The polymorphism of the gene cytochrome b (cytb) fragment of mitochondrial DNA (mtDNA) and the migratory activity of red-backed voles (Myodes rutilus Pallas, 1779) were first investigated in a zone of local radioactive contamination, the Eastern Urals radioactive trace zone (EURT). The results suggest high haplotype diversity in both samples from the EURT zone and the adjacent territory (9–10 km) compared with the reference one (220 km). The nucleotide diversity and mean number of paired differences between haplotypes proved to be the greatest in voles from the adjacent site with the radiation level corresponding to the background values. Our assumption about the association of genetic diversity with rodent migrations from the EURT zone was verified in field experiments employing group marking of the population with the biomarker rhodamine B. Migrants (males and females) of different functional status were revealed at background sites. Long-distance movement of 9500 m is the maximum known for M. rutilus. The EURT zone is a source of genetic diversity in rodent populations in adjacent territories due to interpopulation gene flow patterns (transmission by migrants of the radiation-induced effects). MtDNA can serve as an effective biomarker of radionuclide exposure in the natural environment. Combined usage of ecological and molecular biomarkers is advisable for monitoring in rodents from zones of local radionuclide contamination.

First time in the East Urals radioactive trace zone (EURT) (Chelyabinsk region, Southern Urals) small mammals from natural population with rhodamine B (RB) label, received in last year were revealed. The aim of this study was to estimate long-distance movements (LDM) of small mammals during the autumn–winter season by method of group marking with bait containing RB. One-time ingestion of bait with RB ensures systemic marking, which fixed in keratin-containing structures (hairs, claws, vibrissae). Retention time of RB-label for wood mouse (Sylvaemus uralensis Pallas, 1811) was 338 days, for common shrew (Sorex araneus Linnaeus, 1758) – 312 days, for red-backed vole (Myodes rutilus Pallas, 1779) – 251 days. It has allowed for the first time to estimate LDM of wintering individuals during autumn–winter season from EURT zone to adjacent territories and vice versa. It was found that S. uralensis are able to settle within 10800 m, M. rutilus – 9500 m, S. araneus – 9300 m. These data are the maximum recorded distance for these species. There is a predominance of females both among wintering settled animals and distant migrants. Probably LDM of females is evolutionary more favorable to population as they serve as the potential reserve of a genetic variety. LDM provides spatial and functional connectivity of mouse-sized mammal’s populations and possibility of genetic information exchange between population groupings on both the impact and background territories. The technique of group marking with bait containing RB has shown the efficiency at research of spatial structure of small mammals during the autumn-winter period. It is advisable to include it in monitoring system in areas of local technogenic pollution as well as to use it to calibrate samples of animals in the study of remote effects of radiating and other toxic effects.

Using the method of group biomarking with rhodamine B, new data on migratory patterns (natal dispersal and breeding dispersal) of the pygmy wood mouse ( Sylvaemus uralensis (Pallas 1811)) outside its home range were obtained by studying the long-distance locomotion of small mammals on the Eastern Urals Radiation Reserve (Chelyabinsk region, Southern Urals). Long-distance locomotion (1500 m) over 14 hours in the dark part of the day was registered for two yearling males for the first time, allowing for the possible speed of movement of S. uralensis to be estimated. Taking into account that the main activities of rodents occur during evening and morning twilight, the actual time could be considerably shorter. Both dispersers were under-yearling males of different functional status. One of them was a young animal captured during spring reproduction (May 2019) in the year of birth. The other male was young, captured before leaving in winter (October 2021) and not reproducing in the year of birth. Group biomarking by rhodamine B made it possible to estimate the night-time distance and the speed of movement of S. uralensis , also allowing an episode of external contamination by the biomarkers of transient specimens (October 2021) that visited the marking plot, but that did not touch the bait, to be revealed. Our results allow us to conclude that long-distance locomotion of individuals of different functional statuses beyond the home area is normal in S. uralensis.

New information on the distribution of the yellow-necked mouse (Apodemus flavicollis Melchior, 1834) to the east is presented. For the first time (since 1975) the species was recorded in the northern part of the Ilmenskii Reserve (Chelyabinsk oblast, Southern Urals). The main conformational and craniometric characteristics of individuals are presented. Regular monitoring studies suggest that the invasion A. flavicollis in the aboriginal biotic community occurred no earlier than the winter–spring period and no later than June 2020. The likelihood of an anthropogenic influence in the conditions of the reserve regime is practically excluded. We believe that climate change (global warming) is a possible cause of the invasion. The place where the yellow-necked mouse was found in the Ilmenskii Nature Reserve (55°17′04.6′′ N, 60°14′45.1′′ E) is the easternmost point of the modern range of the species.

