Characteristics of erythrocyte lipids in blood of tundra voles (Microtus oeconomus Pall.) inhabiting areas with increased natural radioactivity

Interrelations between the lipid characteristics of the blood erythrocytes and 226Ra accumulation in the body of tundra voles (Microtus oeconomus Pall.) inhabiting areas with different levels of the radiation background were investigated. It is shown that the ratio of the phospholipid (PL) fractions which cause the blood erythrocyte structure depends on the phase of the population cycle, as well as on the sex and age of tundra voles. The statistically significant interrelation between lysoforms and the sphingomielin content has been revealed in the blood erythrocyte PL of tundra voles; its scale somewhat differs for the animals from the reference and Ra areas. The peroxide concentration in the blood erythrocyte lipids of tundra voles from the Ra area exceeded the control values in all mature groups of the animals trapped at the depression phase of the population density. The 226Ra content in the bodies of the tundra voles which were trapped in the Ra area at the increased phase of the population cycle is for certain higher than that for the animals from the reference area. Interrelations between the lipid peroxidation parameters in the blood erythrocytes and the body 226Ra content for separate sex-age groups of tundra voles have been revealed.     

Phospholipid composition of blood erythrocytes of tundra voles (<Emphasis Type="Italic">Microtus oeconomus</Emphasis> Pall.) inhabiting under different radioecological conditions

Phospholipid composition has been studied in blood erythrocytes of tundra voles Microtus oeconomus inhabiting territories with normal and increased levels of natural radioactivity in different phases of the population cycle. It has been shown that rearrangement in the lipid component of blood erythrocyte membranes of tundra voles from radioactively polluted areas are associated with intensification of the lipid peroxidation (LPO) processes and are similar to those observed at the organism natural aging. It has been noted that the capability for peroxide oxidation in erythrocyte lipids is one of the most sensitive stages of the LPO processes to action of the low-intensity radiation in the natural habitat of animals. The change of the populational cycle phases, which is accompanied by hormonal rearrangements in the animal body, produces an essential effect on the degree of expression of the radiation-induced changes of the studied parameters.     

Habitat use by singing voles and tundra voles in the southern Yukon

Summary We investigated how far competitive interactions influence the use of habitats and relative abundance of two species of Microtus in the southwestern Yukon. We worked in the ecotone between alpine tundra and subalpine shrub tundra where populations of singing voles (Microtus miurus) and tundra voles (M. oeconomus) overlap little.We removed tundra voles from shrub tundra on one live-trapping area to look at the effect on the contiguous population of singing voles in alpine tundra. The removal of tundra voles did not affect the distribution or relative abundance of singing voles. The spatial distribution of these species and their movements within habitats suggest that they have a strong habitat preference.Populations of small mammals in the area are extremely dynamic and the relative importance of competitive interactions may change as density varies. At present we have no evidence that competition affects habitat use in M. miurus.     

The role of interspecies differences in the ratio of choline-containing phospholipid fractions of rodent erythrocytes in response of these cells to the effect of membranotropic compounds

In in vitro experiments, interspecies differences were revealed in the erythrocyte responses in varied rodent species—laboratory mice (Mus musculus L.), tundra voles (Microtus oeconomus Pall.) and bank voles (Myodes glareolus Pall.)—to the effect of chemical agents able to interact with membrane lipids and disrupt the membrane structure (detergent Triton X-100, oxidative stress inductor AAPH, antioxidant ionol or BHT, uranyl ion). It was hypothesized that these differences are due to physicochemical peculiarities of the erythrocyte membrane structure, specifically, the ratio of choline-containing fractions of phospholipids (phosphatidylcholine and sphingomyelin). The use of blood erythrocytes as an in vitro experimental model to study the mechanisms of toxicity as well as antioxidant and membrane-protective properties of compounds of different nature was shown to imply the choice of an adequate source of erythrocytes in view of considerable speciesdependent structural specificity of the lipid component of mammalian erythrocyte membranes.     

