New insights from Thailand into the maternal genetic history of Mainland Southeast Asia

Abstract

Tai-Kadai (TK) is one of the major language families in Mainland Southeast Asia (MSEA), with a concentration in the area of Thailand and Laos. Our previous study of 1234 mtDNA genome sequences supported a demic diffusion scenario in the spread of TK languages from southern China to Laos as well as northern and northeastern Thailand. Here we add an additional 560 mtDNA genomes from 22 groups, with a focus on the TK-speaking central Thai people and the Sino-Tibetan speaking Karen. We find extensive diversity, including 62 haplogroups not reported previously from this region. Demic diffusion is still a preferable scenario for central Thais, emphasizing the expansion of TK people through MSEA, although there is also some support for gene flow between central Thai and native Austroasiatic speaking Mon and Khmer. We also tested competing models concerning the genetic relationships of groups from the major MSEA languages, and found support for an ancestral relationship of TK and Austronesian-speaking groups.

Fig. 1

Map showing sample locations and haplogroup distributions. Blue stars indicate the 22 presently studied populations (Tai-Kadai, Austroasiatic, and Sino-Tibetan groups) while red and green circles represent Tai-Kadai and Austroasiatic populations from the previous study [7]. Population abbreviations are in Supplementary Table S1

Fig. 2

Three demographic models for the ABC analysis of CT origins: demic diffusion (a); cultural diffusion (b); and continuous migration (c)

Fig. 3

Five demographic models for the ABC analysis of the relationships of populations from four MSEA language families. Model 1 (a), Model 2 (b), and Model 3 (c) are based on Starosta (2005) [11], Sagart (2004, 2005) [9, 10] and Peiros (1998) [8], respectively, while Model 4 (e) and Model 5 (f) are based on the present geographic distributions of the languages (ISEA for AN and MSEA for ST, TK, and AA); see Supplementary Text for further details

Fig. 4

MDS plots based on the Φ_st distance matrix for 70 populations (after removal of three outliers: TN1, TN2, and SK). Red, black, and dark blue symbols indicate AA, TK, and ST populations, respectively. The stress value is 0.0804. Population abbreviations are shown in Supplementary Table S1

Fig. 5

The BSP plots for five different trends found in 22 populations; KSK2, MO6, LU4 (a), KSK1 (b), KPA (c), KPW, MO7, KPW, TKH, LU1-LU2, YU3-YU6, CT6-CT7 (d), and LU3, CT1-CT5 (e). Population abbreviations are listed in Table 1. Each line is the median estimated maternal effective population size (y-axis) through time from the present in years (x-axis)