Parental care in captive red-backed vole (Clethrionomys rutilus)

Parental behavior in ten pairs of male and female red-backed voles, Clethrionomus rutilus, was studied under laboratory conditions. Significant sex differences were found in total time spent in the nest, time spent by adults alone in the nest, grooming time, and nest-building activity; in half of the males under study, the level of paternal care was extremely low. These findings indicate different paternal contributions of female and male red-backed voles into the rearing of young, in agreement with the spatial-ethological structure of populations of this species. Parental behavior of C. rutilus is discussed in comparison with that of other species of the subfamily Microtinae.     

Participation of apoptotic proteins in hypothalamic regulation of the population volume of the red-backed vole (Clethrionomys rutilus)

The content of the antiapoptotic protein Bcl-2 and of the proapoptotic enzyme caspase-3 in the paraventricular nucleus (PVN) of sexually immature red-backed voles is studied in the course of the population cycle. The significant change of the Bcl-2 and procaspase-3 in the PVN neurons is established at all cycle phases. The low volume of population (under the most favorable conditions of the existence of the animals) is revealed to be characterized by the moderately increased or high expression of the Bcl-2 protein alongside with low or moderately increased caspase-3 activity. This is suggested to provide the PVN adequate reaction at the low population volume. At high population volume (under conditions of increased stress in the overcrowded population at the phase of peak and especially of fall), a significant decrease of the Bcl-2 expression is established with simultaneous increase of the caspase-3 activity. The disbalance in synthesis of apoptotic proteins seems to lead to disturbances of PVN functions at phases of peak and fall and, as a consequence, to a decrease of adaptive possibilities of these animals, which might be one of important causes of essential elimination of the animals at the autumn-winter period.     

Substance P and neurokinin-1 immunoreactivities in the neural circadian system of the Alaskan northern red-backed vole, Clethrionomys rutilus

The suprachiasmatic nucleus (SCN) of the hypothalamus houses the main mammalian circadian clock. This clock is reset by light-dark cues and stimuli that evoke arousal. Photic information is relayed directly to the SCN via the retinohypothalamic tract (RHT) and indirectly via the geniculohypothalamic tract, which originates from retinally innervated cells of the thalamic intergeniculate leaflet (IGL). In addition, pathways from the dorsal and median raphe (DR and MR) convey arousal state information to the IGL and SCN, respectively. The SCN regulates many physiological events in the body via a network of efferent connections to areas of the brain such as the habenula (Hb) in the epithalamus, subparaventricular zone (SPVZ) of the hypothalamus and locus coeruleus of the brainstem-areas of the brain associated with arousal and behavioral activation. Substance P (SP) and the neurokinin-1 (NK-1) receptor are present in the rat SCN and IGL, and SP acting via the NK-1 receptor alters SCN neuronal activity and resets the circadian clock in this species. However, the distribution and role of SP and NK-1 in the circadian system of other rodent species are largely unknown. Here we use immunohistochemical techniques to map the novel distribution of SP and NK-1 in the hypothalamus, thalamus and brainstem of the Alaskan northern red-backed vole, Clethrionomys rutilus, a species of rodent currently being used in circadian biology research. Interestingly, the pattern of immunoreactivity for SP in the red-backed vole SCN was very different from that seen in many other nocturnal and diurnal rodents.     

Hantavirus antibody occurrence in bank voles (Clethrionomys glareolus) during a vole population cycle

Puumala virus, genus Hantavirus, is the etiologic agent of nephropathia epidemica, a mild form of hemorrhagic fever with renal syndrome. The bank vole (Clethrionomys glareolus) is the natural reservoir species of this hantavirus. We initiated sampling of bank voles at sites of recently identified human nephropathia epidemica cases and paired control sites in the fall of 1995 in coastal areas of northern Sweden. Sites were trapped annually in spring and fall until 1999. Prevalence of antibody to Puumala virus was similar among local bank vole populations in the two types of sites over time. During peak years, however, the absolute number of bank voles was higher in case sites than control sites. Consequently, the likelihood of Puumala virus exposure was increased at case sites during population highs. This would imply that the risk of Puumala virus exposure to conspecifics and humans is habitat and site dependent with a temporal component.     

Circadian organization of a subarctic rodent, the northern red-backed vole (Clethrionomys rutilus)

Arctic and subarctic environments are exposed to extreme light: dark (LD) regimes, including periods of constant light (LL) and constant dark (DD) and large daily changes in day length, but very little is known about circadian rhythms of mammals at high latitudes. The authors investigated the circadian rhythms of a subarctic population of northern red-backed voles (Clethrionomys rutilus). Both wild-caught and third-generation laboratory-bred animals showed predominantly nocturnal patterns of wheel running when exposed to a 16:8 LD cycle. In LL and DD conditions, animals displayed large phenotypic variation in circadian rhythms. Compared to wheel-running rhythms under a 16:8 LD cycle, the robustness of circadian activity rhythms decreased among all animals tested in LL and DD (i.e., decreased chi-squared periodogram waveform amplitude). A large segment of the population became noncircadian (60% in DD, 72% in LL) within 8 weeks of exposure to constant lighting conditions, of which the majority became ultradian, with a few individuals becoming arrhythmic, indicating highly labile circadian organization. Wild-caught and laboratory-bred animals that remained circadian in wheel running displayed free-running periods between 23.3 and 24.8 h. A phase-response curve to light pulses in DD showed significant phase delays at circadian times 12 and 15, indicating the capacity to entrain to rapidly changing day lengths at high latitudes. Whether this phenotypic variation in circadian organization, with circadian, ultradian, and arrhythmic wheel-running activity patterns in constant lighting conditions, is a novel adaptation to life in the arctic remains to be elucidated.     