Rapid, landscape scale responses in riparian tundra vegetation to exclusion of small and large mammalian herbivores

Productive tundra plant communities composed of a variety of fast growing herbaceous and woody plants are likely to attract mammalian herbivores. Such vegetation is likely to respond to different-sized herbivores more rapidly than currently acknowledged from the tundra. Accentuated by currently changing populations of arctic mammals there is a need to understand impacts of different-sized herbivores on the dynamics of productive tundra plant communities. Here we assess the differential effects of ungulate (reindeer) and small rodent herbivores (voles and lemmings) on high productive tundra vegetation. A spatially extensive exclosure experiment was run for three years on river sediment plains along two river catchments in low-arctic Norway. The river catchments were similar in species pools but differed in species abundance composition of both plants and vertebrate herbivores. Biomass of forbs, deciduous shrubs and silica-poor grasses increased by 40–50% in response to release from herbivory, whereas biomass of silica-rich grasses decreased by 50–75%. Hence both additive and compensatory effects of small rodents and reindeer exclusion caused these significant changes in abundance composition of the plant communities. Changes were also rapid, evident after only one growing season, and are among the fastest and strongest ever documented in Arctic vegetation. The rate of changes indicates a tight link between the dynamics of productive tundra vegetation and both small and large herbivores. Responses were however not spatially consistent, being highly different between the catchments. We conclude that despite similar species pools, variation in plant species abundance and herbivore species dynamics give different prerequisites for change.     

Comparative analysis of phospholipid composition in blood erythrocytes of various species of mouse-like rodents

Comparative analysis of quantitative phospholipid composition of blood erythrocytes was performed on various species of mouse-like rodents. In erythrocyte phospholipids of common voles there was revealed a relatively low sphingomyelin content, not characteristic of mammals. A hypothesis is put forwards that the unique lipid composition in common vole erythrocytes might be one of adaptation mechanisms for survival of the animals under conditions of pathogenic stress.     

Population dynamics of tundra voles in relation to configuration of willow thickets in southern arctic tundra

The areal extent and configuration of thickets of willow shrubs are currently changing in the Arctic both as an effect of global warming and changed browsing pressure of reindeer. These changes have been predicted to impact the distribution and abundance of wildlife species relying on willow thickets as habitat. We assessed the relation between variables quantifying willow thicket configuration and population dynamics of tundra voles (Microtus oeconomus) in three riparian regions in Finnmark, northern Norway, which were subject to intense browsing by semi-domesticated reindeer. The tundra vole, which exhibits 5-year population cycles in Finnmark, is the dominant small rodent species in riparian landscape elements in southern arctic tundra. In the course of a 4-year trapping study, tundra vole populations went through the cyclic phases of increase, peak and crash, however, with distinct differences between the three regions in the population dynamics. Within regions, the occupancy pattern during the increase phase was positively related to willow thicket configuration (in particular edge density and willow height) only in the region attaining the highest abundance and occupancy. However, local abundance was not clearly related to habitat features within any regions. The lack of consistency in the response of tundra vole populations to willow thicket configuration, as well as the positive relation between the degree of thicket shredding and tundra vole habitat occupancy in one of the regions, indicates that tundra voles will not be much affected by climate or browsing induced changes in the shrubbiness of the tundra in the future.     

Occurrence of a Syngamus sp. in tundra voles (Microtus oeconomus) collected on St. Lawrence Island, Bering Sea.

A species of syngamid nematode belonging to the genus Syngamus was found in the respiratory tract (terminal trachea to bronchi) of tundra voles (Microtus oeconomus) collected on St. Lawrence Island, Alaska (USA). Its prevalence in June 1989 was greater than 29% (12 of 41 male voles and seven of 24 females) in the village of Savoonga, while no nematodes were found from 41 voles collected in the village of Gambell. Lesions included dilatation of parasitized respiratory ducts and peribronchial and perivascular cuffing by lymphoid cells, mainly plasma cells, in parasitized lobes. Morphologically, this syngamid species differed from S. microtinae reported previously from the same host species as well as from other syngamids known from avian hosts.     

