Japanese Field Research Articles

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.

Characterization of complete genome sequence of genotype VI and VII velogenic Newcastle disease virus from Japan.

The complete genome sequences of three strains of Newcastle disease virus (NDV) isolated from vaccinated commercial layer flocks in Japan in the span of three decades were characterized. All strains had genome lengths of 15,192 nucleotides consisting of six genes in the order of 3'-NP-P/V/W-M-F-HN-L-5'. The general genomic characteristics of the Japanese field strains were consistent with previously characterized class II NDV, except for those belonging to early genotypes (genotype I-IV), which lack the six nucleotide insertion at nucleotide positions 1,648-1,653 of the nucleoprotein (NP) gene. Phylogenetic analysis showed that the Japanese strains could be classified into genotypes VIc and VIIe using the complete genome sequence and the complete coding sequence of the fusion (F) gene according to the unified NDV classification system. Characterization of functional domains and neutralizing epitopes of the F and hemagglutinin-neuraminidase (HN) proteins of Japanese field strains revealed a total of 31 amino acid substitutions, as compared to vaccine strains Ishii and B1, which were widely used in Japan. Although virus neutralization (VN) test showed that poor flock immunity due to vaccination failure or partial and non-uniform immunization maybe the major factors involved in the mechanism of breakthrough infection of the Japanese field strains, approximately two to threefold decrease in the VN titers of the field NDV strains possessing a point mutation (E347K or E347G) at the linear epitope of the HN protein was observed, as compared to vaccine strain B1 and field strain 2440/69, which lack the point mutation. This study may be a useful reference in characterizing future ND outbreaks in vaccinated chickens and as a genetic map for future investigations regarding vaccine designs, reverse genetics systems, and development of molecular diagnostic tools to prevent future ND outbreaks in vaccinated poultry flocks.

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. ...

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.

Description of Anaerobacterium chartisolvens gen. nov., sp. nov., an obligately anaerobic bacterium from Clostridium rRNA cluster III isolated from soil of a Japanese rice field, and reclassification of Bacteroides cellulosolvens Murray et al. 1984 as Pseudobacteroides cellulosolvens gen. nov., comb. nov.

An obligately anaerobic bacterial strain designated T-1-35(T) was isolated as a dominant cultivable cellulose-degrading bacterium from soil of a Japanese rice field as an anaerobic filter-paper degrader. Cells of strain T-1-35(T) stained Gram-positive and were non-spore-forming rods with rounded ends, 0.8-1.0×3.5-15.0 µm, and motile by means of two to four polar flagella. Cells of strain T-1-35(T) exhibited pleomorphism: in aged cultures (over 90 days of incubation), almost all cells were irregularly shaped. Although no spore formation was observed, cells tolerated high temperatures, up to 90 °C for 10 min. The temperature range for growth was 15-40 °C, with an optimum at 35 °C. The pH range for growth was 5.5-9.0, with an optimum at pH 8.0-8.5 (slightly alkaliphilic). Strain T-1-35(T) fermented some carbohydrates to produce ethanol and lactate as the major products. Major cellular fatty acids were iso-C16 : 0 and iso-C13 : 0 3-OH. Phylogenetic analysis based on the 16S rRNA gene sequence revealed that strain T-1-35(T) belonged to Clostridium rRNA cluster III. The closest relative of strain T-1-35(T) was Bacteroides cellulosolvens WM2(T), with 16S rRNA gene sequence similarity of 93.4 %. Phenotypic, physiological and molecular genetic methods demonstrated that strain T-1-35(T) was distinct from its phylogenetic relatives (members of Clostridium rRNA cluster III) because it predominantly produced ethanol, iso-C13 : 0 3-OH was a major cellular fatty acid and it always exhibited pleomorphism. On the basis of the results of a polyphasic taxonomic study, strain T-1-35(T) is considered to represent a novel genus and species, Anaerobacterium chartisolvens gen. nov., sp. nov. The type strain of Anaerobacterium chartisolvens is T-1-35(T) ( = DSM 27016(T) = NBRC 109520(T)). In addition, from the results of our phylogenetic analysis and its phenotypic features, the species Bacteroides cellulosolvens Murray et al. 1984 is proposed to be reclassified in the new genus Pseudobacteroides as Pseudobacteroides cellulosolvens gen. nov., comb. nov., with the type strain WM2(T) ( = ATCC 35603(T) = DSM 2933(T) = NRCC 2944(T)).

