Japan, it is known that B chromosomes were confirmed only in individuals (2n = 46 + B chromosome) from Hokkaido, Japan. There is no report of the presence of B chromosomes from other localities in the Japanese Islands. In this study, we analyzed the chromosomal constitutions of 43 individuals of A. argenteus from three localities in Honshu, Japan. A total of three individuals from central Honshu showed 2n = 47, and each individual carrieda dot-like B chromosome. In addition, these B chromosome features were analyzed by differential staining methods, and the C- and QM-banding patterns of the B chromosomes were identical to those of the X chromosomal heterochromatic region showing the delayed-fluorescent response. Thus, it is considered that these B chromosomes would be derived from the heterochromatin of the X chromosomes, as reported in previously published papers.

Nest site use by the small Japanese field mouse: possibility of nest height change in the presence of the Siberian flying squirrel

Nest site use by the small Japanese field mouse: possibility of nest height change in the presence of the Siberian flying squirrel

5-Azadeoxycytidine induced heteromorphic undercondensation in the C-blocks of X chromosomes of three mammalian species, Pipistrellus abramus, Millardia meltada, and Apodemus argenteus

5-Azadeoxycytidine induced heteromorphic undercondensation in the C-blocks of X chromosomes of three mammalian species, Pipistrellus abramus, Millardia meltada, and Apodemus argenteus

Reproductive Activity of the Small Japanese field mouse (Apodemus argenteus) in Yamaguchi Prefecture, Japan

The small Japanese field mouse (Apodemus argenteus) is endemic to Japan that is distributed on all of the main islands of Japan, including Hokkaido, Honshu, Shikoku and Kyushu, and on smaller islands larger than approximately 150 km 2 (Nakata et al. 2009). It is widely distributed from lowlands to alpine zones, and is semi-arboreal, feeding mainly on seeds, fruits, and arthropods (Abe et al. 2005). The breeding season of this species varies geographically; reproduction peaks in the summer in Hokkaido and in sub-alpine zones of Honshu (Miyao et al. 1963; Fujimaki 1969; Kimura 1977; Tateishi 2006), in the spring and summer in the lowlands and low montane areas of Honshu (Yukawa 1973; Murakami 1974; Nishikata 1979; Torii and Tanaka 1989; Shibata 2000), and in the winter in Kyushu (Yoshida 1972). In Yamaguchi Prefecture, located in the westernmost part of Honshu, characterization of this species is very limited and its life cycle and breeding season remain unknown. Therefore, this study sought to determine the reproductive activity of the small Japanese field mouse in Yamaguchi Prefecture.

Different Nest Site Selection of Two Sympatric Arboreal Rodent Species, Siberian Flying Squirrel and Small Japanese Field Mouse, in Hokkaido, Japan

