The lateral scent organs of Arvicola terrestris (Rodentia: Microtinae)

The lateral scent organs of Arvicola terrestris (L.) are basically similar in construction to those of A. scherman (Shaw), and differ in that they do not express long cylinders of secretion at the end of the breeding season, and that frequent epidermal vesicles are observed. During the year the organ of the male undergoes a cycle of activity with a peak in secretory activity shortly following the peak in the cycle of testis weight. Bilateral castration causes a marked involution of the organ in the male, which can be reconstituted by the administration of exogenous testosterone.     

Physiological consequences of captive conditions in water voles (Arvicola terrestris)

Re-introductions of captive-bred animals are increasingly common in wildlife conservation and it is important that they fulfil their potential. To foster this goal we examined variations in stress levels in a captive-bred population of water voles Arvicola terrestris in response to housing conditions and radio-collaring, using weight loss and leukocyte coping capacity (LCC) as measures of relative stress, to investigate the impacts of housing conditions, handling and radio-collaring on this species. Thirty-eight water voles (22 males and 16 females) were used in the investigation, 25 housed in outdoor enclosures and 13 in laboratory cages. During the 6-week study, LCC, body weight and urine refractive index (URI, an indicator of hydration levels) were recorded once a week for each individual in weeks 1, 2, 4 and 6. After the first sample, radio-collars were attached to 20 individuals (10 males and 10 females) taken from both housing types. Throughout the experiment laboratory-cage housed voles weighed less, had lower LCC scores – indicating a reduced ability to combat infection – and had higher URIs than outdoor-enclosure voles. This suggests that the laboratory-cage voles were more stressed and dehydrated than the outdoor-enclosure voles. Weights and LCC scores of both housing groups decreased as the study progressed, suggesting that elements of the study, such as repeated handling, may have caused stress to both groups. Evidence suggested a short-term effect of radio-collaring on immuno-competence. We conclude that captive housing conditions, repeated manipulation and radio-collaring had demonstrable physiological effects on the water voles studied. We recommend that the effects of husbandry and tagging practices upon captive-bred mammals be closely studied as part of the quest to improve the success of the re-introductions to which they contribute.     

Evidence for social difference in the flank organ secretion of Arvicola terrestris (Rodentia: Microtinae)

Gas-liquid chromatographic and mass spectroscopic analysis of secretion from the flank organs of Arvicola terrestris (L.) reveals a complex mixture of long chain esters, with the possible addition of some other substances and certainly cholesterol. Each g.l.c. peak consists of a series of isomers of the particular compound.
By comparing the proportion of the total peak height contributed by individual peaks, it was possible to analyse chromatograms to identify differences in pattern of peak height proportion between the sexes, between adult and juvenile animals of each sex, between families and between populations. There is little obvious difference between the sexes but quite marked differences between adult and juvenile animals. Comparison of samples taken from a population in June, when density was low and the breeding season had just begun and September, when density was high and the breeding season was drawing to a close, showed marked differences—especially in females. Cholesterol is a very important constituent of female flank organ secretion in June but much less important in September. Families born in captivity show significant differences between chromatogram peak patterns. The occurrence of highly significant differences between populations suggests the presence of olfactory dialects. It is not known whether this is genetically or environmentally influenced.
These observations indicate the range of difference in sebaceous output found in one species of rodent, and suggest that sexual condition and group affiliation is expressed in glandular secretion thought to be used for range demarcation.     

Early embryonic mortality in the water vole (Arvicola terrestris L.)

A morphological study of forty-eight 3-4-day old embryos from eight females of the water vole (Arvicola terrestris L.) was carried out. The data obtained demonstrated that early embryonic losses in the water vole might be 30?C35%, and the main cause of these losses is anomalies of oogenesis.     

Phylogeographic structure and postglacial evolutionary history of water voles (Arvicola terrestris) in the United Kingdom

The phylogeographic pattern of mitochondrial DNA variation in water voles (Arvicola terrestris) from 57 localities across the United Kingdom and representative samples from Spain, France, Switzerland and Finland was determined from sequence variation in the central portion of the control region. Twenty-seven different haplotypes were resolved which formed two distinct phylogenetic clades. This major division separated haplotypes found in Scotland from those found in England and Wales. Nested clade analysis of haplotypes indicated that such a division was a consequence of allopatric fragmentation. The haplotypes found in Switzerland, France and Spain clustered with Scottish haplotypes, whereas the haplotype from Finland clustered with the English/Welsh haplotypes. These patterns indicate that contemporary Scottish populations are derived from an Iberian glacial refugium, whereas English and Welsh populations are derived from an eastern European refugium. As such, the postglacial recolonization of the United Kingdom must have involved two colonization events, either in different localities with no subsequent contact, or as two waves separated over time, with the second wave of colonizers displacing the first. An analysis of molecular variance (AMOVA) identified significant population genetic divergence within both the major clades, indicative of restricted gene flow and regional population isolation. The implications of both phylogeographical and population genetic structure are discussed in context with the conservation of water voles in Britain.     