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

A Role ofBradyrhizobium elkaniiand Closely Related Strains in the Degradation of Methoxychlor in Soil and Surface Water Environments

We have reported that a leguminous bacterial strain, Bradyrhizobium sp. strain 17-4, isolated from river sediment, phylogenetically very close to Bradyrhizobium elkanii, degraded methoxychlor through O-demethylation and oxidative dechlorination. In the present investigation, we found that B. elkanii (USDA94), a standard species deposited in the Culture Collection, degraded methoxychlor. Furthermore, Bradyrhizobium sp. strain 4-1, also very close to B. elkanii, isolated from Japanese paddy field soil, degraded methoxychlor. These B. elkanii and closely related strains degraded methoxychlor through almost identical metabolic pathways, and cleaved the phenyl ring and mineralized. In contrast, another representative Bradyrhizobium species, B. japonicum (USDA110), did not degrade methoxychlor at all. Based on these findings, B. elkanii and closely related strains are likely to play an important role not only in providing the readily biodegradable substrates but also in completely degrading (mineralizing) methoxychlor by themselves in the soil and surface water environment.

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.

ACTN3 R577X Genotype is Associated with Sprinting in Elite Japanese Athletes

The ACTN3 R577X genotype has been found to associate with sprint/power phenotypes in all elite athlete cohorts investigated. This association has not been extensively studied in elite Asian athletes. The present study was undertaken to investigate the association between the ACTN3 R577X genotype and elite Japanese track and field athlete status. 299 elite Japanese track and field athletes (134 sprint/power athletes; 165 endurance/middle-power athletes) and 649 Japanese controls were genotyped for the ACTN3 R577X polymorphism. All athletes were of national or international level. Sprint/power athletes showed a higher frequency of RR + RX genotype than controls (111/134 [82.8%] vs. 478/649 [73.7%], P = 0.025 under the R-dominant model), while there was no significant difference between endurance/middle-power athletes and controls (126/165 [76.4%] vs. 478/649 [73.7%], P = 0.48 under the R-dominant model). Sprinters with the RR + RX genotype had significantly faster personal best times for the 100 m than those with XX genotype (10.42 ± 0.05 s vs. 10.64 ± 0.09 s, P = 0.042); no such association was found in the 400 m sprinters (47.02 ± 0.36 s vs. 47.56 ± 0.99 s, P = 0.62). ACTN3 R577X genotype is associated with sprint/power performance in elite Japanese track and field athletes, especially short sprint performance.

Degradation of the Persistent Organic Pollutant [14C]Heptachlor in Japanese Field Soils

The fate of [(14)C]heptachlor in Saitama soil and the degradation of [(14)C]heptachlor in four Japanese field soils over 112 d after application were investigated. Heptachlor was degraded mainly to cis-heptachlor epoxide by a biotic process and to 1-hydroxychlordene by an abiotic process in the field soils. Volatilization of heptachlor and cis-heptachlor epoxide from the soil was observed over the experimental period. The amount of 1-hydroxychlordene produced in the soils appeared to be related to the soil water contents. Because heptachlor and heptachlor epoxides are predicted to volatilize to the atmosphere and to persist in soils, these compounds are thought to spread among Japanese environmental compartments even after a ban on their use.

Aminivibrio pyruvatiphilus gen. nov., sp. nov., an anaerobic, amino-acid-degrading bacterium from soil of a Japanese rice field

A novel anaerobic bacterium that could ferment amino acids and organic acids was isolated from an anaerobic, propionate-oxidizing enrichment culture originating from soil of a rice field in Japan. Cells of the isolate, designated strain 4F6E(T), were Gram-staining-negative, oxidase- and catalase-negative, non-spore-forming, vibrio-shaped, motile rods (0.8×2.0-2.5 µm) with two or three lateral flagella. Growth occurred at 20-42 °C (optimum at 37-40 °C), at pH 6.4-8.4 (optimum at pH 7.3) and at 0-1.5 % (w/v) NaCl (optimum at 0-0.5 %). Good growth occurred on glycine, serine, cysteine, pyruvate and citrate, whereas poor growth was observed on threonine, glutamine, L-malate, α-ketoglutarate, peptone and Casamino acids. In co-culture with the hydrogen-utilizing methanogen Methanobacterium formicicum JCM 10132(T), strain 4F6E(T) oxidized alanine, valine, leucine, isoleucine, methionine, aspartate, glutamate, histidine, asparagine and fumarate. Yeast extract was required for growth. The G+C content of genomic DNA was 61.9 mol%. A phylogenetic analysis based on comparison of the 16S rRNA gene sequence showed that the type strains of Fretibacterium fastidiosum, Aminobacterium colombiense and Aminobacterium mobile, members of the family Synergistaceae, were the closest relatives of strain 4F6E(T), with low sequence similarities (89.3, 89.5 and 86.2 %, respectively). Strain 4F6E(T) contained iso-C13 : 0 (24.43 %), iso-C15 : 0 (16.47 %) and C19 : 1ω11c/C19 : 1ω9c (16.32 %) as the major fatty acids, which differed from those of F. fastidiosum, Aminobacterium colombiense and Aminobacterium mobile. On the basis of phenotypic, chemotaxonomic and phylogenetic differences between strain 4F6E(T) and the type strains of F. fastidiosum and Aminobacterium species, we propose that strain 4F6E(T) represents a novel genus and species, Aminivibrio pyruvatiphilus gen. nov., sp. nov. The type strain of Aminivibrio pyruvatiphilus is strain 4F6E(T) ( = JCM 18417(T) = DSM 25964(T)).

