Distribution and parameters of genetic polymorphism in northern red-backed vole (<Emphasis Type="Italic">Clethrionomys rutilus</Emphasis>) and bank vole (<Emphasis Type="Italic">Clethrionomys glareolus</Emphasis>) in West Siberia

This article presents data on the genetic variability of the northern red-backed vole and the bank vole that live sympatrically in West Siberia. The two species of voles have comparable, relatively high indices of genetic variability of inter simple sequences repeats DNA. The proportion of polymorphic DNA markers is 95–98%, and the Nei’s genetic diversity index is 0.33–0.35. A total of 47–58% of allozyme loci in the voles are polymorphic, and the average heterozygosity per locus is 0.058 in the northern red-backed vole and 0.054 in the bank vole. Interpopulation differentiation is less pronounced in the red-backed vole (F _ST 0.293) compared to the bank vole (F _ST 0.475). Individuals of the hybrid line of the bank vole with the mitochondrial haplotype of the red-backed vole have been found by PCR typing of cytochrome b gene fragment of mtDNA. The distribution boundary of the hybrid line of bank voles goes farther to the northeast than was shown in earlier works. The proportion of hybrid specimens range from 2 to 34%. The indices of genetic variability in the hybrid line of the bank vole are lower than those of the parental species.     

Gene conversion in the mitochondrial genome on interspecific hybridization in voles of the <Emphasis Type="Italic">Clethrionomys</Emphasis> genus

The phenomenon of interspecific hybridization accompanied by transfer of the mitochondrial genome from the northern red-backed vole (Clethrionomys rutilus) to the bank vole (Cl. glareolus) in northeastern Europe is well known already for 25 years. However, the possibility of recombination between homologous segments of maternal and paternal mtDNAs of the voles during fertilization was not previously studied. Analysis of data on variability of nucleotide sequences of the mitochondrial gene for cytochrome b in populations of red-backed and bank voles in the area of their sympatry has shown that as a result of interspecific hybridization, the mitochondrial gene pool of bank voles contains not only mtDNA haplotypes of red-backed vole females, but also mtDNA haplotypes of bank voles bearing short nucleotide tracts of red-backed vole mtDNA. This finding supports the hypothesis that an incomplete elimination of red-backed vole paternal mtDNA during the interspecific hybridization between bank vole females and red-backed vole males leads to the gene conversion of bank vole maternal mtDNA tracts by homologous ones of mtDNA of red-backed vole males.     

Episomal maintenance of plasmids with hybrid origins in mouse cells

Bovine papillomavirus type 1 (BPV1), Epstein-Barr virus (EBV), and human herpesvirus 8 genomes are stably maintained as episomes in dividing host cells during latent infection. The mitotic segregation/partitioning function of these episomes is dependent on single viral protein with specific DNA-binding activity and its multimeric binding sites in the viral genome. In this study we show that, in the presence of all essential viral trans factors, the segregation/partitioning elements from both BPV1 and EBV can provide the stable maintenance function to the mouse polyomavirus (PyV) core origin plasmids but fail to do so in the case of complete PyV origin. Our study is the first which follows BPV1 E2- and minichromosome maintenance element (MME)-dependent stable maintenance function with heterologous replication origins. In mouse fibroblast cell lines expressing PyV large T antigen (LT) and either BPV1 E2 or EBV EBNA1, the long-term episomal replication of plasmids carrying the PyV minimal origin together with the MME or family of repeats (FR) element can be monitored easily for 1 month under nonselective conditions. Our data demonstrate clearly that the PyV LT-dependent replication function and the segregation/partitioning function of the BPV1 or EBV are compatible in certain, but not all, configurations. The quantitative analysis indicates a loss rate of 6% per cell, doubling in the case of MME-dependent plasmids, and 13% in the case of FR-dependent plasmids in nonselective conditions. Our data clearly indicate that maintenance functions from different viruses are principally interexchangeable and can provide a segregation/partitioning function to different heterologous origins in a variety of cells.     