Numerous vertebrates use tree cavities as nest resources. Mammals such as Carnivora (Zalewski 1997; Wilson and Nielsen 2007), rodents (Taulman 1999; Shibata et al. 2004; Holloway and Malcolm 2007), bats (Sedgeley and O’Donnell 1999; Boonman 2000; Willis and Brigham 2007), and marsupials (Lindenmayer et al. 1991; Smith et al. 2007; Crane et al. 2010), as well as birds (Aitken et al. 2002; Martin et al. 2004; Adamik and Kral 2008), use tree cavities for daily rest, reproduction, and/or overwintering. Sympatric cavity-users often partition their nest cavities to avoid interspecific competition (van Balen et al. 1982; Martin et al. 2004; Shafique et al. 2009). In Hokkaido, northern Japan, there are two cavitynesting rodents, the Siberian flying squirrel (Pteromys volans) (Nakama and Yanagawa 2009; Suzuki et al. 2011) and the small Japanese field mouse (Apodemus argenteus) (Nakata et al. 2009). There may be competition between these two rodents for tree cavities, but their favored nest sites have not yet been compared. Do they select tree cavities of different types, and, if so, what characteristics are their selections based on? These rodents have different physical and ecological characteristics. Pteromys volans (weight, 110 to 142 g; head and body length, 130 to 167 mm; Hanski et al. 2000; Asari et al. 2007; Oshida 2009) is 5 to 14 times heavier than A. argenteus (weight, 10 to 20 g; head and body length, 65 to 100 mm; Nakata et al. 2009). In addition, P. volans, which is an aerial and arboreal user, spends most of its time in the canopy and almost never walks on the ground, even when crossing wide fields (Selonen and Hanski 2003, 2004). Apodemus argenteus also uses arboreal space (Imaizumi 1978; Abe et al. 1989; Sekijima 2004), and it is able to climb to a height of 18 m (Ida et al. 2004). However, it more frequently uses foods on and under the ground than above the ground (Abe 1986). These differences in size and habit between the two species may result in different choices of tree cavities. Larger species of cavity-nesting mammals and birds tend to nest in larger cavities with larger entrances (Martin et al. 2004). Larger flying squirrels use larger trees with larger entrances than do smaller flying squirrel species (Shafique et al. 2009). Larger bird species also nest in larger entrance cavities than do smaller species (van Balen et al. 1982). Thus, we hypothesized that P. volans, with a larger body than that of A. argenteus, would nest in trees with greater diameters at breast height and in larger cavities with larger entrances. In addition, we hypothesized that P. volans, which is usually active in the upper layer of trees, would nest in higher cavities than A. argenteus, which commonly lives on and under the ground. We examined these hypotheses by surveys of tree cavities and nest boxes.

Interspecific Differences in Tannin Intakes of Forest-Dwelling Rodents in the Wild Revealed by a new Method Using Fecal Proline Content

Mammalian herbivores adopt various countermeasures against dietary tannins, which are among the most widespread plant secondary metabolites. The large Japanese wood mouse Apodemus speciosus produces proline-rich salivary tannin-binding proteins in response to tannins. Proline-rich proteins (PRPs) react with tannins to form stable complexes that are excreted in the feces. Here, we developed a new method for estimating the tannin intake of free-living small rodents, by measuring fecal proline content, and applied the method to a field investigation. A feeding experiment with artificial diets containing various levels of tannic acid revealed that fecal proline content was clearly related to dietary tannin content in three species (A. speciosus, Apodemus argenteus, and Myodes rufocanus). We then used fecal proline content to estimate the tannin intakes of these three forest-dwelling species in a forest in Hokkaido. In the autumn, estimated tannin intakes increased significantly in the Apodemus species, but not in M. rufocanus. We speculated that an increase in tannin intake during autumn may result from consumption of tannin-rich acorns. This hypothesis was consistent with population fluctuation patterns of the three species, which were well-synchronized with acorn abundance for the Apodemus species but not for M. rufocanus.

Microhabitat segregation between Apodemus argenteus and A. speciosus in northern Kyushu.

Microhabitat segregation between Apodemus argenteus and A. speciosus in northern Kyushu.

Bartonella japonica sp. nov. and Bartonella silvatica sp. nov., isolated from Apodemus mice

