Reconstructing the human genetic history of mainland Southeast Asia: Insights from genome-wide data from Thailand and Laos

Thailand and Laos, located in the center of Mainland Southeast Asia (MSEA), harbor diverse ethnolinguistic groups encompassing all five language families of MSEA: Tai-Kadai (TK), Austroasiatic (AA), Sino-Tibetan (ST), Hmong-Mien (HM), and Austronesian (AN). Previous genetic studies of Thai/Lao populations have focused almost exclusively on uniparental markers and there is a paucity of genome-wide studies. We therefore generated genome-wide SNP data for 33 ethnolinguistic groups, belonging to the five MSEA language families from Thailand and Laos, and analyzed these together with data from modern Asian populations and SEA ancient samples. Overall, we find genetic structure according to language family, albeit with heterogeneity in the AA-, HM-, and ST-speaking groups, and in the hill tribes, that reflects both population interactions and genetic drift. For the TK speaking groups, we find localized genetic structure that is driven by different levels of interaction with other groups in the same geographic region. Several Thai groups exhibit admixture from South Asia, which we date to ∼600–1000 years ago, corresponding to a time of intensive international trade networks that had a major cultural impact on Thailand. An AN group from Southern Thailand shows both South Asian admixture as well as overall affinities with AA-speaking groups in the region, suggesting an impact of cultural diffusion. Overall, we provide the first detailed insights into the genetic profiles of Thai/Lao ethnolinguistic groups, which should be helpful for reconstructing human genetic history in MSEA and selecting populations for participation in ongoing whole genome sequence and biomedical studies

Genetic structure of Khon Mueang populations along a historical Yuan migration route in Northern Thailand

The genetic structure and diversity of the Khon Mueang, who constitute the majority of the current northern Thai populations, is poorly understood. In present study, 433 unrelated individuals from 10 Khon Mueang villages, located in different geographic areas along historical Yuan migration route, were analyzed using the mtDNA hypervariable region (HVR) 1 and 17 Y chromosome short tandem repeats (Y-STRs) as markers. The studied populations from the Chiang Mai-Lamphun basin showed the evidence of demographic expansion and gene flow process in this area. Genetic structure of the geographically diverse Khon Mueang was driven by geography, while genetic differentiation of Chiang Mai-Lamphun populations was shaped by genetic exchange with the neighbouring populations in the area. Contrasting patterns of mtDNA and Y chromosome variations, influenced by sex-bias rates of migration and admixture, suggests that male and female Khon Mueang do not have identical demographic histories

Complete mitochondrial genomes of Thai and Lao populations indicate an ancient origin of Austroasiatic groups and demic diffusion in the spread of Tai–Kadai languages

The Tai–Kadai (TK) language family is thought to have originated in southern China and spread to Thailand and Laos, but it is not clear if TK languages spread by demic diffusion (i.e., a migration of people from southern China) or by cultural diffusion, with native Austroasiatic (AA) speakers switching to TK languages. To address this and other questions, we obtained 1234 complete mtDNA genome sequences from 51 TK and AA groups from Thailand and Laos. We find high genetic heterogeneity across the region, with 212 different haplogroups, and significant genetic differentiation among different samples from the same ethnolinguistic group. TK groups are more genetically homogeneous than AA groups, with the latter exhibiting more ancient/basal mtDNA lineages, and showing more drift effects. Modeling of demic diffusion, cultural diffusion, and admixture scenarios consistently supports the spread of TK languages by demic diffusion

Cultural variation impacts paternal and maternal genetic lineages of the Hmong-Mien and Sino-Tibetan groups from Thailand

The Hmong-Mien (HM) and Sino-Tibetan (ST) speaking groups are known as hill tribes in Thailand; they were the subject of the first studies to show an impact of patrilocality vs. matrilocality on patterns of mitochondrial (mt) DNA vs. male-specific portion of the Y chromosome (MSY) variation. However, HM and ST groups have not been studied in as much detail as other Thai groups; here we report and analyze 234 partial MSY sequences (∼2.3 mB) and 416 complete mtDNA sequences from 14 populations that, when combined with our previous published data, provides the largest dataset yet for the hill tribes. We find a striking difference between Hmong and IuMien (Mien-speaking) groups: the Hmong are genetically different from both the IuMien and all other Thai groups, whereas the IuMien are genetically more similar to other linguistic groups than to the Hmong. In general, we find less of an impact of patrilocality vs. matrilocality on patterns of mtDNA vs. MSY variation than previous studies. However, there is a dramatic difference in the frequency of MSY and mtDNA lineages of Northeast Asian (NEA) origin vs. Southeast Asian (SEA) origin in HM vs. ST groups: HM groups have high frequencies of NEA MSY lineages but lower frequencies of NEA mtDNA lineages, while ST groups show the opposite. A potential explanation is that the ancestors of Thai HM groups were patrilocal, while the ancestors of Thai ST groups were matrilocal. Overall, these results attest to the impact of cultural practices on patterns of mtDNA vs. MSY variation

