Contrasting phylogeographic histories between the continent and islands of East Asia: Massive mitochondrial introgression and long-term isolation of hares (Lagomorpha: Lepus)

Hares of the genus Lepus are distributed worldwide, and introgressive hybridization is thought to be pervasive among species, leading to reticulate evolution and taxonomic confusion. Here, we performed phylogeographic analyses of the following species of hare across East Asia: L. timidus, L. mandshuricus, L. coreanus, and L. brachyurus collected from far-eastern Russia, South Korea, and Japan. Nucleotide sequences of one mitochondrial DNA and eight nuclear gene loci were examined, adding sequences of hares in China from databases. All nuclear DNA analyses supported the clear separation of three phylogroups: L. timidus, L. brachyurus, and the L. mandshuricus complex containing L. coreanus. On the other hand, massive mitochondrial introgression from two L. timidus lineages to the L. mandshuricus complex was suggested in continental East Asia. The northern population of the L. mandshuricus complex was mainly associated with introgression from the continental lineage of L. timidus, possibly since the last glacial period, whereas the southern population of the L. mandshuricus complex experienced introgression from another L. timidus lineage related to the Hokkaido population, possibly before the last glacial period. In contrast to continental hares, no evidence of introgression was found in L. brachyurus in the Japanese Archipelago, which showed the oldest divergence amongst East Asian hare lineages. Our findings suggest that glacial-interglacial climate changes in the circum-Japan Sea region promoted distribution shifts and introgressive hybridization among continental hare species, while the geographic structure of the region contributed to long-term isolation of hares on the islands, preventing inter-species gene flow.

Chromosomal Aberrations in Large Japanese Field Mice (Apodemus speciosus) Captured near Fukushima Dai-ichi Nuclear Power Plant

Since the Fukushima Dai-ichi Nuclear Power Plant accident, radiation effects on nonhuman biota in the contaminated areas have been a major concern. Here, we analyzed the frequencies of chromosomal aberrations (translocations and dicentrics) in the splenic lymphocytes of large Japanese field mice (Apodemus speciosus) inhabiting Fukushima Prefecture. A. speciosus chromosomes 1, 2, and 5 were flow-sorted in order to develop A. speciosus chromosome-specific painting probes, and FISH (fluorescence in situ hybridization) was performed using these painting probes to detect the translocations and dicentrics. The average frequency of the translocations and dicentrics per cell in the heavily contaminated area was significantly higher than the frequencies in the case of the noncontaminated control area and the slightly and moderately contaminated areas, and this aberration frequency in individual mice tended to roughly increase with the estimated dose rates and accumulated doses. In all four sampling areas, the proportion of aberrations occurring in chromosome 2 was approximately >3 times higher than that in chromosomes 1 and 5, which suggests that A. speciosus chromosome 2 harbors a fragile site that is highly sensitive to chromosome breaks induced by cellular stress such as DNA replication. The elevated frequency of chromosomal aberrations in A. speciosus potentially resulting from the presence of a fragile site in chromosome 2 might make it challenging to observe the mild effect of chronic low-dose-rate irradiation on the induction of chromosomal aberrations in A. speciosus inhabiting the contaminated areas of Fukushima.

The cryptic Y-autosome translocation in the small Indian mongoose, Herpestes auropunctatus, revealed by molecular cytogenetic approaches

In initial studies of the eutherian small Indian mongoose (Herpestes auropunctatus), the Y chromosome could not be identified in somatic cells. The male chromosome number is uniquely odd, 2n = 35, whereas that of females is 2n = 36. Previous reports indicated that this unique karyotype resulted from a translocation of the ancestral Y chromosome to an autosome. However, it has been difficult to identify the chromosomes that harbor the translocated Y chromosomal segment because it is an extremely small euchromatic region. Using a Southern blot analysis, we detected four conserved Y-linked genes, SRY, EIF2S3Y, KDM5D, and ZFY, in the male genome. We cloned homologues of these genes and determined their sequences, which showed high homology to genes in two carnivore species, cat and dog. To unambiguously identify the Y-bearing autosome, we performed immunostaining of pachytene spermatocytes using antibodies against SYCP3, γH2AX, and the centromere. We observed trivalent chromosomes, and the associations between the distal ends of the chromosomes were consistent with those of Y and X1 chromosomes. The centromere of the Y chromosome was located on the ancestral Y chromosomal segment. We mapped the complementary DNA (cDNA) clones of these genes to the male chromosomes using fluorescence in situ hybridization (FISH), and the linear localization of all genes was confirmed by two-colored FISH. These Y-linked genes were localized to the proximal region of the long arm of a single telomeric chromosome, and we successfully identified the chromosome harboring the ancestral Y chromosomal segment.