Natural infections of small mammals with blood parasites on the borderland of boreal and temperate forest zones

Blood parasites of small mammals living in Białowieża Forest (eastern Poland) were investigated between 1996 and 2002. The following haemoparasite species were found:Trypanosoma (Herpetosoma) evotomys in bank voleClethrionomys glareolus; T. (H.) microti in root voleMicrotus oeconomus; Babesia microti in root vole;Hepatozoon erhardovae in bank vole andHepatozoon sp. in root vole. Some non-identifiedBartonella species were found in bank vole, root vole, field voleMicrotus agrestis, yellow-necked mouseApodemus flavicollis, common shrewSorex araneus, Eurasian water shrewNeomys fodiens, and Mediterranean water shrewN. anomalus. The prevalence and diversity of blood parasites were lower in shrews than small rodents. Totally, 52.0% of bank voles, 50.0% of root voles, 32.5% of common shrews, and 41.2% of Eurasian water shrews were infected with any of the blood parasites. Mixed infections were seldom observed in bank vole (17.3% of investigated individuals) and root vole (14.7%). No animals were infected with three or four parasites simultaneously. Infection of Białowieża small mammals with haemoparasites seemed to be similar to those described in other temperate forest regions rather than boreal ones. Infection rates of rodent species seem to be higher in their typical habitats: for bank vole it was the highest in mixed forest, whereas for root vole in sedge swamp. The results suggest that Arvicolidae play a greater role than Muridae or Soricidae in maintenance ofBabesia andHepatozoon foci in natural environments of central Europe.     

Reproductive investment under fluctuating predation risk: Microtine rodents and small mustelids

Summary We studied the reproductive investment of microtine rodents (bank vole (Clethrionomys glareolus),Microtus epiroticus andMicrotus agrestis) in western Finland under predation risk from small mustelids. During 1984–1992, the yearly mean litter size of overwintered bank voles was smaller at high least weasel and stoat densities than at low densities (close to 3 versus 4–5). In addition, the annual mean litter size of young bank voles was negatively correlated to the least weasel density. In youngM. agrestis voles, the yearly late summer litter size was negatively associated with the autumn density of small mustelids. In the crash phase of the vole cycle (1989 and 1992), we removed small mustelids (mainly least weasels) from four unfenced areas in late April to late May and studied the reproduction of voles in four removal and comparable control areas (each 2–4 km²). Reduction of small mustelids significantly increased the proportion of pregnant bank vole females, but not that of pregnantMicrotus vole females. We conclude that predation risk apparently reduced reproductive investment of free-living bank vole females; these voles appear to trade their current parental investment against future survival and reproductive prospects. Accordingly, the presence of small mustelids (or their scent) may slow down the reproductive rate of voles. As antipredatory behaviours occurred on a large scale, our results add evidence to the hypothesis that crashes in multiannual vole cycles are driven by small mustelid predators.     

Competition, predation and interspecific synchrony in cyclic small mammal communities

Although competition and predation are considered to be among the most important biotic processes influencing the distribution and abundance of species in space and time, the relative and interactive roles of these processes in communities comprised of cyclically fluctuating populations of small mammals are not well known. We examined these processes in and among populations of field voles, sibling voles, bank voles and common shrews in western Finland, using spatially replicated trapping data collected four times a year during two vole cycles (1987–1990 and 1997–1999). Populations of the four species exhibited relatively strong interspecific temporal synchrony in their multiannual fluctuations. During peak phases, we observed slight deviations from close temporal synchrony: field vole densities peaked at least two months earlier than those of either sibling voles or bank voles, while densities of common shrews peaked even earlier. The growth rates of all four coexisting small mammal species were best explained by their own current densities. The growth rate of bank vole populations was negatively related to increasing densities of field voles in the increase phase of the vole cycle. Apart from this, no negative effects of interspecific density, direct or delayed, were observed among the vole species. The growth rates of common shrew populations were negatively related to increasing total rodent (including water voles and harvest mice) densities in the peak phase of the vole cycle. Sibling voles appeared not to be competitively superior to field voles on a population level, as neither of these Microtus voles increased disproportionately in abundance as total rodent density increased. We suggest that interspecific competition among the vole species may occur, but only briefly, during the autumn of peak years, when the total available amount of rodent habitat becomes markedly reduced following agricultural practices. Our results nonetheless indicate that interspecific competition is not a strong determinant of the structure of communities comprised of species exhibiting cyclic dynamics. We suggest that external factors, namely predation and shortage of food, limit densities of vole populations below levels where interspecific competition occurs. Common shrews, however, appear to suffer from asymmetric space competition with rodents at peak densities of voles; this may be viewed as a synchronizing effect.     