Two bacterial strains, Fuji 18-1(T) and Fuji 23-1(T), were isolated from the blood of the small Japanese field mouse (Apodemus argenteus) and the large Japanese field mouse (Apodemus speciosus), respectively, specimens of which were captured in the forest of Mount Fuji, Japan. Phenotypic characterization (growth conditions, incubation periods, biochemical properties and cell morphologies), DNA G+C contents (40.1 mol% for strain Fuji 18-1(T) and 40.4 mol% for strain Fuji 23-1(T)) and sequence analyses of the 16S rRNA genes indicated that both strains were members of the genus Bartonella. Using rpoB and gltA sequencing analysis, the highest sequence similarities between strains Fuji 18-1(T), Fuji 23-1(T) and other recognized species of the genus Bartonella showed values considerably lower than 91.4 % and 89.9 % in the rpoB gene and 89.1 % and 90.4 % in the gltA gene, respectively. It is known that similarities of 95.4 % for the rpoB gene and 96.0 % for the gltA gene can be applied as cut-off values for the designation of novel species of the genus Bartonella. In a phylogenetic tree based on the merged set of concatenated sequences of seven loci [16S rRNA, ftsZ, gltA, groEL, ribC and rpoB genes and the intergenic spacer region (ITS)], strains Fuji 18-1(T) and Fuji 23-1(T) formed a distinct clade from other recognized species of the genus Bartonella. These data support the classification of strains Fuji 18-1(T) and Fuji 23-1(T) as novel species of the genus Bartonella. The names Bartonella japonica sp. nov. and Bartonella silvatica sp. nov. are proposed for these novel species. The type strains of Bartonella japonica sp. nov. and Bartonella silvatica sp. nov. are Fuji 18-1(T) (=JCM 15567(T)=CIP 109861(T)) and Fuji 23-1(T) (=JCM 15566(T)=CIP 109862(T)), respectively.

Female-biased sex allocation of offspring by an Apodemus mouse in an unstable environment.

We investigated the effects of population fluctuation on the offspring’s sex allocation by a weakly polygynous mouse, Apodemus argenteus, for 3 years. In acorn-poor seasons, heavier mothers invested more in sons, and lighter mothers invested more in daughters. In acorn-rich seasons, heavier mothers invested more in daughters, and lighter mothers invested more in sons. Maternal body condition and litter size affected the sex allocation. Furthermore, there was a maternal investment trade-off between a son’s birth mass and the number of daughters. Based upon the effect of population fluctuation on the lifetime reproductive success of each sex, we proposed the new “safe bet hypothesis”. This hypothesis predicts that frequent and unpredictable change in female distribution, which is often caused by abrupt fall in food condition, favors female-biased maternal investment to offspring by polygynous mammals and is applicable to many small mammals inhabiting in unstable environments.

The Role of Nick Formation in Delayed Quinacrine Mustard Fluorescence in the C-heterochromatin ofApodemus argenteus

Chromosomes stained with fluorochromes, including quinacrine mustard (QM), emit the brightest fluorescence immediately after exposure to excitation light, and the fluorescence gradually fades with an increase in exposure time. However, in the QM-stained chromosomes of the small Japanese field mouse Apodemus argenteus, most C-heterochromatic regions emit weak fluorescence immediately after exposure to blue light, and they become brightly fluorescent by prolonged exposure (delayed QM fluorescence). We proposed recently that the delayed QM fluorescence is somehow related to nicks produced in C-heterochromatic DNA by blue light irradiation. To test this possibility, we examined the chromosomal distribution of nicks by in-situ nick translation and changes, if any, in the QM fluorescence pattern after methylene blue (MB) -mediated photooxidation, which is considered to induce nicks in chromosomal DNA. It was found that C-heterochromatic regions fluoresced brightly without any delay after exposure to blue light, and that nicks increased considerably in the same regions after the MB-mediated photooxidation. It seems, therefore, that photooxidation and strand breaks in DNA (including nicks) are responsible for the induction of delayed QM fluorescence. Trypsin digestion, on the other hand, abolished delayed QM fluorescence. Thus, not only DNA but also chromosomal protein(s) are involved in the unusual sequence of QM fluorescence patterns in A. argenteus.

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.

The status of the genus Hokkaidocephala Tenora, Gulyaev &amp;amp; Kamiya, 1999 (Cestoda: Anoplocephalidae), parasites of the endemic Japanese field mice (Apodemus spp.)

