Apodemus Speciosus Research Articles

Secondary dispersal of Dioscorea japonica (Dioscoreaceae) bulbils by rodents

We examined rodent dispersal of Dioscorea japonica bulbils. Bulbils dispersed by rodents may travel farther from their parent plants than those dispersed by gravity alone. To confirm the presence of secondary dispersal and the types of vector, we used an automatic camera to photograph animals that approached bulbils. To clarify secondary dispersal distance, we set marked bulbils at eight sites and searched for the bulbils once they were removed from their original locations by a disperser. We took photographs of mice (Apodemus speciosus) approaching the bulbils. In June, 10 of 333 bulbils that were moved germinated. We also measured the primary dispersal distance at four sites by dropping bulbils from heights of 0.5, 3.0, and 12.0 m. We then compared primary and secondary dispersal distances. The mean secondary dispersal distance was significantly greater than the primary dispersal distance for dispersal heights of 0.5 and 3.0 m, but less than that for a 12.0-m dispersal height. This indicates that rodents may disperse bulbils farther than gravity alone when bulbils drop from lower heights but they contribute little to dispersal for bulbils that drop from greater heights (e.g., from the top of the canopy). Thus, we confirmed the occurrence of rodent dispersal of bulbils and rodents might to some extent contribute to the dispersal and establishment of bulbils.

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.

Applicability of artificial burrows to studies of natural populations of two species of wood mice, Apodemus speciosus and A. argenteus

Applicability of artificial burrows to studies of natural populations of two species of wood mice, Apodemus speciosus and A. argenteus

Investigation of Reservoir Animals of <i>Leptospira</i> in the Northern Part of Miyazaki Prefecture

We surveyed reservoir animals of leptospires in the northern part of Miyazaki Prefecture, where a cluster of human leptospirosis had occurred during the summer of 2006. Leptospira was isolated from 6 of 57 large Japanese field mice (Apodemus speciosus). The serogroups of the isolates were Autumnalis (5 strains) and Hebdomadis (1 strain) and the partial nucleotide sequences of their flaB genes suggested that the isolates belonged to L. interrogans. The human patient sera reacted specifically with the Leptospira strain isolated from the mice captured around the area where each patient occurred, suggesting that mice are the source of human infection. We also detected leptospiral DNAs by flaB-polymerase chain reaction in the kidneys of large feral animals; wild boars (positive ratio 10.3%; 4 of 39) and deer (19.2%; 10 of 52). The Leptospira spp. harbored by these animals were deduced to be L. interrogans (in 5 animals) and L. borgpetersenii (in 9 animals) by the nucleotide sequences of the amplicons. Anti-Leptospira antibodies were also detected among symptomatic hound dogs. These results suggest that these feral animals may cause leptospirosis and pose a potential risk to hunters and workers in the meat processing industry.

Prevalence and genetic diversity of Bartonella species isolated from wild rodents in Japan.

Here, we describe for the first time the prevalence and genetic properties of Bartonella organisms in wild rodents in Japan. We captured 685 wild rodents throughout Japan (in 12 prefectures) and successfully isolated Bartonella organisms from 176 of the 685 rodents (isolation rate, 25.7%). Those Bartonella isolates were all obtained from the rodents captured in suburban areas (rate, 51.8%), but no organism was isolated from the animals captured in city areas. Sequence analysis of rpoB and gltA revealed that the Bartonella isolates obtained were classified into eight genetic groups, comprising isolates closely related to B. grahamii (A-I group), B. tribocorum and B. elizabethae (B-J group), B. tribocorum and B. rattimassiliensis (C-K group), B. rattimassiliensis (D-L group), B. phoceensis (F-N group), B. taylorii (G-O group), and probably two additional novel Bartonella species groups (E-M and H-P). B. grahamii, which is one of the potential causative agents of human neuroretinitis, was found to be predominant in Japanese rodents. In terms of the relationships between these Bartonella genetic groups and their rodent species, (i) the A-I, E-M, and H-P groups appear to be associated with Apodemus speciosus and Apodemus argenteus; (ii) the C-K, D-L, and F-N groups are likely implicated in Rattus rattus; (iii) the B-J group seems to be involved in Apodemus mice and R. rattus; and (iv) the G-O group is probably associated with A. speciosus and Clethrionomys voles. Furthermore, dual infections with two different genetic groups of bartonellae were found in A. speciosus and R. rattus. These findings suggest that the rodent in Japan might serve as a reservoir of zoonotic Bartonella infection.

