Hereditary predisposition of water voles (Arvicola amphibius L.) to seizures in response to handling.

Finding out the hereditary predisposition to seizures in response to specif ic external stimuli is important for understanding the causes of epileptiform conditions, developing new methods for their prevention and therapies. In the water vole, individuals with convulsive seizures are found both in natural and laboratory conditions. The data of long-lasting maintenance and breeding of water voles in vivarium conditions were analyzed in order to establish a hereditary predisposition to convulsive seizures, and the inf luence of sex and age on their development. In the vivarium, seizures are provoked by handling and are observed in 2.4 % of voles caught in the natural population with cyclic f luctuations in abundance. Seizures are observed more often in individuals caught in the phases of decline and depression of abundance than in individuals caught in the phases of rise or peak. Convulsive states are probably an element of adaptive behavior formed in the predator-prey system. In natural conditions, individuals predisposed to convulsive seizures may have a selective advantage when under increasing pressure from predators. Convulsive seizures in response to handling were noted in 29.8 % of descendants of captive-bred water voles. The proportion of such individuals increased signif icantly if one or both parents had convulsive states, which indicates the presence of a hereditary predisposition to seizures. In parent-offspring pairs, a signif icant correlation was found between the average age of onset of the f irst seizures in parents and their offspring, r = 0.42, p <0.01. The minimum age of registration of seizures in the water vole is 39 days, the maximum is 1105 days, and the median is 274 days. Predisposition to seizures is not related to sex. Genes that control the occurrence of seizures have a pleiotropic effect on life span, since individuals with seizures live longer in vivarium conditions than individuals with a normal phenotype. The water vole can serve as a suitable model object for studying the nature of convulsive states and the evolution of longevity.

[Correlations of reproductive parameters of water vole females (Arvicola amphibius) with morphometric and hormonal characteristics].

Fluctuations in water vole population size depend on abiotic and intra-population factors affecting the physiological condition of females. The relationship between variability in reproductive success and morpho-physiological characteristics of female during pregnancy is studied quite poorly. In standard vivarium conditions, the morphometric and hormonal characteristics of female were assessed at different stages of pregnancy (first trimester--days 4-7, second trimester--days 8-14, third semester--days 15-20), and their relationship with potential and actual fecundity and the level of embryonic lethality was elucidated. The general regression model was used in the data analysis. Positive correlations were found between potential fecundity and the female body mass at mating, body mass index and blood testosterone level. The reproductive parameters under study were independent of the blood thyroxin level. A positive correlation was established between the level of embryonic loss and the indices of liver and lung functions. Liver and spleen are essential for the maintenance of the female body mass homeostasis during the reproductive period.

Effects of seasonal, ontogenetic, and genetic factors on lifespan of male and female progeny of Arvicola amphibius.

The water vole (Arvicola amphibius) in the forest-steppe of West Siberia is known to have wide fluctuations in abundance. These fluctuations are accompanied by changes in birth and death rates, sex-age structure of the population, and individual morphophysiological and behavioral characteristics of the animals. Survival of the animals depends on season, phase of population cycle, and sex. Based on the data of long-term captive breeding of water voles, the maximal lifespan of males was found to be 1188 days and that of females, 1108 days. There were no differences between the sexes in mean lifespan. The probability of living 2 years or longer was 0.21. Individuals who began breeding at an older age had a significantly longer lifespan and produced more offspring. The survival curves of the spring-born animals were steeper than of those summer-/autumn-born. Maternal factors had a differential effect on males and females with respect to lifespan. Male lifespan correlated negatively with maternal age, parity, and litter size, whereas female lifespan did not correlate with these characteristics. To estimate heritability, parent-offspring correlations of lifespan were calculated, as well as full-sib intraclass correlations. No statistically significant correlation was found for lifespan between sons and mothers, sons and fathers, and daughters and fathers. Daughters' lifespan correlated positively with maternal lifespan (r = 0.21, p < 0.001). Female full-sibs and male full-sibs had the same intraclass correlations, 0.22, p < 0.001.

[Dynamics of morphophysiological characteristics 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 fat, 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 thyroxin level was significantly lower (16.2 +/- 0.8 and 21.7 +/- 1.4 pmpl/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 breeding of offspring.

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

A morphological study of forty-eight 3-4-day embryos from eight females of the water vole (Arvicola terrestris L.) was conducted. The data obtained demonstrated that early embryonic losses in the water vole can be 30-35%, and the main cause of these losses is anomalies of oogenesis.

[Protein content in urine of male and female water vole (Arvicola amphibious) at the period of spring growth and sexual maturation].

The study was carried out on the captive bread water voles Arvicola amphibious kept in vivarium. At the first decade of January, March, and June, the body length and anogenital distance were measured, the body mass was determined, and urine was collected for determination of its protein content. The obtained results have shown that the protein content depends on sex of the animals and is connected with the reproductive status of males and their dimension-weight characteristics. The urinary protein excretion level in females remained stable at different months, whereas in males its sharp rise was noted at the period of spring growth and sexual maturation. The significant sexual differences were established in March and enhanced in June. In March the urine protein content in males was noted to correlate positively with the body mass and length and with the anogenital distance. The males reached sexual maturity at the earlier calendar terms than the females did; in sexually mature males the urine protein content was significantly higher than in the sexually immature ones.

[Physical state of mother at the period of pregnancy and sexual maturation of descendants-sons of the water vole (Arvicola terrestris L.)].

The role of characteristics of the maternal medium (the mother's physical state at periods of pregnancy and lactation, calendar terms of birth, the number of pups, and the ratio of sexes in the litter) has been elucidated in regulation of growth and the sexual maturation of the water vole male pups. The anogenital distance was used as an indirect supravital evaluation of the mass of testicles. The physical state of females was estimated by a change of the body mass at the period of pregnancy or lactation with aid of parameters characterizing deviation of the female body mass after the end of each reproductive cycle stage from the calculated value found from the empirical regression equation. Sons of the females whose body mass increment for the period of pregnancy exceeded the expected value or was equal to it were growing faster. Results of regression analysis have shown that the the anogenital distance in the 19-week old males is dependent statistically significantly only on the physical state of the mother at the period of their embryonic development.

[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.

[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.

[Genetic-ecology monitoring of cycling populations of water voles (Arvicola terrestris L.) in the south of Western Siberia]. / Genetiko-ékologicheskii monitoring tsikliruiushchei populiatsii vodianoi polevki (Arvicola terrestris L.) na ioge Zapadnoi Sibiri.

Long-term studies on the role of the structural and functional organization of a population in reproduction control showed that the optimum level of reproduction is maintained via a complex of ethological, physiological, and genetic mechanisms. The coat color genes have a pleiotropic effect on the reproductive capacity of females and the potential for social dominance in males. The relative reproductive success of brown water voles is greater when the population size increases, whereas dark-brown individuals gain the advantage at peaks of population size. At the peak followed by a decrease in abundance, dark brown males usually held higher social ranks in the experimental groups. The results of field and laboratory experiments showed that high-ranking males gain reproductive advantage. Changes in the genetic structure in the course of population cycle depend on relative differences in fitness demonstrated by animals of different coat color under conditions of changing population size. The fact that females actively choose their mates is important for differentiation of males with respect to their adaptive value, prevention of inbreeding, and the maintenance of heterogeneity of populations as the basis of their stability.