Myotis petax is a common and widespread Asian bat species, whose intraspecific sequence variability remains poorly understood. In this work we analyzed the variability of the mitochondrial control region and craniometric measurements for an extensive sample set originating from the entire species range. This made it possible to identify the main genetic lineages and to compare their distribution with the morphological groups. From our investigations, we found that the prevalent genetic lineages, namely, "Siberia," "Amur," and "Okhotsk," appear to be connected to large river systems. The cohabitation of various genetic lineages occurs only in territories where different river basins are connected, such as the Primorsky Territory, Khabarovsk Territory, Transbaikalia Territory, and Mongolia. Moreover, we discovered that the five morphological groups (Siberia, Okhotsk, Amur, Kunashir, and Korea) are partially correlated with previously identified genetic lineages and subspecies. However, M. p. petax and M. p. loukashkini were the only two out of the five subspecies that could be well-defined using specific mtDNA sequences and morphological descriptions. Nonetheless, the subspecies M. p. ussuriensis does not have a distinct genetic lineage to allow for their classification. Notably, a specific mix of morphological group and a genetic lineage characterize the "Amurian morphological form," which may support its validity as a subspecies rank. That notwithstanding, more information is needed to fully unravel the intraspecific structure of M. petax in the southern Far East and potential contact zones of diverse forms.

For the first time in Russia, the intraspecific structure of the brown rat Rattus norvegicus was studied using the mitochondrial control region (D-loop) as a molecular marker. The mtDNA sequence was determined in brown rats from eight regions of European and Asian Russia. Three rat clades were identified, including one in European Russia and two in Asian Russia. The synanthropic subspecies R. n. norvegicus was found to have two, European and Asian, lineages. The European lineage included haplotypes from central and southern regions of Russia, and the Asian lineage included haplotypes from Eastern Siberia and the Russian Far East. The exoanthropic subspecies R. n. caraco from the Russian Far East formed a separate genetic lineage.

Genetic structure of the Maximowicz’s vole Alexandromys maximowiczii was assessed using data on the mtDNA control region variability, and the high level of genetic variability was revealed for the species as a whole. Three phylogenetic groups (“east,” “west,” and “south”) were distinguished, and within the “east” group, three subclades (“Chit,” “Amur,” and “Khab”) were identified. All phylogenetic groups and subclades were characterized by mainly allopatric geographical distribution across the species range with one “hybrid” sampling found in the vicinity of the settlement of Savvo-Borzya (Zabaykalsky krai), the individuals of which had different variants of the mt genotype. One individual carried the “west” variant, and the second one—the “east”/“Amur” variant. The revealed phylogeographic structure was generally congruent with the differentiation pattern as revealed by the chromosomal forms, but did not agree with the previously accepted subspecies system. Complex intraspecific subdivision of the Maximowicz’s vole, revealed at different organization levels (molecular genetic, as well as chromosomal), reflects not only complex geography of the study area, but also the history of dynamic changes in the natural environment.

For the first time in Russia, a study of the intraspecific structure of the brown rat (Rattus norvegicus) was carried out using the mitochondrial marker of the control region (D-loop) of mtDNA. MtDNA sequences of brown rats from 8 regions of the European and Asian parts of Russia were analyzed. Three clades of rats have been identified: in the European part of Russia –1, in the Asian part – 2. Synanthropic subspecies – R. n. norvegicus is represented by european and asian lineages. The european lineage included haplotypes from the regions of central and southern Russia, and the Asian lineage included haplotypes from Eastern Siberia and the Far East. The previously described free living subspecies, R. n. caraco from the Russian Far East was represented as separate genetic lineage.

Alexandromys evoronensis is the endemic vole of the Russian Far East. The range of the species is still unclear. Previously, this species was found in two intermontane areas of the Khabarovsk Krai and one area of the Amur Oblast. We recorded this species in a new location in August 2021 and August 2022. It is a small intermountain area of the western spurs of the Bureinsky Range, in the Tyrma River valley, Khabarovsk Krai (50°01'17.55''N, 132°03'02.60''E). A total of eight Evoron voles were caught here. Karyotyping of one female (2n = 36) revealed a similarity with the karyotype of the Argi chromosomal race of the A. evoronensis. New records of the voles in the Tyrma River valley expand the range of Evoron vole and indicate more southerly habitats than previously stated.

