Post by Admin on Dec 19, 2021 20:17:12 GMT
Demographic Changes
Demographic expansion of Thai/Lao populations is noticeably detected in both paternal and maternal lineages at the beginning of the Holocene, ∼10 ka (fig. 6). In this period, increasing and more stable temperatures might have facilitated population expansion (Wen et al. 2016). The male Ne increase during the Holocene is primarily driven by the O2a2a* and O2a1c* lineages (fig. 8). The Holocene expansion might thus be related to an expansion of HM paternal lineages, as O2* (O-M122*) is thought to have arisen at the beginning of the Holocene near Tibet (van Driem 2017). According to this hypothesis, the bearers of this haplogroup became the progenitors of the “Yangtzean” or HM paternal lineages, and contributed this lineage to the ancient AA who carried O1b1a1a* or O-M95* by sharing of knowledge about rice agriculture. However, further sequencing of MSY lineages belonging to the HM populations are needed to verify this hypothesis.
During the Neolithic period, other significant expansions are observed in almost all ethnicities and many MSY haplogroups, that is, O1b1a1a1b*, O1b1a1a1a*, and R* (fig. 8). Previously, it was suggested that the demographic expansion pattern in the Neolithic in SEA shows strong expansion dynamics, different characteristics than the Paleolithic expansion, and sex-specific expansion patterns, with earlier expansions in female than in male lineages. (Wen et al. 2016). The expansion signals in our results coincide with the beginning of the SEA Neolithic ∼5–4.5 ka, during which farming expanded from China to SEA (Bellwood 2018). The farming technology for food production could support a higher population density than hunting–gathering, as agriculture could produce a more steady food supply, and males could avoid hunting dangerous animals; thus, effective population size would increase (Jobling et al. 2004; Yan et al. 2014). The farmer expansion ∼4 ka was probably related to ancestral AA-speaking hill tribes with predominantly O-M95* lineages that knew rice agriculture (van Driem 2017; Lipson et al. 2018; McColl et al. 2018). However, the movement of Neolithic groups from southern China to MSEA probably involved not only AA groups but also TK groups (Bellwood 2018). In our study, a Neolithic expansion signal was observed for the MSY in all studied groups, indicating a large demographic expansion and probable admixture among the ancestors of indigenous southern Chinese groups during the Neolithic period. Haplogroup R1a was previously suggested to show a similar expansion, with paternal population growth during ∼6.5–4 ka observed globally (Poznik et al. 2016; Wang et al. 2016).
In addition, we found another significant expansion during the Bronze age ∼2 ka that involves TK-speaking populations, reflected by some haplogroups prevalent in the TK, for example, O1a* (fig. 8). This TK-related expansion is consistent with the strong expansion detected in the BSP of Xishuangbanna Dai (fig. 7) and corresponds with the results of a recent ancient DNA study (McColl et al. 2018). The southward expansion of the indigenous southern Chinese TK speakers to MSEA was probably driven by the Han Chinese expansion from the Yellow River basin to southern China during the Qin dynasty, starting ∼2.5 ka (Bellwood 2018). The migration and expansion of prehistoric TK groups during the Bronze Age has had a profound influence on the modern Thais and Laotians in term of languages and genes. Nowadays, TK languages are mostly concentrated in present-day Thailand and Laos, and the relatively high level of TK genetic homogeneity might be also driven by this recent expansion.
Our previous mtDNA modeling to explore the migration and expansion of prehistoric TK groups during the Bronze Age supported the spread of TK languages via demic diffusion and admixture (Kutanan et al. 2017; Kutanan, Kampuansai, Brunelli, et al. 2018). Here, a similar modeling approach for the MSY data found weak support for cultural diffusion of TK languages. Although we built the model based on historical sources (supplementary fig. 6, Supplementary Material online), the models did not generate the observed variation (supplementary fig. 7, Supplementary Material online), indicating that the analyzed models do not correspond to the real paternal population history. A possible reason for this striking difference between maternal and paternal histories might be warfare. Historically, many areas of Thailand saw frequent warfare involving various TK groups ∼200–500 ya (Penth 2000). As a result, forced migrations were imposed upon the losing side and men were taken captive more often than women because men could be used to strengthen the victors’ armies. This could result in a different history for the TK male versus female population. More complex demographic models could therefore more accurately capture the paternal history of Thai/Lao populations.