Deer-proof fence prevents regeneration of Picea jezoensis var. hondoensis through seed predation by increased woodmouse populations

The indirect consequence of sika deer (Cervus nippon) grazing on the regeneration of Picea jezoensis var. hondoensis through its effect on the small rodent population was assessed by evaluating seed predation by mice inside and outside the deer-proof fence on Mt Ohdaigahara, central Japan. Following construction of the deer-proof fence, Sasa nipponica, which covers the forest floor and is the main forage of deer, grew thicker inside the fence due to the absence of deer grazing than outside of the fence. Higher numbers of two species of woodmice (Apodemus speciosus and A. argenteus) were found inside the fence, possibly because the thick S. nipponica growth provides better cover. Inside the fence, more seeds of P. jezoensis var. hondoensis were eaten by the mice than outside the fence. These results suggest that the mouse populations inside the fence increased due to changes in S. nipponica cover, which subsequently increased seed predation by the mice, possibly preventing regeneration of P. jezoensis var. hondoensis.

Improved walnut-feeding skills with experience in wood mice, Apodemus speciosus

The wood mouse Apodemus speciosus can consume the hard-walled walnut species Juglans ailanthifolia. The mice gnaw holes on two sides of the shell and then pick the meat from the holes. However, not all mice are able to eat these walnuts, because the shells are extremely hard and the process is labour-intensive. To consume all of the meat it is more efficient to eat from holes on the raphe than to attempt to eat from other parts of the shell. We examined the effect of experience on the walnut-feeding skills of mice in the field. Feeding behaviours were compared among mice from habitats with and without walnut trees. Mice from habitats with walnut trees tended to consume nuts more efficiently than mice from habitats without walnut trees. We also observed the feeding behaviour of mice in an experimental area into which walnuts were artificially placed over a period of one year. This manipulation increased the proportion of mice that were able to eat nuts frequently and efficiently. Therefore, the walnut-feeding skills of mice improved with experience. Because individual mice acquired efficient feeding during the 14-day period of walnut conditioning, trial-and-error learning may be an important mechanism contributing to this behaviour.

A Trend of Central Versus Peripheral Structuring in Mitochondrial and Nuclear Gene Sequences of the Japanese Wood Mouse, Apodemus speciosus

A phylogeographic analysis was performed on Japanese endemic wood mice (Apodemus speciosus) using nuclear interphotoreceptor retinol binding protein (IRBP) gene sequences (1,152 bp), together with previously published mitochondrial cytochrome b (cyt b) data. In the IRBP analysis, 40 haplotypes were recovered from 84 individuals by statistical and subcloning methods. Substantial sequence variation was determined from the IRBP data (pi=0.0047), and no significant evidence of recombination was detected. From the phylogenetic analysis, the 40 haplotypes fell into two major groups with geographic associations, irrespective of the karyotype groups (2n=46 and 2n=48), yielding a trend of central (Hokkaido, Honshu, Shikoku, Kyushu, and Sado) and peripheral (Izu, Oki, Tsushima, and Satsunan Is.) groupings. This geographic pattern is similar to that observed in the cyt b data, with a different insular grouping of Sado, Hokkaido, Izu, and Satsunan islands, and also to that of morphological features. In both gene data sets, nested clade analyses revealed allopatric fragmentation in the "peripheral island clades" and range expansion in the "central island clades." A mismatch analysis using cyt b data also suggested expansion of the central islands clade. Thus, the trend of central vs. peripheral structuring may be attributable to past demographic dynamics in the two distinct haplotype clades, such as range expansion of one clade in the central area of the Japanese Islands, leaving the other clade in the periphery.

