Dynamics of morphophysiological charateristics 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 adipose tissue, 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 thyroxine level was significantly lower (16.2 ± 0.8 and 21.7 ± 1.4 pmol/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 lactation of offspring.     

Parasites and pathogens in wild populations of water voles (Arvicola amphibius) in the UK

The water vole (Arvicola amphibius) is Britain’s most endangered mammal, having gained protection under Schedule 5 of the Wildlife and Countryside Act in 2008. We present an overview of a range of naturally occurring pathogens and parasites in this rare species, which might negatively impact population persistence for small or declining populations. Wild water voles were live-captured in 2004 and 2006 from sites throughout the UK and were screened for a range of pathogens. These included: Puumala virus, Campylobacter spp., Escherichia coli, Salmonella enterica, Leptospira spp., Bartonella spp., Toxoplasma gondii, Giardia spp., Cryptosporidium spp., Babesia microti and Trypanosoma spp. E. coli was the most prevalent with 46/74 (62.2%; 95% CI, 51–73) individuals infected. One vole was co-infected with seven different pathogens whilst 20% of individuals were pathogen-free.     

Growth differences and dimorphic expression of growth hormone (GH) in female and male Cynoglossus semilaevis after male sexual maturation

Half-smooth tongue sole, Cynoglossus semilaevis, is an ideal model to investigate the regulatory mechanisms of sexual growth dimorphism in fish species. The aim of the study was to investigate the effect of differential age of sexual maturity for females and males on growth and GH mRNA expression in C. semilaevis. The body weight differences between the sexes were not significant in C. semilaevis at age 5 months when females and males were all immature. Significant differences in body weight between the sexes were found after early sexual maturation of males at the age of 9 months. The body weight of 21-month-old females (621.4 ± 86.4g), still not immature, was even 3.28 times higher than that of the males (189.7 ± 14.4g). The cDNAs encoding GH in C. semilaevis was cloned. The GH gene is 2924bp long and consists of six exons and five introns. The results of qRT-PCR showed that GH mRNA levels of the immature females were not significantly different from that of immature males at age 5 months. However, GH mRNA levels of the immature females were significantly higher compared with those of the mature males at age 9 months (P<0.05). At age 11 months, GH mRNA levels of females were even 6.4-fold higher than that of males. In conclusion, for the first time we show that early sexual maturity of males is the main cause of sexual growth dimorphism in C. semilaevis and exert significant effect on GH mRNA expression.     

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.     

Physical state of mother at the period of pregnancy and sexual maturation of descendants-sons of the water vole (<Emphasis Type="Italic">Arvicola terrestris</Emphasis> 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 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.     

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

A morphological study of forty-eight 3-4-day old embryos from eight females of the water vole (Arvicola terrestris L.) was carried out. The data obtained demonstrated that early embryonic losses in the water vole might be 30?C35%, and the main cause of these losses is anomalies of oogenesis.     

Effect of prenatal stress on the hypothalamo-hypophyseal-adrenal system activity and fat metabolism in the male water vole Arvicola terrestris

The HPA axis function and the fat metabolism were studied in adult male water voles born to intact mothers and mothers deprived of food on the 15th and 18th days of their pregnancy. The HPA response to emotional stress was relatively low in experimental males in winter. The hormonal response to a 24-hrs food deprivation diminished in experimental group only in February. The blood level of free fatty acids was increased in experimental group as compared to the control one. The short maternal food deprivation modified adaptive abilities of their male progeny.     

Agouti locus may influence reproduction under food deprivation in the water vole (Arvicola terrestris)

The effect of 16-hr food deprivation on day 3 and again on day 5 of pregnancy on the fecundity of female water voles homozygous (ae/ae) or heterozygous (A/ae) for, an allele at the Agouti (A) locus, non agouti extreme (ae) was studied. 63 A/ae females (mated to ae/ae males) produced 115 food-deprived and 115 control pregnancies, and 52 ae/ae females (mated to A/ae males) produced 55 food-deprived and 57 control pregnancies. Regardless of the experimental group, pregnant ae/ae females weighed less than A/ae females. The effect of food deprivation on fecundity depended on the Agouti-locus genotype of the female. In food-deprived A/ae females, fecundity was diminished due to fewer successful pregnancies (P < 0.001) and lower survival of the young (P < 0.05). In food-deprived ae/ae females, reproductive performance was not changed; a somewhat reduced rate of successful pregnancies was compensated for by significantly increased (P < 0.002) postnatal survival of the young. In progeny weaned from food-deprived mothers, the frequency of A/ae females was diminished. Resistance of ae/ae females to the negative effect of nutritional stress, and predominance of ae/ae young in progeny produced by food-deprived mothers, may favour the maintenance of polymorphism for the Agouti-locus in natural populations of the water vole.     

Polymorphism of the fur pigmentation genes and the hormonal adaptation system in the water vole (Arvicola terrestris)

Postnatal ontogenesis of hormonal system of hypophysis - adrenal glands and hormonal reaction under stress conditions were examined in adult water mouse, which had polymorphic fur color genes. Black females (genotype aa), opposite to brown ones, (genotype AA, Aa) had changed postnatal ontogenesis of adrenal glands function and they had not hormonal reaction to the two days water deprivation.     