Genetic structure,ecological versatility,and skull shape differentiation in Arvicola water voles (Rodentia,Cricetidae)

Water voles from the genus Arvicola display an amazing ecological versatility, with aquatic and fossorial populations. The Southern water vole (Arvicola sapidus) is largely accepted as a valid species, as well as the newly described Arvicola persicus. In contrast, the taxonomic status and evolutionary relationships within Arvicola amphibiussensu lato had caused a long-standing debate. The phylogenetic relationships among Arvicola were reconstructed using the mitochondrial cytochrome b gene. Four lineages within A. amphibiuss.l. were identified with good support: Western European, Eurasiatic, Italian, and Turkish lineages. Fossorial and aquatic forms were found together in all well-sampled lineages, evidencing that ecotypes do not correspond to distinct species. However, the Western European lineage mostly includes fossorial forms whereas the Eurasiatic lineage tends to include mostly aquatic forms. A morphometric analysis of skull shape evidenced a convergence of aquatic forms of the Eurasiatic lineage toward the typically aquatic shape of A. sapidus. The fossorial form of the Western European lineage, in contrast, displayed morphological adaptation to tooth-digging behavior, with expanded zygomatic arches and proodont incisors. Fossorial Eurasiatic forms displayed intermediate morphologies. This suggests a plastic component of skull shape variation, combined with a genetic component selected by the dominant ecology in each lineage. Integrating genetic distances and other biological data suggest that the Italian lineage may correspond to an incipient species (Arvicola italicus). The three other lineages most probably correspond to phylogeographic variations of a single species (A. amphibius), encompassing the former A. amphibius, Arvicola terrestris, Arvicola scherman, and Arvicola monticola.     

The effect of diet quality on gut anatomy in British voles (Microtinae)

Three species of British voles, the bank vole Clethrionomys glareolus, the field vole Microtus agrestis and the water vole Arvicola terrestris were maintained on diets of seed and plant leaf material to investigate changes in gut anatomy. C. glareolus and M. agrestis showed significant changes in most regions of the gut; they developed longer and heavier tracts when on a highfibre diet. This response may be important in enabling these animals to withstand seasonal changes in diet quality.     

Dynamics of morphophysiological charateristics in female water voles (Arvicola amphibius L.) during pregnancy

Pregnancy and lactation need increased energy consumption and are accompanied by morphological and physiological changes of various maternal organs and systems. In water voles, connection of female interior characteristics has been poorly studied. Under standard vivarium conditions, we evaluated morphophysiological parameters of non-reproducing females and of females at the early (1–7 days), intermediate (8–14 days), and late (15–21 days) stages of pregnancy. There were established effect of the reproductive state on mass of abdominal and brown adipose tissue, liver, adrenals, spleen and an increment of body mass (without uterus with embryos). In pregnant females, as compared with the non-pregnant ones, the blood thyroxine level was significantly lower (16.2 ± 0.8 and 21.7 ± 1.4 pmol/l) and the blood testosterone level was higher (1.29 ± 0.19 and 0.83 ± 0.09 nmol/l). The blood glucose content fell in the end of pregnancy. Dynamics of morphophysiological parameters at the period of pregnancy reflects the compensatory body reactions providing preservation of embryos and preparation to lactation of offspring.     

A heterochronic interpretation of the origin of digging adaptations in the northern water vole, Arvicola terrestris (Rodentia: Arvicolidae)

The Palaearctic genus Arvicola includes two species: the south‐western water vole A. sapidus, and the northern water vole A. terrestris. The latter has semiaquatic and/or subterranean populations, while populations of A. sapidus are always semiaquatic. According to the current phylogenetic and palaeontological data, adaptation to semiaquatic life is plesiomorphic for the genus Arvicola. We studied the ontogenetic allometry of skull and long bones of the semiaquatic A. sapidus, a semiaquatic population of A. terrestris (A. t. italicus), and two fossorial populations of A. terrestris (A. t. scherman and A. t. monticola). Animals from fossorial populations were smaller than were those from semiaquatic populations. We found that most of the ontogenetic allometric exponents of characters linked to digging in the skull and in the long bones were significantly higher in A. t. monticola, a fossorial clade, than they were in the semiaquatic populations. On the other hand, there may have been an evolutionary lag between invasion of the hypogeic habitat and the acquisition of fossorial adaptations in A. t. scherman. We showed statistically that the morphological differences linked to the invasion of a hypogeic habitat are already present in juvenile animals and, according to these results, suggest that these morphological differences are the direct expression of genetic changes rather than the outcome of epigenetic factors of mechanical origin. Moreover, we tried to ascertain whether the apomorphic shape of the skull and long bones in the fossorial populations of A. terrestris (compared with the primitive condition that would have been retained by the semiaquatic A. sapidus) are the outcome of a heterochronic process. Optimization by squared change parsimony supported the hypothesis of an apomorphic reduction of body size linked to the invasion of the subterranean habitat. The comparison of the ontogenetic trajectories of both skull shape and long bone shape suggested that a heterochronic process was involved in this morphological transformation. By using the ‘clock model’ method, this mechanism was identified as ‘accelerated dwarfism’ affecting both the skull and long bones. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 87 , 381–391.     