Selective consumption of acorns by the Japanese wood mouse according to tannin content: a behavioral countermeasure against plant secondary metabolites

AbstractWe examined the presence of selective consumption against tannins in acorns as a pre‐ingestive countermeasure to plant secondary metabolites by using the Japanese wood mouse (Apodemus speciosus) and acorns of Quercus serrata, which contained ca. 6.4% tannins on a dry weight basis. In addition, the presence of selective consumption against proteins was also examined. In the acorn‐feeding experiment, 18 wood mice were allocated to two groups: the experienced group (N = 9), which had previous experience in feeding on acorns, and the inexperienced group (N = 9), which had no experience. Mice of both groups were fed only acorns for 3 nights. Selectivity against tannins (an index estimated from the tannin content in control, remaining, and ingested acorns) was significantly positive in the experienced group, indicating the presence of selective consumption against tannins. In contrast, mice in the inexperienced group did not show significant selectivity against tannins. Comparing the selectivity indices directly between two groups, however, they did not differ significantly. Selective consumption against proteins rather than that for proteins also occurred in the experienced group, but it was thought to be a byproduct resulted from the selectivity against tannins. Selective consumption against tannins can mitigate the negative effects of tannins by decreasing tannin intake.

Effects of acorn abundance on density dependence in a Japanese wood mouse (Apodemus speciosus) population

AbstractWe analysed the effects of Quercus crispula acorn abundance on the density dependence of the large Japanese wood mouse Apodemus speciosus using time series data (1992–2007). The data were obtained in a forest in northern Hokkaido, Japan, by live‐trapping rodents and directly counting acorns on the ground. Acorn abundance in one year clearly influenced the abundance of wood mice in the following year in all models examined based on the Gompertz and Ricker model; in addition, the abundance of wood mice had effects on the population. Acorn abundance influenced the strength of density dependence (intraspecific competition) of the wood mouse population. When the abundance of acorns was high, density dependence was relaxed, and as a result the equilibrium density at which the population growth rate decreased to zero became higher. Those effects of acorn abundance were regarded as a nonlinear perturbation effect (sensu Royama 1992). The nonlinearity of density dependence was also detected; higher densities had stronger effects on population growth rates.

Geographic variation in walnut seed size correlates with hoarding behaviour of two rodent species

AbstractSeeds of the Japanese walnut, Juglans ailanthifolia, are usually scatter‐hoarded by two rodent species, the Japanese squirrel Sciurus lis and the field mouse Apodemus speciosus, but only by the latter in several areas where S. lis is absent. We examined seed‐size‐mediated interactions of these three species across a wide geographic range. Field tracking of walnuts with miniature radio‐transmitters revealed that squirrels hoarded larger seeds more frequently and at greater distances than smaller seeds. In contrast, mice hoarded smaller seeds more frequently and transported them farther than larger seeds. These seed dispersers could affect the evolution of seed size because seeds hoarded at sites farther from source trees are known to survive better until germination and as seedlings. We expect that larger seeds may be advantageous in regeneration if the main seed dispersers are squirrels, whereas smaller seeds may be advantageous if mice are the dominant dispersers. These predictions were supported by the fact that seed size was smaller on islands inhabited only by mice and at the edge of the squirrel distribution, compared to areas where mice and squirrels are both common.

Seed predation and dispersal of glabrous filbert (Corylus Heterophylla) and pilose filbert (Corylus Mandshurica) by small mammals in a temperate forest, northeast China

We investigated the seed dispersal of glabrous filbert (Corylus heterophylla) and pilose filbert (Corylus mandshurica), two large-seeded shrub species in a temperate forest, northeast China, September 2006. Small mammals such as Apodemus speciosus, Clethrlonomys rufocanus, and Eutamias sibiricus, were regarded as the main dispersal agents. More seeds were harvested by small mammals in pilose filbert (98%) than in glabrous filbert (87.5%) till our last survey. Seed removal rates differed between the two species. Fewer seeds of glabrous filbert (17.5%) were eaten in situ than pilose filbert (57.5%). More seeds of glabrous filbert were removed (70%), stay intact after removal (25.5%), eaten after removal (16%) than pilose filbert. However, more seeds were cached after removal in pilose filbert than in glabrous filbert (10.5 and 4%, respectively). Fewer tagged seeds of pilose filberts (14%) were missed than glabrous filberts (24.5%). About 8 and 12 primary caches were found in glabrous filbert and pilose filbert seeds respectively, indicating scatter hoarding. All of the removed seeds were distributed within 10 m of seed stations for both filberts. The average dispersal distances for glabrous filbert did not differ from pilose filbert. Only a small proportion of the caches remained till our last survey (2 and 1%, respectively). Based on the results, we found a difference in dispersal patterns of glabrous filbert and pilose filbert seeds. Evidences showed that glabrous filberts might be a less preferred seed species for small seed-eating mammals compared with pilose filbert, probably due to its harder and thicker husk and low seed profitability.