Excreted urine,bladder urine,and the delay of sexual maturation in female house mice

A series of experiments tested effects of excreted and bladder urine of group- and singly-caged female house mice (Mus musculus) on sexual maturation of young female mice caged alone or in groups of eight. Puberty was determined by vaginal smears. A maturation-delaying pherompne was present in bladder urine of all female mice and excreted urine of group-caged females, but not in excreted urine from singly-caged females. Test mice treated with bladder urine homogenized with urethras from singly-caged females matured at the same age as controls. Apparently the urethras or associated glands of singly-caged females produce a substance which deactivates the maturation-delaying pheromone contained in bladder urine.     

Parasite fauna of the water vole (Arvicola terrestris) and its nests in the south of Western Siberia

Fauna of parasitic and free-living arthropods associated the water vole Arvicola terestris and its nests in various landscape zones and subzones of the south of Western Siberia has been studied. Total abundance of gamasid mites and ticks (Gamasoidea, Ixodidae), fleas and nidicolous arthropods in nests is high, and the set of nidicolous and parasite species is quite diverse, but everywhere the parasite fauna is characterized by a small amount of species reaching a high abundance: Laelaps muris on the voles, Haemogamasus ambulans in nests, Ixodes apronophorus and Megpbotris walkeri both on the voles and nests. Parasitic arthropods living on the voles or in their nests are characterized by higher and stables indices of infection, while these parameters for free-living arthropods were variable. The list of mesostigmatic mites parasitizing the water vole and its nests in the south of Western Siberia (Adamovich, Krylov, 2001) has been considerably supplemented. In total, the fauna of parsitiform mites (Acari: Mesostigmata and Ixodiddes) and fleas (Siphonaptera) associated with the water vole in the south of Western Siberia is represented by 97 arthropod species of 19 families, including 74 species of mesostigmatic mites (Gamasoidea), 6 species of ticks (Ixodidae) and 17 species of fleas.     

Social cues influence growth and sexual maturation of the male musk shrew (Suncus murinus)

Musk shrews were maintained from weaning (20 days of age) for 20 or 40 days in one of several social conditions. In Exp. 1, young males housed with adult females gained more weight and had heavier sex accessory organs than did young males housed with an adult male or reared alone. In Exp. 2 this same pattern of accelerated growth and sexual maturation was found when males were reared directly with an adult female or in a split cage where a wire barrier served to separate the male and his adult female cagemate. In Exp. 3, males were reared in cages containing clean or soiled bedding: soiled bedding was taken once every 5 days from the cage of an adult male, or a female. Under these conditions differences in the weights of reproductive tissues showed minimal variation with housing condition after 20 days of treatment. At that time males reared in soiled bedding taken from the cage of an adult female had accelerated development compared with control males. In Exp. 4, males were housed alone or in a split cage with an adult female which was separated by a wire mesh or a solid, opaque barrier. Males separated by a solid barrier from their female cagemates for 40 days had reproductive tissue weights equivalent to those measured in males reared alone. Taken together these results suggest that the presence of an adult female has dramatic effects on body growth and development of reproductive target tissues in young male musk shrews. Male-female social interactions could play an important role in the timing of puberty in this opportunistically breeding tropical mammal.     

Major histocompatibility complex (MHC) heterozygote superiority to natural multi-parasite infections in the water vole (Arvicola terrestris)

The fundamental role of the major histocompatibility complex (MHC) in immune recognition has led to a general consensus that the characteristically high levels of functional polymorphism at MHC genes is maintained by balancing selection operating through host–parasite coevolution. However, the actual mechanism by which selection operates is unclear. Two hypotheses have been proposed: overdominance (or heterozygote superiority) and negative frequency-dependent selection. Evidence for these hypotheses was evaluated by examining MHC–parasite relationships in an island population of water voles (Arvicola terrestris). Generalized linear mixed models were used to examine whether individual variation at an MHC class II DRB locus explained variation in the individual burdens of five different parasites. MHC genotype explained a significant amount of variation in the burden of gamasid mites, fleas (Megabothris walkeri) and nymphs of sheep ticks (Ixodes ricinus). Additionally, MHC heterozygotes were simultaneously co-infected by fewer parasite types than homozygotes. In each case where an MHC-dependent effect on parasite burden was resolved, the heterozygote genotype was associated with fewer parasites, and the heterozygote outperformed each homozygote in two of three cases, suggesting an overall superiority against parasitism for MHC heterozygote genotypes. This is the first demonstration of MHC heterozygote superiority against multiple parasites in a natural population, a mechanism that could help maintain high levels of functional MHC genetic diversity in natural populations.     

Influence of Reproductive Status: Home Range Size in Water Voles (Arvicola amphibius)

The relationship between home range and reproductive status of water voles (Arvicola amphibius) was studied by radio-tracking on an island off the coast of northern Norway in 2006–2009. The aim was to test assumptions about the species’ social structure relative to other microtines. Juveniles used fairly small ranges (about 400 m²), with no difference between males and females. Subadults, overwintered voles in April, had ranges similar to juveniles. Reproductively active males (mean 2774.0 m²) increased their range seven-fold relative to juvenile males, with ranges on average 3.3 times larger than adult females (mean 848.3 m²), which also expanded their range. Most litters were born in May and June, and as reproduction ceased in July adult males reduced their range whilst females did not. Body mass or year did not influence home range size. Overlap of home ranges varied, but could be extensive in both adult males and females. The water vole had a social structure similar to some Microtus species, but females appeared to be non-territorial and males perhaps conditioned territorial and non-territorial.     

Acceleration of sexual maturation in female rats by male stimulation.

In comparison to controls reared in isolation, female rats reared in the presence of an adult male from weaning attained puberty 5 days earlier when living in groups or almost 9 days earlier when living singly with a male. Accelerated sexual development occurred in the absence of accelerated physical growth.