It may be that the MSY sequences do not harbor enough information to distinguish among the different demographic scenarios. However, comparison of genetic differences (Φst and corrected pairwise differences) among the groups used in the simulations does support a real contrast in the maternal versus paternal histories for the major TK groups in each region, and also finds genetic heterogeneity among these major groups. The northern Thai people showed closer genetic relationship with the Dai than AA groups in both mtDNA and MSY, supporting the demic diffusion model, whereas the ethnic Lao are closer to Dai for mtDNA but for MSY they are related to both Dai and AA rather equally, suggesting demic diffusion for the maternal history and admixture for the paternal history. The central Thai MSY sequences could be of AA origin because they are genetically more similar to the AA groups than the Dai, supporting cultural diffusion, but for mtDNA they are related to both Dai and AA rather equally, supporting admixture in central Thailand as found previously (Kutanan, Kampuansai, Brunelli, et al. 2018). Overall, these results suggest that the demographic history of Khon Mueang, ethnic Lao, and central Thais are different, possibly reflecting either different migration routes or different small TK groups that expanded from China (Higham and Thosarat 2012). In addition, different patterns of admixture for males versus females could have occurred in ethnic Lao and central Thais. Archaeological and historical evidence indicate that prior to the TK migration, there were existing rich civilizations in the area, for example, the Dvaravati of the Mon and Chenla of the old Khmer. With the arrival of TK groups, the Mon people were incorporated by intermarriage into Tai society and adopted the increasing dominant Thai language as their own (Higham and Thosarat 2012). Our results suggest that there was variation in the pattern of cultural diffusion/admixture involving males versus females in different groups in the area of northeastern and central Thailand and Laos. Such admixture could also have had an impact on the patterns of genetic diversity in the matrilocal versus patrilocal groups, which might then contribute to diminishing the genetic signal attributable to residence pattern.
Finally, another more recent expansion signal was detected in the northern Thai AA-speaking Lawa, involving haplogroups O2a2b* and N* (figs. 6 and 8). Historical evidence indicates that after the arrival of the TK groups in northern Thailand, the native Lawa groups were fragmented and moved to the mountains (Penth 2000), resulting in cultural and geographical isolation. In support of this model of isolation and drift, we note that the most negative Tajima’s D value is observed in the LW3 group, which suggests population expansion after a bottleneck (fig. 2D).
Conclusion
We compared high-resolution mtDNA and MSY sequences and found contrasts in the maternal and paternal genetic history of various Thai/Lao groups, in particular the hill tribes, the major TK groups in different regions, and the AA- and ST-speaking groups, as well as significant genetic heterogeneity among samples from the same ethnolinguistic group from different locations (figs. 1 and 4). These contrasting patterns reflect the influence of different factors in different Thai/Lao groups, for example, cultural practices in the hill tribes coupled with genetic drift in some population, as well as gene flow in the lowland Mon and TK groups. This new MSY study from Thai/Lao males provides more insight into the past demographic history in the paternal line and, along with our previous mtDNA studies, is generally in agreement with recent ancient DNA studies in SEA that indicate two demographic expansions from southern China to MSEA, with the first involving the ancestors of AA groups and the second involving TK groups (Lipson et al. 2018; McColl et al. 2018). Overall, the contrasting results for the maternal versus paternal history of some Thai/Lao groups supports the importance of detailed studies of uniparental markers, as such contrasts would not have been revealed by studying autosomal markers in just a few Thai/Lao groups. Additional ancient DNA studies, coupled with more detailed genome-wide data from present-day populations, will provide a complete reconstruction of the genetic history of this region.