Effects of acorn masting on population dynamics of three forest‐dwelling rodent species in Hokkaido, Japan

AbstractThe effects of the abundance of acorns of the oak, Quercus crispula, on the population dynamics of three rodent species (Apodemus speciosus, A. argenteus, and Clethrionomys rufocanus) were analyzed using time series data (1992–2006). The data were obtained in a forest in northern Hokkaido, Japan, by live trapping rodents and directly counting acorns on the ground. Apodemus speciosus generally increased in abundance following acorn masting. However, the clear effect of acorn abundance was not detected for the other two rodent species. Acorns of Q. crispula contain tannins, which potentially have detrimental effects on herbivores. Apodemus speciosus may reduce the damage caused by acorn tannins with tannin‐binding salivary proteins and tannase‐producing bacteria, whereas such physiological tolerance to tannins is not known in the other two rodent species. The differences in the effects of acorns between the three species may be due to differences in their physiological tolerance to tannins.

Survey of Babesia microti Infection in Field Rodents in Japan: Records of the Kobe‐Type in New Foci and Findings of a New Type Related to the Otsu‐Type

Of 247 rodents comprising 5 genera and 7 species collected at 17 sites throughout Japan from 2003 to 2005, Babesia microti was detected microscopically and by polymerase chain reaction (PCR) in 36 rodents comprising 2 genera and 3 species from 12 sites. Based on the analysis of small subunit ribosomal RNA gene (SSUrDNA) sequences, the Kobe-type, the etiological type of the first Japanese case of human infection was found in Apodemus speciosus and Apodemus argenteus in Aomori, the northernmost prefecture of the Japanese mainland, while the U.S.-type was found on Hokkaido Island and the Otsu-type was widely distributed. In addition, a new Otsu-related type was detected exclusively in Eothenomys andersoni in Nagano, a prefecture in central Japan. The sequences of internal transcribed spacer 1 to 2 (ITS1/2) of the present Kobe- and Otsu-types were almost identical to those of the same types previously identified. The ITS1/2 sequence of the U.S.-type identified in Hokkaido in this survey was somewhat different from that of the U.S.-type strain originating from the U.S.A., with approximately 95% identity. This value was similar to the 94% identity found between the ITS1/2 sequences of the Otsu-type and the new Otsu-related type. The new Otsu-related type of B. microti was isolated as the Nagano strain, which was serologically differentiated from the other type strains of B. microti. The divergence and distribution of genotypes are important factors in investigating the epidemiology of human B. microti infection in Japan.

都市近郊域における異なる土地利用タイプとアカネズミの生息との関係

Recently, the urban areas have been expanding in metropolis, and therefore the reduction of semi-natural environment in suburban areas has become a serious problem. In this study, the relationship between land use pattern and the distribution of Japanese field mouse (Apodemus speciosus) in the suburban area was investigated for open space effects and factors in several land use types on conserving population and maintaining corridors for the mice. The mice distributions were surveyed by the capture-recapture method of trapping in the Niiharu area, Yokohama City, Japan. As a result, the mice utilized the natural and agricultural land use and the number of captures were large in secondary forests in particular. However, no mice were collected in the urban land use, such as roads and residential areas. It was recognized that the mice could use the river bank and greenways as corridor and agricultural landscape as habitat within 100m from the forest edge. These results indicated the development of biotope mapping and prediction of suitable habitat for urban ecological network. From now on, size and distribution of urban open spaces need to be discussed.

Reproductive activity of the large Japanese field mouse (Apodemus speciosus) in the Oze district in northeastern Honshu, Japan

Reproductive activity of the large Japanese field mouse (<i>Apodemus speciosus</i>) in the Oze district in northeastern Honshu, Japan

Microhabitat use of wood mice ranging from a reserved belt with evergreen broad-leaved trees to a coniferous plantation

