Fluctuating asymmetry of rodent cranial structures in an industrial pollution gradient

Fluctuating asymmetry (FA) of the mandible shape has been analyzed in bank voles from the zones affected by pollution from three copper smelters in the Urals. It has been shown that there is the necessity for a detailed analysis of the material, since the level of FA may depend on population parameters. Regardless of the pollution level, FA of the mandible region including the lower part of the mandibular body, ramus and processes is higher than in the diastema region. A gradient effect of toxic exposure on FA has been revealed: an increase in its level under increasing technogenic impact is clearly manifested along local pollution gradients.     

High levels of fluctuating asymmetry in populations of Apodemus flavicollis from the most contaminated areas in Chornobyl

Random deviations from the perfect symmetry of normally bilaterally symmetrical characters for an individual with a given genotype occur during individual development due to the influence of multiple environmental factors. Fluctuating asymmetry (FA) is often used as a measure of developmental instability, and can be estimated as the variance of the distribution of differences between the left and right sides. We addressed the question of whether levels of FA were elevated in radioactively contaminated populations living around Chornobyl compared to those in reference populations of the yellow-necked mouse (Apodemus flavicollis). In addition, we studied amounts of directional asymmetry (DA) when one side is larger than the other on average. There was a significant difference among populations, including reference populations, in the amount of both FA and DA. A higher level of FA was documented for the contaminated populations in close proximity to the failed Chornobyl reactor for both the asymmetry of size and shape. The FAs of size and shape were highest in populations from the most contaminated locations in the Chornobyl exclusion zone. Although the directional asymmetry of shape was also highest in the contaminated populations, it was not significantly different from those in most of the reference populations. Populations from less contaminated areas inside the Chornobyl exclusion zone did not express FA values different from those of the reference populations outside the affected area. FA of skulls of A. flavicollis may indicate the degree to which the level of radioactive contamination affects the development of animals at Chornobyl. However, the mechanisms leading to these effects are not clear and probably vary from population to population. There were significant correlations between the overall right to left differences for the Procrustes aligned shape configurations, centroid sizes, and intramuscular (137)Cs. Detectable effects of radiation on developmental stability probably start to occur between 0.132 and 0.297 microGy/h.     

Population dynamics and changes in the population structure of a polymorphic colony of northern mole voles

Long-term (1985–1999) stationary observations on a polymorphic population of northern mole voles (Ellobius talpinus Pall.) in Kurgan oblast, Russia, using a mark-recapture method yielded original data on the population dynamics and population structure of a polymorphic colony consisting of animals of three color morphs (black, brown, and intermediate or transitional). The period when the northern mole vole population dynamics was studied (15 years) consisted of five distinct three-year population phases: depression, growth, peak (stabilization), decline to depression, and the next growth phase. It was shown that the population dynamics and changes in the population structure of northern mole voles in the Kurtamysh colony are cyclic.     

Spatial population structure in forest voles of the genus <Emphasis Type="Italic">Clethrionomys</Emphasis> in the southern taiga of the Middle Irtysh region

A comparative analysis of spatial population structure in the northern red-backed vole (Clethrionomys rutilus Pall.) and large-toothed red-backed vole (Cl. rufocanus Sund.) has been performed in the middle taiga zone of the Middle Irtysh region (Omsk oblast). Populations of these species are represented by sets of territorial groups whose numbers and spatial distribution change from year to year depending on the ratio of these species in a biotope and their population density. There is no significant interspecific competition between cohabitant Cl. rutilus and Cl. rufocanus. In particular, this follows from the fact that the population density and distribution pattern of one species are independent of those of the other species. It has been found that the size of home ranges in Cl. rutilus inversely depends on its population density, with that in Cl. rufocanus remaining approximately the same at different population densities, and that the structure of the resident part of the population in both species changes during the season, as voles from neighboring habitats or dispersing voles settle in the study area.     