Volume and ion regulating renal functions in the big gerbil (Rhombomys opimus L.) and the water vole (Arvicola terrestris L.)

1. After iso-osmotic salt loading (1% NaCl, 1.25% KCl, 0.75% MgCl2 solutions, each load making up 5% body weight) the water voles excreted 66.2% sodium, 84.4% potassium, 18.8% magnesium over a 4 hr period. The big gerbil excreted 20%, 58.9% and 7.1% respectively over the same period. The volume of the water excreted was greater in the case of the water vole. 2. There were no considerable changes in plasma ion concentration in rodents of the species studied after salt loading. 3. The gerbils and water voles had no significant changes in the renal cortex electrolyte concentrations as a result of isotonic salt loads. The highest sodium cortico-papillar gradient was found in the gerbils when experimenting with the isotonic NaCl loading. It was somewhat lower with the KCl load, and significantly lower with water and MgCl2 loads. 4. Under the same experimental conditions, no major changes in the papilla sodium concentration were found in the water voles. 5. The concentrations of potassium, calcium and magnesium were practically alike in all zones of the renal tissue of both rodent species, ion loads producing no effect. 6. The comparison of the renal volume and ion regulating function in rodents with different urine osmotic concentration systems proves the independent existence of renal functions. The greater rate of renal fluid and ion excretion in the water voles is coupled with less specific ion regulation.     

Correlation between urine malondialdehyde level and males reproductive success in the water vole (Arvicola terrestris L.)

The study was conducted in water vole (Arvicola terrestris L.) reared and bred in captivity. During the breeding season, voles were caged in heterosexual pairs for two weeks. If mating did not occur, new pairs were formed with unfamiliar partners. In the end of the breeding season, the individual male's reproductive characteristics were summarized, and the level of malondialdehyde (MDA) in their urine was assessed. As indicated by urine MDA concentration, the intensity of lipid peroxidation in males which could not became fathers was significantly higher than in fertile males. In the last group, the negative correlation between average numbers of pups in litter and urine MDA concentration was revealed. It is possible, that a causal factor of water vole males lowered fertility is oxidative stress.     

Verification of the color genotype based on morphological analysis of fur pigmentation of brown and black water voles Arvicola terrestris L.]

Qualitative and quantitative analysis of fur pigmentation in brown and black water voles (Arvicola terrestris L.) was performed. Morphology of pigment granules, their distribution along the hair layers and histology of hair bulbs were studied. Morphological data and the results of the analysis of segregation in the progeny, when brown voles were self-crossed and crossed with black ones, led to conclusion that fur colour of water voles is mediated by genes from the agouti series, precisely, black colour is determined by the extreme non-agouti allele (aeae genotype), and in brown voles which are homo- or heterozygous the colour is determined by the agouti allele (AA or Aae genotypes).     

Examples of short- and long-term changes of dental pattern in Scottish voles (Rodentia; Microtinae)

An isolated population of the bank vole, Clethrionomys glareolus, at Loch Tay, Perthshire, which was found to have abnormally complex third upper molars in 1955-57, was re-examined in 1972 and found to have reverted to normal. Subfossil teeth of the field vole, Microtus agrestis, from the island of Jura, Inner Hebrides, dating back to at least 2000 BP have been compared with recent specimens from the island. They demonstrate a slight but progressive reduction in the size of the postero-medial ridge of M¹ that is characteristic of certain marginal     

The impact of American mink Mustela vison and European mink Mustela lutreola on water voles Arvicola terrestris in Belarus