Variability in the number and morphotypes of macro, mini, and micro B chromosomes of Apodemus peninsulae in the valley Zeya River from Amur oblast is described. Micro B chromosomes were found in the karyotypes of the Korean field mice from the Far East of Russia for the first time. Two opposite trends in the geographic variability of B chromosome morphotypes have been identified. The first one is caused by the presence/absence of mini and/or micro, in addition to macro B chromosomes, in animals from the right and left river banks in the northeastern part of the Upper Zeya Plain, as well as in the northern part of the Amur–Zeya Plain. The second trend is clinal variability characterized by a gradual increase in three combined geographic populations of A. peninsulae of numerical parameters of B chromosomes: index x̄В Max micro, x̄В Max macro, the number of morphotypes, the number of clones in mosaics, and the proportion of mosaics in the direction from north to south of the Zeya River Valley. The revealed diversity of A. peninsulae B chromosome morphotypes for 13 regions allows us to re-evaluate the geographical variability of additional chromosomes of this species in the Russian Far East. Adaptive value of B chromosome morphotypes for the species has been also assumed.

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.

As a result of analysis of the control region of mtDNA for the Evoron vole, a high haplotype (97%) and nucleotide (1.53%) diversity was found. The data obtained indicate a low level of genetic differentiation of populations. At the same time, populations geographically located closer are subdivided more strongly than remote ones. In general, there is agreement between the data on the variability of the mitochondrial DNA control region and chromosome races. However, if the data of chromosomal analysis indicate the preservation of the more ancient variants of the karyotype in the Evoron-Chukchagir Lowland (“ evoron ” chromosomal race), then the data of molecular genetic analysis testify in favor of the preservation of the most ancient mt haplotype (106-19) in the population of the Upper Bureya Depression (argi race).

The genetic structure of the reed vole ( Alexandromys fortis (Büchner 1889)) from the northern periphery of its distribution area was studied using the variability of the mtDNA control region. A high haplotype and nucleotide diversity has been shown in the northern part of the species range. The diversity is due to the presence of two lineages that form phylogenetic subclades within the NORTH lineage on dendrograms. The MAIN haplotypes have a wide geographic distribution. Basically, the distribution of the ISL haplotypes is confined to the islands of the Rimsky-Korsakov Archipelago (Bolshoy Pelis and Matveev) in the Sea of Japan and in the Barguzin Depression in Buryatia. They are also found in mainland populations, albeit with low frequencies, only in the south of the Russian Far East. The ISL haplotypes are noted to be close to those previously identified based on fossil material from cave deposits in the south of Primorsky Krai. Several alternative hypotheses concerning the ways of the formation of such a phylogeographic structure are considered. Small areas with local favorable environmental features are suggested to have persisted at the northern periphery of the reed vole distribution, where the species could have survived the Pleistocene and retained the ISL haplotypes that might have appeared earlier than the MAIN haplotypes. Those local areas can be considered as microrefugia, which could have played important roles in maintaining the high genetic diversity of the species in the southern part of the Russian Far East. Secondary colonization events by individuals with the MAIN haplotypes could have occurred already after the completion of the climatic minimum and the wide expansion of the species to the north from a southern macrorefugium. The existence of two macrorefugia, in which two subclades, MAIN and ISL, were formed, followed by random fixations of rarer ISL haplotypes in small isolated populations, is also hypothesized.

The large Japanese field mouse (Apodemus speciosus) is endemic to the Japanese islands and Kunashir Island in Russia. Variability in the morphology of 722 molars was studied for the first time for the population of this species from Kunashir Island, which allowed us to identify seven new traits for the species. According to data obtained when studying modern and paleontological material (recent, Holocene, Late Pleistocene, Middle Pleistocene), mice of Kunashir Island lack some traits of molars previously described for the large Japanese field mouse from Honshu Island; at the same time, stabilization of the morphology was noted for the remaining traits. Varying frequency was demonstrated for the new traits. This can be caused either by the small number of founders or the passage of the Kunashir population through sharp declines in numbers. It is possible that a change in the frequency of some molar phenes in different historical epochs could be associated with the transition of mice to another type of feed following changes in the climate and the prevailing vegetation.

Closely related mammalian species often have differences in chromosome number and morphology, but there is still a debate about how these differences relate to reproductive isolation. To study the role of chromosome rearrangements in speciation, we used the gray voles in the Alexandromys genus as a model. These voles have a high level of chromosome polymorphism and substantial karyotypic divergence. We investigated testis histology and meiotic chromosome behavior in the captive-bred colonies of Alexandromys maximowiczii, Alexandromys mujanensis, two chromosome races of Alexandromys evoronensis, and their interracial and interspecies hybrids, to explore the relationship between karyotypic differences and male hybrid sterility. We found that the seminiferous tubules of the males of the parental species and the interracial hybrids, which were simple heterozygotes for one or more chromosome rearrangements, contained germ cells at all stages of spermatogenesis, indicating their potential fertility. Their meiotic cells displayed orderly chromosome synapsis and recombination. In contrast, all interspecies male hybrids, which were complex heterozygotes for a series of chromosome rearrangements, showed signs of complete sterility. Their spermatogenesis was mainly arrested at the zygotene- or pachytene-like stages due to the formation of complex multivalent chains, which caused extended chromosome asynapsis. The asynapsis led to the silencing of unsynapsed chromatin. We suggest that chromosome asynapsis is the main cause of meiotic arrest and male sterility in the interspecies hybrids of East Asian voles.

