A review of studies on the chromosome sets of Palaearctic mammals carried out by Russian karyologists and an important contribution to improving the taxonomy of mammals were made for the first time. For many mammal species, the process of speciation was associated with variability in the number and morphology of the chromosomes; therefore, the karyotypes are often used as diagnostic peculiarities of morphologically similar cryptic species (sibling species). The prospects for cytogenetic studies in the field of speciation (particularly, an enhancement of reproductive isolation, initiated by chromosomal rearrangements, by selection) are discussed.

This paper is a revision of the original description of the karyotype of the sable Martes zibellina. It presents data on the mitotic metaphase chromosomes of the female and male of this species and a comparison of their sets with those of closely allied species in the genus Martes. Additionally, a description of the synaptonemal complex (SC) is provided in the early to middle prophase of meiosis in the sable spermatocytes. Comparative analysis confirmed the stability and similarity of the main cytogenetic parameters of sables and martens (2n = 38, NFa = 64–68, X is the average submetacentric and Y is the smallest meta-, submeta-, or acrocentrics). A slight polymorphism associated with the representation of one- or two-armed small elements of the diploid set of chromosomes is revealed. These characteristics are of little use for the development of the intraspecific taxonomy of the sable, but can be useful in determining phylogenetic relationships at the species and generic levels, as well as to identify the consequences of natural hybridization of allied species in the genus Martes.

A review of original and published data on invasions of sibling species of Microtus from the group "arvalis" (East European vole, M. rossiaemeridionalis; common vole, M. arvalis; and Altai vole, M. obscurus) is given. Two stages of invasions differing in duration are established. These stages defined the formation of the modern ranges of these species and had an influence on evolutionary processes. The first stage is connected with agricultural development of Eurasia from the early Neolithic to the broad plowing of lands in the second half of the 20th century. Northern expansion of the range following the deforestation for plowing uses and southern expansion as a result of irrigation of arable lands are peculiar to all three sibling species. The second stage is due to expansion of the transport network and growth of traffic in the 20th century. The latter is characteristic of M. rossiaemeridionalis. The natural and historical reasons for the formation a contact zone between M. arvalis and M. obscurus are reconstructed. Original maps of the modern distribution of sibling Microtus species of the "arvalis" group, as well as natural and historical factors that influenced the formation of their ranges, are provided.

Results of the analysis of IRBP (interphotoreceptor retinoid-binding protein) nuclear DNA gene variability in birch mice of the genus Sicista reflect monophyly of the betulina group and confirm the substantial genetic isolation of the sibling species S. betulina and S. strandi within this group. Using Tamura’s 3‑parameter model T92, it is shown that the mean genetic distances between S. betulina and S. strandi are 0.7%, comparable to the interspecific genetic distances for sibling species from other groups of birch mice. Their intraspecific differentiation, which is particularly well-expressed in S. strandi, is also identified. Differentiation between the northern and southern populations of S. strandi, comparable to the interspecific differences (D = 0.8%), and isolation of the Carpathian specimen of S. betulina from other European and Siberian sample sets (D = 0.2%) are shown.

Abstract—Chromosomal (routine, C-banding) and molecular (mitochondrial cytb gene sequencing) data for Sicista of the betulina group from the northern (Valdai National Park), central (the main watershed of East European Plain), and southeastern (Upper Volga Basin) parts of Valdai and, for comparison, from the Moscow and Central Chernozem regions are presented and generalized. The affiliation of birch mice from Valdai and the Moscow area to the 32-chromosomal S. betulina, and that from the Central Chernozem area to S. strandi (2n = 44) were confirmed. Birch mice were collected in various biotopes: specimens from Valdai National Park were caught in coniferous forests with nemoral covering, other selections of S. betulina were caught in mixed forests, and S. strandi were caught in a forest–steppe. Priority chromosomal (C-banding) and molecular (cytb) data indicating the originality of the S. betulina population from Valdai National Park, which are different by the studied genetic traits from other samples of the species from Valdai and the Moscow area and from S. strandi, were obtained. Evolutionary and ecological aspects of the results were discussed.

A new protocol for the identification of two sibling species of voles Microtus arvalis and M. rossiaemeridionalis was proposed by electrophoresis of blood proteins in polyacrylamide gel (PAGE). Animals captured in ten districts of Moscow, Kaluga, and Samara oblasts and Moscow natural territories (1030 individuals), as well as those taken from vivarium collections (five hybrids of the two species), were studied. A comparison of electrophoresis in PAGE, agarose gel, and cellulose acetate plates was carried out. The use of different organs and tissues for species identification was assessed. The relative electrophoretic mobility and the mass of a species-specific blood protein of the southern vole were determined.