Radiation dose rates estimation and allozyme variability in the population of the northern red-backed vole (Clethrionomys rutilus) from the East-Ural Radioactive Trace

The paper estimates the external (due to radionuclides accumulated in the soil) and internal (due to incorporated radionuclides) exposure of rodents that live in the head of the East Urals Radioactive Trace (EURT). It is shown that in the last decades the dose rates were lower than the values that lead to a doubling the number of mutations in the allozyme loci in mammals. The variability of the eight allozyme loci in populations of northern red-backed voles from the EURT zone and their neighboring plots, as well as the territories of the Urals and Trans-Urals with background levels of radioactive contamination, are analyzed. No differences in the pattern and frequency of allozymes that would distinguish the EURT samples from a number of other populations of the Urals, were found. In the control sample “Sysert’,” “unique” for the Ural populations of northern red-backed voles, alleles of the loci Got and Sod were marked, conspecific to a closely related species-the bank vole. This fact can be regarded as evidence of recent cross-species hybridization.     

Transfer of mitochondrial DNA from the northern red-backed vole (Clethrionomys rutilus) to the bank vole (C. glareolus)

Summary Using a silver staining method to detect DNA fragments produced by restriction enzymes, it was possible to compare mitochondrial DNAs (mtDNAs) from 85 individuals of the bank vole (Clethrionomys glareolus) trapped at 25 localities in Fennoscandia. There are two distinctly different mtDNA lineages, one occurring in southern and central Fennoscandia and the other in the northern parts. A fragment comparison method shows about 12.7% nucleotide sequence divergence between these two lineages. This major difference between animals of the same species could theoretically be explained by intraspecific lineage survivorship independent of species hybridization, or by introduction of an atypical mtDNA via hybridization with a closely related species. Analysis of mtDNAs from the two otherClethrionomys species present in Fennoscandia (C. rutilus andC. rufocanus) shows that the mtDNA of northernC. glareolus is very similar to that ofC. rutilus and that the mtDNA lineages of these two species cluster together in a phenogram, with small genetic distances among them. By contrast, electrophoresis of proteins encoded by 17 nuclear loci reveals fixed allelic differences between these two species at 8 loci. Hence the presence of two distinctly different mtDNA lineages withinC. glareolus may be a consequence of a limited episode of hybridization betweenC. glareolus andC. rutilus, probably during the postglacial recolonization of Fennoscandia 8000–13,000 years ago.     

The reproductive cycle of the Skomer vole (Clethrionomys glareolus skomerensis)

A histological examination has been made of the reproductive organs of the Skomer vole to study the reproductive cycle and fertility of this race of the Bank vole ( Clethrionomys glareolus ) in its insular habitat. The main aim of the work was to compare the cycle with that of Clethrionomys on the mainland of Britain which was similarly investigated by Brambell & Rowlands (1936).     

Reproduction of the bank vole, Clethrionomys glareolus, in northern and southern Sweden during several seasons and in different phases of the vole population cycle

The breeding biology of the bank vole was studied in northern and southern populations in Sweden in the years 1973–76. Trapped specimens supplied organ weights and histological data, which were utilized to describe the breeding season, number and size of litters, reproductive losses, spermatogenesis, and sexual maturation. In the north the populations are cyclic. During the increase phase of the cycle the breeding season was long, litter sizes and gonad weights were large, and there was maturation of yearlings in the summer. During the peak phase reproduction was impaired in all these respects. In southern Sweden there was no cyclicity, and the reproductive events varied less, but in 1976 the litters were larger than usual and the season was much extended.
In the south the voles born during the early part of the season regularly became sexually mature during their first summer. The differences in reproductive biology are related to population dynamics and discussed in terms of different hypotheses concerning vole population cyclicity.     

Regulation of reproduction rate in a cyclic population of the red-backed vole,Clethrionomys rufocanus bedfordiae