Wood mice Apodemus speciosus and Apodemus argenteus are potentially important seed dispersers and predators of Quercus and Castanopsis in Japan. We investigated the existence of two species of wood mice in warm-temperate forests ranging from a reserved belt of evergreen broad-leaved trees to a coniferous plantation, and analyzed the relationship between wood mouse occurrence and environmental factors to confirm their microhabitat use. We used two-way analysis of variance to analyze differences in the captured number of each wood mouse species in two trapping seasons as well as two stand types to confirm the interaction between the stand type and trapping season. Apodemus speciosus were often captured in the reserved belt, while captures of A. argenteus were independent of season and stand types. It is reasonable to conclude from the results of the trends in occurrence that the two species of wood mice showed different uses of the microhabitat. The result of linear discriminant analysis made it clear that the distance from the reserved belt had much to do with the difference in microhabitat use between the two species in the fruiting season of Quercus and Castanopsis. On average, A. speciosus moved 19.9m during nonfruiting and 61.3m during fruiting, while A. argenteus moved 8.1m during nonfruiting, and 29.0m during fruiting from analysis of the recapture position. The results indicate that both species of mice move around during the fruiting season more than in the nonfruiting season.

Lactobacillus apodemi sp. nov., a tannase-producing species isolated from wild mouse faeces

A Gram-positive, rod-shaped, non-endospore-forming bacterium, strain ASB1(T), able to degrade tannin, was isolated from faeces of the Japanese large wood mouse, Apodemus speciosus. Comparative analysis of the 16S rRNA gene sequence revealed that the strain could be assigned as a member of the genus Lactobacillus. The nearest phylogenetic neighbours were determined as Lactobacillus animalis DSM 20602(T) (98.9 % 16S rRNA gene sequence similarity) and Lactobacillus murinus ASF 361 (98.9 %). Subsequent polyphasic analysis, including automated ribotyping and DNA-DNA hybridization experiments, confirmed that the isolate represents a novel species, for which the name Lactobacillus apodemi sp. nov. is proposed. The DNA G+C content of the novel strain is 38.5 mol%. The cell-wall peptidoglycan is of type A4alpha L-lys-D-asp. The type strain is ASB1(T) (=DSM 16634(T)=CIP 108913(T)).

Morphological variation of large Japanese field mice, Apodemus speciosus on the Izu and Oki Islands

ABSTRACT Morphological variation was examined in large Japanese field mice, Apodemus speciosus, of five populations from the Izu Islands (from Oshima, Shikinejima, Niijima, Kozushima and Miyakejima), four from the Oki Islands (from Dogo, Nishinoshima, Nakanoshima and Chiburijima), and four from the Japanese mainland of Honshu. Univariate and multivariate (PCA) analyses were conducted on the basis of body-, mandible-, and molar-measurements. Overall, the insular mice had a tendency toward gigantism, and also showed marked morphological differentiation among the islands. The sizes of the mandible and molar were inversely correlated to island area and temperature, thus suggesting a selective effect. Although faunal diversity might be related to the morphological variation in size, there was no clear relationship between the morphological variation and biotic factors such as predation and competition. The populations from the Izu Islands underwent marked morphological divergence, suggesting founder effects. T...

Role of Tannin-Binding Salivary Proteins and Tannase-Producing Bacteria in the Acclimation of the Japanese Wood Mouse to Acorn Tannins

We studied the defense mechanisms against the negative effects of tannins in acorns by using the Japanese wood mouse (Apodemus speciosus) and acorns of a Japanese deciduous oak Quercus crispula, which contain 9.9% tannins on a dry weight basis. For the experiment, we allocated 26 wood mice into two groups: acclimated (N = 12) and nonacclimated (N = 14). Mice in the nonacclimated group were fed only acorns for 10 d after 4 wk of receiving a tannin-free diet. In contrast, mice in the acclimated group received ca. 3 g acorns daily in addition to the tannin-free diet for the first 4 wk, then they were fed only acorns for 10 d. Body weight, food intake, and digestibility were monitored. In addition, the amount of salivary proline-rich proteins (PRPs) and abundance of tannase-producing bacteria (TPB) in the feces of mice were measured. Of the 14 mice in the nonacclimated group, 8 died, whereas only 1 of the 12 in the acclimated group died. During the first 5 d of feeding acorns only, mice in the nonacclimated group lost, on average, 17.5% of their body mass, while those in the acclimated group lost only 2.5%. Food intake, dry matter digestibility, and nitrogen digestibility were higher in the acclimated group than in the nonacclimated group. The results indicate that wood mice can mitigate the negative effects of tannins by acclimation. Path analysis revealed that increased secretion of PRPs and abundance of Lactobacillus type of TPB might explain the acclimation to tannins.