The role of neighborhood relations in maintenance of the spatial-ethological structure of local settlements as exemplified by the water vole (Arvicola amphibius).

Adult males of the water vole have been found experimentally to recognize their neighbors and react to them differently depending on the degree of spatial proximity in nature. Most tensions (estimated by the number of aggressive acts in the encounters) were observed between distant neighbors (from neighboring settlements), which did not belong to the same groups with established hierarchy and a relatively reduced aggression. These are probably perceived as the most likely competitors (because of their spatial proximity). At the same time, male voles kept away from the obviously unfamiliar ones, though they do not express any apparent aggression.

Dynamics of testosterone concentration in male steppe lemmings (Lagurus lagurus) in the reproductive cycle reflects the species-specific mating system.

In the blood of male steppe lemmings, relatively low background levels of testosterone were detected, this is characteristic of a monogamous species. A significant increase in testosterone level, more expressed in sexually active males, was observed at the initial stage of formation of reproductive couples. Apparently, in the future, the couple will exist in a stable relationship, and, hence, the maintenance of a high testosterone level becomes excessive. The decrease in, and the relative "normalization" of, the hormone level during the existence of the pair, including raising of the young, promotes higher expression of the male paternal care of the offspring at the species level.

[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.

[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.

[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.

[Immune system and behavioural strategies of reproduction under parasitic pressure]. / Immunnaia sistema i realizatsiia povedencheskikh strategii razmnozheniia pri parazitarnykh pressakh.

Since both reproduction and immunocompetence are costly, the negative reciprocal relationships between function were found in many species. Due to reproductive immunosuppression, some fraction of seasonally breeding populations of small mammals reproduces in the first breeding season, while others reproduce in the next one. Enhancement of breeding efforts under the increased risk of mortality and the reproductive delay until recovery are the polar variants of mating behavior of parasitized individuals. However the parasite-induced changes of odor, visual or acoustic signals limit the mating success of the infected hosts. The direct influence of the immune system, regularly activated by infections, to chemicals signals can be answer to the question: why these signals are honest? Decrease in strange infection risk by kin breeding can be a satisfactory strategy of an isolated population. Nevertheless, many species follow the inbreeding avoidance strategy, where the major histocompatibility complex (MHC) genes play key role in kin recognition. The advantage of MHC heterozygosity was found at the all steps of the breeding cycle; including mating choice, fertilization, pre- and postnatal development. So, the relationships between immune system and neuroendocrine regulation of behavior give proximal explanations of the evolutionary stable strategies of breeding behavior.

Influence of genetic dissimilarity of mother and fetus on progesterone concentrations in pregnant mice and adaptive features of offspring.

Concentrations of progesterone in blood plasma and tissue were studied in pregnant mice of strains BALB/cLac and C57BL/6J. Both intra- and interstrain mating and embryo transplantations were used as models of homo- and heterotopic pregnancy. On day 4 of heterotopic pregnancy, plasma progesterone concentrations of females of both strains were higher than those in females of both strains undergoing homotopic pregnancy. In addition, tissue progesterone content of hybrid embryos was higher than that of purebred embryos. Adrenocortical responses to social conflict as indicators of stress resistance were studied in progeny aged 2-3 months. There was a minimal increase in plasma glucocorticoid concentrations in heterotopic transplantants after 15 min pair-matching tests and 30 min crowding compared with those of other progeny, including purebred male mice of BALB/cLac and C57BL/6J strains, homotransplantants and reciprocal hybrids. Thus, genetic dissimilarity of mother and fetuses plays an important role in progesterone provision during pregnancy and also modifies development of progeny.

[Genetic-physiologic mother-fetus relationships and their effect on the adaptive traits of the offspring]. / Genetiko-fiziologicheskie vzaimootnosheniia mat'-plod i ikh vliianie na adaptivnye priznaki potomkov.

Using our own data and literature, we present analysis of genetic-physiological mechanisms providing for stable reproduction of mammals. Using multiparous species (such as minks, mice, water voles), we demonstrate that embryonic and early postnatal mortality of the offspring makes a significant contribution to stabilization of the actual fertility rate at a level optimal for the species. Studies of phenogenetics of fertility of inbred mice and their hybrids have demonstrated the definitive role of immunogenetic relationships between mother and fetuses in establishing of vitally important characteristics of the offspring. Antigenic differences between mother and fetuses observed in crosses between different strains and in experiments on allogenic transplantation of embryos provide stimulate the hormonal support of pregnancy (increase the level of progesterone) and the rate of embryonic development. It has been shown that antigenic stimulation of mother's immune system has a modifying effect on physiological and behavioral characteristics of the offspring and specifically on certain components of their reproductive success. In studies of the olfactory choice of mating partners by mouse and water vole females we established that mammals are capable of "predicting" the optimal phenotypic combination of parents leading to the most effective development of the offspring.

[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.