We studied the relative growth rate of seedlings and aboveground and underground organs, as well as functional traits of leaves and absorbing roots in the invasive species Heracleum sosnowskyi and congeneric native species H. sibiricum. The plants were grown in laboratory conditions and the functional plant traits of 21- and 35-day-old seedlings were analyzed. The relative growth rate (RGR) of H. sosnowskyi differed from that of H. sibiricum by 2.5 times, but the growth of plants in height and in area of leaves was similar. Plant biomass and total leaf area were twice as high in 35-day-old seedlings of invasive species. Structural features of the leaves in 35-day-old H. sosnowskyi seedlings were a lower leaf thickness and a higher leaf density. The invasive species had a lower root mass ratio, but the roots were more branched with a greater ratio of absorbing roots and a better development of the root hairs. As a result, H. sosnowskyi had a higher growth rate of absorbing roots (by 2 times) and a larger absorbing surface in relation to the total root surface. We concluded that the structural and functional traits of the leaves and roots provided a 2 times higher net assimilation rate (NAR) and 2.5 times larger RGR in the invasive species H. sosnowskyi.

Karyotypes of 29 specimens of Microtus oeconomus from nine localities of its Holarctic area in Eastern Europe (Novgorod, Nizhny Novgorod, Kaluga, Moscow and Ryazan regions) were investigated using methods of differential staining of chromosomes (G-, AgNOR-banding). In Valdai district of Novgorod region, at the edge of the main massif of this species range in the Western Palaearctic, a polymorphic population (2n = 31, n = 2; 2n = 30, n = 6) was revealed. This polymorphic population is similar to that from isolates in Fennoscandia, but differs from the studied by the authors karyologically stable populations (2n = 30) in central parts of Eastern Europe (Nizhny Novgorod (n = 14), Kaluga (n = 1), Moscow (n = 3), Ryazan (n = 3) regions), as well as from the majority of other stable populations from Lapland to Alaska (2n = 30) investigated earlier. Using G-banding, the nature of the chromosomal rearrangement revealed in the M. oeconomus population at the edge of the main part of this species range in the Western Palaearctic (the centric fission of chromosome pair No 8 registered only in the heterozygotic state unlike isolated populations from Fennoscandia) was specified. In the Valdai Upland, in the peripheral root vole populations, as well as in the isolated populations in Fennoscandia, NOR-bearing pairs (AgNOR-banding) were shown not to participate in the formation and maintenance of the chromosomal polymorphism found. The revealed chromosomal polymorphism, which is responsible for the features of the population-genetic structure of this species, does not agree with the traditional view on the M. oeconomus intraspecific system. The obtained and generalized data on the stability and variability of the M. oeconomus karyotype in Eastern Europe that specify the mechanism and limits of distribution of the found chromosomal mutation in the species range are considered in the light of historical reconstructions, although some other hypotheses (the hypothesis of genome instability on the periphery of species area and the mutagen hypothesis) are also attracted to discuss the results.

Оценено влияние двустороннего цитотоксического удаления малоизученной каудальной части гиппокампа ( 30 его полного объема) на обучение рыжих полевок Clethrionomys (Myodes) glareolus в водном тесте Морриса. Использована версия теста, предназначенная для оценки долговременной пространственной памяти. Показано, что удаление влияет на динамику обучения, замедляя его, а также снижает на ранних этапах обучения точность запоминания местоположения платформы. Полученные данные свидетельствуют об участии этой области в контроле пространственного обучения грызунов.

The involvement of the caudal hippocampus in spatial learning is presently uncertain, compared to the well established role of the dorsal region. Therefore voles (Clethrionomys glareolus) with large (about 1/3 of the whole hippocampus) caudal cytotoxic lesions were tested in the Morris water maze. A version of the test intended to measure long term spatial memory was used. The lesion inhibited the learning process, as well as reducing the accuracy of platform location memory at early stages of training. The data obtained indicate the involvement of this area in control of spatial learning in rodents.

Molecular markers of cryptic cytogenetical differentiation were shown in chromosomal polymorphic Pan-European model group of rodents Microtus arvalis s. l. by FISH analysis. The polytypy of 46-chromosomes karyotypes determined by the sites of interstitial telomeric sequences (ITS) and ribosomal DNA emphasizes the genetical isolation of M. arvalis s. s. and M. obscurus.

The taxonomy of striped hamsters from the supraspecies complex Cricetulus barabensis sensu lato (Rodentia, Cricetidae) is still controversial. The morphological and genetic differences between them are insufficient. In laboratory hybridization experiments, we obtained F1 and F2 hybrids from different combinations of mating between three chromosomal races. We found no evidence of reduced viability and fertility in the hybrids. In order to specify the distribution and detect natural hybridization, we analyzed the chromosomes of animals from potentially contacting populations of “barabensis” and “pseudogriseus” in southern Buryatia and central Mongolia. Two specimens with an abnormal karyotype were found in the “barabensis” population from the vicinity of Kharkhorin (central Mongolia), which can be considered as a result of distant hybridization. Karyological analysis of the hamster populations in southern Buryatia revealed parapatricity of the two chromosomal races, but regular hybridization between them was not found. In general, our data suggest that there is no intensive genetic interchange between the two chromosomal races.