The present study reconsiders the status of the genus Hokkaidocephala Tenora, Gulyaev &amp; Kamiya, 1999 by examining available specimens of the type species H. apodemi (Iwaki, Tenora, Abe, Oku &amp; Kamiya, 1994) (syn. Andrya apodemi) and comparing them with related anoplocephaline cestodes. It is shown that Hokkaidocephala apodemi does not differ fundamentally from related genera in the development of the reproductive organs, contrary to the argument of Tenora et al. (1999). In Hokkaidocephala and related genera (Anoplocephaloides Baer, 1923 s. str. and Microcephaloides Haukisalmi, Hardman, Hardman, Rausch &amp; Henttonen, 2008), sperm appears in the seminal receptacle (female organ) simultaneously or slightly earlier than in the seminal vesicles (male organs) and the ovary and vitellarium are absent in postmature proglottides where testes still persist and usually reach their maximum size. However, Hokkaidocephala is considered here a valid genus differentiated from the related genera by its unique uterine structure and development. Presently, Hokkaidocephala includes two host-specific species [H. apodemi and H. baeri (Rausch, 1976) n. comb. (= Anoplocephaloides baeri Rausch, 1976)] parasitizing endemic Japanese field mice (primarily Apodemus argenteus).

Effects of a Typhoon on Foraging Behavior and Foraging Success of Macaca fuscata on Kinkazan Island, Northern Japan

We studied the effects of typhoon damage on the food habits, time budgets, and moving distances of Japanese macaques (Macaca fuscata) on Kinkazan Island, northern Japan. Before the typhoon (pre-typhoon phase), the macaques fed on various food items, including fruit in trees (Swida macrophylla) and nuts (Torreya nucifera) on the ground. After the typhoon passed (post-typhoon phase), the macaques fed intensively on the seeds of Perilla frutescens (a forb) and the nuts of Quercus serrata on the ground. One may attribute the changes to decreased food availability or foraging efficiency of fruits and nuts on the ground, due to their concealment by leaf litter and mud and their consumption by other animals, such as sika deer (Cervus nippon) and field mice (Apodemus argenteus). In the post-typhoon phase, the macaques fed more quickly on seeds of Perilla frutescens, spent less time traveling, and moved over shorter distances. The differences may be due to changes in the distribution of staple foods between the 2 phases. We also evaluated the energy intake and energy balance of the macaques in both phases, based on observations of foraging and nutritional analyses of the food items. There is no significant difference in either parameter between the 2 phases. The changes in food habits and movement behavior may have compensated for the reduced food availability or foraging efficiency caused by the typhoon. Both behavioral changes and nutritional issues are important when investigating the effects of storms on animal ecology.

Uniparental care and activity of nursing females of Apodemus argenteus during the lactation period on Mt. Asama, Central Japan

92008 ?? 33 1114 Received 19.4.2007 ; a cepted 30.1.2008 Copyright © 20 8 MSJ Introduction The a e of neonates in mammals is primarily the responsibility of females because of their ability to lactate, while the contribution of paternal care, a central issue in mammalogy, has been studied mainly under experimental conditions (e.g. Wilson et al. 1993; Gubernick et al. 1994; Cantoni and Brown 1997; Patris and Baudoin 2000). The frequency of reproductive periods in the Japanese field mouse Apodemus argenteus, one of the smallest rodents endemic to Japan, varies from one in summer to two in spring and autumn or one in autumn to winter, corresponding to mean temperatures during the reproductive periods (Nishikata 1979). In Central Japan, where A. argenteus reproduction occurs in spring and autumn, the clear overlap of the home ranges of the two sexes and the exclusive distribution of the males’ home ranges suggest that A. argenteus is likely monogamous (Oka 1992). Paternal care may affect the growth of neonates (e.g. Schradin and Pillay 2005), and indeed the experimental removal of A. argenteus adult males resulted in a decreased body weight of neonates (Oka 1991). In contrast, in northern Japan, A. argenteus experience only one reproductive period annually, and recent paternity tests using genotype analyses have indicated that these mice have a polygynous mating system (Ohnishi et al. 2000). However, Ohnishi et al. (2000) did not document the presence of males in the nursing nests. Here, we conducted direct observations of the nursing nests of A. argenteus in Central Japan to determine which sexes nursed and their nighttime nursing patterns. We also describe the neonatal developmental process.