The Sex Specific Genetic Variation of Energetics in Bank Voles,Consequences of Introgression?

Interaction between mitochondrial and nuclear genomes is expected to affect energetic phenotypes of traits linked to mitochondrial physiology, further influencing the fitness. A rodent, the bank vole (Myodes glareolus), has a population structure completely or partially introgressed with mitochondria from its relative, the red vole (M. r utilus). Females that carried either bank vole mitochondria or mitochondria from the introgressed species were repeatedly mated with males of both mtDNA types. We found that in males, but not in females, morpho-physiological phenotypes are affected by sire type, causing decreases in body mass (BM) and basal metabolic rate (BMR; including BM corrected, rBMR) in individuals sired by fathers carrying introgressed mitochondria. Higher effect sizes for the proportion of additive genetic variation (and 5.6, 1.9 and 3.6 times higher narrow sense heritability for BM, BMR and rBMR, respectively), and lower for proportion of environmental variation were detected in progeny of non-introgressed males. Our data indicate that co-adapted and possibly co-introgressed nuclear genes related to energetic physiology have an important role in adaptation to the northern conditions in bank voles, and that sex linked nuclear genes are a potential source for variation in basal metabolic rate.     

Functional features of microbial communities in the digestive tract of field voles (Microtus rossiaemeridionalis and Clethrionomys glareolus)

The nitrogen-fixating and cellobiohydrolase activity, the nitrogen (N) and carbon (C) contents, and the number of microorganisms in the prestomach, cecum, and colon of two vole species were studied: the southern vole (Microtus rossiaemeridionalis) and the bank vole (Clethrionomys glareolus), which is characterized by a mixed type of diet. The nitrogen-fixating activity in the cecum was found to be the highest in the voles compared with the mammals studied earlier. The seasonal dynamics of both nitrogenase and cellobiohydrolase activities was registered in the southern vole. The structure of the microbial complex in the southern vole is more varied and includes microorganisms associated with plant substrates.     

Landscape features and helminth co-infection shape bank vole immunoheterogeneity,with consequences for Puumala virus epidemiology

Heterogeneity in environmental conditions helps to maintain genetic and phenotypic diversity in ecosystems. As such, it may explain why the capacity of animals to mount immune responses is highly variable. The quality of habitat patches, in terms of resources, parasitism, predation and habitat fragmentation may, for example, trigger trade-offs ultimately affecting the investment of individuals in various immunological pathways. We described spatial immunoheterogeneity in bank vole populations with respect to landscape features and co-infection. We focused on the consequences of this heterogeneity for the risk of Puumala hantavirus (PUUV) infection. We assessed the expression of the Tnf-α and Mx2 genes and demonstrated a negative correlation between PUUV load and the expression of these immune genes in bank voles. Habitat heterogeneity was partly associated with differences in the expression of these genes. Levels of Mx2 were lower in large forests than in fragmented forests, possibly due to differences in parasite communities. We previously highlighted the positive association between infection with Heligmosomum mixtum and infection with PUUV. We found that Tnf-α was more strongly expressed in voles infected with PUUV than in uninfected voles or in voles co-infected with the nematode H. mixtum and PUUV. H. mixtum may limit the capacity of the vole to develop proinflammatory responses. This effect may increase the risk of PUUV infection and replication in host cells. Overall, our results suggest that close interactions between landscape features, co-infection and immune gene expression may shape PUUV epidemiology.     

Development of Type 1 Diabetes in Wild Bank Voles Associated With Islet Autoantibodies and the Novel Ljungan Virus

