The diet composition of the social vole at the beginning stage of colonization of a zonal plain in a clayey semidesert of the Trans-Volga region

The botanical composition and the ratio of various plants in the diet of Microtus socialisPall. were determined by microhistological cuticular-coprological analysis of undigested remains. Microtus socialis disappeared from the zonal plain of the Volga-Ural interfluve in the early 1970s and appeared again in 2009. The role of grains in their nutrition became more important, and the ratio of wormwoods sharply decreased. The feeding patterns observed are caused by the long-term absence of these massive phytophages and reflect significant changes in the habitat over the last 40 years.     

Gamasid mites of small mammals in the semi-desert territories of Saratov Trans-Volga region

New data on the species composition and comparative analysis of gamasid mites occurring on small mammals in the semi-desert territories of Saratov Trans-Volga region are reported. In all, 18 species of gamasid mites (9 genera, 5 families) were found, including 9 species which had not been previously recorded in the region: Hypoaspis (Stratiolaelaps) miles Berlese, 1882, H. (Geolaelaps) heselhausi Oudemans, 1912, H. (G.) lubrica Oudemans et Voigts, 1904, Laelaps multispinosus Banks, 1909, L. jettmari Vitzthum, 1930, Cyrtolaelaps mucronatus G. et. R. Canestrini, 1881, Haemogamasus citelli Bregetova et Nelzina, 1952, Hirstionyssus eusoricis Bregetova, 1956, and Hi. ellobii Bregetova, 1956; 5 of these species are new to Saratov Province.     

Hibernation in the Eversman hamster (Allocricetulus eversmanni Brandt, 1859) from the Saratov Trans-Volga region

The hibernation of the Eversman hamster is proven for the first time. The body temperature measured with a thermoaccumulator implanted into the abdominal cavity dropped down to +5°C several times during the winter. This species differs from other hibernating mammals in the peculiarities of its seasonal fluctuation of steroid hormones (cortisol, progesterone, estradiol, and testosterone) and in the absence of fat deposits before hibernation.     

The development of social behaviour in the vole (Microtus agrestis)

Juvenile voles of the species Microtus agrestis investigated the bodies of other juveniles with the nose, by touching the dorsal surface from snout to tail. Play movements often followed such nosing contacts and augmented further contacts. The most important scent stimulating play was produced by the skin at the back of the head. The secretion of the nose and mouth region may convey sexual identity, the rump region and feet individual identity.
Young born in the spring and early summer often interacted and played, the autumn young seldom. The behaviour of overwintering sexually immature adults was similar to that of the autumn juveniles. It is suggested that this seasonal difference in the behaviour of juveniles has consequences for subsequent mature males, and that this developmental factor may have an important effect on the annual population cycle.     

Adrenal analysis for critique of the social stress theory in natural populations of a montane vole

Summary The vole,Eothenomys smithi, in highlands of Shikoku was studied to disclose ups and downs of adrenal activities under the influence of the breeding level in natural populations. It has proved that the vole's adrenal in both sexes may be much more strongly by rise and fall of the fertility as well as by shift of the age structure in populations than the rat's. Therefore, as for perhaps all kinds of small mammals, we consider necessary to follow a pertinent procedure to avoid thoroughly these sources of error in studies to draw any conclusion for or against theChristian's theory. The present data analysed by such a method failed to afford any confirmative proofs; the fact that the pregnancy rate was increased in parallell to the density is against his view. However, never the whole content of the theory has been invalidated by these results.     

