ИСТИНА

Presence of gene flow between Siberian (Phylloscopus (collybita) tristis) and Eastern-European (Ph. c. abietinus) chiffchaffs has been debated over decades and still attracts the attention of researchers. In our earlier works we obtained evidence for the gene flow and hybridization between subspecies based on comparative analysis. Here we use an extensive analysis of our data collected in 2008-2010 in two parts of the hybrid zone: southern (Southern Ural Mountains) and northern (Arkhangelsk region). We considered data on phenotypical (plumage coloration), acoustic (territorial song) and genetic (mtDNA, cytochrome b) traits. We discovered tristis haplotype dominance and hypothesize its active introgression into population. Classifying the population of the hybrid zone based on plumage coloration, we found an equal percentage of Siberian (34%), European (37%) and hybrid (28%) individuals. Here we define hybrids as birds with very little portions of yellow on the ventral side of the body in comparison with plenty of yellow in abietinus and absolutely no yellow in tristis. In contrast, tristis haplotype clearly dominates in the hybrid population: 41% of individuals classified as hybrids or abietinus by coloration have mtDNA of Siberian chiffchaff. Thus, we hypothesize that tristis mtDNA tends to replace abietinus in the hybrid zone, while phenotypic traits of abietinus are kept intact in the population. The similar tendency was found for acoustic traits: Siberian song clearly dominates in the population. In the hybrid population besides tristis itself, phenotypic hybrids mostly sing the Siberian song and even 21% of abietinus perform it. On the contrary, European type of song was not encountered among pure tristis individuals. Moreover, vocal repertoire analysis revealed that mixed singers incorporate into their song most of vocal elements typical for tristis, but use only a fraction of vocal repertoire of European chiffchaffs. Studies of the subspecies distribution within local populations in the southern part of hybrid zone revealed a sharp geographical boundary in the distribution of Siberian chiffchaff. Geographically, this boundary coincides with Zilmerdak mountain ridge, and abietinus prevalence changes into mixed population over only 15 km. In contrast, no such boundary can be identified for at the Northern part of studied region. It remains an open question if similar boundary wasn’t found on the north or it is unique for the Ural population. There are some facts supporting the latter. Zilmerdak mountain ridge takes most of the precipitation and as a consequence splits different forests types, creating an ecological boundary. Finally, our new data on subspecies distribution from the Northern Russia can be used to refine boundaries of the contact zone. The most intensive hybridization occurs in central and eastern parts of Arkhangelsk region. Slightly to the south the contact zone includes southern parts of Komi republic, which is mainly inhabited by Siberian chiffchaff.