Ecological Analysis of Spleen Hypertrophy in Cyclomorphic Rodents Taking into Account the Type of Ontogeny

The functional approach at the level of physiological functional groups (PFGs) reflecting two types of ontogeny was used to analyze spleen hypertrophy in five species of rodents. In addition to a wide variation of spleen weight, its hypertrophy was observed: in bank voles (Clethrionomys glareolus), the spleen weight was as great as 3.5 g versus the normal value of 100–150 mg. The variation range of the relative spleen weight was estimated. For example, in the dominant species, C. glareolus, this range was considerable (from 2 to 125). A distinct relationship with the types of animal ontogeny was revealed. The genus specificity of the phenomenon—its occurrence in three species of Clethrionomys voles and absence in Microtus voles and mice—was determined in the study region. The animals with normal and hypertrophied spleens did not differ from each other significantly in their vital activity (at least, with respect to the parameters studied). The voles with hypertrophied spleens normally reproduced, and the hypertrophy was asymptomatic. These findings suggest that the populations have adapted to a damaging factor (or factors) in the course of a prolonged coevolution. This parameter is regarded as the indicator of the presence of a damaging factor in the population.     

The Diet of the Great Gray Owl,Strix nebulosa,at Different Levels of Prey Abundance during the Nesting Season

Variation in the diet of the Great Gray Owl, a specialist predator, at different levels of prey abundance in different biotopes was studied in the middle Transural region. Microtus voles were found to be the main prey, with shrews being alternative prey. In different plots, two types of change in the diet were observed during the nesting season: (1) substitution of Microtus voles inhabiting meadow biotopes by Microtus voles characteristic of forest habitats, and (2) substitution of the latter by shrews.

     

Seasonal modulation of sex-related differences in hippocampus size and spatial behavior in bank voles, Clethrionomys glareolus (Rodentia, Cricetidae)

Male and female bank voles (Clethrionomys glareolus) were compared with respect to seasonal variation in hippocampus size and dynamics of spatial behavior during the annual population cycle. The winter decrease in the size of the hippocampus (the brain region involved in the processing of spatial information about the environment) in young autumn-born voles coincided in time with reduction of their home ranges and did not differ significantly between males and females. The growth of the hippocampus in spring, after winter regression, was higher in males (19–28% in different populations) than in females (8–20%) and coincided with an increase in spatial activity, which was also more distinct in males. A significantly greater hippocampus size in males during the breeding period correlated with their higher mobility (reflected in capture rate) and greater size of home ranges. Thus, parallel seasonal modulation of sex-related differences in hippocampus size and spatial behavior was revealed: sexual dimorphism in these characters was insignificant among young voles in autumn; disappeared in winter; manifested itself again, synchronously in both characters, in early spring (with the onset of puberty); and reached a peak in summer.     

Energy and immune parameters of northern red-backed voles (<Emphasis Type="Italic">Clethrionomys rutilus</Emphasis>) at different population densities in the Kolyma River basin

Several parameters of energy and immune homeostasis in immature red-backed voles at different phases of the population cycle have been evaluated and compared over three cycles (2002–2009). It has been found that a specific morphophysiological type of population is characteristic of each phase of the cycle. The values of all physiological parameters recorded at high and low population densities significantly differ from each other, with their values being usually intermediate at a medium density. The level of most energy and immune parameters at the phase of population peak corresponds to that observed under stress. Supposedly, stress contributes to suppression of reproduction and increased mortality of the voles.     

Population Dynamics of Forest Voles (Clethrionomys,Rodentia) in Northern European Russia

Long-term data sets on the population dynamics of forest voles in northern European Russia were analyzed. Eastward and northward trends in changes of the ratio between model species and the degree of their dominance were revealed. In virtually all sites studied, the numbers of the northern red-backed and bank voles changed synchronously; however, the population dynamics became less synchronous as the distance between study areas increased.     

Growth rate,reproductive capacity,and survival rate of European water voles taken from natural populations at different phases of the population cycle

Growth rate, reproductive characteristics, and survival rate of European water voles taken from the population at the peak, decline, depression, and increase phases of population cycle were compared under standard vivarium conditions. In November to March, the growth rate of decline-phase males was higher, while that of decline-phase females was lower than in other animals. Decline-phase males were also more successful in reproduction than males taken at other phases. The survival rate of decline-phase females was reduced in the winter period.     