Offspring growth, survival and reproductive success in the bank vole: a litter size manipulation experiment

To estimate the optimality of brood size, it is essential to study the effects of brood size manipulation on offspring survival and reproductive success. Moreover, testing the generality of the hypothesis of reproductive costs requires experimental data from a diversity of organisms. Here I present data on the growth, survival and reproductive success of bank vole Clethrionomys glareolus individuals from manipulated litters. Furthermore, the survival of mothers whose litter size was manipulated was studied. At weaning, the mean weight of pups from enlarged litters was lower and from reduced litters higher compared to control litters. After winter, at the start of the breeding season, individuals from enlarged litters, especially males, were still lighter than individuals from the other two treatments. Litter enlargements did not increase the number of reproducing female offspring per mother, nor did the litter sizes of female offspring differ between treatments. There were no differences between treatments in winter survival of offspring after weaning, but among female offspring, weaning weight explained the survival probabilities over winter. A higher weight of females at winter determined the probability of starting to reproduce in spring. The survival of mothers did not seem to be influenced by litter manipulation performed the previous year. According to the results, mothers nursing enlarged or reduced litters do not gain any fitness benefits in terms of number of offspring surviving to breeding. The results are consistent with the majority of experiments conducted in birds, which have found costs of enlarged brood appearing as offspring trade-offs rather than parent trade-offs. Received: 14 December 1997 / Accepted: 1 March 1998     

The effects of social environment on adult neurogenesis in the female prairie vole

In the mammalian brain, adult neurogenesis has been found to occur primarily in the subventricular zone (SVZ) and dentate gyrus of the hippocampus (DG) and to be influenced by both exogenous and endogenous factors. In the present study, we examined the effects of male exposure or social isolation on neurogenesis in adult female prairie voles (Microtus ochrogaster). Newly proliferated cells labeled by a cell proliferation marker, 5-bromo-2'-deoxyuridine (BrdU), were found in the SVZ and DG, as well as in other brain areas, such as the amygdala, hypothalamus, neocortex, and caudate/putamen. Two days of male exposure significantly increased the number of BrdU-labeled cells in the amygdala and hypothalamus in comparison to social isolation. Three weeks later, group differences in BrdU labeling generally persisted in the amygdala, whereas in the hypothalamus, the male-exposed animals had more BrdU-labeled cells than did the female-exposed animals. In the SVZ, 2 days of social isolation increased the number of BrdU-labeled cells compared to female exposure, but this difference was no longer present 3 weeks later. We have also found that the vast majority of the BrdU-labeled cells contained a neuronal marker, indicating neuronal phenotypes. Finally, group differences in the number of cells undergoing apoptosis were subtle and did not seem to account for the observed differences in BrdU labeling. Together, our data indicate that social environment affects neuron proliferation in a stimulus- and site-specific manner in adult female prairie voles.     

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.     

Diversity of phytophagous beetles (Coleoptera: Chrysomeloidea,Curculionoidea) in steppe communities in the forest-steppe of the High Trans-Volga region

A total of 551 species from 10 families of phytophagous beetles (superfamilies Chrysomeloidea and Curculionoidea) have been recorded in the steppe communities of the High Trans-Volga forest-steppe zone, 62% of which belong to the steppe landscape-geographic complex. The vast majority of the species belong to three families: Curculionidae (254 species; 46%), Chrysomelidae (186 species; 34%), and Apionidae (51 species; 9%). The regional steppe fauna has a complex arealogical structure combining the Western Scythian and Sarmatian elements, as well as relict species of the Angarian origin and some Eastern European ones. The highest diversity of phytophagous beetles is observed in the zonal meadow steppe communities (299 species; 54%). The most specific are the petrophilous steppe complexes which also include the greatest number of relict forms. Xerophilous Kazakhstan- Turanian species are mostly concentrated in the saline steppe communities of the southernmost forest-steppe zone. The species diversity is also high (249 species) in the open ruderal communities dominated by species characteristic of the pioneer stages of the steppe successions. Some steppe reservations include over 50% of the entire regional fauna of phytophagous beetles. The species diversity in the steppe localities decreases northward due to a gradual decrease in the number and proportion of the Scythian species: from 55% in the middle of the foreststeppe zone to 36% near its northern boundary. The species diversity of the slope communities in the forest-steppe zone is at least not lower than that in the similar areas of the steppe zone. The ratio of the number of Curculionoidea species to that of plant species is very high, reaching about 3: 4 in the model steppe localities of the High Trans-Volga forest-steppes, as compared to 1: 2 in the zonal steppe communities (according to the published data). The data considered confirm the significance of the forest-steppe zone as an important biodiversity center in the East European Plain and as a reservation of relicts of different origins.     

