Origins of East Caucasus Gene Pool: Contributions of Autochthonous Bronze Age Populations and Migrations from West Asia Estimated from Y-Chromosome Data

The gene pool of the East Caucasus, encompassing modern-day Azerbaijan and Dagestan populations, was studied alongside adjacent populations using 83 Y-chromosome SNP markers. The analysis of genetic distances among 18 populations (N = 2216) representing Nakh-Dagestani, Altaic, and Indo-European language families revealed the presence of three components (Steppe, Iranian, and Dagestani) that emerged in different historical periods. The Steppe component occurs only in Karanogais, indicating a recent medieval migration of Turkic-speaking nomads from the Eurasian steppe. The Iranian component is observed in Azerbaijanis, Dagestani Tabasarans, and all Iranian-speaking peoples of the Caucasus. The Dagestani component predominates in Dagestani-speaking populations, except for Tabasarans, and in Turkic-speaking Kumyks. Each component is associated with distinct Y-chromosome haplogroup complexes: the Steppe includes C-M217, N-LLY22g, R1b-M73, and R1a-M198; the Iranian includes J2-M172(×M67, M12) and R1b-M269; the Dagestani includes J1-Y3495 lineages. We propose J1-Y3495 haplogroup’s most common lineage originated in an autochthonous ancestral population in central Dagestan and splits up ~6 kya into J1-ZS3114 (Dargins, Laks, Lezgi-speaking populations) and J1-CTS1460 (Avar-Andi-Tsez linguistic group). Based on the archeological finds and DNA data, the analysis of J1-Y3495 phylogeography suggests the growth of the population in the territory of modern-day Dagestan that started in the Bronze Age, its further dispersal, and the microevolution of the diverged population

ADMIXTURE plot (k = 6).

<p>Ancestry proportions of 1,194 individuals as revealed by ADMIXTURE.</p

Correlations between matrices of genetic, geographic and linguistic distances among Balto-Slavic populations.

<p>Correlations between matrices of genetic, geographic and linguistic distances among Balto-Slavic populations.</p

Distribution of the average number of IBD segments between groups of East-West Slavs (a), South Slavs (b), and their respective geographic neighbors.

<p>The x-axis indicates ten classes of IBD segment length (in cM); the y-axis indicates the average number of shared IBD segments per pair of individuals within each length class.</p

The Balto-Slavic populations analyzed in this study and the tree of Balto-Slavic languages.

<p>The map (lower panel) shows the geographical distribution of Balto-Slavic populations (colored areas) within Europe. The symbols on the map represent the geographic location of the populations genotyped. The map was created in the GeneGeo software as described previously [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0135820#pone.0135820.ref068" target="_blank">68</a>,<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0135820#pone.0135820.ref075" target="_blank">75</a>]. A manually constructed consensus phylogenetic tree of the Balto-Slavic languages (upper panel) is based on the StarlingNJ, NJ, BioNJ, UPGMA, Bayesian MCMC, Unweighted Maximum Parsimony methods. Ternary nodes resulting from neighboring binary nodes were joined together if the temporal distance between them was ≤ 300 years. StarlingNJ dates are proposed (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0135820#pone.0135820.s008" target="_blank">S2 File</a>).</p

Genetic structure of the Balto-Slavic populations within a European context according to the three genetic systems.

<p>a) PC1vsPC3 plot based on autosomal SNPs (PC1 = 0.53; PC3 = 0.26); b) MDS based on NRY data (stress = 0.13); c) MDS based on mtDNA data (stress = 0.20). We focus on PC1<i>vs</i>PC3 because PC2 (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0135820#pone.0135820.s002" target="_blank">S1 Fig</a>) whilst differentiating the Volga region populations from the rest of Europeans had a low efficiency in detecting differences among the Balto-Slavic populations–the primary focus of this work.</p

Genetic Heritage of the Balto-Slavic Speaking Populations: A Synthesis of Autosomal, Mitochondrial and Y-Chromosomal Data

The Slavic branch of the Balto-Slavic sub-family of Indo-European languages underwent rapid divergence as a result of the spatial expansion of its speakers from Central-East Europe, in early medieval times. This expansion–mainly to East Europe and the northern Balkans–resulted in the incorporation of genetic components from numerous autochthonous populations into the Slavic gene pools. Here, we characterize genetic variation in all extant ethnic groups speaking Balto-Slavic languages by analyzing mitochondrial DNA (n = 6,876), Y-chromosomes (n = 6,079) and genome-wide SNP profiles (n = 296), within the context of other European populations. We also reassess the phylogeny of Slavic languages within the Balto-Slavic branch of Indo-European. We find that genetic distances among Balto-Slavic populations, based on autosomal and Y-chromosomal loci, show a high correlation (0.9) both with each other and with geography, but a slightly lower correlation (0.7) with mitochondrial DNA and linguistic affiliation. The data suggest that genetic diversity of the present-day Slavs was predominantly shaped in situ, and we detect two different substrata: ‘central-east European’ for West and East Slavs, and ‘south-east European’ for South Slavs. A pattern of distribution of segments identical by descent between groups of East-West and South Slavs suggests shared ancestry or a modest gene flow between those two groups, which might derive from the historic spread of Slavic people