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.     

Chromosomal evolution in the genus Clethrionomys

The karyotypes of Clethrionomys rufocanus and C. glareolus are presented using G- and C-banding techniques. There is intraspecific polymorphism in Clethrionomys rufocanus for a pericentric inversion. The main difference between the karyotypes of the two species is considered to result from a reciprocal translocation.     

Plasma esterase polymorphism in the Bank vole, Clethrionomys glareolus, in Britain

Three hundred and eighty-three Clethrionomys glareolus from 20 localities in England, Wales and Scotland were typed for plasma esterase and a genetic polymorphism was discovered. The esterase was named Es-1. Breeding tests suggested that three alleles were segregating: Es-1^o when homozygous results in complete absence of enzyme activity. The active alleles Es-1^f and Es-1^s code for enzyme variants which migrate more rapidly and less rapidly, respectively, under starch gel electrophoresis. Of these active alleles, Es-1^f is morc common in the north of Britain and Es-1⁸ in the south. A 23-month field study on two areas at Wicken Fen, Cambridgeshire, suggested that animals possessing Es-1^s survived less well at high population densities, perhaps through their being more likely to emigrate.     

Morphological variations in the preputial gland of wild bank voles, Clethrionomys glareolus

The size and appearance of the preputial glands of Clethrionomys glareolus showed variations which were associated with season, sex and maturation. The glands were by far largest in mature males followed by mature females, and subadult males and females, in that order. There was a positive relationship between the length, fresh weight and dry weight of the glands. The possible role of the preputial glands in relation to territorially, social status and sexual attraction is discussed.     

Delayed implantation in lactating bank voles, Clethrionomys glareolus.

The time of blastocyst implantation in lactating and non-lactating female bank voles was studied. In primiparous females implantation started 4 days and 9-11 h after mating. A delayed implantation of at least 1 1/2 days was found in lactating, multiparous females when compared to non-lactating, multiparous and primiparous females.     

Maternal effort and male quality in the bank vole, Clethrionomys glareolus.

Parental investment in reproduction is adjusted according to potential benefits in terms of offspring survival and/or mating success. If male quality affects the reproductive success of a female, then females mating with high-quality males should invest more in reproduction. Although the subject has been of general interest, further experimental verification of the hypothesis is needed. We studied whether female bank voles (Clethrionomys glareolus) adjusted their maternal effort according to male quality, measured as mating success. To enable the measurement of maternal effort during nursing separately from male genetic effects the litters were cross-fostered. Further, the genetic background of male quality was examined. Male quality did not correlate with litter size or offspring size at birth. Offspring growth was positively related to food consumption and milk production of mothers. However, these direct measurements of maternal effort were independent of male quality. Male mating success appeared to be significantly heritable indicating that there are genetic benefits. Still, females did not adjust maternal effort according to the genetic quality of their offspring. We suggest that female bank voles gain significant genetic benefits from mating with high-quality males whereas they cannot improve their reproductive success by increasing maternal effort.     

Individual variation and repeatability of basal metabolism in the bank vole, Clethrionomys glareolus

Basal metabolic rate (BMR) is a fundamental energetic trait and has been measured in hundreds of birds and mammals. Nevertheless, little is known about the consistency of the population-average BMR or its repeatability at the level of individual variation. Here, we report that average mass-independent BMR did not differ between two generations of bank voles or between two trials separated by one month. Individual differences in BMR were highly repeatable across the one month interval: the coefficient of intraclass correlation was 0.70 for absolute log-transformed values and 0.56 for mass-independent values. Thus, BMR can be a meaningful measure of an individual physiological characteristic and can be used to test hypotheses concerning relationships between BMR and other traits. On the other hand, mass-independent BMR did not differ significantly across families, and the coefficient of intraclass correlation for full sibs did not differ from zero, which suggests that heritability of BMR in voles is not high.     