The diel dynamics of vertical migrations in hortobiontic spiders (Aranei) in the clay semidesert of the northern Caspian region

The diel periodicity of vertical migrations of herbage-dwelling spiders has been studied in natural habitats of clay semidesert of the northern Caspain (Transvolga) region. Steppe habitats (microdepressions) and desert habitats (microelevations) are shown to have much in common: the abundance and the family composition of spider populations of both biotopes are similar; they slightly differ only during the hot summer season. The amplitude of diel fluctuations in spider abundance is relatively great, which is typical of open cenoses under semiarid conditions. In spring and autumn, the peaks of spider abundance in both types of habitats are at night, when air temperature is minimal. In summer, in addition to the nighttime abundance peaks, there are daytime peaks of similar size, due mostly to the increased activity of “southern” taxa, the Thomisidae in desert associations and the Thomisidae + Salticidae in steppe associations. The diel periodicity of vertical migrations in hortobiontic spiders is a complicated phenomenon determined by a number of factors. It is to some extent conditioned by environmental parameters and by vertical migrations of their potential prey, phytophagous insects. Thus, the ecological niches in spiders of different taxa are separated in time according to their morphological and behavioral adaptation to climatic conditions. This separation probably alleviates competition between populations of different taxa.     

Immunocompetence and high metabolic rates enhance overwinter survival in the root vole,Microtus oeconomus

Despite its presumed significance, the association between immune defence, energy expenditures and overwinter survival is rarely studied. We analysed individual variation in immunocompetence quantified as neutrophil-to-lymphocyte ratio (N/L), total white blood cells (WBC) and natural antibody levels, along with resting (RMR) and peak metabolic rates (PMR) and mortality during three consecutive winter seasons in a natural population of the root vole, Microtus oeconomus. In early winter, WBC count was negatively correlated with RMR, whereas N/L ratio was negatively correlated with swim-elicited PMR. We suggest that while the first correlation reflected the trade-off between energy allocation in immunocompetence and other metabolically demanding processes, the latter correlation stemmed from stress-induced immunosuppression elicited by the necessity to cope with swimming in frequently flooded habitat. In addition, the analysis carried out during the first year of study characterized by a high population density and prevalence of infestation with a blood parasite—Babesia spp., showed that its intensity was inversely correlated with the N/L ratio. In summary, our results suggest that elevated N/L ratio increases the winter survival of free-ranging rodents by increasing their ability to cope with parasitic infections.     

A relict bank vole lineage highlights the biogeographic history of the Pyrenean region in Europe

The Pyrenean region exhibits high levels of endemism suggesting a major contribution to the phylogeography of European species. But, to date, the role of the Pyrenees and surrounding areas as a glacial refugium for temperate species remains poorly explored. In the current study, we investigated the biogeographic role of the Pyrenean region through the analyses of genetic polymorphism and morphology of a typical forest-dwelling small mammal, the bank vole ( Myodes glareolus ). Analyses of the mitochondrial cytochrome b gene and the third upper molar (M³) show a complex phylogeographic structure in the Pyrenean region with at least three distinct lineages: the Western European, Spanish and Basque lineages. The Basque lineage in the northwestern (NW) Pyrenees was identified as a new clearly differentiated and geographically localized bank vole lineage in Europe. The average M³ shape of Basque bank voles suggests morphological differentiation but also restricted genetic exchanges with other populations. Our genetic and morphological results as well as palaeo-environmental and fossils records support the hypothesis of a new glacial refugium in Europe situated in the NW Pyrenees. The permissive microclimatic conditions that prevailed for a long time in this region may have allowed the survival of temperate species, including humans. Moreover, local differentiation around the Pyrenees is favoured by the opportunity for populations to track the shift of the vegetation belt in altitude rather than in latitude. The finding of the Basque lineage is in agreement with the high level of endemic taxa reported in the NW Pyrenees.     