Herbivores inhibit climate-driven shrub expansion on the tundra

Recent Pan-Arctic shrub expansion has been interpreted as a response to a warmer climate. However, herbivores can also influence the abundance of shrubs in arctic ecosystems. We addressed these alternative explanations by following the changes in plant community composition during the last 10 years in permanent plots inside and outside exclosures with different mesh sizes that exclude either only reindeer or all mammalian herbivores including voles and lemmings. The exclosures were replicated at three forest and tundra sites at four different locations along a climatic gradient (oceanic to continental) in northern Fennoscandia. Since the last 10 years have been exceptionally warm, we could study how warming has influenced the vegetation in different grazing treatments. Our results show that the abundance of the dominant shrub, Betula nana , has increased during the last decade, but that the increase was more pronounced when herbivores were excluded. Reindeer have the largest effect on shrubs in tundra, while voles and lemmings have a larger effect in the forest. The positive relationship between annual mean temperature and shrub growth in the absence of herbivores and the lack of relationships in grazed controls is another indication that shrub abundance is controlled by an interaction between herbivores and climate. In addition to their effects on taller shrubs (>0.3 m), reindeer reduced the abundance of lichens, whereas microtine rodents reduced the abundance of dwarf shrubs (<0.3 m) and mosses. In contrast to short-term responses, competitive interactions between dwarf shrubs and lichens were evident in the long term. These results show that herbivores have to be considered in order to understand how a changing climate will influence tundra ecosystems.     

Effects of Populational Factors on Phospholipid Composition of Various Tissues in Natural Populations of the Tundra Vole Microtus oeconomus

The lipid composition of tissue membranes was studied in tundra voles at different phases of population cycle. At the period of depression of the volume of population, there were found a sharp rise of the content of lysophosphatidylcholine (LPC) in lipids of liver and spleen, the appearance of trace amounts of lysoforms in the brain tissue, and a reduction of portion of main fractions, particularly phosphatidylethanolamine (PE), in all studied tissues. It is at this period that the minimal content of more easily oxidizable fractions in phospholipids (PL) of all tissues was observed, with the maximal PC/PE ratio in lipids of liver and brain in most animal groups studied, which indicates the greatest rigidity of tissue membranes and minimal ability of lipids to oxidation. These particularities of the lipid fractional composition in vole tissues at different phases of population cycle are closely associated with the physiological state of the animals, specifically with their hormonal status depending on the population cycle phase, while elevation in the blood of stress-realizing hormones provides prerequisites for hyperactivation of peroxide oxidation of lipids (POL). The revealed pronounced changes of the tissue phospholipid composition in voles from natural populations at the depression of the population size can be considered as a part of non-specific reaction and associated intensification of POL processes.     

Occurrence of natural tularemia foci in Kamchatka

The focus of tularemia in the Ust-Kamchatsky region belongs probably to the flood-plain and swamp type with muskrats and tundra voles being the main carriers. In autumn 1980 for the first time three cultures were isolated in this region: 1 from a tundra vole and 2 from muskrats. The presence of antibodies to tularemia antigen in Norway rats was revealed in the passive hemagglutination test.     

Small rodents in the shrub tundra of Yamal (Russia): Density dependence in habitat use?

Northern small rodents are well known for their population cycles which represent a key process for the functioning of arctic and boreal ecosystems. Habitat use often changes in the course of the cycle. Higher densities can either lead to spill-over into secondary habitats or to increased habitat specificity because of interspecific competition. Here we investigate whether voles in the shrub tundra of southern Yamal exhibit density dependent habitat use. Voles were trapped at the Erkuta Tundra Monitoring Site (N 68.2°, E 69.2°) in three characteristic habitats over five years covering all phases of the population cycle. Our analyses focused on the two most numerous species Microtus gregalis (52% of individuals caught) and M. middendorffii (36%). A small-scale spill-over effect was observed for M. gregalis, which increasingly used the open habitat adjacent to their preferred willow thickets at high abundance. At a larger scale no such effect was observed for the two Microtus species – a result which is explained by the overall moderate densities of voles and the large spatial extent of the primary habitat of M. middendorffii: moist moss dwarf shrub tundra.     