Wild bank voles (Clethrionomys glareolus) may develop diabetes in laboratory captivity. The aim of this study was to test whether bank voles develop type 1 diabetes in association with Ljungan virus. Two groups of bank voles were analyzed for diabetes, pancreas histology, autoantibodies to glutamic acid decarboxylase (GAD65), IA-2, and insulin by standardized radioligand-binding assays as well as antibodies to in vitro transcribed and translated Ljungan virus antigens. Group A represented 101 trapped bank voles, which were screened for diabetes when euthanized within 24 hours of capture. Group B represented 67 bank voles, which were trapped and kept in the laboratory for 1 month before being euthanized. Group A bank voles did not have diabetes. Bank voles in group B (22/67; 33%) developed diabetes due to specific lysis of pancreatic islet beta cells. Compared to nondiabetic group B bank voles, diabetic animals had increased levels of GAD65 (P < .0001), IA-2 (P < .0001), and insulin (P = .03) autoantibodies. Affected islets stained positive for Ljungan virus, a novel picorna virus isolated from bank voles. Ljungan virus inoculation of nondiabetic wild bank voles induced beta-cell lysis. Compared to group A bank voles, Ljungan virus antibodies were increased in both nondiabetic (P < .0001) and diabetic (P = .0015) group B bank voles. Levels of Ljungan virus antibodies were also increased in young age at onset of newly diagnosed type 1 diabetes in children (P < .01). These findings support the hypothesis that the development of type 1 diabetes in captured wild bank voles is associated with Ljungan virus. It is speculated that bank voles may have a possible zoonotic role as a reservoir and vector for virus that may contribute to the incidence of type 1 diabetes in humans.     

Effects of Postnatal Stress on the Development of Type 1 Diabetes in Bank Voles (Clethrionomys glareolus)

Wild bank voles (Clethrionomys glareolus) kept in the laboratory under barren housing conditions develop high incidences of type 1 diabetes mellitus due to beta cell– specific lysis in association with the appearance of GAD65, IA-2, and insulin autoantibodies. Wild-caught and immediately analyzed voles show no histological signs of diabetes, and the disease may therefore be induced by circumstances related to the housing of the animals in captivity. We tested the possibility that postnatal stress by either maternal separation or water immersion at different intervals would induce diabetes in adult bank voles. We found that low-frequent stress during the first 21 days of life increases, whereas high-frequent stress markedly reduces, the incidence of type 1 diabetes in adulthood. These results differentiate the role of early-experienced stress on subsequent type 1 diabetes development and emphasize that the bank vole may serve as a useful new animal model for the disease.     

Dampening of population cycles in voles affects small mammal community structure,decreases diversity,and increases prevalence of a zoonotic disease

Long‐term decline and depression of density in cyclic small rodents is a recent widespread phenomenon. These observed changes at the population level might have cascading effects at the ecosystem level. Here, we assessed relationships between changing boreal landscapes and biodiversity changes of small mammal communities. We also inferred potential effects of observed community changes for increased transmission risk of Puumala virus (PUUV) spread, causing the zoonotic disease nephropatica epidemica in humans. Analyses were based on long‐term (1971–2013) monitoring data of shrews and voles representing 58 time series in northern Sweden. We calculated richness, diversity, and evenness at alpha, beta, and gamma level, partitioned beta diversity into turnover (species replacement) and nestedness (species addition/removal), used similarity percentages (SIMPER) analysis to assess community structure, and calculated the cumulated number of PUUV‐infected bank voles and average PUUV prevalence (percentage of infected bank voles) per vole cycle. Alpha, beta, and gamma richness and diversity of voles, but not shrews, showed long‐term trends that varied spatially. The observed patterns were associated with an increase in community contribution of bank vole (Myodes glareolus), a decrease of gray‐sided vole (M. rufocanus) and field vole (Microtus agrestis) and a hump‐shaped variation in contribution of common shrew (Sorex araneus). Long‐term biodiversity changes were largely related to changes in forest landscape structure. Number of PUUV‐infected bank voles in spring was negatively related to beta and gamma diversity, and positively related to turnover of shrews (replaced by voles) and to community contribution of bank voles. The latter was also positively related to average PUUV prevalence in spring. We showed that long‐term changes in the boreal landscape contributed to explain the decrease in biodiversity and the change in structure of small mammal communities. In addition, our results suggest decrease in small mammal diversity to have knock‐on effects on dynamics of infectious diseases among small mammals with potential implications for disease transmission to humans.     

