Functional characteristics of the adrenals in the ontogeny of male water voles Arvicola terrestris with various fur colorings

Studies have been made of the effect of colour mutations on the adrenal function in growing male voles. In postnatal life, the level of 11-oxycorticosteroids in the blood exhibited similar changes in brown (wild phenotype) and black (mutant) voles. The highest level was found in 1-2-month animals; a decrease took place to the 6th month which was followed by a secondary increase at the age of 8 months. Corticosteron production in vitro is the highest in brown males 5-month. In black voles, after 2 months the production remains unchanged, being rather high. In 5-, 6- and 8-month voles, corticosteron production in vitro increased, but not decreased after prior incubation. In mutant voles, the adrenals are more sensitive to stimulating effect of ACTH (5 units per 1 g of the adrenals) and inhibitory effect of estradiol (40 ng/100 mg) in vitro.     

Polymorphism of the fur pigmentation genes and the hormonal adaptation system in the water vole (Arvicola terrestris)

Postnatal ontogenesis of hormonal system of hypophysis - adrenal glands and hormonal reaction under stress conditions were examined in adult water mouse, which had polymorphic fur color genes. Black females (genotype aa), opposite to brown ones, (genotype AA, Aa) had changed postnatal ontogenesis of adrenal glands function and they had not hormonal reaction to the two days water deprivation.     

The postnatal ontogenetic characteristics of adrenal function in female water voles Arvicola terrestris with different fur colors

Studies have been made of the effect of colour mutation on the development of the adrenals in female aquatic voles. Colour mutation in homozygote results in retarded growth rate of the whole body and the adrenals, as well as in postnatal changes in the dynamics of corticosteron content in the blood. Obviously, the effect of colour mutation on plasma concentrations of corticosteron is realised mainly via extra-adrenal mechanisms since no differences were found in corticosteron production by the adrenals and in the adrenal reaction to ACTH (5 U/g of the adrenals) in vitro in growing aquatic voles. During postnatal life, mutant black females exhibited lower sensitivity of the adrenals to the inhibitory influence of estradiol (40 ng/100 mg of the adrenals) as compared to wild phenotype animals.     

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.     

Widespread gene flow and high genetic variability in populations of water voles Arvicola terrestris in patchy habitats

Theory predicts that the impact of gene flow on the genetic structure of populations in patchy habitats depends on its scale and the demographic attributes of demes (e.g. local colony sizes and timing of reproduction), but empirical evidence is scarce. We inferred the impact of gene flow on genetic structure among populations of water voles Arvicola terrestris that differed in average colony sizes, population turnover and degree of patchiness. Colonies typically consisted of few reproducing adults and several juveniles. Twelve polymorphic microsatellite DNA loci were examined. Levels of individual genetic variability in all areas were high ( H _O= 0.69–0.78). Assignments of juveniles to parents revealed frequent dispersal over long distances. The populations showed negative F _IS values among juveniles, F _IS values around zero among adults, high F _ST values among colonies for juveniles, and moderate, often insignificant, F _ST values for parents. We inferred that excess heterozygosity within colonies reflected the few individuals dispersing from a large area to form discrete breeding colonies. Thus pre-breeding dispersal followed by rapid reproduction results in a seasonal increase in differentiation due to local family groups. Genetic variation was as high in low-density populations in patchy habitats as in populations in continuous habitats used for comparison. In contrast to most theoretical predictions, we found that populations living in patchy habitats can maintain high levels of genetic variability when only a few adults contribute to breeding in each colony, when the variance of reproductive success among colonies is likely to be low, and when dispersal between colonies exceeds nearest-neighbour distances.     

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.     

The effects of increased dietary cellulose on the anatomy, physiology and behaviour of captive water voles, Arvicola terrestris (L.) (Rodentia: Microtinae)

1. Wild water voles and captives on high fibre diets had significantly longer and heavier digestive tracts (especially the caecum) than captives fed a low fibre diet. 2. Increasing dietary cellulose increased food intake, faecal output and metabolic rate, and decreased digestibility. Some but not all added cellulose was digested. 3. The passage of food through the digestive tract was significantly faster on the diet with added cellulose. 4. Coprophagy included eating directly from the anus and eating faecal pellets from the floor of the cage. The frequency of the latter type increased significantly for animals on a high fibre diet.     

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.     

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.     

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.     

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.     

