N. S. Poplavskaya

Genetic structure of urban population of the common hamster (Cricetus cricetus)

Over the past half-century, the common hamster (Cricetus cricetus), along with range-wide decline of natural populations, has actively populated the cities. The study of the genetic structure of urban populations of common hamster may shed light on features of the habitation of this species in urban landscapes. This article is focused on the genetic structure of common hamster populations in Simferopol (Crimea), one of the largest known urban populations of this species. On the basis of the analysis of nucleotide sequences of the cytochrome b gene and mtDNA control region, and the allelic composition of ten microsatellite loci of nDNA, we revealed that, despite the fact that some individuals can move throughout the city at considerable distances, the entire population of the city is represented by separate demes confined to different areas. These demes are characterized by a high degree of the genetic isolation and reduced genetic diversity compared to that found for the city as a whole.

Superspecies Complex Cricetulus barabensis sensu lato: Karyotype Divergence and Interrelation in Natural Contact Zones

Three different chromosomal forms of striped hamsters that belong to the superspecies complex Cricetulus barabensis sensu lato (Cricetidae, Rodentia), namely, “barabensis”, “pseudogeiseus”, and “griseus”, were studied to determine their relationships based on different biological and genetic species concepts and using the morphological, karyomorphs, molecular, and hybridization data. The results of craniometry suggest that differences between these karyotypes are rather of subspecies level. Cytogenetic differences also proved to be insignificant and correspond to the level of chromosomal races within a single species. An analysis of cytochrome b mitochondrial gene (cytb) differences of about 2.3–4.1% between the forms studied, which suggest intraspecific distinctions or those between allied species. Hybridization experiments, which produced various litters from mating between three karyomorphs, also confirmed both male and female fertility. In nature, there are several zones where contact is possible between the “barabensis” and “pseudogeiseus” karyomorphs. In one of these zones, in Central Mongolia, atypical karyotypes were found in two male specimens using chromosomal analysis. Taking into account the chromosome number and shape, this karyotype could be attributed to a hybrid between the second and subsequent generations. However, typing the cytb gene and intron localized to Y chromosome (DBY1) did not reveal any traces of recent or ancient hybridization. In another zone, in South Buryatia, where the contact could be expected between the karyomorphs studied, the “barabensis” and “pseudogeiseus” populations are separated by the Chikoi River and the distance between them does not exceed 5 km. Nevertheless, neither karyological nor molecular analysis detected any hamsters with nonstandard karyotypes or any traces of gene flow. An analysis of the entire cytb nucleotide sequence, as well as the Tajima’s test, the distribution of pairwise differences, and the level of nucleotide diversity suggest that both contact zones have formed long ago; the absence of gene flow cannot be explained by their recent formation. Thus, the evolutionary formation of each of the three karyomorphs that were the subject of our study appears to be independent.

Sporadic disorders in the meiotic prophase I in Cricetulus barabensis hybrids (Cricetidae, Rodentia) do not lead to reproductive isolation between karyomorphs

Electron microscopy analysis of the synaptonemal complex was carried out for the first time in Cricetulus barabensis pseudogriseus, fertile F1 hybrids of C. b. pseudogriseus × C. b. griseus, C. b. griseus × C. b. barabensis, and back-cross hybrids C. b. pseudogriseus × (F1 C. b. pseudogriseus × C. b. griseus). Meiotic disturbances were identified in the nuclei of single hybrid spermatocytes, including atypical synapsis, associations of autosomes with a sex bivalent, and sex body formation errors. Our study confirms the results of the molecular genetic and craniometric analysis of these forms. Despite the geographical segregation, three chromosomal forms of Cricetulus barabensis complex do not establish reliable cytogenetic barriers.

New data on the distribution of chromosomal races in the supraspecies complex Cricetulus barabensis sensu lato (Rodentia, Cricetidae) and analysis of reproductive barriers among them

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.

Microsatellite loci variation and investigation of gene flow between two karyoforms of Cricetulus barabensis sensu lato (Rodentia, Cricetidae)

We examine the diversity of six microsatellite loci and partial RAG1 exon of “barabensis” and “pseudogriseus” karyoforms in Cricetulus barabensis sensu lato species complex. A total of 435 specimens from 68 localities ranging from Altai to the Far East are investigated. The results of the population structure analysis (factor analysis and NJ tree based on Nei genetic distances) support subdivision into two well-differentiated clusters corresponding to the two karyoforms. These karyoforms are also well differentiated by the level of microsatellite variability. In several “barabensis” specimens, we found microsatellite alleles that are common in “pseudogriseus” populations but are otherwise absent in “barabensis.” Most of these specimens originate from a single population in one of the zones of potential contact between karyoforms, Kharkhorin in Central Mongolia. These molecular results are consistent with previously published karyological data in suggesting that rare hybridization events between the two chromosomal races occur in nature.

