[A search for Y-chromosomal species-specific markers and their use for hybridization analysis in ground squirrels].

In four ground squirrel species from the Volga region-yellow (Spermophilus fulvus), russet (S. major), little (S. pygmaeus), and speckled (S. suslicus)--four hybridization variants (major/fulvus, major/pygmaeus, major/suslicus, and pygmaeus/suslicus) have been reliably described. Earlier we have shown that populations of S. major from the Volga region were characterized by wide introgression of mtDNA from S. fulvus and S. pygmaeus, which probably, resulted from ancient hybridization. In this study, the same populations were used to analyze the introgression of the Y chromosome, which (unlike mtDNA) is paternally inherited. Three genes, ZfY, SRY, and SmcY were tested as Y-chromosomal candidate markers. It was demonstrated that Y chromosome of ground squirrels lacked the ZfY gene, while its homologous structure, ZfY(X), was presumably linked to the X chromosome. The SRY region examined was rather conservative. In particular, the sequences determined in S. major and S. fulvus were identical, while three out of four substitutions found in S. pygmaeus were located in the coding region. The SmcY gene was found to be the most suitable marker, providing distinguishing of all of the four ground squirrel species by nine nucleotide substitutions. Introgression at the Y chromosome was observed only in two cases: in one S. major individual (out of 51 phenotypically pure animals) caught in the major/fulvus sympatry zone, and in four (one litter) out of fourteen S. fulvus individuals caught in close vicinity of the sympatry zone of these two species. Among 28 S. pymaeus and 9 S. suslicus individuals, no foreign SmcY genes were detected. Two colonies of the "hybrid accumulation" type were examined with eight major/suslicus hybrids analyzed in the first and seventeen major/fulvus hybrids in the second colony. The prevalence of the S. major paternal lineages was observed in both colonies (87.5 and 82.4%, respectively). The data obtained suggest that compared to wide mtDNA introgression, introgression of Y chromosome in the Volga region ground squirrels is statistically significantly less frequent event.