A longitudinal cline characterizes the genetic structure of human populations in the Tibetan plateau.

Tzen-Yuh Chiang,Choongwon Jeong,Cynthia M Beall,Maniraj Neupane,Benjamin M Peter,Anna Di Rienzo,John Novembre,Geoff Childs,Buddha Basnyat,Sienna R Craig

doi:10.1371/journal.pone.0175885

Abstract

Indigenous populations of the Tibetan plateau have attracted much attention for their good performance at extreme high altitude. Most genetic studies of Tibetan adaptations have used genetic variation data at the genome scale, while genetic inferences about their demography and population structure are largely based on uniparental markers. To provide genome-wide information on population structure, we analyzed new and published data of 338 individuals from indigenous populations across the plateau in conjunction with worldwide genetic variation data. We found a clear signal of genetic stratification across the east-west axis within Tibetan samples. Samples from more eastern locations tend to have higher genetic affinity with lowland East Asians, which can be explained by more gene flow from lowland East Asia onto the plateau. Our findings corroborate a previous report of admixture signals in Tibetans, which were based on a subset of the samples analyzed here, but add evidence for isolation by distance in a broader geospatial context.

Highlights

The Tibetan plateau covers a vast geographic area stretching roughly 2,500 km in east-west direction and 1,000 km in north-south direction, corresponding to a quarter of the size of the United States
Unsupervised genetic clustering analysis using the program ADMIXTURE [18] shows that a majority of ancestry in Tibetans appears to be derived from components most highly represented in Tibetans, while they have varying level of lowland East Asians ancestry (S2 Fig)
When East Asian outgroups were used, the D statistics for many pairs of Tibetans significantly deviated from zero, showing that some Tibetan samples are genetically closer to lowland East Asians than the others (Fig 2A, S3 Fig)

Summary

Introduction

The Tibetan plateau covers a vast geographic area stretching roughly 2,500 km in east-west direction and 1,000 km in north-south direction, corresponding to a quarter of the size of the United States. We investigated the genetic structure of Tibetan populations using genome-wide variation data of 338 Tibetan individuals, including Sherpa, from 12 localities in the plateau, spanning over 1,500 km east-west and 700 km northsouth (Fig 1A, S1 Table) [1,2,8,11,12,13,14].

Results

Conclusion