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The dynamics of the number and genetic structure of populations is one of the leading factors determining the success of the existence of populations in time and space. Based on observations (changes in numbers) and molecular genetic analysis data (CR and cyt b), the dynamics of the demographic and genetic structure of the populations of russet (Spermophilus major Pall.) and speckled (S. suslicus Güld.) ground squirrels in the sympatry zone were studied. A similar cyclical nature of the temporal dynamics of the genetic structure of populations in both sympatric species is shown.In the russet ground squirrel, a more ecologically plastic species and prone to migratory activity, population genetic processes occur on a large scale.The explosive demographic situation associated with the passage of populations through the “bottleneck” state is one of the factors leading to interspecific hybridization.

Background. The study of the zone contacts of species, namely hybrid zones and sympatry zones, is an urgent task of evolutionary biology and modern zoology. Long-term monitoring of changes in the spatial and genetic structure of sympatry zones with parallel study of morphological, phenotypic and bioacoustic features of the hybrid population makes it possible to find out the mechanisms and consequences of the process of random interspecific hybridization. The purpose of the work is to monitor the state of the sympatry zone of Speckled and Russet Ground squirrels in the Volga region at the points of contact of the species and to identify interspecific hybrids in contact colonies by a complex of molecular genetic markers, by color indicators and by parameters of acoustic signals. Materials and methods. On the territory of Ulyanovsk region 9 colonies were surveyed: 6 combined colonies with specific separation on microstations, 3 mixed colonies without separation. In contact colonies, it was captured and marked 24 individuals of both species and possible interspecific hybrids. Molecular genetic analysis was conducted on 5 markers (D-loop, Hoxb5, р53, ZfX, SmcY) for determination of individuals’ origin. Sound signals and color indicators of 11 large, 11 speckled ground squirrels and 5 presumed interspecific hybrids were analyzed. Statistical analysis of obtained data were perform in STATISTICA 10.0. Results. A study of the sympatry zone of the large and speckled ground squirrel on the territory of the Ulyanovsk region showed that as of 2023, only 5 (out of 10 in 2019) contact colonies remained. In the colony “Kargino” for the first time during the entire period of monitoring work, a female with a genotype indicating her origin as a result of direct crossing of a female S. major (m) and a male S. suslicus was captured. Intermediate inheritance of traits of parental species by hybrids of russet and speckled ground squirrels, which appeared as a result of random hybridization in the sympatry zone, is shown. Conclusions. By 2023, a depressive situation had developed in the sympatry zone of the russet and speckled ground squirrels, which led to the emergence of random interspecific hybridization at the points of contact of species. Monitoring studies of long-term contact colonies of this pair of sympatric species should be considered promising and potentially effective for the tasks of studying the hybridization of ground squirrels of the Volga region.

Simple Summary: The role of hybridization in biological evolution and cases of hybridogenic speciation is one of the most complicated but also interesting and actively studied topics. Russet ground squirrel Spermophilus major is known as a fine biological species according to a number of criteria—morphological, ecological, and behavioral, respectively. Nevertheless, a large body of evidence has accumulated on the hybridization of S. major with four neighboring Spermophilus species. Our goal was to identify their contribution to the nuclear and mitochondrial genome of S. major, and to propose a hypothesis describing the hybridization history in space and time. We found that 36% of S. major individuals had extraneous alleles, and every contacting species contributed to S. major's genetic variability. Our data suggested at least five independent hybridization events that were associated with shifts in the species ranges due to paleoclimate changes. Two of them were potentially accompanied by mitochondrial captures with replacement of the mitochondrial genome of one of the hybridizing species. We highlight the potential threat to the existence of S. major as a species under the current conditions of population decline along with the simultaneous influx of extraneous genes. It is also particularly important to emphasize the necessity of protecting this inhabitant of unique steppe communities. Among the numerous described cases of hybridization in mammals, the most intriguing are (a) cases of introgressive hybridization deeply affecting the evolutionary history of species, and (b) models involving not a pair of species but a multi-species complex. Therefore, the hybridization history of the russet ground squirrel Spermophilus major, whose range has repeatedly changed due to climatic fluctuations and now borders the ranges of four related species, is of great interest. The main aims of this study were to determine the direction and intensity of gene introgression, the spatial depth of the infiltration of extraneous genes into the S. major range, and to refine the hypothesis of the hybridogenic replacement of mitochondrial genomes in the studied group. Using phylogenetic analysis of the variability of mitochondrial (CR, cytb) and nuclear (SmcY, BGN, PRKCI, c-myc, i6p53) markers, we determined the contribution of neighboring species to the S. major genome. We showed that 36% of S. major individuals had extraneous alleles. All peripheral species that were in contact with S. major contributed towards its genetic variability. We also proposed a hypothesis for the sequence and localization of serial hybridization events. Our assessment of the S. major genome implications of introgression highlights the importance of implementing conservation measures to protect this species. [ABSTRACT FROM AUTHOR]