Biological index of environmental lead pollution: accumulation of lead in liver and kidney in mice

Lead (Pb) is known to be highly poisonous, and the acute poisoning of Cd causes the abdominal pains, vomiting, and shock. The digestive and nervous symptom is observed in the chronic lead poisoning. It was also known that the defect in hemoglobin synthesis by Pb produce anemia. The release of Pb into the environment presents a source of exposure for wild animals. In this study, we examined the utility of a new Pb-monitoring index in mice administered Pb. A solution containing 0.02, 0.2, 2, or 4 ppm lead chloride (PbCl2) was administered intraperitoneally to mice, and the Pb contents of the kidney and liver were determined at designated time points. The mean Pb content of both organs increased depending on the administered Pb dosage. Although the results of control was near the detection limits, the administration of 4 ppm in 4 weeks resulted in Pb levels of 260 mg ppm/wet weight and 110 ppm wet weight in the kidney and liver, respectively. However, there were no significant relationships among administered dose, duration of Pb treatment, and liver or kidney Pb content. Then, values in all mice administered control or 0.02 mg Pb were located inside the ellipse, representing the confidence area of the new index, and values in all mice administered more than 2 mg Pb were located outside the ellipse. These results confirm that animals exposed to high concentrations of Pb would be detected by this new index.

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 ((134)Cs and (137)Cs) 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).

Feral cat diet and predation on endangered endemic mammals on a biodiversity hot spot (Amami–Ohshima Island, Japan)

Context There has been concern that feral cats have negative impacts on the endangered endemic mammals of Amami-Ohshima Island, Japan, including the Amami rabbit, Pentalagus furnessi, Ryukyu long-tailed giant rat, Diplothrix legata, and Amami spiny rat, Tokudaia osimensis. However, no diet study of feral cat has been conducted to support the necessity of an urgent feasible feral-cat management for the island. Aims The aims of the present study were to analyse feral-cat diet on Amami-Ohshima Island by using scat analysis and estimate the potential predation impact of feral cats on endangered mammals on the island. Methods The diet of feral cats was studied using scat analysis. We estimated the number of prey, percentage of prey, frequency of occurrence (the percentage of scats in a sample containing a particular prey item), percentage of biomass (biomass of the same prey item divided by the total consumed biomass ×100) and daily consumed biomass (DCB). Key results Three endangered endemic mammals were the main prey species of the feral cat diet (65% of total DCB). The percentage contributions of these species on DCB were long-tailed giant rat (34.7%), Amami spiny rat (21.9%) and Amami rabbit (12%). Conclusions Mammals, especially endangered endemic mammals, were main prey species of feral cat on Amami Island. In Amami Island, where native and invasive rodents coexisted, feral cats consumed more native (56.6%) than invasive (22.2% for Rattus rattus) species. Implications Feral cats are likely to be having a significant impact on endangered endemic mammals on the island. To ensure the long-term survival of these endemic species, active management of the feral-cat population should be considered.

Evaluating the "recovery level" of endangered species without prior information before alien invasion

For maintaining social and financial support for eradication programs of invasive species, quantitative assessment of recovery of native species or ecosystems is important because it provides a measurable parameter of success. However, setting a concrete goal for recovery is often difficult owing to lack of information prior to the introduction of invaders. Here, we present a novel approach to evaluate the achievement level of invasive predator management based on the carrying capacity of endangered species estimated using long-term monitoring data. In Amami-Oshima Island, Japan, where the eradication project of introduced small Indian mongoose is ongoing since 2000, we surveyed the population densities of four endangered species threatened by the mongoose (Amami rabbit, the Otton frog, Amami tip-nosed frog, and Amami Ishikawa's frog) at four time points ranging from 2003 to 2011. We estimated the carrying capacities of these species using the logistic growth model combined with the effects of mongoose predation and environmental heterogeneity. All species showed clear tendencies toward increasing their density in line with decreased mongoose density, and they exhibited density-dependent population growth. The estimated carrying capacities of three endangered species had small confidence intervals enough to measure recovery levels by the mongoose management. The population density of each endangered species has recovered to the level of the carrying capacity at about 20–40% of all sites, whereas no individuals were observed at more than 25% of all sites. We propose that the present approach involving appropriate monitoring data of native organism populations will be widely applicable to various eradication projects and provide unambiguous goals for management of invasive species.

