Unusual heteromorphic bivalents in the common vole (Microtus arvalis) from Belorussia.

Electron microscopic analysis was carried out on the synaptonemal complexes of 10 male common voles (Microtus arvalis) caught in 1990 in Belorussia. In the early pachytene stage of spermatocytes of four males, a heteromorphic bivalent has been found in one of five large autosomes. In the central region of the bivalent one of the lateral elements is in the form of a D-loop, characteristic of insertion/deletion heterozygotes. However, high-resolution G-band staining of mitotic chromosomes from fibroblasts shows no significant differences in the G-band pattern between homologs.     

Organization of extended repeats in heterochromatin in sex chromosomes in the common vole species Microtus group "arvalis"

Two long repeats, MS3 and MS4, are predominantly located in sex-chromosomal heterochromatin in common vole species. Their tandem arrangement was revealed by means of the PCR analysis of genomic DNAs of four Microtus species and by restriction mapping of clones selected from a M. rossiaemeridionalis genomic library. Several mobile elements proved incorporated in a monomeric unit of each repeat and amplified together with its other components. In addition, LINE inserts were found in MS4 tandem arrays. The copy number of both repeats per haploid genome was estimated at 100-300 for euchromatin and 20,000-40,000 for the M. rossiaemeridionalis genome. The repeats were assumed to be the major component of sex-chromosomal heterochromatin DNA.     

Certain aspects of interactions between cohabiting sibling species Microtus arvalis and M. rossiaemeridionalis

Some aspects of interspecific interactions between sibling species of common vole were studied at the Chernogolovka Scientific Research Station (severtsov Institute for Problems of Ecology and Evolution, Russian Academy of Sciences) from 1992 to 2001. In the marking plot and indoors, East European vole demonstrated high tolerance to the anthropogenic stress considering that it was the most abundant species in the studied area transformed by human economic activity and that it used buildings as temporary shelters. When cohabiting the marking plot, common and East European voles demonstrated different territorial distribution and circadian activity, which can be considered as an adaptation to avoiding competitive interactions of ecologically similar species.     

Possible atypical course of tularemia (persistence) in the common vole Microtus arvalis Pall

The possibility of the atypical course of tularemia with the prolonged persistence of Francisella tularensis in common voles (M. arvalis), the twin species of East European voles (M. rossiaemeridionalis), was studied. Experiments were made on 33 animals grown in the laboratory. F. tularensis strain 165 was used. The animals were infected by feeding them according to the previously developed scheme. 7 out of 33 voles showed the atypical course of tularemia: in 3 voles the disease took a prolonged course with bacteriuria and death on days 25-34; 3 other voles with bacteriuria registered before days 33, 66 and 172 (the term of observation) survived. The surviving animals were killed on day 183, and the presence of bacteria in their organs and seroconversion were established. One vole excreted no bacteria with urine and had no bacteria in its organs (the animal was examined on day 156), but in its blood specific antibodies were detected. To determine bacteriuria, the immunofluorescence test was used together with biological assays. Thus, M. arvalis, like M. rossiaemeridionalis studied earlier, can harbor F. tularensis at the period between epizootics. When voles of the former species penetrate stacks of straw and hayricks, conditions appear for the transfer of the infection to the latter species, M. rossiaemeridionalis. Therefore, in the foci of the meadow-field type each of these two species of voles may be not only of epizootic, but also of epidemic importance.     

Transalpine colonisation and partial phylogeographic erosion by dispersal in the common vole (Microtus arvalis)

The colonisation history and genetic structure of the common vole ( Microtus arvalis ) was investigated in the region of the Alps by analysing the mitochondrial cytochrome b gene (mtDNA) and 19 microsatellite loci (nucDNA) for 137 voles from 52 localities. mtDNA data provided a much refined distribution of three highly divergent evolutionary lineages in the region compared to previous studies. Although high mountain ranges are widely accepted to be barriers for colonisation processes for many organisms and especially small terrestrial mammals, our phylogeographic analyses showed clear evidence of four transalpine colonisation events by the common vole. Individual-based phylogenetic analyses of nucDNA and two alternative Bayesian-clustering approaches revealed a deep genetic structure analogous to mtDNA. Incongruence between nucDNA and mtDNA at the individual level was restricted to the regions of contact between the lineages. mtDNA patterns and strong female philopatry in M. arvalis suggest that the crossings of the Alps occurred during the colonisation of the region when it was free from ice after the last glaciation. nucDNA patterns suggest that some of the transalpine elements of this phylogeographic pattern were subsequently eroded by male-biased gene flow. We conclude that the combination of phylogeography and landscape genetics at the individual level can provide very detailed insights into colonisation events and may even allow differentiation between historical and more recent processes.     

