[Fluctuating asymmetry of craniometric characters in rodents (Mammalia: Rodentia): interspecific and interpopulational comparisons].

Ontogenetic instability was studied in four rodent species (Ellobius talpinus, Microtus arvalis, M. rossiaemeridionalis, Mus musculus). It was measured by fluctuating asymmetry (FA) of 21 craniometric characters. Each species was represented by two populations differing in average level of chromosomic instability and in degree of anthropogenic influence. Relation between FA and individual age was observed in none of the studied species. The level of cranial structure FA in rodents is probably formed during embryogeny or early postnatal ontogeny and is not changing significantly during the further development. The studied species showed distinct differences in the degree of ontogenetic instability of the axial skull, but not of the mandible. No connection was found between craniometric character FA and technogenic stress. The differences of cranial FA level among the studied species of rodents agree with their systematic position and the sequence of their evolutionary divergence.

[Factors of maintaining chromosome polymorphism in common vole Microtus arvalis Pallas, 1779: reduced fertility and meiotic drive].

The common vole Microtus arvalis (the form obscurus) exhibits polymorphism of a pericentric inversion in chromosome pair 5 throughout the species range. In the Urals populations, the frequency of an acrocentric variant of the heteromorphic chromosome is very low (on average 3.2%) and virtually does not change annually. The factors of maintaining stable chromosomal polymorphism in the common vole were studied under conditions of a laboratory colony. Heterozygous and homozygous for the acrocentric chromosome females showed a significant reduction of the reproductive output irrespective of the male karyotype. This effect was manifested mostly in litter size at birth. A number of cytogenetic and exophenotypic characteristics, as well as parent--offspring transmission of this chromosome in crosses of various types, were examined. We have found meiotic drive in favor of the acrocentric, as a result of which the frequency of the acrocentric (without taking into account the postnatal mortality) totaled over all cross variants (0.48) was significantly higher than that expected with random segregation (0.42). It is likely that meiotic drive of the acrocentric largely compensates for the reduced fertility of its carriers, being among the factors of maintaining it in natural populations.

Chromatid gaps as a marker of mutagenic effect of environmental pollution in commensal and wild rodents of the Ural mountains.

It was supposed earlier that achromatic gaps could be used as markers of mutagenic effect of environmental pollution, especially under weaker clastogenic influences. The frequencies of true chromosome aberrations and those of chromatid gaps were estimated in house mice and common voles from Uralian localities with various mutagenic potential of environment. Gaps and breaks were distinguished according to the CBIS system. In several localities, rodents displayed highly significant increase of the rates of cells with chromosome aberrations and with gaps as compared to the baseline values; only in the common vole, the P level for the gap increase was 0.056. The mean gap rate was correlated significantly with that of chromosome aberrations, not only with chromatid breaks, but with the aberrations of other types, too. This parameter appears not to be more sensitive indicator of environmental mutagens than true chromosome mutations, when mutagenic impact is not very powerful, as it was in the localities investigated. The house mouse can be recommended as an effective test species for ecogenetic monitoring.

[Chromosomal instability in rodents from the EURT territory: interspecies comparison]. / Khromosomnaia nestabil'nost' u gryzunov s territorii Vursa: mezhvidovye sravneniia.

The common vole (Microtus arvalis) and the mole vole (Ellobius talpinus) were trapped in the Eastern Urals Reserve (initial soil pollution 500-1000 Ci/km2) where many dozens of generations came to pass after the 1957 accident in the plant "Mayak" and in the Middle and South Urals and Transurals localities with global level of the 90Sr pollution. At present the average internal dose rate from 90Sr was 0.413 mGy/day in M. arvalis and 0.985 mGy/day in E. talpinus. The total accumulated doses from external and internal sources were 0.4-0.5 Gy per year. Frequencies of cell with chromosome aberrations and gaps and rates of aneuploidy and polyploidy were analyzed. In the common vole from EURT, the frequency of aberrant cells was significantly higher (4.57%) than in three control populations (0.44-0.86%). In the mole vole, all the cytogenetic parameters did not exceed the control ones. Absence of the genomic response in E. talpinus could be caused by the protective activity of melanin-related metabolites or by heritable factors, which may have arisen as a result of mutagenic pressure and have spread in the population in question both by selection and genetic drift, due to considerable isolation of local demes of E. talpinus.

[Chromosomal and ontogenetic instability in sibling species of common vole (Microtus arvalis group): comparative aspects]. / Khromosomnaia i ontogeneticheskaia nestabil'nost' u vidov-dvoinikov obyknovennoi polevki (gruppa Microtus arvalis): sravnitel'nye aspekty.