Genetic and linguistic correlation of the Kra-Dai-speaking groups in Thailand

The Kra-Dai linguistic family includes Thai and Lao as well as a great number of languages spoken by ethnic minorities in Southeast Asia. In Thailand, a dozen of other Kra-Dai languages are spoken in addition to Thai, the national language. The genetic structure of the Kra-Dai-speaking populations in Thailand has been studied extensively using uniparentally inherited markers. To extend this line of genetic investigation, this study used 15 autosomal microsatellites of 500 individuals from 11 populations, belonging to nine Kra-Dai ethnicities, namely, the Kaleung, Phu Thai, Saek, Nyo, Lao Isan, Yuan, Black Tai, Phuan and Lue. These ethnolinguistic groups are dispersed in three different geographic regions of Thailand, that is, Northern, Northeastern and Central. The results show a very low average of pairwised F(st) (0.0099), as well as no population substructure based on STRUCTURE analysis, indicating genetic homogeneity within the Kra-Dai-speaking group, possibly owing to shared linguistic ancestry. The Mantel test, an analysis of molecular variance, and the approximate Bayesian computation procedure employed to evaluate potential factors for driving genetic diversity revealed that language is the predominant factor affecting genetic variations, whereas geography is not. The result of distance-based clustering analyses and spatial analysis of molecular variance revealed genetic distinctions of some populations, reflecting the effects of genetic drift and gene flow on allele frequency within populations, in concordance with the result of R-matrix regression. The genetic and linguistic affiliations of the contemporary Kra-Dai-speaking groups are consistent with each other despite certain deviation due to various evolutionary factors that may have occurred during their migrations and resettlements

Close genetic relationship between central Thai and Mon people in Thailand revealed by autosomal microsatellites

Central Thailand is home to diverse populations with the central Thai constituting the major group, while the Mon, who migrated from southern Myanmar, are sparsely distributed within the region. A total of 338 individuals of eight central Thai (246 samples) and three Mon populations (92 samples) were newly genotyped. When combined with our previously published Mon data, this provides a total of 139 Mon samples. We found genetic similarity between the central Thai and Mon and weak sub-structuring among Thais from central, northern, and northeastern Thailand. The forensic parameter results show high discrimination values which are appropriate for forensic personal identification and paternity testing in both the central Thai and Mon; the probabilities of excluding paternity are 0.999999112 and 0.999999031, respectively, and the combined discrimination power is 0.9999999999999999999999 in both groups. This regional allelic frequency on forensic microsatellites may serve as a useful reference for further forensic investigations in both Thailand and Myanmar

Genetic affinity and admixture of northern Thai people along their migration route in northern Thailand: evidence from autosomal STR loci

The Khon Mueang (KM) are the largest group of northern Thai people. Our previous mtDNA studies have suggested an admixture process among the KM with the earlier Mon-Khmer-speaking inhabitants of this region. In this study, we evaluate genetic affinities and admixture among 10 KM populations in northern Thailand lying along the historical Yuan migration route, and 10 neighboring populations belonging to 7 additional ethnic groups: Lawa, Mon (Mon-Khmer-speaking groups), Shan, Yuan, Lue, Khuen and Yong (Tai-speaking groups) by analyzing 15 hypervariable autosomal short tandem repeat loci. The KM exhibited close relationships with neighboring populations, especially the Tai-speaking groups, reflecting an admixed origin of the KM. Admixture proportions were observed in all KM populations, which had a higher contribution from the parental Tai than the Mon-Khmer groups. Different admixture patterns of the KM along the migration route might indicate high heterogeneity among the KM. These patterns were not directly associated with geographical proximity, suggesting other factors, like variation in the timing of admixture with the existing populations may have had an important role. More genetic data from different marker systems solely transmitted through the male or female lineages are needed to complete the description of genetic admixture and population history of the K