The productivity of the combined use of the method of morphophysiological indicators (MMPI) and functional-ontogenetic approach in population studies is shown based on the example of analysis of the phenomenon of splenomegaly (SM) in rodents. A solution of the problem of analysis of spleen with a giant variation range is proposed, namely, to analyze the spleen index separately for normal spleen and spleen with SM. It is shown that there is no morphophysiological peculiarity in individuals with different functional statuses in the studied states. It is established that SM does not significantly influence the processes of animal vital activity. The maximum proportion of animals with SM was recorded in reproducing groups, which is due to a high intensity of metabolic processes. It is proved that SM is infectious in the study area. Feral herd infection agents are identified and the mechanism of SM development is considered. The criteria for the correspondence of organs to morphophysiological indicators, as well as the use of spleen as an ecological indicator, are substantiated. All the obtained materials suggest the adaptation of the studied bank vole population to a long-term effect of the infectious factor, which was historically formed in the process of the long-term coevolution of the parasite-host system.

In 2010 (a year of drought), the true winter breeding (TWB) of the pygmy wood mouse (S. uralensis) was first recorded in the Southern Urals and confirmed by the morphological parameters and age markers. The young born in winter fulfilled successfully their reproductive potential under favorable climatic conditions. The true winter breeding and the age cross of animals during the year of drought promoted the maximum population growth and enhanced population genetic heterogeneity. In subsequent years, TWB of S. uralensis became common, which is regarded as a climatic pattern. Extreme drought rearranged the rodent community and caused TWB of S. uralensis, which resulted in a higher abundance of the species.

Migrations of rodents in the zone of local radioactive contamination (East Urals Radioactive Trace, Southern Urals) at different phases of population dynamics are analyzed for the first time. The absence of any isolation of the rodents in the zone of this radioactive trace is convincingly demonstrated and the migration distances are estimated. As is shown, migration decreases the probability for transfer and fixation of adaptations in the chain of generations in vagile rodent species and increases the within-population genetic diversity of animals in adjacent regions. The need to consider the migration factor in a wide range of studies on assessment of biological effects in the zones of local technogenic contamination is confirmed.

Adaptive strategies of cyclomorphic rodent populations (Rodentia) under extreme conditions of droughts (in 1975 and 2010) have been analyzed on the basis of functional–ontogenetic approach. The following features of these strategies have been revealed: minimization of metabolic processes, block of sexual maturation, intergenerational crossing, prolongation of breeding period, and species-specific features in the dynamics of intrapopulation processes. Profound changes in the level of long-term oscillations of abundance after the drought have been noted in different species. Evidence is provided for the possibility of extremely rapid population rearrangements on an evolutionary scale that are fixed in a series of generations.

The variability of four microsatellite loci of rodents, caught from the head part of Eastern Urals Radioactive Trace (EURT), along with the rodents inhabiting contiguous zone with background radiation level and distant reference territory, was analyzed for the first time. Differences in the parameters of genetic diversity between northern red-backed voles from the EURT zone and from the reference population were detected. An increase in some indices of genetic diversity in animals from a contiguous to the EURT zone was found; this is probably associated with animal migration and configuration of the area of pollution. A transfer of radiation-induced effects to the contiguous territories and a decrease in the possibility of fixation of adaptations in a series of generations of mobile rodent species in the area of local radioactive pollution are consequences of migrations. The results of the study make it possible to recommend microsatellite markers for the analysis of radiation-induced effects in rodents as model objects of radioecological monitoring.

The role of polyalternativeness of small mammals' ontogeny development (belongings of individuals to alternative pathways of the ontogeny development) in the estimation of effects of ionizing radiation is considered. It is shown that biological consequences of acute (laboratory experiment) and chronic (inhabiting the Eastern Urals Radioactive Trace zone) ionizing radiation in rodents significantly depend on the belonging of individuals to the pathway of ontogeny. Specificity of the response of the population to acute and chronic irradiation is revealed. It is concluded that it is necessary to take into account the belonging of individuals to the pathway of ontogeny development in a wide spectrum of investigations at the analysis of any biological parameters in small rodents in the zones of local technogenic contamination.