Effect of mother's physical condition during pregnancy and lactation on postnatal growth and reproductive success of offspring in water vole Arvicola terrestris L

Postnatal growth, life span, and probability of reproduction in the adult state depended on the mother's physical condition during pregnancy and lactation in water vole. The white fat weight in the female abdominal cavity was shown to significantly increase in pregnancy and to decrease in late lactation. As an indicators for nutritional state of females, their body weight difference after parturition (or in late lactation) and expected from the regression equation relating individual body weight at the beginning and the end of each reproductive stage were used (physical condition indexes in pregnancy or lactation). The correlation of the physical condition index in pregnancy with the storage fat weight was 0.67. The metabolic resources of the mother's body proved to favor faster offspring development. The female offspring weight at the age of 3 and 10 weeks as well as adult ones positively correlated with the mother's nutritional state in pregnancy, while the male offspring weight demonstrated a similar correlation at the age of 3 and 6 weeks. Increased negative energy balance during lactation proved to decrease the offspring weight in both sexes after separation from mother and at the age of 6 weeks. High nutritional state of mother in pregnancy favored both the probability of reproduction and life span of female offspring. The reproduction of male offspring did not depend on the mother's physical condition. The life span peaked in male offspring of mothers in a nutritional state below average in pregnancy and above average in lactation. Thus, the physical condition of the mother's body is an important sex-dependent factor of phenotypic variation in the offspring body weight, reproductive competence, and life span.     

Three-dimensional geometric morphometric analysis of the humerus: Comparative postweaning ontogeny between fossorial and semiaquatic water voles (Arvicola)

Different types of locomotion in phylogenetically close rodent species can lead to significantly different growth patterns of certain skeletal structures. In the present study, we compared the allometric and phenotypic trajectories of the humerus in semiaquatic (Arvicola sapidus) and fossorial (Arvicola scherman) water vole taxa, using three-dimensional geometric morphometrics, to investigate the relationships between functional and ontogenetic differences. Results revealed shared humerus traits between A. sapidus and A. scherman, specifically an expansion of the epicondylar and deltopectoral crests along postnatal ontogeny. In both species, the humerus of young specimens is more robust than in adults, possibly as a compensatory response for lower bone stiffness. However, significant interspecific differences were detected in all components of allometric and phenotypic trajectories. Noticeably divergent allometric trajectories were observed, probably as a result of different functional pressures exerted on this bone. Important differences in the form of the adult humerus between taxa were also found, particularly in features located in muscle insertion zones. Furthermore, the allometric regression revealed certain shape variation not associated with size in A. scherman, suggesting mechanical stress produced by the persistent digging activity during adulthood. A. scherman is a chisel-tooth digger that shares several traits in the humerus morphology with scratch-digger rodent species. Nevertheless, these shared characteristics are less pronounced in fossorial water voles, which is congruent with the different implications of the forelimb in the digging activity in these two types of diggers.     

Parasites and pathogens in wild populations of water voles (Arvicola amphibius) in the UK

The water vole (Arvicola amphibius) is Britain’s most endangered mammal, having gained protection under Schedule 5 of the Wildlife and Countryside Act in 2008. We present an overview of a range of naturally occurring pathogens and parasites in this rare species, which might negatively impact population persistence for small or declining populations. Wild water voles were live-captured in 2004 and 2006 from sites throughout the UK and were screened for a range of pathogens. These included: Puumala virus, Campylobacter spp., Escherichia coli, Salmonella enterica, Leptospira spp., Bartonella spp., Toxoplasma gondii, Giardia spp., Cryptosporidium spp., Babesia microti and Trypanosoma spp. E. coli was the most prevalent with 46/74 (62.2%; 95% CI, 51–73) individuals infected. One vole was co-infected with seven different pathogens whilst 20% of individuals were pathogen-free.     

Effect of prenatal stress on the hypothalamo-hypophyseal-adrenal system activity and fat metabolism in the male water vole Arvicola terrestris

The HPA axis function and the fat metabolism were studied in adult male water voles born to intact mothers and mothers deprived of food on the 15th and 18th days of their pregnancy. The HPA response to emotional stress was relatively low in experimental males in winter. The hormonal response to a 24-hrs food deprivation diminished in experimental group only in February. The blood level of free fatty acids was increased in experimental group as compared to the control one. The short maternal food deprivation modified adaptive abilities of their male progeny.     

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.     

Parasite fauna of the water vole (Arvicola terrestris) and its nests in the south of Western Siberia

Fauna of parasitic and free-living arthropods associated the water vole Arvicola terestris and its nests in various landscape zones and subzones of the south of Western Siberia has been studied. Total abundance of gamasid mites and ticks (Gamasoidea, Ixodidae), fleas and nidicolous arthropods in nests is high, and the set of nidicolous and parasite species is quite diverse, but everywhere the parasite fauna is characterized by a small amount of species reaching a high abundance: Laelaps muris on the voles, Haemogamasus ambulans in nests, Ixodes apronophorus and Megpbotris walkeri both on the voles and nests. Parasitic arthropods living on the voles or in their nests are characterized by higher and stables indices of infection, while these parameters for free-living arthropods were variable. The list of mesostigmatic mites parasitizing the water vole and its nests in the south of Western Siberia (Adamovich, Krylov, 2001) has been considerably supplemented. In total, the fauna of parsitiform mites (Acari: Mesostigmata and Ixodiddes) and fleas (Siphonaptera) associated with the water vole in the south of Western Siberia is represented by 97 arthropod species of 19 families, including 74 species of mesostigmatic mites (Gamasoidea), 6 species of ticks (Ixodidae) and 17 species of fleas.