Association between depressive symptoms and metabolic syndrome in Japanese community-dwelling older people: a cross-sectional analysis from the baseline results of the Fujiwara-kyo prospective cohort study

OBJECTIVE

Metabolic syndrome contains many risks for medical diseases such as cardiovascular disease and diabetes, which might precipitate depressive symptoms in the older people. However, the association between depressive symptoms and metabolic syndrome in Japanese community-dwelling older people is unclear. This study was performed to answer this important question.

METHODS

Cross-sectional analyses were performed on 3796 community-dwelling independent older people (≥ 65 years, 1911 men and 1885 women) from the 2007-2008 baseline examination of the Fujiwara-kyo study, a prospective cohort study on successful aging. Depressive symptoms were assessed using the 15-item short form of the Geriatric Depression Scale and metabolic syndrome was defined according to the 2005 International Diabetes Federation. Covariates were social supports, negative life events, health behavior, education, cognitive function, anthropometric status, and others. Multiple logistic regression analyses were performed to determine the relationships between depressive symptoms and these variables.

RESULTS

The prevalence of depressive symptoms (Geriatric Depression Scale-15 ≥ 6) and metabolic syndrome were 14.8% and 16.6%, respectively. Significant protective factors against depressive symptoms were higher education, more opportunity for drinking of alcohol, better social supports, and more walking daily. Metabolic syndrome was statistically associated with depressive symptoms (adjusted odds ratio = \ 1.32, 95% confidence interval = 1.03-1.68). Other risk factors significantly associated with depressive symptoms were sleep disturbance, visual or hearing impairment, and negative life events.

CONCLUSIONS

The present study showed an association between metabolic syndrome and depressive symptoms in ambulatory Japanese older people, as in western countries.

Anterior transpetrosal approach to the prepontine epidermoids

We have operated on nine patients with a prepontine epidermoid extending to the bilateral cistern or the unilateral middle fossa using the anterior transpetrosal approach since 1986. The preoperative symptoms were unilateral trigeminal neuralgia, hearing disturbance, gait disturbance, double vision, facial hypesthesia, hemifacial spasm, and dysphagia. The most common neurological sign was unilateral trigeminal nerve disturbance. In two patients with useful hearing preoperatively lost, the labyrinth and mastoid air cells as well as the petrous apex were resected to extend the surgical field. Tumors were totally removed, except for capsules that were tightly adhered to the brain stem, cranial nerve, and vessels. The trigeminal neuralgia, hemifacial spasm, and dysphagia disappeared, but double vision improved only one out of three cases, and facial hypesthesia was unchanged in all cases. There were no postoperative deaths. New abducens palsy appeared in four cases and cerebrospinal fluid (CSF) leakage appeared in three cases postoperatively, but later these symptoms disappeared. In one case, postoperative chemical meningitis developed, and a ventricular shunt was required later to treat hydrocephalus. Postoperative follow-up, an average of 5,7 years, did not show any increases in any of the tumors. Based on our experience, we conclude that the anterior transpetrosal approach is more useful than the retromastoid suboccipital approach to resect the epidermoid located mainly in the prepontine cistern.