Spatio-temporal patterns of habitat use in voles and shrews modified by density, season and predators

1.?Although the intrinsic habitat preferences of a species can be considered to be fixed, the realized habitat use depends on the prevailing abiotic and biotic conditions. Often the core habitats are occupied by dense and stable populations, while marginal habitats become occupied only at times of high density. In a community of interacting species, habitat uses of different species become inter-related, for example an increased density of a strong competitor forcing a weaker competitor to use more marginal habitats. 2.?We studied the spatio-temporal distribution patterns of three common small mammal species, the bank vole Myodes glareolus; the field vole Microtus agrestis; and the common shrew Sorex araneus, in a 4-year trapping study carried out on six large islands, each containing a mixture of three main habitat types (forest, field and clear-cut). We experimentally released least weasels (Mustela n. nivalis) to some of the islands to see how the focal species respond to increased predation pressure. 3.?Both vole species were largely restricted to their core habitats (bank voles to forests and field voles to fields) at times of low population density. With increasing density, the relative habitat use of both species increased in the clear-cut areas. The common shrew was a generalist in its habitat use at all population densities. 4.?The release of the weasels changed the habitat use of all study species. 5.?The vole species showed a stronger aggregated pattern than the common shrew, especially at low population density. The vole aggregations remained in the same localities between seasons, except in the case of bank voles after the weasels were released. 6.?Bank voles and field voles avoided each other at high density. 7.?We conclude that intrinsically differential habitat requirements and flexibility to modify habitat use facilitate the coexistence of the two competing vole species in mosaic landscapes consisting of boreal forests and open habitats.     

The Tien Shan vole (Microtus ilaeus; Rodentia: Cricetidae) as a new species in the Late Pleistocene of Europe

Grey voles (subgenus Microtus) represent a complex of at least seven closely related and partly cryptic species. The range of these species extends from the Atlantic to the Altai Mountains, but most of them occur east of the Black Sea. Using ancient DNA analyses of the Late Pleistocene specimens, we identified a new mtDNA lineage of grey voles in Europe. Phylogenetic analysis of mitochondrial DNA cytochrome b sequences from 23 voles from three caves, namely, Emine–Bair–Khosar (Crimea, Ukraine), Cave 16 (Bulgaria), and Bacho Kiro (Bulgaria), showed that 14 specimens form a previously unrecognized lineage, sister to the Tien Shan vole. The average sequence divergence of this lineage and the extant Tien Shan vole was 4.8%, which is similar to the divergence of grey vole forms, which are considered distinct species or being on the verge of speciation; M. arvalis and M. obscurus or M. mystacinus and M. rossiaemeridionalis. We estimated the time to the most recent common ancestor of the grey voles to be 0.66 Ma, which is over twice the recent estimates, while the divergence of the extant Tien Shan vole and the new lineage to be 0.29 Ma. Our discovery suggests that grey voles may have been more diversified in the past and that their ranges may have differed substantially from current ones. It also underlines the utility of ancient DNA to decipher the evolutionary history of voles.     

A comparison of paternal behaviour in the meadow vole Microtus pennsylvanicus,the pine vole M. pinetorum and the prairie vole M. cchrogaster

Paternal care in microtines has been studied infrequently and few studies have compared patterns of direct and indirect paternal investment. The paternal behaviour of three vole species, the meadow vole (Microtus pennsylvanicus), the pine vole (M. pinetorum) and the prairie vole (M. ochrogaster) was examined in a semi-natural setting. Prairie and pine voles were found to exhibit high levels of paternal care. Prairie vole males contributed the most direct care by remaining in the natal nest for long periods of time in contact with the pups. Pine voles contributed less direct care than prairie voles as they spent less time in the natal nest with their offspring. In addition, both prairie and pine vole males were observed to groom their pups and retrieve them back to the nest area. Prairie vole males also engaged in such indirect forms of care as nest construction and maintenance, while pine voles provided indirect care in the form of tunnel construction and food caching. Meadow vole males were the least paternal of the three species and rarely engaged in either direct or indirect care. These findings support predictions that M. pennsylvanicus is promiscuous and that male and female meadow voles occupy separate territories. They are also consistent with studies which indicate that prairie and pine voles are monogamous and have a structured social organization with members interacting closely with one another.     