Rainfall, ambient temperature, and Clethrionomys californicus capture frequency

Sixty Western Red-backed Voles Clethrionomys californicus inhabiting an old-growth mixed conifer forest in north-western California (USA) were studied over 2 years to assess relationships among vole capture frequency, rainfall, and ambient temperature. Red-backed Voles were encountered more often and recapture rates per vole doubled with the tripling of yearly rainfall. In addition, more voles were captured during wet months than dry months. Analysed over weekly intervals, captures were positively correlated with the amount of weekly rainfall, a greater proportion of the known vole population was encountered during wet weeks than dry weeks, and increased weekly rainfall resulted in an increased proportion of the vole population captured. Significant relationships were not found between daily rainfall and vole captures, but both minimum and maximum daily ambient temperatures were lower when voles were trapped. Vole captures increased with decreases in daily and weekly minimum and maximum ambient temperatures. Weekly rainfall in combination with minimum weekly temperatures accounted for the greatest explanation of variability in vole capture frequencies. These results document that rainfall and ambient temperature have an impact on Western Red-backed Vole capture frequency; thus these weather variables should be addressed as covariates in analyses focused on capture data for this species.     

Protein polymorphisms and their genetic control in the red-backed vole, Clethrionomys rufocanus bedfordiae

Twenty enzymatic and non-enzymatic proteins in a wild population of red-backed voles, Cletrionomys rufocanus bedfordiae , were investigated by electrophoresis. Seven enzymatic and non-enzymatic protein systems were found to be polymorphic. Breeding data indicated that the mode of inheritance of the enzyme systems ME-1, ME-2, GPD and EST were consistent with a Mendelian law. Two systems, 6 PGD and SOD, were estimated to be genetically controlled from the electrophoretic patterns and mother-offspring comparison of phenotypes. In the Tf system two new additional phenotypes were observed, but their inheritance could not be elucidated. Gene frequencies at seven loci were also investigated in 88 animals. There was no significant deviation from Hardy-Weinberg equilibrium.     

Behavioural development of conspecific odour preferences in bank voles,Clethrionomys glareolus

Biological odours of conspecifics are known to have strong influences on behavioural interaction in bank voles Clethrionomys glareolus. This experiment tested two hypotheses. (1) Olfactory cues from familiar and unfamiliar mature opposite-sex conspecifics differ in their attractiveness to males and females, and their behavioural reactions change with age. (2) A genetically based mechanism is involved in female recognition of kin.In a two-choice preference test, prepubertal males and females were more attracted to familiar than to unfamiliar odours of opposite-sex conspecifics, as manifested by more time spent sniffing familiar voles. As the young reached sexual maturity they shifted their odour preferences. Mature males and females preferred the novel odour of unrelated opposite-sex conspecifics to that of relatives. The results of experiments testing the second hypothesis indicate that females use a genetically based mechanism to recognise their kin. Young and mature females were able to recognise the odour of their biological but socially unknown fathers, and showed the same pattern of behaviour as females in previous experiments.The possible biological functions of kin recognition in bank voles are discussed.     

Long-term fitness benefits of polyandry in a small mammal, the bank vole Clethrionomys glareolus

Polyandry, i.e. mating with multiple males within one reproductive event, is a common female mating strategy but its adaptive function is often unclear. We tested whether polyandrous females gain genetic benefits by comparing fitness traits of monandrous (mated twice with a single male) and polyandrous (mated twice with two different males) female bank voles Clethrionomys glareolus. We raised the offspring in the laboratory until adulthood and measured their body size, before releasing them to outdoor enclosures to overwinter. At the onset of the breeding season in the following spring, we found that offspring of polyandrous females performed significantly better at reproduction than those of monandrous females. This was mainly due to sons of polyandrous females producing significantly more offspring than those of monandrous females. No significant differences were found for offspring body mass or winter survival between the two treatments. Our results appear to provide evidence that bank vole females gain long-term benefits from polyandry.     

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.     

