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.

The Common hamster (Cricetus cricetus) is the rodent with one of the largest range (6 million km 2). There were four phylogenetic lineages earlier recovered in Western Europe, Ukraine and Bryansk Province of Russia: "North", "Рannonia", E1 and E0. E1 was previously reported from SouthEastern Poland and Western Ukraine and never been found in sympatry with "Pannonia" although the closest distance between them was estimated as 20 km. The question is whether the sympatry of E1 and E0 phylogroups exists? Special survey was arranged across Moscow, Tula, Bryansk, Oryol, Kursk, Voronezh and Lipetsk provinces to get the answer. Sequence analysis of the mtDNA control region and the cyt b gene from the tissue samples was carried out in the common hamsters captured in these areas and their belonging to a certain phylogroup was determined. For the first time a case of sympatry was revealed-in the city of Mtsensk vicinity (Oryol province). Here we discovered hamsters the both lineages-E0 and E1 at the same habitat. Hypothetically E1/E0 ranges boundary runs from Ukrainian Sumy province to NorthEast by line dividing the Russian Kursk and Oryol provinces. The existence of subclades within both E1 and E0 phylogroups suggests that diversification of phylogenetic lineages of the Common hamster in Eastern Europe may result from not single but multiple climatic events during the second half of Late Pleistocene. The phylogeographic structure of the species in Eastern Europe may be more complex than it currently known.

Traditionally, urbanization has been seen as a negative phenomenon for biota. However, changes in the environmental parameters induced by urbanization might be favorable for some species. Over the past half‐century, the common hamster has actively populated cities, establishing populations in some European, Russian and Kazakhstan cities. Based on integrative methods, we investigated free‐range common hamsters inhabiting Simferopol from 2015 to 2018 to reveal possible adaptations to the urbanized environment across several parameters, including lifespan, hibernation period, reproductive activity and body mass. Results show that in urban areas, the common hamster demonstrates an extremely short hibernation period compared to other localities, possibly due to enhanced food resources from urban forestry (walnuts, locus and hazelnut), allowing the species to start breeding very early (February) and finish as late as October. We present the first evidence of polyandry for this species: mating of receptive females with several males and subsequent confirmation of multiple paternity. Despite high reproductive potential, the lifespan of the common hamster in urban conditions is generally very short (less than 1 year). We speculate that in the process of synurbization, the common hamster's innate plasticity across many life history traits permits it to successfully colonize throughout a wide range of habitats, with the ability to form novel adaptations to urban environments.

Based on our analysis of long-term (2015–2021) observations carried out at a registration spot in the park named after Yu. A. Gagarin (Simferopol, Crimea), patterns were revealed in the spatial distribution of burrows of the Common hamster (Cricetus cricetus L., 1758) depending on the state of the tree and shrub layer, as well as disturbance factors. It is shown that the leading factor influencing the spatial distribution of burrows is the location of trees, and the total number of burrows is mainly affected by the projective covering by shrubs; these factors were revealed as a result of cluster analysis for the spatial-geographical formulation of the problem and crosscorrelation analysis. It is assumed that the use of spatial modeling makes it possible to identify environmental factors, including plant communities, influencing the choice and exploitation of microhabitats by animals, as well as to find approaches to the analysis of the implementation of behavioral patterns during the development and exploitation of a habitat.