Detection and genotyping of Cryptosporidium spp. in large Japanese field mice, Apodemus speciosus

The genus Cryptosporidium, which is an obligate intracellular parasite, infects various vertebrates and causes a diarrheal disease known as cryptosporidiosis. Wild rodents are naturally infected with zoonotic Cryptosporidium; thus, they are potential reservoirs of the parasites. Mice are common rodents frequently found in agricultural areas and have many opportunities to contact other wild animals, livestock, and humans. Irrespective of the potential risk, there are few epidemiologic studies of Cryptosporidium in wild mice because of their low economic importance and the difficulty in conducting surveys. Hence, the species and genotypes of Cryptosporidium in wild mice living around various areas remain unclear. We investigated the species and genotype distribution and prevalence of Cryptosporidium in the large Japanese field mouse (Apodemus speciosus) in an agricultural site in Osaki, Miyagi Prefecture, Japan. In total, 15 mice were captured and examined in this study. By microscopic analysis, only one mouse (JFM 3) was determined to be Cryptosporidium-positive, while the parasite were detected in four mice (JFM 3, 6, 10, and 15) by a molecular approach using partial SSU rRNA gene sequences. Based on nucleotide sequence and phylogenetic analysis, the Cryptosporidium isolates were identified as C. ubiquitum (from JFM 10) and C. muris (from JFM 3 and 6). In contrast, the Cryptosporidium in JFM 15 was not identified as a known species or genotype and is therefore proposed as a novel genotype; the Naruko genotype. More molecular data are necessary to elucidate the taxonomic identity of this novel Cryptosporidium genotype. The C. muris Japanese field mouse genotypes showed marked divergence compared to that in a previous report. The large Japanese field mouse might thus represent a reservoir of multiple Cryptosporidium spp.

Correlation of seedling size and branch number with disease resistance of Pinus thunbergii seedlings to Bursaphelenchus xylophilus

SummaryJapanese black pine (Pinus thunbergii) seedlings resistant to pine wood nematode (PWN; Bursaphelenchus xylophilus) are routinely selected in Japanese field inoculation trials. Correlations between morphological factors (such as height, stem diameter at ground level and number of branches on seedlings) and disease resistance were examined to improve the production efficiency of 1‐year‐old black pine seedlings for inoculation. Family relatedness and environmental conditions strongly affected seedling resistance; accordingly, logistic regression analysis was used to separate effects of these two variables. Height and stem diameter at ground level significantly correlated with disease resistance in seedlings inoculated with PWN. Because (a) interactions between stem diameter at ground level and environmental condition were significant and (b) height did not interact with any other factor, it was concluded that height of 1‐year‐old Japanese black pine seedlings independently correlated with PWN resistance. Thus, field inoculation tests should use tall seedlings to achieve enhanced survival rates.

Antigenic variation among recent Japanese isolates of bovine coronaviruses belonging to phylogenetically distinct genetic groups

Bovine coronaviruses (BCoVs) isolated in Japan consist of four genetic groups, as determined by phylogenetic analysis using the polymorphic region (aa 456–592) of the S glycoprotein gene. Japanese field isolates of BCoV, reference Kakegawa strain, and vaccine strain 66/H were analyzed for their antigenic properties by indirect immunofluorescence and neutralization testing. There were no significant differences observed among these BCoVs in direct immunofluorescence tests. However, antigenic differences were observed between BCoVs in the neutralization tests, although there was no clear indication of a distinct serotype. A monoclonal antibody, 4H4, against the Kakegawa strain belonging to group 1 lacked significant neutralizing activity for viruses of groups 2, 3, and 4. Therefore, we speculate that the genetic differences between these groups may have altered their antigenicity. Analysis of mutant viruses resistant to neutralization by 4H4 revealed that the antigenic site of the Kakegawa strain maps to amino acid position 284 of the S glycoprotein. This site is not homologous to a known antigenic site (aa 528) of the Quebec strain belonging to group 1, and it is not located in the conformational domain comprising domain I (aa 351–403) and domain II (aa 517–621). This amino acid constitutes a neutralization epitope of BCoV, which is distinct from aa 528 of the Quebec strain. These results indicate antigenic evolution of BCoV between the genetic groups circulating in Japan.