Long-term dynamics of heavy metal concentrations in the food and liver of bank voles (<Emphasis Type="Italic">Myodes glareolus</Emphasis>) in the period of reduction of emissions from a copper smelter

Long-term changes in the contents of heavy metals (Cu, Zn, Cd, Рb) in the food and liver of bank voles (Myodes glareolus) inhabiting areas exposed to pollution from the Middle Ural Copper Smelter (MUCS) in the period of reduction of its emissions (1990–2015). The results show that 50-fold reduction of emissions has not resulted in an equivalent decrease in the dietary and body concentrations of metals: in the impact zone (1–2 km from the MUCS), Cu, Zn, and Pb concentrations remain unchanged, while Cd concentrations have increased twofold by the end of the observation period; in the background zone (20 km), Cu, Zn, and Cd concentrations remain unchanged, while Pb concentrations have decreased by a factor of 1.7–2.5; and no directed changes have been revealed in moderately polluted plots (4–6 km). The accumulation of heavy metals in the animal body depends primarily on the contents of these elements in food and on the system of elementspecific homeostatic barriers providing effective protection from the toxic effect of heavy metals.     

Variation in transfer factor of radiocaesium in bank voles (Clethrionomys glareolus) in clear cut and mature forest sites after the Chernobyl accident

Bank voles that were collected between 1986 and 2004 at sites in Chernobyl fallout areas of northern Sweden showed higher (137)Cs activity concentrations at the mature forest sites compared to clear cuts. This difference was not attributed to differences in ground deposition between sites but to differences in aggregated transfer rates to voles. Differences in transfer between forest types were evident for all years 1986-2004 but the change occurred at different rates in the two habitats. The apparent transfer factor between bilberry (Vaccinium myrtillus) and voles was positively related and indicated that a biomagnification was about 1.5 from vegetation to these small mammalian herbivores. The aggregated transfer factor to bank voles measured in the forest habitat, although starting at higher levels declined faster with time than clear cut sites and the differences between the forest habitat and the clear cut areas diminished with time. After the Chernobyl accident in 1986 the mean level in bank vole was 514Bq/kg fresh mass (SD=505) that increased to 1485Bq/kg (SD=881) in 1988. The activity concentration declined thereafter. The bank voles collected in similar habitats in 2004 contained on average 1022Bq/kg (SD=723). Still 18 years after the radionuclide fallout over Sweden high activity concentrations in voles could be found.     

Chernov’s compensation principle and the effect of rodent community completeness on the variability of bank vole (<Emphasis Type="Italic">Clethrionomys glareolus</Emphasis>) population in the Middle Urals

Using methods of geometric morphometrics, significant differences have been revealed in manifestations of variability and morphological disparity in allochronous samples from the population of model species, the bank vole (Clethrionomys glareolus Schreb. 1780), in the Middle Urals at different levels of rodent community (taxocene) completeness in different years. Two states of the taxocene—oligospecific (two species) and polyspecific (five species)—and the level of relative abundance of bank voles (high or low) have been taken into account. Comparative analysis of variation in the size and shape of the mandible in same-aged (late-summer) young of the year has shown that significant morphogenetic differences exist between the animals sampled from the rodent taxocene at its different states (oligospecific and polyspecific) and, to a lesser extent, at high and low levels of abundance. The level of variation and the parameter of intragroup morphological disparity (MNND) in the mandible shape reach a maximum when the community has a reduced composition and decrease to a minimum when its composition is complete (i.e., in the oligo- and polyspecific taxocene). A parallelism is observed in the manifestation of morphofunctional changes of the mandible in male and female voles under conditions when the taxocene has high abundance and oligospecific composition or low abundance but polyspecific composition. Different morphogenetic responses of the population to oligo- and polyspecific composition of the community are considered as a compensatory increase of morphological disparity in the dominant species (the bank vole) under conditions of incomplete composition of the taxocene and low population density, in accordance with Chernov’s ecological compensation principle.     

Body condition and reproductive characteristics of female water voles (Arvicola terrestris L.)

The relationship between long-term dynamics of reproductive parameters and body condition were studied in female water voles from a cycling population. Body condition was estimated from the deviation of body weight (excluding the weight of the uterus with embryos) from the theoretically expected weight calculated from the equation of body weight regression with respect to body length. As the index of body condition increases upon transition from decline to peak in the population cycle, the numbers of corpora lutea and live embryos also increase and the risk of resorption of the entire litter becomes lower.     

Biological consequences of increased natural radiation background for Microtus oeconomus Pall. populations

The results of long-term investigations (1981-1999) on the state of Microtus oeconomus Pall. (tundra vole) population, living under the increased natural radiation background for a long time (for more than 100 generations), are presented. Population density dynamics, morphophysiological parameters, state of the lipid peroxidation regulatory system in different tissues and the cytogenetic effects in bone marrow cells of animals have been analyzed. It is shown that tundra voles from the studied radioactively contaminated areas differ from those on natural radiation background area for the parameters measured. The results of this long-term investigation show that qualitatively new sub-populations of tundra vole on these areas have evolved, which are able to survive in radioactively contaminated environment.     