Arctic Small Rodents Have Diverse Diets and Flexible Food Selection

The ecology of small rodent food selection is poorly understood, as mammalian herbivore food selection theory has mainly been developed by studying ungulates. Especially, the effect of food availability on food selection in natural habitats where a range of food items are available is unknown. We studied diets and selectivity of grey-sided voles (Myodes rufocanus) and tundra voles (Microtus oeconomus), key herbivores in European tundra ecosystems, using DNA metabarcoding, a novel method enabling taxonomically detailed diet studies. In order to cover the range of food availabilities present in the wild, we employed a large-scale study design for sampling data on food availability and vole diets. Both vole species had ingested a range of plant species and selected particularly forbs and grasses. Grey-sided voles also selected ericoid shrubs and tundra voles willows. Availability of a food item rarely affected its utilization directly, although seasonal changes of diets and selection suggest that these are positively correlated with availability. Moreover, diets and selectivity were affected by availability of alternative food items. These results show that the focal sub-arctic voles have diverse diets and flexible food preferences and rarely compensate low availability of a food item with increased searching effort. Diet diversity itself is likely to be an important trait and has previously been underrated owing to methodological constraints. We suggest that the roles of alternative food item availability and search time limitations for small rodent feeding ecology should be investigated.

Nomenclature

Annotated Checklist of the Panarctic Flora (PAF), Vascular plants. Available at: http://nhm2.uio.no/paf/, accessed 15.6.2012.     

The parameters of antioxidant status of tissues in the offspring of tundra vole (Microtus oeconomus Pall.) inhabiting areas with increased natural radioactivity

The parameters of the lipid peroxidation regulatory system (the antioxidative and antiperoxidant activities, the peroxide content, the lipid peroxidation intensity) in the tissues and the activities of the antioxidative defence enzymes (the peroxidase activity in blood, the superoxide dismutase activity in the blood erythrocytes) are studied in progeny of tundra vole which are reproduced from parent inhabiting areas with different radioecological environment during a long time. The progeny had the preservation of the changed antioxidant status. The scale of the changing of the investigating parameters depend on the state of radionucleoids contamination of areas where tundra voles are caught, sex of rodents, the content of antioxidants in lipids of tissues of parents.     

Seasonal changes in the energy metabolism of subarctic rodents

In widespread species, northern taiga voles, most significant differences in the intensity of energy metabolism (M), maximum (Mmax) and reserve (Mres) metabolism were observed at winter temperatures (-5-20 degrees C): Clethrionomys rutilus greater than C. rufocanus greater than Microtus oeconomus; differences in seasonal increase of Mmax and Mres exhibit an inverse proportion. Seasonal changes in M and Mmax in autochthonous tundra rodents indicate that Lemmus sibiricus belongs to a more eurybiont species as compared to Dicrostonyx torquatus. The main characteristic feature of seasonal adaptation of M in lemmings, as compared to voles, is the evident decrease of M value in winter which is accompanied by a more significant increase of Mmax and Mres. Operative pattern and high seasonal mobility of chemical thermoregulation in lemmings are suggested which account for adaptation of these animals mainly to short-term extreme effects of low temperatures.     

Importance of large and small mammalian herbivores for the plant community structure in the forest tundra ecotone