Semen quantity and quality correlate with bank vole males’ social status

Laboratory studies reveal that in several rodent species the females prefer dominant males as mating partners. Here we investigate the correlation between bank vole males’ social rank and their sperm quality and quantity. We used agonistic encounters to determine males’ social status. Sperm quality was assessed by its motility, viability, maturity, morphology and sperm tail membrane integrity. Relatively more dominant males were heavier than males of lower social status. The males’ social position affected the testes, seminal vesicles and coagulation gland development. The weights of these reproductive organs were significantly higher in more dominant males than in more subordinate males. Sperm counts and the values of the other parameters describing sperm quality were higher in high-ranking males than in subordinates. Our results suggest that bank vole females benefit from choosing and mating with high-ranking males by obtaining more and better-quality sperm.     

Effects of competition and season on survival and maturation of young bank vole females

In territorial microtines intra-specific density dependent processes can limit the maturation of individuals during the summer of their birth. This may have demographic consequences by affecting the number and the age distribution of breeding individuals in the population. Little is known about this process on a community level, though populations of many northern microtine species fluctuate in synchrony and are known to interfere socially with each other. We experimentally studied the influence of the field vole Microtus agrestis on maturation, breeding, space use and survival of weanling bank voles, Clethrionomys glareolus. Two additive competition experiments on bank vole populations were conducted in large outdoor enclosures, half of them additionally housing a field vole population. In a mid-summer experiment low population density and absence of older breeding females minimised intra-specific competition. Survival was not affected by the presence of field voles. Season had a significant effect on both the probability of maturation and breeding of the weanlings. Competition with field voles significantly delayed breeding, and coupled with seasonal effects decreased the probability of breeding. In a late-summer experiment breeding and survival of bank vole weanlings were studied for three weeks as part of a high density breeding bank vole population. Weanlings did not mature at all nor were their space use and survival affected by the presence of field voles. Our results show that competition with other species can also have an impact on breeding of immatures. In an extreme seasonal environment, even a short delay of breeding may decrease survival chances of offspring. Seasonal and competition effects together may thus limit the contribution of year born females to reproductive output of the population. Other studies have shown that adult breeding bank voles suffer lower survival in the presence of field voles, but this study showed no survival effects on the weanlings. Thus it might be beneficial for weanlings to stay immature especially in the end of the breeding season and postpone reproduction to the next breeding season if densities of competing species are high.     

Gap colonization in the Patagonian semidesert: seed bank and diaspore morphology

We report work on a cold, windy South American steppe dominated by tussock grasses and shrubs of small stature that, together, cover only half of the soil surface. Our objective was to find out why seedlings and juveniles of these dominant species are generally absent from the bare or poorly-populated spots (gaps) that exist between established individuals. We hypothesized that matrix-forming species fail to colonize gaps because of a lack of properly-placed seeds, contained in diaspores which because of their morphology are blown away from gaps that otherwise would constitute safe sites for recruitment. We evaluated diaspore size and wing loading (weight:area ratio) for all common species in the community, collected seed-bank samples in different occasions and microsites, and performed detailed field observations for one gap-dwelling species during several years. We found that: 1) Seeds of the dominant, matrix-forming species are uncommon in the soil bank of the center of the gaps between established vegetation. 2) Seeds of the dominant species are more abundant towards the edges of the gaps than at their center. 3) Diaspores of those species present in the seed bank of the gaps are smaller than diaspores of absent species; contrary to expectations, not all gap-dwelling species had larger diaspore wing loading than non-gap species. 4) Seeds and adult densities of the most common gap species (the annual Camissonia dentata ), were correlated between them and across subsequent years. We conclude that it is not an overall shortage of seeds that precludes the dominant species from becoming established in the gaps, but rather the seeds' uneven spatial distribution. We further argue that gaps would be suitable sites for recruitment, but large diaspore size makes seeds of the dominant species to be blown away by the strong westerly winds.