Search

Analysis of the frequencies of karyotypic variants in the hybrid zone between the Sok and Serov chromosomal races of the common shrew Sorex araneus revealed that the zone has a complex configuration. A large part of the contact zone is located in a monotonous mid taiga zone, where there are no significant barriers to limit dispersion of shrews. Another part of the zone runs along the Pechora River (Komi Republic). Analysis of distribution of the diagnostic chromosomes on a transect along the Pechora River showed that the hybrid zone could be described by opposing metacentric clines. Individuals of both pure Sok and Serov races, as well as F1 hybrids, were found only on the left bank of the Pechora River. The right bank was occupied only by the Serov race, and F1 hybrids were rare there. The observed number of interracial hybrids in the center of the zone does not differ from that expected in the case of random breeding. This allows us to define this zone as unimodal. The standard width of the zone is about 40 km. This is considerably higher than all known cases of hybrid zones with the same level of karyotypic differences between parental races: two pairs of diagnostic metacentric chromosomes with monobrachial homology. We discuss possible causes of this phenomenon. [ABSTRACT FROM AUTHOR]

In this review, we describe karyotypic, morphological, and genetic structuring of population in the common shrew Sorex araneus (Lipotyphla, Mammalia), and try to explain some unclear and contradictory aspects of this structuring on the basis of population approach. The subdivision of this species into more than 76 parapatric chromosomal races does not correspond to its morphological and genetic structuring. Chromosomal hybrid zones are formed in the areas of contact between the races. The frequency of interracial F1 hybrids is low in nature, but we have shown that mating between different races in captivity occurs quite readily, although the postnatal survival of hybrids is reduced. We suggest that this species is subdivided into relatively small populations characterized by the unity of functioning, which is ensured by the predominant dispersal of individuals from each of the populations within their population space. It should also be emphasized that the main provisions set forth by Stanislav S. Shvarts in his conceptual monograph The Evolutionary Ecology of Animals are still relevant today. [ABSTRACT FROM AUTHOR]

The Moscow and Seliger chromosomal races of the common shrew differ by Robertsonian fusions and possibly whole-arm reciprocal translocations (WARTs) such that their F hybrids produce a chain-of-eleven configuration at meiosis I and are expected to suffer substantial infertility. Of numerous hybrid zones that have been described in the common shrew, those between the Moscow and Seliger races involve the greatest chromosomal difference. We collected 211 individuals from this zone to generate a total dataset of 298 individuals from 187 unique global positioning system (GPS) locations within the vicinity of interracial contact. We used a geographic information system (GIS) to map the location of the hybrid zone, which follows a direct route between two lakes, as would be anticipated from tension zone theory. Even within the central area of the hybrid zone, there is a much higher frequency of pure race individuals than hybrid, making this a clear example of a bimodal zone in the sense of . The zone runs through good habitat for common shrews, but nevertheless it is very narrow (standard cline widths: 3-4 km), as would be anticipated from low hybrid fitness. There is clear potential for an interruption to gene flow and build-up of reproductive isolation. As found in some other hybrid zones, there is a high frequency of novel genetic variants, in this case, new chromosomal rearrangements. Here, we report a de novo Robertsonian fission and a de novo reciprocal translocation, both for the first time in the common shrew. There is an extraordinarily high frequency of de novo mutations recorded in F hybrids in the zone and we discuss how chromosomal instability may be associated with such hybrids. The occurrence of a de novo Robertsonian fission is of considerable significance because it provides missing evidence that fissions are the basis of the novel acrocentric forms found and apparently selected for in certain common shrew hybrid zones. [ABSTRACT FROM AUTHOR]

Combination of different dispersal modes may itself, without external obstacles, lead to the appearance of subdivided populations and maintain the existence of independent population systems. The common shrew, a mammal convenient for studying different levels of intraspecific differentiation, was the object of the study. Empirical data have been used for simulation taking into account the change of dispersal modes in the population area. The obtained results agree with empirical data on the distribution of races and hybrids in the hybrid zone of chromosome races Moscow and Seliger. Change of the dispersal mode may maintain independent population dynamics and, in the case of chromosome races, prevent the migration of parental individuals into the territory of the other race. [ABSTRACT FROM AUTHOR]