Demographic expansion of Thai/Lao populations is noticeably detected in both paternal and maternal lineages at the beginning of the Holocene, ∼10 ka (fig. 6). In this period, increasing and more stable temperatures might have facilitated population expansion (Wen et al. 2016). The male Ne increase during the Holocene is primarily driven by the O2a2a* and O2a1c* lineages (fig. 8). The Holocene expansion might thus be related to an expansion of HM paternal lineages, as O2* (O-M122*) is thought to have arisen at the beginning of the Holocene near Tibet (van Driem 2017). According to this hypothesis, the bearers of this haplogroup became the progenitors of the “Yangtzean” or HM paternal lineages, and contributed this lineage to the ancient AA who carried O1b1a1a* or O-M95* by sharing of knowledge about rice agriculture. However, further sequencing of MSY lineages belonging to the HM populations are needed to verify this hypothesis.
During the Neolithic period, other significant expansions are observed in almost all ethnicities and many MSY haplogroups, that is, O1b1a1a1b*, O1b1a1a1a*, and R* (fig. 8). Previously, it was suggested that the demographic expansion pattern in the Neolithic in SEA shows strong expansion dynamics, different characteristics than the Paleolithic expansion, and sex-specific expansion patterns, with earlier expansions in female than in male lineages. (Wen et al. 2016). The expansion signals in our results coincide with the beginning of the SEA Neolithic ∼5–4.5 ka, during which farming expanded from China to SEA (Bellwood 2018). The farming technology for food production could support a higher population density than hunting–gathering, as agriculture could produce a more steady food supply, and males could avoid hunting dangerous animals; thus, effective population size would increase (Jobling et al. 2004; Yan et al. 2014). The farmer expansion ∼4 ka was probably related to ancestral AA-speaking hill tribes with predominantly O-M95* lineages that knew rice agriculture (van Driem 2017; Lipson et al. 2018; McColl et al. 2018). However, the movement of Neolithic groups from southern China to MSEA probably involved not only AA groups but also TK groups (Bellwood 2018). In our study, a Neolithic expansion signal was observed for the MSY in all studied groups, indicating a large demographic expansion and probable admixture among the ancestors of indigenous southern Chinese groups during the Neolithic period. Haplogroup R1a was previously suggested to show a similar expansion, with paternal population growth during ∼6.5–4 ka observed globally (Poznik et al. 2016; Wang et al. 2016).
In addition, we found another significant expansion during the Bronze age ∼2 ka that involves TK-speaking populations, reflected by some haplogroups prevalent in the TK, for example, O1a* (fig. 8). This TK-related expansion is consistent with the strong expansion detected in the BSP of Xishuangbanna Dai (fig. 7) and corresponds with the results of a recent ancient DNA study (McColl et al. 2018). The southward expansion of the indigenous southern Chinese TK speakers to MSEA was probably driven by the Han Chinese expansion from the Yellow River basin to southern China during the Qin dynasty, starting ∼2.5 ka (Bellwood 2018). The migration and expansion of prehistoric TK groups during the Bronze Age has had a profound influence on the modern Thais and Laotians in term of languages and genes. Nowadays, TK languages are mostly concentrated in present-day Thailand and Laos, and the relatively high level of TK genetic homogeneity might be also driven by this recent expansion.
Our previous mtDNA modeling to explore the migration and expansion of prehistoric TK groups during the Bronze Age supported the spread of TK languages via demic diffusion and admixture (Kutanan et al. 2017; Kutanan, Kampuansai, Brunelli, et al. 2018). Here, a similar modeling approach for the MSY data found weak support for cultural diffusion of TK languages. Although we built the model based on historical sources (supplementary fig. 6, Supplementary Material online), the models did not generate the observed variation (supplementary fig. 7, Supplementary Material online), indicating that the analyzed models do not correspond to the real paternal population history. A possible reason for this striking difference between maternal and paternal histories might be warfare. Historically, many areas of Thailand saw frequent warfare involving various TK groups ∼200–500 ya (Penth 2000). As a result, forced migrations were imposed upon the losing side and men were taken captive more often than women because men could be used to strengthen the victors’ armies. This could result in a different history for the TK male versus female population. More complex demographic models could therefore more accurately capture the paternal history of Thai/Lao populations.