Polymorphic microsatellite loci and PCR multiplexing in the common vole,Microtus arvalis

We isolated and characterized 14 dinucleotide microsatellite loci in the common vole Microtus arvalis (Palas). Two multiplex panels both comprising seven loci were developed. Application to a set of 21 individuals allowed clear and easy characterization of allele sizes except for two loci which were then withdrawn from further analyses. The number of alleles ranged from four to 19 per locus with the observed heterozygosity ranging from 0.55 to 0.95. These sets of microsatellite loci provide high throughput capacity for population genetic studies at a minimum cost.     

Correlations between weather conditions and common vole (Microtus arvalis) densities identified by regression tree analysis

Population dynamics of fluctuating and cyclic rodent populations can be impacted by particular weather parameters. In temperate areas there are interrelations between different weather parameters, which make identification difficult. However, this is necessary because small rodents are relevant for both the food web and crop damage especially in the face of climate change. We used both, boosted regression tree and classification and regression tree methods to identify weather conditions correlating with the active burrow index (ABI) of common voles (Microtus arvalis) from 1974 to 1998 in the high outbreak risk area of Central Germany. Highest ABI occurred in perennial crops in fall with a maximum of more than 2000 active burrows per 1000 m². Boosted regression tree analysis showed that between 12 and 20 weather parameters could have a relative influence on vole ABIs ranging from 2% to 19%. Classification and regression tree analysis highlighted that the number of days with snow cover in December and March, rainfall amount in spring and maximum temperature in October seem to be key indicators for ABIs in the following year in spring. Monthly maximum temperatures of February to June and the amount of precipitation in April and July were correlated to ABIs in fall. Quantitative validation showed an agreement of ABI distribution on regional scale >85%. This represents the first study to identify complex weather conditions including single parameter thresholds correlated with common vole abundance in a temperate area. The results have the potential to aid the development of predictive models for small rodent dynamics and they inspire further detailed search for regulative mechanisms of small mammal dynamics.     

Experimental adiaspiromycosis of the common vole (Microtus arvalis) and other small wild mammals after intraperitoneal inoculation

After intraperitoneal inoculation ofE. crescens to nine species of wild small mammals, six species of rodents (Apodemus flavicollis, A. sylvaticus, Clethrionomys glareolus, Microtus agrestis, M. arvalis, Mus musculus) developed generalized adiaspiromycosis. The course of experimental infection corresponded to the infections of laboratory animals provoked in the same manner of inoculation. The authors studied the affliction of individual organs, the dynamics of growth of adiaspores in the organs of the abdominal cavity and in the lungs and followed up morphological changes in the adiaspores. In fresh cover glass preparations, the presence of manifestations was demonstrated justifying considerations on the capacity of multiplication of the adiaspiromycosis agent in the host organism.     

Intrapopulation autosomal polymorphism in the common vole Microtus arvalis from the Transcaucasian region

The broad autosomal polymorphism in form obscurus of common voles Microtus arvalis from the Transcaucasian region that is associated with the variation of subtelocentric chromosome pair 5, as well as the mechanism and evolutionary significance of this polymorphism, are discussed. Based on the morphological analysis of heterozygotes for chromosome pair 5 after differential G-, C-, and Ag-NOR-banding and on the measurements of homologues, the following conclusion has been made. The occurrence of the acrocentric chromosome 5 is the result of a double chromosomal rearrangement: a pericentric inversion and a duplication of the chromosomal material. The mutation has been found throughout the entire territory of Armenia. In spite of such a wide distribution, the mutation frequency in populations is extremely low. Neither a definite pattern of geographic distribution nor a clinal variation was found for this mutation. This mutation is likely to occur independently in different M. arvalis populations and is apparently neutral. Homozygotes for chromosome pair 5 are described for the first time.     