Both theoretical arguments and empirical evidence suggests that herbivory in general and mammalian winter herbivory in particular is important in arctic–alpine ecosystems. Although knowledge of the effect of herbivores on specific plants and communities is quite extensive, little is known about the relative impact of large and small vertebrate herbivores and how it might vary among different habitats. To address this key issue, we established exclosures with two different mesh sizes in forest and nearby tundra at three different sites in four contrasting locations in the forest–tundra ecotone in northernmost Sweden and Norway. Plant community composition was recorded annually in three permanent plots within each exclosure and an unfenced control. Local densities of vertebrate herbivores were estimated in spring and autumn from 1998 to 2002. Reindeer (Rangifer tarandus) were the most abundant large vertebrate while Norwegian lemmings (Lemmus lemmus) and grey‐sided voles (Clethrionomys rufocanus) were the most common small vertebrates. The study reveals that voles and lemmings have larger effects on the vegetation than reindeer in both habitats in all four locations, even though densities of reindeer differ between locations and only two locations experienced lemming peaks during the period of the experiment. The relative abundance of five of the fifteen most common species was significantly influenced by voles and lemmings whereas only a single species was significantly influenced by reindeer. Different analyses give contrasting results on the importance of herbivory in forest versus open heathlands. A principal component analyses revealed that herbivory influenced the vegetation more in open heathlands than in forests. However, an importance index of herbivores did not differ between forest and open heathlands. Moreover, none of the plant species responded differently in the two habitats, when herbivores were removed. Our results suggest that intense and localised selective foraging by small mammals may have a more marked effect on vegetation than transient feeding by reindeer.     

Population ecology of leptospires. 1. An experience with evaluation of leptospira count in a carrier and the intensity of elimination in the urine

The number of L. hebdomadis and L. grippotyphosa in the body of tundra voles (Microtus oeconomicus) has been shown to be approximately 500-800 million; about 100 million of them are daily eliminated from the body of a vole with urine. About 70% of the total volume and separate portions of urine contain leptospires, a single portion of urine containing about 2 million microbial cells. These data have proved to be the same for both L. hebdomadis and L. grippotyphosa.     

Food deprivation in the common vole (<Emphasis Type="Italic">Microtus arvalis</Emphasis>) and the tundra vole (<Emphasis Type="Italic">Microtus oeconomus</Emphasis>)

Arvicolinae voles are small herbivores relying on constant food availability with weak adaptations to tolerate prolonged food deprivation. The present study performed a comparative analysis on the responses to 4–18 h of food deprivation in the common vole (Microtus arvalis) and the tundra vole (Microtus oeconomus). Both species exhibited rapid decreases in the plasma and liver carbohydrate concentrations during phase I of fasting and the decline in the liver glycogen level was more pronounced in the tundra vole. The plasma thyroxine concentrations of the common vole decreased after 4 h. Lipid mobilization (phase II of fasting) was indicated by the increased plasma free fatty acid levels after 8–18 (the common vole) or 4–18 h (the tundra vole) and by the elevated lipase activities. In the tundra vole, the plasma ghrelin concentrations increased after 12 h possibly to stimulate appetite. Both species showed increased liver lipid concentrations after 4 h and plasma aminotransferase and creatine kinase activities after 12–18 h of food deprivation implying liver dysfunction and skeletal muscle damage. No signs of stimulated protein catabolism characteristic to phase III of fasting were present during 18 h without food.     

Complex estimation of thyroid gland state in tundra voles, inhabiting the natural radioactive polluted sites

Behow is presented the complex state of thyroid gland of tundra voles living in high level natural radioactivity conditions (Ukhta region of Komi Republic) by morphological and functional criteria. High sensitivity of thyroid gland under natural chronic irradiation of whole organism is noticed. The essential changes in the morphological structure and in the hormone level of the thyroid gland are found in animals, which live for a long time in the conditions of the radioactive pollution. It is determined, that the inside population processes influence on the structure and on the funcition of the thyroid gland.     

Distribution of water bugs (Heteroptera: Nepomorpha, Gerromorpha) over latitudinal zones in the northeast of European Russia

Data on the taxonomic composition of water bugs (Heteroptera: Nepomorpha, Gerromorpha) in the northeast of European Russia are given. A total of 34 water-bug species, which belong to 16 genera and 8 families, are recorded. The species diversity of Nepomorpha and Gerromorpha changes northwards: 33 occur in the taiga zone and only 8 species occur in the tundra zone. The bulk of the fauna consists of Eurosiberian (29%) and trans-Eurasian (26%) species; in latitude-related terms, the temperate group is most richly represented (64%). The species composition of the aquatic and semiaquatic heteropteran fauna of the region is especially similar to that of the tundra and taiga zones of Western Siberia.