—In an intermontane kettle in the southwestern spurs of the Bureinskii Mountain Range, in the Bureya River basin, the Ussuri white-toothed shrew has been recorded for the first time. This locality lies north of the previously supposed species distribution range in the southern part of the Russian Far East. Study of the female karyotype has allowed us to describe the morphology of the chromosomes of Crocidura lasiura (2 n = 40, NF = 54). The karyotype differs from the earlier published information (2 n = 40, NF = 56) in the number of subtelocentric autosomes. The data obtained expand the northern range limit of the Ussuri white-toothed shrew and show variability in the number of chromosome arms (NFa = 50, 52).

On September 6, 2022, Aleksey Nikolaevich Tuyrin, the founder and permanent executive secretary of the scientific peer-reviewed journal Biota and Environment of Natural Areas, passed away at the age of 72. During period 1976–2020 he worked at the National Scientific Center of Marine Biology, and then at the Federal Scientific Center of the Far East Asia Terrestrial Biodiversity, Far Eastern Branch of the Russian Academy of Sciences. Aleksey Nikolaevich devoted his whole life to conservation of the unique nature of Primorsky Krai. All of us, members of the journal’s editorial board, will remember him with gratitude and continue his life’s work.

The Chinese hamster (Cricetulus griseus) and striped hamster (Cricetulus barabensis) are very closely related species with similar karyotypes. The karyotypes differ from each other by one Robertsonian rearrangement and X-chromosome morphology. The level of the tandem repeat (TR) sequences’ evolutional variability is high. The aim of the current work was to trace the TR distribution on the chromosomes of two very closely related species. The striped hamster genome has not yet been sequenced. We classified the Chinese hamster TR in the assemblies available and then compared the mode of the TR distribution in closely related species. Chinese and striped hamsters are separate species due to the relative species specificity of Chinese hamster TR and prominent differences in the TR distribution in both species. The TR variation observed within homologous striped hamster chromosomes is caused by a lack of inbreeding in natural populations. The set of TR tested could be used to examine the CHO lines’ instability that has been observed in heterochromatic regions.

An assessment of polymorphism and the level of differentiation in insular and mainland populations of the field mouse was carried out. Specimens of four islands in the Peter the Great Bay of the Sea of Japan and four regions on the mainland of the of the Russian Far East South were tested. Nuclear markers of 5 microsatellite loci were studied. The results demonstrate higher allelic diversity in the mainland part of the range, with a significantly higher level of differentiation in the insular part of the range.

The mtDNA control region variability of Microtus rossiaemeridionalis (Rodentia, Arvicolini) from two invasive populations of the Russian Far East was studied. The results demonstrated a lower genetic diversity in the East European vole population from Sovetskaya Gavan than in the population from the city of Khabarovsk. Wright’s F statistic did not reveal any heterogeneity in the samples from these populations. It was suggested that the discovered haplotypes belong to the EU subclade of the European lineage.

The vole Alexandromys evoronensis (Kovalskaya et Sokolov, 1980) with its two chromosomal races, "Evoron" (2n = 38-41, NF = 54-59) and "Argi" (2n = 34, 36, 37, NF = 51-56) is the endemic vole found in the Russian Far East. For the "Argi" chromosomal race, individuals from two isolated populations in mountain regions were investigated here for the first time using GTG-, GTC-, NOR methods. In the area under study, 8 new karyotype variants have been registered. The karyotype with 2n = 34 has a rare tandem fusion of three autosomes: two biarmed (Mev6 and Mev7) and one acrocentric (Mev14) to form a large biarmed chromosome (Mev6/7/14), all of which reveal a heterozygous state. For A. evoronensis, the variation in the number of chromosomes exceeded the known estimate of 2n = 34, 36 and amounted to 2n = 34, 36, 38-41. The combination of all the variations of chromosomes for the species made it possible to describe 20 variants of the A. evoronensis karyotype, with 11 chromosomes being involved in multiple structural rearrangements. In the "Evoron" chromosomal race 4 chromosomes (Mev1, Mev4, Mev17, and Mev18) and in the "Argi" chromosomal race 9 chromosomes (Mev6, Mev7, Mev14, Mev13, Mev11, Mev15, Mev17, Mev18, and Mev19) were observed. Tandem and Robertsonian rearrangements (Mev17/18 and Mev17.18) were revealed in both chromosomal races "Evoron" and "Argi".