Populations of chromosomal sibling species Microtus arvalis and Microtus rossiaemeridionalis were studied in Ural region in habitats affected by high radiation and the control ones. Frequency of chromosome disturbances in the marrow cells and fluctuating asymmetry (FA) of 8 craniometric characters were investigated. In impact populations the frequency of chromosome aberration was very high. Such frequency was also maintained in the offspring of the first laboratory generation of M. arvalis. In natural and control populations of both species frequently occurred individuals with anomalies in sex chromosome. Individuals of M. rossiaemeridionalis from Totsky radioactive region (forest-steppe zone) were characterized by very high integrative FA in comparison with control populations (southern taiga). At the same time neighboring impact and control populations of M. arvalis from southern taiga did not differ in this character. Despite the high level of caryotype divergence M. arvalis and M. rossiaemeridionalis showed similarity in mutation process that causes chromosome disturbances in somatic and germinative cells. Probably the level of FA of measured characters in both species is connected rather with geographical location than with man influence.

[Viral infectious and chromosome aberrations in Bank Vole from natural and laboratory populations]. / Virusnye infektsii i khromosomnye narusheniia u Ryzhei polevki iz prirodnykh i laboratornykh populiatsii.

The frequency of chromosome damage was studied in the carriers of virus of the hemorrhagic fever with renal syndrome (Puumala virus) and in noninfected animals from two laboratory colonies and two natural populations of bank vole. In the laboratory colony, where Puumala virus persisted for three years, multiaberrant ("rogue") cells were found in the bone marrow; the mean frequencies of both structural and numeral chromosome abnormalities were significantly enhanced. In the other laboratory colony, no Puumala virus was detected during all 30 years of its existence, but the mean frequencies of structural chromosome damage were increased to the same degree probably due to the prolonged breeding under laboratory conditions, which resulted in suppression of immunity and DNA repair. The voles from the natural populations were more resistant to the clastogenic viral effect, but they also had multiaberrant cells which served as indicators of viral infection. The data obtained support the hypothesis that viral infections increase mutation rate, contributing thereby to the evolution process.

[Chromosomal instability in offspring of voles in unfavorable radiation zones]. / Khromosomnaia nestabil'nost' u potomkov polevok iz zony radiatsionnogo neblagopoluchiia.

A high frequency of cells having chromosomal aberrations was shown to be preserved in the first generation of laboratory offspring of common voles, whose ancestors were captured near the East Ural radioactive track (EURT). In F2 and F3, a decrease in frequency was observed. Most likely, the cytogenetic effects observed were caused by environmental contamination with plutonium in the locality of capture. An increased chromosomal instability observed in the first laboratory generation of nonirradiated common voles was caused by reversible modifications in the expression of mutator genes inherited from parents exposed to alpha-irradiation rather than by classic mutations occurred in specific loci.

[Hereditary chromosome instability in the common vole (Microtus arvalis) from the region of the Kyshtym nuclear accident--fact or hypothesis?]. / Nasleduemaia khromosomnaia nestabil'nost' u obyknovennoi polevki (Microtus arvalis) iz raiona Kyshtymskoi iadrenoi avarii--fakt ili gipoteza?

In bone marrow cells of common voles living within the Eastern Urals radioactive track (EURT) and adjacent area, the frequency of chromosomal aberrations was higher than in cells of control animals. In several animals, the proportion of aberrant cells was significantly higher; cells with multiple chromosomal lesions prevailed among the aberrant cells. Frequency of chromosomal aberrations did not depend on the absorbed dose of beta-radiation. Taking into account the radiation background in trapping sites, the level of cytogenetic damage in the animals studies should be considered unexpectedly high. Outside the EURT, two voles with mutant karyotypes were caught. It was hypothesized that carriers of hereditary chromosome instability appeared in the population studies as a result of exposure to ionizing radiation.

The HSR chromosome 1 in the house mouse, Mus musculus, from regions of the Urals polluted by mutagens.

The incidence of the HSR chromosome 1 was examined in Mus musculus musculus from 12 localities of the Middle and South Urals and Northwestern Siberia. The HSR chromosome was found in 7 localities, its frequency varying from 5 up to 18%. The HSR incidence was shown to correlate with the mean pooled frequency of aneuploidy and polyploidy in bone marrow, but not with the mean proportion of cells carrying structural chromosome aberrations. In mice heterozygous for HSR the rate of aneuploidy and polyploidy was significantly higher than in animals with standard karyotype, on average by a factor 2.35. HSRs tend to be more abundant in localities adjacent to sites of radiation incidents with contamination mainly by 90Sr.

Chromosomal speciation and folliculogenesis in the semisterile interspecific hybrids of the varying lemmings, genus Dicrostonyx.

Karyotypes of Dicrostonyx torquatus torquatus and D. vinogradovi that are very similar phenotypically differ at least by 13-14 chromosomal rearrangements including centric and tandem fusions, fissions and paracentric inversion. In their male hybrid F1 spermatogenesis is arrested on early pre-meiotic stages, the female hybrids are semisterile. Histological investigation of ovaries has demonstrated reduced number of follicles, higher percentage of atretic follicles and an acceleration of folliculogenesis in hybrids as compared with the parental forms. As a result of the acceleration, the number of mature follicles and ovulations is not significantly diminished in the hybrid females, and their semisterility is caused, to a great extent, by high prenatal loss which most likely arises from the chromosomal imbalance in F2 hybrids. Thus, the mechanism suggested by the concept of chromosomal speciation is active, but not alone in forming reproductive isolation between twin species of the varying lemming.