Additional copies of CBX2 in the genomes of males of mammals lacking SRY, the Amami spiny rat (Tokudaia osimensis) and the Tokunoshima spiny rat (Tokudaia tokunoshimensis)

Tokudaia osimensis (the Amami spiny rat) and Tokudaia tokunoshimensis (the Tokunoshima spiny rat) have a sex chromosome composition of XO/XO, no Y chromosome. The mammalian sex-determining gene, SRY, is also absent in these species, which indicates that these spiny rats exhibit a novel sex-determining mechanism that is independent of SRY. To identify a candidate gene that controls this mechanism, the copy numbers and chromosomal locations of 10 genes with important functions in gonadal differentiation were determined: ATRX, CBX2 (M33), DMRT1, FGF9, NR0B1 (DAX1), NR5A1 (Ad4BP/SF1), RSPO1, SOX9, WNT4, and WT1. Multiple bands were detected for NR0B1 in Southern blot analysis, which suggested the presence of multiple copies of the gene in the genomes of these two species. CBX2 was localized to two loci in both sexes of the two species by fluorescence in situ hybridization mapping: 3q24 and 6p11.2 in T. osimensis and 10q25-q26 and 14q12-q13.1 in T. tokunoshimensis. Quantification of copy numbers in the two species by quantitative real-time PCR indicated that there were two or three more copies of CBX2 per haploid genome in males (T. osimensis, n = 3; T. tokunoshimensis, n = 2) than in females (T. osimensis, n = 4; T. tokunoshimensis, n = 2), whereas NR0B1 was present as a single copy in both. The results suggest that additional copies of CBX2 in males might be involved in a novel sex-determining mechanism in species that lack SRY.

The process of a Y-loss event in an XO/XO mammal, the Ryukyu spiny rat

The Ryukyu spiny rat, Tokudaia osimensis, has an XO/XO sex chromosome constitution, lacking a Y chromosome and the mammalian sex-determining gene SRY. To investigate the Y-loss event, we traced three proto-Y-linked genes, RBMY1A1, EIF2S3Y, and KDM5D, in the genome. The original Y-linked RBMY1A1 was lost as well as SRY, and the remaining RBMY1A1 was a processed pseudogene on autosome. In contrast, EIF2S3Y and KDM5D were conserved in genomes of both sexes as a result of their translocation from the Y chromosome to the X chromosome and/or autosomes. Furthermore, these genes were expressed in gonads and brains of both sexes. Our study indicated a loss of Y-linked genes with important male functions to be necessary for the Y chromosome to disappear. These functions might have been retained through the acquisition of new genes, and therefore, the Y-loss has had no harmful effect on the maintenance of this species.

Distribution and abundance of the Amami rabbit Pentalagus furnessi in the Amami and Tokuno Islands, Japan

The Amami rabbit Pentalagus furnessi is a rare forest-dwelling form endemic to the Amami and Tokuno Islands in Japan. In order to estimate the distribution and abundance of the Amami rabbit we counted their faecal pellets along forest roads and streams as well as within the forests on Amami and Tokuno Islands during January 1993–March 1995. The number of pellets/ km along a stream gave a practical index for measuring relative abundance. The rabbit was estimated to be distributed over about 370 sq km on Amami Island and 33 sq km on Tokuno Island. There was a large variance in faecal abundance among the survey routes. Some populations were completely isolated and thought to be very small. The size of a local population was positively correlated with those of neighbouring populations and the amount of mature forest relative to other serai stages. We compared the results of this survey with those of previous surveys to find that the total population of this species appears to be declining. Some conservation measures are proposed for forest habitat management, designed to avert the decline of the Amami rabbit and to ensure its preservation.

Comparative chromosome painting map between two Ryukyu spiny rat species, Tokudaia osimensis and Tokudaia tokunoshimensis (Muridae, Rodentia)

Ryukyu spiny rats (genus Tokudaia) are indigenous species that are confined to three islands of the Nansei Shoto archipelago, Amami-Oshima, Tokunoshima and Okinawa-jima, Japan. Tokudaia tokunoshimensis from Tokunoshima Island and Tokudaia osimensis from Amami-Oshima Island are closely related taxonomically, although their karyotypes are quite different: the diploid chromosome numbers and sex chromosome constitution are 2n=45, X0/X0 for T. tokunoshimensis and 2n=25, X0/X0 for T. osimensis. We conducted comparative chromosome painting with chromosome-specific DNA probes of the laboratory mouse (Mus musculus) to molecularly examine the chromosome homology between T. tokunoshimensis and T. osimensis, and deduced a possible ancestral karyotype of Tokudaia species and the process of evolutionary chromosome rearrangements. The proposed ancestral karyotype with the diploid number of 2n=48, XX/XY was similar to the karyotype of T. tokunoshimensis, and the karyotype of T. osimensis would then have been established through at least 14 chromosomal changes, mainly centric fusion and tandem fusion, from the ancestral karyotype. The close karyological relationship between the ancestral karyotypes of Tokudaia and Apodemus also suggests that the chromosomal evolution in the Tokudaia-Apodemus lineage has been very slow and has accelerated only recently in the branch leading to T. osimensis.

