In the heartland of Eurasia: the multilocus genetic landscape of Central Asian populations

Abstract

Located in the Eurasian heartland, Central Asia has played a major role in both the early spread of modern humans out of Africa and the more recent settlements of differentiated populations across Eurasia. A detailed knowledge of the peopling in this vast region would therefore greatly improve our understanding of range expansions, colonizations and recurrent migrations, including the impact of the historical expansion of eastern nomadic groups that occurred in Central Asia. However, despite its presumable importance, little is known about the level and the distribution of genetic variation in this region. We genotyped 26 Indo-Iranian- and Turkic-speaking populations, belonging to six different ethnic groups, at 27 autosomal microsatellite loci. The analysis of genetic variation reveals that Central Asian diversity is mainly shaped by linguistic affiliation, with Turkic-speaking populations forming a cluster more closely related to East-Asian populations and Indo-Iranian speakers forming a cluster closer to Western Eurasians. The scattered position of Uzbeks across Turkic- and Indo-Iranian-speaking populations may reflect their origins from the union of different tribes. We propose that the complex genetic landscape of Central Asian populations results from the movements of eastern, Turkic-speaking groups during historical times, into a long-lasting group of settled populations, which may be represented nowadays by Tajiks and Turkmen. Contrary to what is generally thought, our results suggest that the recurrent expansions of eastern nomadic groups did not result in the complete replacement of local populations, but rather into partial admixture.

Figure 1

Geographic location of the 26 Central Asian populations sampled. Linguistic affiliation as well as admixture proportions from putative parental origins (Central/South Asia, East Asia, Europe and Middle East) are also indicated. See Table 1 for acronyms.

Figure 2

Correspondence analysis (CA) based on the table of allele counts in Central Asia (a). The first two factorial components (FC) are represented, and their relative contribution to the total inertia are indicated. Colors indicate language affiliation; blue: Indo-Iranian speakers; orange: Turkic speakers. CA based on the table of allele counts in Eurasian populations (b). Colors represent major geographic regions; green: Europe; gray: Middle East; purple: Central/South Asia; red: East Asia.

Figure 3

Population structure inferred from microsatellite data using the software package STRUCTURE. K represents the number of putative clusters. Each individual is represented by a vertical line, divided into up to K colored segments, each of which represents the individual's estimated membership fraction to that cluster. Each output represents the matrix of membership coefficients averaged over 40 independent runs with CLUMPP. The data consisted in 767 individuals from 26 Central Asian populations genotyped at 27 microsatellite loci, plus 869 individuals from 44 African and Eurasian populations from the HGDP-CEPH Human Genome Diversity Cell Line Panel. See Table 1 for acronyms.