Phylogeographic structure of the Common hamster (Cricetus cricetus L.): Late Pleistocene connections between Caucasus and Western European populations

The Common hamster (Cricetus cricetus) is one of the most endangered mammals in Western and Central Europe. Its genetic diversity in Russia and Kazakhstan was investigated for the first time. The analysis of sequences of an mtDNA control region and cytochrome b gene revealed at least three phylogenetic lineages. Most of the species range (approximately 3 million km2), including central Russia, Crimea, the Ural region, and northern Kazakhstan), is inhabited by a single, well-supported phylogroup, E0. Phylogroup E1, previously reported from southeastern Poland and western Ukraine, was first described from Russia (Bryansk Province). E0 and E1 are sister lineages but both are monophyletic and separated by considerable genetic distance. Hamsters inhabiting Ciscaucasia represent a separate, distant phylogenetic lineage, named “Caucasus”. It is sister to the North phylogroup from Western Europe and the contemporary phylogeography for this species is discussed considering new data. These data enabled us to develop a new hypothesis to propose that in the Late Pleistocene, the continuous range of the Common hamster in the northern Mediterranean extended from the central and southern parts of modern France to the Caucasus; however, its distribution was subsequently interrupted, likely because of climate change.

Karyotype Evolution and Phylogenetic Relationships of Cricetulus sokolovi Orlov et Malygin 1988 (Cricetidae, Rodentia) Inferred from Chromosomal Painting and Molecular Data

Sokolovs dwarf hamster (Cricetulus sokolovi) is the least studied representative of the striped hamsters (Cricetulus barabensis species group), the taxonomy of which remains controversial. The species was described based on chromosome morphology, but neither the details of the karyotype nor the phylogenetic relationships with other Cricetulus are known. In the present study, the karyotype of C. sokolovi was examined using cross-species chromosome painting. Molecular and cytogenetic data were employed to determine the phylogenetic position of Sokolovs hamster and to analyze the potential pathways of chromosome evolution in Cricetulus. Both the chromosome and molecular data support the species status of Sokolovs hamster. Phylogenetic analysis of the CYTB data placed C. sokolovi as sister to all other striped hamsters (sequence divergence of 8.1%). FISH data revealed that the karyotype of C. sokolovi is highly rearranged, with the most parsimonious scenario of its origin implying at least 4 robertsonian events and a centromere shift. Comparative cytogenetic data on Cricetinae suggest that their evolutionary history includes both periods of chromosomal conservatism and episodes of rapid chromosomal change.

Synurbization of the common hamster ( Cricetus cricetus L., 1758)

The common hamster (Cricetus cricetus L., 1758) historically formed an extensive range covering much of Europe and Asia. However, in the last 50 years almost throughout the whole range, its number in natural habitats and agrocenoses dropped sharply. At the same time, the common hamster began to settle cities, which could be considered as a biological invasion. Now urban populations are found in Vienna (Austria) and several cities of Germany, the Czech Republic, Slovakia, Poland, and Russia. By example of Simferopol, where the largest urban population exists, we show what resources the species can use in the city and what changes in the ecology and behavior follow this. It is suggested that the major factors promoting the settling of cities by the common hamster are additional environmental resources associated with the specifics of the urban environment: the emergence of new shelters, food sources, etc. We assume that ecological opportunism, polyphagy, and high stress resistance could be crucial for the ability to settle urban environments.

Is the Center of Origin of Long-tailed Hamster Cricetulus longicaudatus Milne-Edwards 1867 (Rodentia, Cricetidae) Located in Tibet?

First data on morphological and mitochondrial variation in the long-tailed hamster Cricetulus longicaudatus is presented. In contrast to genetically monomorphic populations of Mongolia and Tuva, the northeastern part of the Qinghai–Tibetian Plateau was found to harbor several divergent mtDNA lineages. This pattern suggests a recent expansion of the long-tailed hamster to the northern part of its recent range, which started from Tibet, presumably, in the late Middle Pleistocene. Several populations from the northern edge of the species range were found to be morphologically but not genetically distinct. The apparent disagreement between genetic and morphological data can be explained by rapid morphological evolution in peripheral isolates.