Exceptional minute sex-specific region in the X0 mammal, Ryukyu spiny rat

The Ryukyu spiny rats (genus Tokudaia) inhabit only three islands in the Nansei Shoto archipelago in Japan, and have the variations of karyotype among the islands. The chromosome number of T. osimensis in Amami-Oshima Island is 2n = 25, and T. tokunoshimensis in Tokunoshima Island is 2n = 45, and the two species have X0 sex chromosome constitution with no cytogenetically visible Y chromosome in both sexes. We constructed the standard ideograms for these species at the 100 and 200 band levels. Comparing the banding patterns between these species, it was suggested that at least 10 times the number of Robertsonian fusions occurred in T. osimensis chromosomes. However, no karyotypic differences were observed between sexes in each species. To detect the sex-specific chromosomal region of these X0 species we applied the comparative genomic hybridization (CGH) method. Although the male- and female-derived gains and losses were detected in several chromosome regions, all of them were located in the heterochromatic and/or telomeric regions. This result suggested that the differences detected by CGH might be caused by the polymorphism on the copy numbers of repeated sequences in the heterochromatic and telomeric regions. Our result indicated that the sex-specific region, where the key to sex determination lies, is very minute in X0 species of Tokudaia.

PCDDs, PCDFs, and coplanar PCBs in wild terrestrial mammals from Japan: congener specific accumulation and hepatic sequestration

The present study determined the contamination levels and congener-specific accumulation features of dioxins and related compounds (DRCs) in wild terrestrial mammals such as large Japanese field mice (LJFM), lesser Japanese moles (LJMs), and raccoon dogs (RDs) collected from Kanto region in Japan during 2001. The toxic equivalent quantity (TEQ) levels in the carcasses or adipose tissues were in the order of RDs > or = LJMs > LJFM. Comparison of DRC congener profiles in the three species and principal component analysis (PCA) demonstrated a higher contribution of OCDD, T4CB77, and P5CB118 in LJMs. Analysis of liver-adipose distribution of DRC congeners in RDs showed that livers contained significantly higher TEQs than adipose tissues, indicating that liver is a depository organ and critical for determining the toxicokinetics of DRCs. As for most T4, P5, H6CDD/DFs and for P5CB126, H6CB169 and mono-ortho PCB congeners, their liver/adipose concentration ratios in RDs revealed a tendency to increase with hepatic TEQ levels, suggesting TEQ-dependent hepatic sequestration.

Simple indole alkaloids and those with a non-rearranged monoterpenoid unit

This review covers newly isolated simple indole alkaloids, structure determinations, total syntheses and biological activities reported in the literature in 2003.

Bisphenol A-induced apoptosis of cultured rat Sertoli cells

Bisphenol A (BPA) was examined for its effects on cultured Sertoli cells established from 18-day-old rat testes. We demonstrated that exposure of cultured Sertoli cells to BPA decreased the cell viability in a dose- and a time-dependent manner and that exposure to BPA brought about morphologic changes of the cells, such as membrane blebs, cell rounding, cytoskeletal collapse, and chromatin condensation or fragmentation, all of which conform to the morphologic criteria for apoptosis. Immunocytochemistry showed that active caspase-3, a major execution caspase, was expressed in round Sertoli cells positively labeled by the TUNEL method. Co-localization of active caspase-3 and aggregated actin fragments was also observed in the round Sertoli cells. Theses results suggest that BPA induces cell death of Sertoli cells by promoting apoptosis. Apoptosis-inducing cell death was observed in cells exposed to 150-200 microM BPA, while BPA at <100 microM had only slight cytotoxic effects on the cells.

Simple indole alkaloids and those with a nonrearranged monoterpenoid unit

This review covers simple indole alkaloids and those with a nonrearranged monoterpenoid unit. Newly isolated alkaloids, structure determinations, total syntheses and biological activities are included. The literature from January to December 2001 is reviewed and 166 references are cited.