Laboratory tests on sorption and transformation of the insecticide flubendiamide in Japanese tea field soil

Flubendiamide belongs to the modern insecticides applied in Japanese tea cultivation to control smaller tea tortrix and tea leaf roller. Since fate and behavior in soil have been only monitored sparsely and fragmentarily until today, laboratory tests were performed on sorption, leaching, biotransformation and photo-induced biotransformation of flubendiamide in two different soils. In batch equilibrium tests, Kd and KOC values were 15 and 298Lkg−1 for the Japanese tea field soil as well as 16 and 1610Lkg−1 for the German arable field soil classifying flubendiamide to be moderately mobile and slightly mobile, respectively. The affinity to the tea field soil was additionally confirmed by soil column tests where flubendiamide was predominantly retarded in the topsoil layers resulting in a percolate contamination of only 0.002mgL−1. In the aerobic biotransformation tests, flubendiamide did not substantially disappear within the 122-d incubation period. Due to DT50>122 d, flubendiamide was assessed very persistent. Supplementary, photo-induced impacts on biotransformation were studied in a special laboratory irradiation system. Despite a 14-d irradiation period, photo-induced biotransformation in the tea field soil was not identifiable, neither by HPLC/DAD nor by LC/MS/MS. 3-d irradiation tests in photosensibilizing acetone, however, showed that the primary photo-transformation product desiodo-flubendiamide was formed. How far this photochemical reaction may also occur in soil of perennial tea plant stands, however, has to be checked in field studies.

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.

Molecular Cytogenetic Identification and Characterization of Robertsonian Chromosomes in the Large Japanese Field Mouse (Apodemus speciosus) Using FISH

Robertsonian (Rb) karyotypic polymorphism in Apodemus speciosus has interested many researchers with particular referece to the genetic divergence between Rb and non-Rb populations. Failure to find morphologic, biochemical, or genetic differences in previous studies reveals the necessity of focusing on loci on Rb chromosomes, which can be characterized by FISH mapping with DNA probes. In an Rb heterozygote, DNA probes from laboratory mouse chromosomes (MMUs) 1 and 10 were simultaneously hybridized to the long arm of a metacentric and a medium-sized acrocentric chromosome and to the short arm of the metacentric and a small acrocentric chromosome, respectively. Four additional probes derived from each of MMUs 1 and 10 were mapped to the long and short arms, respectively, of the Rb chromosome identified by the above markers. Homologies between the long arm of the Rb chromosome and MMU 1 and between the short arm and MMU 10 were supported by all ten markers, which were dispersed along nearly the entire lengths of the Rb chromosomes. These results indicate that the long and short arms of the Rb chromosomes are homologous to Apodemus speciosus chromosomes 12 and 19 (defined in a previous study), respectively. This ten-marker series can be useful for detecting chromosome-specific divergence between the two karyotypic populations at the gene level.

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.

A Genetic Mechanism for Emergence of Races in Fusarium oxysporum f. sp. lycopersici: Inactivation of Avirulence Gene AVR1 by Transposon Insertion

Compatible/incompatible interactions between the tomato wilt fungus Fusarium oxysporum f. sp. lycopersici (FOL) and tomato Solanum lycopersicum are controlled by three avirulence genes (AVR1–3) in FOL and the corresponding resistance genes (I–I3) in tomato. The three known races (1, 2 and 3) of FOL carry AVR genes in different combinations. The current model to explain the proposed order of mutations in AVR genes is: i) FOL race 2 emerged from race 1 by losing the AVR1 and thus avoiding host resistance mediated by I (the resistance gene corresponding to AVR1), and ii) race 3 emerged when race 2 sustained a point mutation in AVR2, allowing it to evade I2-mediated resistance of the host. Here, an alternative mechanism of mutation of AVR genes was determined by analyses of a race 3 isolate, KoChi-1, that we recovered from a Japanese tomato field in 2008. Although KoChi-1 is race 3, it has an AVR1 gene that is truncated by the transposon Hormin, which belongs to the hAT family. This provides evidence that mobile genetic elements may be one of the driving forces underlying race evolution. KoChi-1 transformants carrying a wild type AVR1 gene from race 1 lost pathogenicity to cultivars carrying I, showing that the truncated KoChi-1 avr1 is not functional. These results imply that KoChi-1 is a new race 3 biotype and propose an additional path for emergence of FOL races: Race 2 emerged from race 1 by transposon-insertion into AVR1, not by deletion of the AVR1 locus; then a point mutation in race 2 AVR2 resulted in emergence of race 3.