Predation rate, prey preference and predator switching: experiments on voles and weasels

We studied the predation rate and prey selection of the least weasel ( Mustela nivalis nivalis ) on its two most common prey species in boreal environments, the bank vole ( Clethrionomys glareolus ) and the field vole ( Microtus agrestis ), in large outdoor enclosures. We also studied the response of weasels to odours of the two species in the laboratory. The enclosure experiment was conducted using constant vole densities (16 voles/ha) but with varying relative abundance of the two species. Weasels showed higher predation rates on bank voles, and males had higher predation rate than females. Females killed disproportionately more of the more abundant prey species, but they preferred bank voles to field voles when both were equally available. Overall, the predation rate also increased with increasing abundance of bank voles. Therefore our results are in agreement with earlier laboratory results showing preference for bank voles, even if no intrinsic preference for odours of either species was observed in our laboratory study. We suggest that the least weasel hunts according to prey availability, prey aggregation and suitability of hunting habitat, and that this causes the observed dependence of least weasels on field voles and emphasises the role of the field vole in the vole-weasel interaction in cyclic vole populations. Furthermore, our results suggest that predation by weasels may facilitate the coexistence of the two vole species via predator switching, and that it may cause the observed synchrony in dynamics between vole species.     

Effects of competition and season on survival and maturation of young bank vole females

In territorial microtines intra-specific density dependent processes can limit the maturation of individuals during the summer of their birth. This may have demographic consequences by affecting the number and the age distribution of breeding individuals in the population. Little is known about this process on a community level, though populations of many northern microtine species fluctuate in synchrony and are known to interfere socially with each other. We experimentally studied the influence of the field vole Microtus agrestis on maturation, breeding, space use and survival of weanling bank voles, Clethrionomys glareolus. Two additive competition experiments on bank vole populations were conducted in large outdoor enclosures, half of them additionally housing a field vole population. In a mid-summer experiment low population density and absence of older breeding females minimised intra-specific competition. Survival was not affected by the presence of field voles. Season had a significant effect on both the probability of maturation and breeding of the weanlings. Competition with field voles significantly delayed breeding, and coupled with seasonal effects decreased the probability of breeding. In a late-summer experiment breeding and survival of bank vole weanlings were studied for three weeks as part of a high density breeding bank vole population. Weanlings did not mature at all nor were their space use and survival affected by the presence of field voles. Our results show that competition with other species can also have an impact on breeding of immatures. In an extreme seasonal environment, even a short delay of breeding may decrease survival chances of offspring. Seasonal and competition effects together may thus limit the contribution of year born females to reproductive output of the population. Other studies have shown that adult breeding bank voles suffer lower survival in the presence of field voles, but this study showed no survival effects on the weanlings. Thus it might be beneficial for weanlings to stay immature especially in the end of the breeding season and postpone reproduction to the next breeding season if densities of competing species are high.     

Mouse polyomavirus enters early endosomes, requires their acidic pH for productive infection, and meets transferrin cargo in Rab11-positive endosomes

Mouse polyomavirus (PyV) virions enter cells by internalization into smooth monopinocytic vesicles, which fuse under the cell membrane with larger endosomes. Caveolin-1 was detected on monopinocytic vesicles carrying PyV particles in mouse fibroblasts and epithelial cells (33). Here, we show that PyV can be efficiently internalized by Jurkat cells, which do not express caveolin-1 and lack caveolae, and that overexpression of a caveolin-1 dominant-negative mutant in mouse epithelial cells does not prevent their productive infection. Strong colocalization of VP1 with early endosome antigen 1 (EEA1) and of EEA1 with caveolin-1 in mouse fibroblasts and epithelial cells suggests that the monopinocytic vesicles carrying the virus (and vesicles containing caveolin-1) fuse with EEA1-positive early endosomes. In contrast to SV40, PyV infection is dependent on the acidic pH of endosomes. Bafilomycin A1 abolished PyV infection, and an increase in endosomal pH by NH4Cl markedly reduced its efficiency when drugs were applied during virion transport towards the cell nucleus. The block of acidification resulted in the retention of a fraction of virions in early endosomes. To monitor further trafficking of PyV, we used fluorescent resonance energy transfer (FRET) to determine mutual localization of PyV VP1 with transferrin and Rab11 GTPase at a 2- to 10-nm resolution. Positive FRET between PyV VP1 and transferrin cargo and between PyV VP1 and Rab11 suggests that during later times postinfection (1.5 to 3 h), the virus meets up with transferrin in the Rab11-positive recycling endosome. These results point to a convergence of the virus and the cargo internalized by different pathways in common transitional compartments.