Spatio‐temporal covariation in abundance between the cyclic common vole Microtus arvalis and other small mammal prey species

Populations of the common vole Microtus arvalis in mid‐western France show cyclic dynamics with a three‐year period. Studies of cyclic vole populations in Fennoscandia have often found inter‐specific synchrony between the voles and other small mammals which share the voles' predators. Although predators are central to the favoured mechanism to explain Fennoscandian vole cycles and the spatial variation of small mammal populations, their role in vole cycles elsewhere, including France, is less clear. Establishing whether alternative prey species in France cycle in parallel with voles as they do in Fennoscandia is thus an important step towards understanding the generality of predators' influence on cyclic vole populations. We applied spatial and temporal autocorrelation and cross‐correlation methods to French populations of M. arvalis and two sympatric non‐cyclic small mammal species, Apodemus sylvaticus and Crocidura russula. Patterns of time‐lagged cross‐correlation between the abundance of M. arvalis and the other two species suggested synchrony in their dynamics beyond that expected of stochastic environmental variation, and indicated a weak three‐year cycle in A. sylvaticus and C. russula that was in phase with that of M. arvalis. We interpret the synchrony between these species as the effect of shared predators and environmental stochasticity. Abundance within species showed weak spatial autocorrelation in June at scales consistent with dispersal being the mechanism responsible, but a more general lack of spatial structure within and between species was consistent with the strong spatial synchrony at regional scales often found in fluctuations of small mammal abundance.     

Gene for structural proteins of the SMC family in the common vole Microtus arvalis]

Genes for four subfamilies of SMC (structural maintenance of chromosomes) proteins have been isolated from the genome of a common vole Microtus arvalis. The high degree of homology between representatives of each SMC protein subfamily of different classes of organisms has been demonstrated. The full-sized copy of a mammalian gene encoding SMC4 protein has been isolated and analyzed for the first time. The SMC proteins enter into the composition of complexes responsible for cohesion of sister chromatids, formation of mitotic chromosomes, recombination, DNA repair, and regulation of gene expression. We discuss the possible participation of the SMC proteins in inactivation of the X chromosome in mammalian females. Common voles of genus Microtus group "arvalis" serve a unique model for the study of the inactivation process.     

An estimation of the degree of the genetic divergence of sibling species Microtus arvalis and Microtus subarvalis (Rodentia) based on electrophoretic analysis

The electrophoretic mobilities of 52 enzymes and proteins were used as measures of the genetic similarity between the sibling species Microtus arvalis and M. subarvalis. The two vole species differed in the electrophoretic mobilities of seven (glucose-6-phosphate dehydrogenase, adenylate kinase, diaphorase, lactate dehydrogenase-A, alpha-galactosidase, 6-phosphogluconate dehydrogenase, and hemoglobin) of these markers. This allowed us to accept the seven markers assayed as species-specific markers. Based on the frequency distribution of the genes at the polymorphic loci of M. arvalis and M. subarvalis, the degree of their genetic similarity was estimated as 0.312 and the genetic distance as 1.164 by Nei's formula. The estimates for genetic similarity were close to those obtained for species recognized as distinct.     

Characteristics of tear proteins in the vole, Microtus arvalis

Tear proteins were detected by polyacrylamide gel electrophoresis in the vole, Microtus arvalis. The tear proteins were separated to 6 to 8 bands and the bands were divided to three regions on the anodic side. In the adult male vole, a male specific band (Vtp-1) was detected in the first region. The first region of adult female and immature voles contained two specific bands (Vtp-2, 3). In the castrated adult males or adult males injected with estrogen, the male specific hand, Vtp-1, disappeared and Vtp-2 and 3 bands appeared. In all castrated voles, the Vtp-1 band appeared and Vtp-2 and 3 bands disappeared after the administration of testosterone. Thus, sex hormone-dependent proteins are present in vole tears.