It may be that the MSY sequences do not harbor enough information to distinguish among the different demographic scenarios. However, comparison of genetic differences (Φst and corrected pairwise differences) among the groups used in the simulations does support a real contrast in the maternal versus paternal histories for the major TK groups in each region, and also finds genetic heterogeneity among these major groups. The northern Thai people showed closer genetic relationship with the Dai than AA groups in both mtDNA and MSY, supporting the demic diffusion model, whereas the ethnic Lao are closer to Dai for mtDNA but for MSY they are related to both Dai and AA rather equally, suggesting demic diffusion for the maternal history and admixture for the paternal history. The central Thai MSY sequences could be of AA origin because they are genetically more similar to the AA groups than the Dai, supporting cultural diffusion, but for mtDNA they are related to both Dai and AA rather equally, supporting admixture in central Thailand as found previously (Kutanan, Kampuansai, Brunelli, et al. 2018). Overall, these results suggest that the demographic history of Khon Mueang, ethnic Lao, and central Thais are different, possibly reflecting either different migration routes or different small TK groups that expanded from China (Higham and Thosarat 2012). In addition, different patterns of admixture for males versus females could have occurred in ethnic Lao and central Thais. Archaeological and historical evidence indicate that prior to the TK migration, there were existing rich civilizations in the area, for example, the Dvaravati of the Mon and Chenla of the old Khmer. With the arrival of TK groups, the Mon people were incorporated by intermarriage into Tai society and adopted the increasing dominant Thai language as their own (Higham and Thosarat 2012). Our results suggest that there was variation in the pattern of cultural diffusion/admixture involving males versus females in different groups in the area of northeastern and central Thailand and Laos. Such admixture could also have had an impact on the patterns of genetic diversity in the matrilocal versus patrilocal groups, which might then contribute to diminishing the genetic signal attributable to residence pattern.
Finally, another more recent expansion signal was detected in the northern Thai AA-speaking Lawa, involving haplogroups O2a2b* and N* (figs. 6 and 8). Historical evidence indicates that after the arrival of the TK groups in northern Thailand, the native Lawa groups were fragmented and moved to the mountains (Penth 2000), resulting in cultural and geographical isolation. In support of this model of isolation and drift, we note that the most negative Tajima’s D value is observed in the LW3 group, which suggests population expansion after a bottleneck (fig. 2D).
Conclusion
We compared high-resolution mtDNA and MSY sequences and found contrasts in the maternal and paternal genetic history of various Thai/Lao groups, in particular the hill tribes, the major TK groups in different regions, and the AA- and ST-speaking groups, as well as significant genetic heterogeneity among samples from the same ethnolinguistic group from different locations (figs. 1 and 4). These contrasting patterns reflect the influence of different factors in different Thai/Lao groups, for example, cultural practices in the hill tribes coupled with genetic drift in some population, as well as gene flow in the lowland Mon and TK groups. This new MSY study from Thai/Lao males provides more insight into the past demographic history in the paternal line and, along with our previous mtDNA studies, is generally in agreement with recent ancient DNA studies in SEA that indicate two demographic expansions from southern China to MSEA, with the first involving the ancestors of AA groups and the second involving TK groups (Lipson et al. 2018; McColl et al. 2018). Overall, the contrasting results for the maternal versus paternal history of some Thai/Lao groups supports the importance of detailed studies of uniparental markers, as such contrasts would not have been revealed by studying autosomal markers in just a few Thai/Lao groups. Additional ancient DNA studies, coupled with more detailed genome-wide data from present-day populations, will provide a complete reconstruction of the genetic history of this region.