In the U.K. the impact of introduced American mink Mustela vison , on water voles Arvicola terrestris , may be exacerbated by habitat loss and fragmentation. Pristine wetlands in Belarus, which American mink invaded in the early 1990s, provide a three-pronged opportunity to test this hypothesis. First, we examine the evidence that, even in the unmanaged wetlands of our Belarussian study site, American mink have reduced water vole populations. Second, we ask whether habitat size, type and isolation mitigate the impact of American mink predation. Thirdly, we explore whether water voles are at greater risk of predation from American than European mink because of their patterns of habitat use. Following the invasion of American mink, water voles were most abundant in small, still-water sites, far from river banks, while American mink were most active in large, running-water sites. Small mammal remains were found in a higher percentage of American than European mink scats, and of these, more were water vole in American mink scats. The occurrence of water voles in scats of both mink species declined after the American mink invaded and established. Our results provide at least circumstantial evidence that American mink limit water vole populations even in unmanaged wetland eco-systems, and that they have a greater impact than their European congener at least partly because they make greater use of isolated marshes. Although by no means providing complete protection, the configuration and dispersion of available habitat mitigated the impact of American mink on water voles. This raises the possibility that habitat restoration, especially through the establishment of isolated enclaves, could help reduce the effect of American mink in the U.K. These observations are of broader interest in the context of assessing the effect of multiple pressures on vulnerable species.     

Patterns in the production of latrines by water voles (Arvicola terrestris) and their use as indices of abundance in population surveys

Water vole latrines were studied on four of the principal rivers in the North Yorkshire Moors National Park. Water voles occupied 'core' and 'peripheral' sites on these rivers. Core sites were marked by latrines and held breeding colonies of voles; animals at core sites were readily captured. Peripheral sites were not marked by latrines, but showed erratic water vole activity as measured by activity indices (tracks m^-1 of muddy bank month^-1). It was never possible to catch voles at these peripheral sites, and there was no evidence of breeding.
Latrines on core sites were not maintained outside the breeding season. The appearance of latrines coincided with the start of the breeding season, and while they were maintained, latrines provided a useful guide to the number of animals in the area. A curvilinear response was obtained between latrine production and date, with production rising steadily from early spring until mid-to-late summer, which suggests that latrines signal sexual activity.
Future studies on the distribution of water voles should use a variety of techniques. Latrine surveys will only be applicable during the breeding season at core sites. Similarly, live-trapping will only detect water voles at core sites. Tracking provides the best evidence that water voles are present at peripheral sites even though they may not be breeding or entering traps.     

Genetic structure of the cyclic fossorial water vole (Arvicola terrestris): landscape and demographic influences

Genetic structure can be strongly affected by landscape features and variation through time and space of demographic parameters such as population size and migration rate. The fossorial water vole (Arvicola terrestris) is a cyclic species characterized by large demographic fluctuations over short periods of time. The outbreaks do not occur everywhere at the same time but spread as a wave at a regional scale. This leads to a pattern of large areas (i.e. some hundreds of km2), each with different vole abundances, at any given time. Here, we describe the abundance and genetic structures in populations of the fossorial water vole. We use the data to try to understand how landscape and demographic features act to shape the genetic structure. The spatial variability of vole abundance was assessed from surface indices, collected in spring 2002 (April) in eastern central France. Genetic variability was analysed using eight microsatellite loci at 23 localities sampled between October 2001 and April 2002. We found some congruence between abundance and genetic structures. At a regional scale, the genetic disruptions were associated with both sharp relief and transition between an area of low abundance and another of high abundance. At a local scale, we observed a variation of the isolation-by-distance pattern according to the abundance level of vole populations. From these results we suggest that the dispersal pattern in cyclic rodent populations varies throughout the demographic cycle.     

Idiogram and trisomy of the water vole (Arvicola terrestris L.), a favourable animal for cytogenetic research

The chromosomes of the water vole (Arvicola terrestris L.) were investigated in 2 female and 5 male animals from three different parts of Sweden. The somatic chromosomes were studied in direct preparations of cornea and bone marrow and in tissue cultures of testis, lung and heart. Meiosis was studied in one male. The chromosome number was 2n=36. No differences in regard to chromosome number and morphology were found among the seven control animals studied. Different chromosome types are represented and the karyotype of the species is favourable for chromosome studies. — An idiogram of the water vole was constructed from measurements of complete chromosome sets from ten heart cells. — In addition to the above normal material one young water vole, trapped in nature, was found to have 37 chromosomes and was trisomic for the smallest autosome. This autosome had a secondary constriction and took part in satellite associations. The cytologic similarities to Down's syndrome in man are striking and it is hoped that the water vole will become a valuable laboratory mammal, especially for elucidation of the chromosomal mechanisms of non-disjunction. The trisomic water vole had no obvious phenotypic abnormalities, but at least one feature was not within normal limits — its tail was unusually short. Also, the development of certain teeth was somewhat aberrant. Whether short tail and dental deformities are symptoms correlated with trisomy for the smallest autosome in the water vole is an open question so far.