Species-Specific Features of Inter- and Intrapopulation Variation in the Level of Chromosome Instability in Rodents

Studies on the common vole Microtus arvalis revealed a distinct cytogenetic response to the influence of ionizing radiation, a wide range of variation in the group average indices of chromosome instability beyond the zone of technogenic impact, and the influence of natural factors (viral infections and fluctuations of population size) on the frequency of chromosome aberrations. In the northern mole vole Ellobius talpinus, neither the mutagenic effect of ionizing radiation nor interpopulation differences in the level of chromosome aberrations in the absence of anthropogenic impact were detected. Variation of genome instability of the rodents is significantly contributed to by species demography and population cycles.     

Chronic exposure to gamma radiation of wild populations of meadow voles (Microtus pennsylvanicus)

Free-ranging, wild meadow voles (Microtus pennsylvanicus) were exposed to gamma radiation from a (137)Cs irradiator in a series of experiments conducted on six 1-ha meadows within a mixed deciduous forest in Manitoba, Canada. Over a period of 1-1.5 years in each of three experiments, vole populations were monitored with capture-mark-release techniques at nominal exposure rates of 200x, 9000x and 40,000x background. No effects on population or individual characteristics were detected up to the highest exposure rate (81 mGy/d). At this level, third generation voles were monitored up to a lifetime dose of about 5.7 Gy, at a measured dose rate of 44 mGy/d. Smaller numbers of overwintered animals survived and reproduced normally at doses up to 10 Gy. These results are discussed in terms of low-LET, external chronic radiation effects on rodents in the laboratory and the field, relative to current views on appropriate benchmarks for the protection of biota.     

Relationships between developmental instability in morphological characters and fitness of <Emphasis Type="Italic">Aphis fabae</Emphasis> population reared on two host plants

Fluctuating asymmetry (FA) and the coefficient of within-environment variation (CV _e) are often used as measures of developmental instability and indicators of developmental deviations. Aphis fabae genotypes generally manifest higher developmental instability on novel host plants, but there is genotypic variability in this respect. Some genotypes have manifested lower developmental instability on nasturtium, where their fitness is higher. At the population level, aphids reared on nasturtium have shown higher developmental instability and lower fitness. When large samples are analyzed and the nonsignificant pattern of correlations is taken into account, the results of the study do not support the hypothesis that developmental instability is always a reliable indicator of fitness. Published in Russian in Ekologiya, 2007, Vol. 38, No. 2, pp. 131–136. The text was submitted by the authors in English.     

The ecology of the red fox (<Emphasis Type="Italic">Vulpes vulpes</Emphasis> L.) in the middle Lena River basin

The population of foxes in the central regions of Yakutia has grown by a factor of four to five during the period from 2000 to 2011–2012, following an increase in the abundance of voles from the genus Microtus. A total of 130 carcasses of foxes taken in 2007–2012 have been examined. Age- and sex-related variation in morphological features has been described. The demographic structure of the population has been studied by estimating animal age from annual layers in the recording structures. Changes in female fertility and involvement in reproduction depending on age and feeding conditions have been analyzed. Changes in the composition of fox diet caused by long-term population depression in the mountain hare and their effect on the dynamics of fox abundance have been revealed. Age- and sex-related characteristics of the condition factor in foxes and sex-related differences in their dietary preferences have been demonstrated.     

The Spatiotemporal Structure of Rodent Populations in the Steppe Zone of Western Siberia

The spatial structure of populations has been studied in two rodent species inhabiting the subzone of meadow steppes of the steppe zone of Omsk oblast: the narrow-sculled vole (Microtus gregalis Pall.) and steppe lemming (Lagurus lagurus Pall.). Their populations are represented by combinations of territorial family groups whose structure and spatial distribution vary by season depending on population density, the phase of the population cycle, and the status of their members in the population. In the areas cohabited by M. gregalis and L. lagurus, the pattern of territory use and the rhythm of animal activity during the day depend primarily on their total density: under conditions of low density, the population groups of both species are spatially separated; at increased density, they are distributed with respect to the pattern of daily activity. Both species jointly use part of the territory but at different times of day: M. gregalis, mainly at night and in the morning; L. lagurus, in the daytime.