Changes of the components of reproduction were analyzed quantitatively in a two-year cyclic population (which has two peaks in alternate years during a five-year census) of the red-backed vole, Clethrionomys rufocanus bedfordiae, with reference to its regulatory mechanism: (1) Variation in sex ratios was not associated with population phase or density, although a higher percentage of females in mature individuals was observed in the increase phase. (2) Females attained to sexual maturity at younger age and at lighter body weight than did males. All the youngest mature individuals were found in the low and the increase phases. Age and size at maturity became older and larger as the population went toward the peak phase. (3) Maturation rate was strongly associated with population phase and density; this component is an important and good parameter to predict population trend. Maturation rates were in the order, the low phase>the increase phase>the peak phase>the decline phase; the differences in the rates among these phases were significant. Maturation rate was somewhat depressed when the population density exceeded about 40 individuals/ha. Changes in age at maturity and in maturation rate are interpreted as derivative phenomena related to the population density and the capacity of the number of mature voles per unit area. (4) The maximum number of mature individuals were 26 males/ha and 29 females/ha; there was almost no increase of the number of mature voles at higher population densities over about 40 individuals/ha. The number of exclusive home ranges per hectare calculated from the observed range lengths did not differ much from the maximum number of mature voles of either sex. (5) Length of breeding period was shorter in the high-density years than in the low-density years; the breeding started earlier and ended earlier in the former than that in the latter. In the increase phase a few voles reproduced in winter. (6) The percentage of pregnant females was significantly lower in the peak phase than those in the other phases.     

The spread of the Bank vole Clethrionomys glareolus in Ireland

The discovery of the Bank vole Clethrionomys glareolus in Ireland and the published information on its spread are reviewed, and the results of a complete resurvey of its distribution, in 1 982 , presented. The rate of spread is extremely variable and somewhat unpredictable. Over suitable habitat—agricultural land with hedges and other cover (and sometimes mountain valleys)—spread may average 2–4.5 kmyr^-1 but can sometimes be very much slower. This might be influenced by the type and extent of hedges and of permanent pasture. High ground and moorland usually prevent spread but there have been dramatic exceptions. In 1982 Bank voles occupied probably the whole of Co. Limerick; most of Co. Kerry, with the exception of substantial parts of the mountainous peninsulas in the southwest and contiguous interior; a large part of Co. Cork, though not the south-east and again excepting portions of the mountainous south-west, together with a substantial strip of east Co. Tipperary, and the south-east quarter of Co. Clare.     

Blood system peculiarities in the bank vole (Clethrionomys glareolus) under chronic environmental pollution

The parameters of peripheral blood and hemopoietic organs in mature and immature bank voles inhabiting a chemically polluted area were studied. Variability of the blood system parameters depending on the level of toxic load and the animals’ reproductive status was determined. Alteration of the cell composition of erythrocytes and leucocytes, the structure of erythrocytes, and the hemoglobin fractions and leucocyte functions describe the adaptive response to the factors of a changed environment more than the concentration of leucocytes, erythrocytes, and blood hemoglobin.     

Fertility of the post-partum bank vole (Clethrionomys glareolus)

Analysis of records of a bank vole breeding colony suggests that fertility is high immediately post partum, declines during established lactation and rises after weaning of young. Mating tests with lactating females and females whose young had been removed at birth showed that receptivity is reduced during lactation, although amongst the females which did mate there was no difference between lactating and non-lactating animals in the proportion which produced litters. However, average size of litters at birth was significantly larger for the lactating than for the non-lactating females. There is some evidence suggesting that this difference may arise after ovulation has occurred. Virgin females were no more receptive or fertile than lactating females.     

Social overwintering and food distribution in the bank vole Clethrionomys glareolus

We studied overwintering in the bank vole Clethrionomys glareolus in four 0.5 ha enclosures in an abandoned field in central Finland in the winter 1987/88. In two of the enclosures food was offered evenly distributed over the whole enclosed area (Even Enclosures = EE), in the two others food was offered in one feeding patch with four feeding chambers 2 m apart (Patchy Enclosures = PE). Food was provided in about the same amount in both enclosures. The experiment commenced in early October, with 13 females and 11 males in EEs and 12 + 13 voles in PEs. After two months the voles in the PEs were concentrated around the feeding patches. Territoriality was not observed in EEs, instead the voles formed small exclusive overwintering groups consisting of 2-3 females and at least one male. The size of the home range of the females and males was identical during mid-winter as the voles were non-breeding. By the onset of breeding, range size increased in both sexes, but significantly more in males, however. The survival was about the same in all populations. Every population showed a mid-winter decline suggesting the effect of the mustelid predators observed in and around the enclosures. In the PEs the overwintering aggregations lasted until the maturation of the first litters. Food distribution affected the spatial distribution of the populations. We conclude that the patchiness of the habitat and especially the availability of food are the most important factors determining the social structure of overwintering populations.     

Haemoglobin polymorphism in the Bank vole, Clethrionomys glareolus, in Britain

Three hundred and twenty-two Clethrionomys glareolus from 17 localities in England, Wales and southern Scotland were typed for haemoglobin and two phenotypes were discovered. They have been designated HbS and HbF. The latter is more electronegative at physiological pH. The nature of the molecular difference between the phenotypes was examined and it was concluded that HbF polymerises more readily than does HbS. Haematological investigations showed that although the red cells of animals with HbF contain more potassium, thereby ensuring electrostatic neutrality, there has not been concomitant dilution of the cell contents. It is suggested that the osmotic stress imposed by this high concentration of particles might be reduced by in vivo polymerisation of haemoglobin. HbS was found to predominate in the north of Britain and HbF in the south. As none of the populations sampled contained animals of both types, it is not yet known whether there is a north-south cline in haemoglobin type, or a sharp disjunction.