Russet ground squirrel (Spermophilus major) is a widespread species with an extended range, partly separated by the Ural Ridge into eastern and western parts. Previously, a hybridization of the russet ground squirrel in contact areas with five other Spermophilus species, accompanied by a wide introgression of their mitochondrial genomes, was found. In the present work, a comparative analysis of the variability of the mtDNA control region of S. major was for the first time carried out throughout the range of the species (without taking into account introgressed haplotypes). It was demonstrated that species-specific haplotypes of S. major are distributed in all parts of its modern area and are characterized by a low level of intraspecific variability. The phylogeographic structure of the russet ground squirrel is slightly differentiated and does not form distinct geographically localized phyletic lines. In general, the range of the species is a single genetic space slightly separated by the Ural Mountains. The spatial distribution of haplotypes indicates the presence of an exchange between the western and eastern parts of the area in the Middle Urals. The indices of genetic diversity are evidence in favor of the expansive type of an increase in the population number, possible expansion of the range from the eastern part in the western direction, and short-term contacts of Cis-Ural and Trans-Ural northern populations. The results of the analysis of S. major genetic variability do not support the accepted subspecies system. [ABSTRACT FROM AUTHOR]

Background. Studies of hybrid zones and animal populations of hybrids in space and time is an actual problem of evolution biology and zoology. Using of molecular markers and bioacoustics in study of hybrid zones and populations helps to reveal not only hybrid origin of individual but also its destiny in population. Goals of work were to study modern distribution and sympatry zone’s state of Speckled and Russet Ground squirrels in Volga Region and to reveal interspecific hybrids in contact colonies basing on complex of molecular markers and parameters of acoustic signals. Materials and methods. On the territory of Ulyanovsk region 72 colonies were surveyed, including 35 colonies of Russet Ground Squirrel, 27 colonies of Speckled Ground Squirrel, 6 combined colonies with specific separation on microstations, 3 mixed colonies without separation and 1 former hybrid colony in Chuvashiya. In a contact colonies (n = 9) 217 samples were collected. Molecular genetic analysis was conducted on 5 markers (D-loop, Hoxb5, р53, ZfX, SmcY) for determination of individuals’ origin. Bioacoustics analysis was based on records of warning signals, processed in *WAV-format with 48 kHz discretization frequency and 16-bit depth. Frequency and interval parameters were obtain with Avisoft-Sonograph software. 148 signals of adult Russet (n = 11, 71 signals) and Speckled Ground squirrels (n = 11, 61 signals) and possible interspecific hybrids (n = 3, 19 signals) were processed. Statistical analysis of obtained data were perform in STATISTICA 10.0. Results. Modern state of Russet and Speckled Ground squirrels’ zone of sympatry quantitatively and structurally differs from previous. Among 72 observed colonies 62 (86 %) are monospecific (S. major – 35, 48,5 %; S. suslicus – 27, 37,5 %) and only 10 are contact (14 %). Genetic structure analysis of 10 modern contact colonies showed that in 6 combined colonies only individuals of contact species were revealed. Unlike of those in 3 mixed colonies hybrids were registered. Stepwise discriminant analysis of acoustic signals’ parameters united in three groups (Russet (n = 11, 69 signals) and Speckled (n = 11, 56 signals) Ground squirrels and their hybrids (n = 3, 18 signals)) revealed intermediate type of inheritance of parental acoustic signs by hybrids. Conclusions. Definite relation between composition and individuals’ number of contact colonies and facts of hybrids foundation in them was revealed. When individuals’ number is depressed or even one of parental species totally absent share of hybrids can reach 75 %. When number of both species is high and there is no separation on microstations hybrids in such colonies were found very rare and probably were result of sporadic hybridization.

The formation of the alarm call's time–frequency characteristics at different stages of individual development was studied on the russet ground squirrel (S. major). The hypothesis about the vocalizations of young individuals of ground squirrels being emitted at lower frequencies than those of adults was tested. The results of the study indicate a differentiated formation of the sound signal in the different sexes of the russet ground squirrel in postnatal ontogenesis. The sound signal in females is formed in the first year of life during the season of activity, whereas it is formed in males in the year following the first hibernation. In terms of the studied call parameters, the voice of adult females is higher than that of young animals of both sexes, while the voice of adult males is lower. The possible causes and significance of the identified sex and age features of the alarm call of the russet ground squirrel are discussed. [ABSTRACT FROM AUTHOR]