Niche differentiation in a postglacial colonizer,the bank vole Clethrionomys glareolus

Species‐level environmental niche modeling has been crucial in efforts to understand how species respond to climate variation and change. However, species often exhibit local adaptation and intraspecific niche differences that may be important to consider in predicting responses to climate. Here, we explore whether phylogeographic lineages of the bank vole originating from different glacial refugia (Carpathian, Western, Eastern, and Southern) show niche differentiation, which would suggest a role for local adaptation in biogeography of this widespread Eurasian small mammal. We first model the environmental requirements for the bank vole using species‐wide occurrences (210 filtered records) and then model each lineage separately to examine niche overlap and test for niche differentiation in geographic and environmental space. We then use the models to estimate past [Last Glacial Maximum (LGM) and mid‐Holocene] habitat suitability to compare with previously hypothesized glacial refugia for this species. Environmental niches are statistically significantly different from each other for all pairs of lineages in geographic and environmental space, and these differences cannot be explained by habitat availability within their respective ranges. Together with the inability of most of the lineages to correctly predict the distributions of other lineages, these results support intraspecific ecological differentiation in the bank vole. Model projections of habitat suitability during the LGM support glacial survival of the bank vole in the Mediterranean region and in central and western Europe. Niche differences between lineages and the resulting spatial segregation of habitat suitability suggest ecological differentiation has played a role in determining the present phylogeographic patterns in the bank vole. Our study illustrates that models pooling lineages within a species may obscure the potential for different responses to climate change among populations.     

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.     

Reservoir Competence of the Vole,Clethrionomys rufocanus bedfordiae,for Borrelia garinii or Borrelia afzelii

In autumn of 1994 and spring of 1995, we examined Borrelia infection among Microtinae voles, Clethrionomys rufocanus bedfordiae, in Hokkaido, Japan. In BSK culturing of the earlobe tissues of 45 C. rufocanus bedfordiae captured, twelve rodents were positive for Borrelia. Eight isolates were used for the polymerase chain reaction (PCR) and the restriction fragment length polymorphism (RFLP) analysis. According to the results, these isolates were classified into B. garinii or B. afzelii. It is considered that a common vole, C. rufocanus bedfordiae, plays a significant role in the transmission and maintenance of B. garinii and B. afzelii, similar to the role of Apodemus speciosus mice.     

棕背Ping昼夜活动节律的研究

The diurnal activity rhythm of Clethrionomys rufocanus was studied under three different food conditions in a laboratory. The activity occurred both in the daytime and at night, but mainly at night (19:00--4:00). The mice fed with Mouse food exhibited six small peaks in their daily activity, and those fed with grass or hay exhib-ited seven, but the peak of the out-nest night activity was 2 ～ 3 hours earlier. The activity amount of out-nest was 30 518.0 ± 3 694.9 s for those fed with grass, the next was 21 811.7 ± 2 288.0 s for those fed with hay,and the least was 15 038.0 ± 666.0 s for those fed with mouse food. The activity amount of feeding was 10867.3± 1 612.1 s for those fed with grass, much more than those fed with mouse food and hay. The activity amount for drinking was 988.5 ± 79.1 s (fed with hay), 568.9 ± 60.9 s (fed with mouse food) and 139.3 ±47.2 s (fed with grass).     

Effect of photoperiod on cultured granulosa cells of the bank vole, Clethrionomys glareolus

Gonadal function of the bank vole females depends on the photoperiod. This experiment was to show whether photoperiod applied on the whole animal in vivo would affect the function of ovarian cells in vitro. Granulosa cells from large ovarian follicles of bank vole reared in long or short photoperiod were cultured as monolayers in control or luteinizing hormone supplemented media. Formation of cell colonies, activity of delta5, 3beta-hydroxy steroid dehydrogenase and progesterone secretion were investigated. First colonies of long day cells were formed already on day 1. On day 2 they enlarged and became abundant. Short day cells formed colonies only on day 2. Colonies of similar size to 2 day colonies of long day cells appeared only on day 6. There were also differences in steroid dehydrogenase activity and in progesterone secretion between long and short day control and hormone treated cultures. We conclude that photoperiod applied in vivo affects ovarian cell function in vitro.