Indian Journal of Human Genetics, Vol. 9, No. 1, Jan-Jun, 2003, pp. 25-28
Pairwise MtDNA-HVRII sequence differences and geographic maternal distances among Korku, an Austro-Asiatic tribe in Central India
Raghavendra V. Rao, Kumarasamy Thangaraj, Alla G. Reddy, V. Sridhar, Lalji Singh
Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad-500007,
NOTE: The nucleotide sequence data reported in the GenBank database under the accession numbers- Korku (n=101): AY 103018 to AY 1031
Code Number: hg03007
Ethno-linguistic and recent molecular evidences were equivocal that tribes belonging to Austro-Asiatic linguistic group were the earliest `out of Africa' migrants in the Indian sub-continent dating back to approximately 60,000 YBP. They comprise of few endogamous groups and were settled in eastern and central India. In the present study it is found among Korku, an endogamous Austro-Asiatic tribe settled in central India, that oldest females pairwise, maternal geographical distances were inversely related with mtDNA-HVRll control region sequence differences, mismatch distribution was unimodal and the most common haplotype had wide geographical distribution. The empirical findings lead to 1) the possibility of an explanation that the Korku, though showed demographic expansion, the place of expansion may not be the area of their present habitation 2) the scope of combining information on maternal distances and mtDNA sequence diversity in deriving demographic history of populations.
Key Words: MtDNA-HVRII, Maternal distances, Austro-Asiatic tribes, India.
Tribes, the autochthons inhabiting main land India, all comprised of three linguistic groups, the Austro-Asiatic, the Dravidian and the Tibeto-Burman.1 They were also conformed to distinct geographical categories. The Austro-Asiatic tribes inhabited eastern and central parts of India, and formed of a number of endogamous populations.2 Earlier study based on autosomal DNA markers and MtDNA coding region RFLP and HVRl control region sequences revealed sub-structuring of Indian tribes as linguistic/geographic categories. The Austro-Asiatic tribes sampled in eastern India showed coalescent age of about 60,000YBP, compared to later ages for Dravidian and Tibeto-Burman groups, in the Indian sub-continent.3 These tribes are distributed over a limited geographic area and the total number of endogamous groups are 39. It is very tempting to note that, a thorough understanding of their demographic history based on maternal and paternal sequence information may bring into relief with much more authenticity, the peopling of the Indian sub-continent. In the present paper, for the first time, we had shown the possibility of combining empirical data on maternal distances with MtDNA sequence diversity, in deriving further information on demographic history of a population.
MATERIAL AND METHODS
Blood sample, 5 to 10 ml, from unrelated individuals belonging to Korku (n=101) tribe in Dharni Taluqa, Amravathy district, Maharastra, India were collected with written informed consent. DNA was isolated from white blood cells using Proteinase-K and phenol-chloroform extraction. MtDNA- HVRll control region sequences were amplified (Primers: Forward (F)- nt 8 to 29, Reverse(R ) nt 408 to 429, annealing temperature 60 C) and directly sequenced using ABI 3700 DNA analyzer and BigDye Terminator(Perkin-Elmer) kit and aligned with control reference sequence using AutoAssembler software. For constructing haplotypes, of the total 348 (065-413) nucleotides sequenced, C-track nucleotides were ignored and positions between 073-263 were utilized in view of high variability. Frequency distribution of haplotypes and nucleotide sequences mismatch distributions were obtained using Arlequin program.4 Maternal birthplaces of Individuals aged 60-85years (n=25) were located on a map with respective haplotypes. Geographic distances between birthplaces were measured in kilometers as crow flies. Pairwise, maternal distances and MtDNA-HVRII sequence differences were computed manually (N=25x25-24/2=300). In calculating pair wise differences, a weightage of 15 was given for each transversion. Mantel test5 for association was computed between Pairwise, maternal geographic distances and MtDNA-HVRII sequence differences.
RESULTS AND DISCUSSION
Observation of 192 nucleotide positions in MtDNA-HVRll control region sequences of 101 Korku tribe belonging to Austro-Asiatic linguistic group yielded 22 variable substitutions of which 4 were transversions. MtDNA-HVRII sequence information on 35 unrelated individuals of Nihal tribe (GenBank accession number AY 103119 to AY 10315) belonging to same linguistic category and co-inhabiting with Korku were also utilized for comparison. All together 48 and 18 haplotypes were scored among Korku and Nihal respectively (Table 1). Frequency distribution varied within and between tribes, the most commonly occurring haplotypes were also found specific to each tribe. The sample size of Nihal is only 35 compared to Korku 101, however the most dominant haplotype No 27 among Nihal is not found in Korku. The results were indicative of the utility of MtDNA control region sequences, which were more appropriate to reveal local population history.6 High substitution rate and reticulation in MtDNA control region were known. The HVRll control region sequences were utilized in view of its low substitution rate compared to HVRl.7 Pairwise mismatch distributions were routinely used to infer recent demographic population expansion8 and among Korku unimodal distribution (data not shown) indicated population expansion.
Maternal birthplaces of individuals of Korku tribe, aged 60-85years were located on a village map of Dharni Taluq of Amravathy district, Maharastra, India along with haplotypes (Figure 1). The most commonly occurring haplotype 9 was found widely distributed, even extending to the neighboring state, the fringe area of the geographic universe of Korku tribe. A Mantel test for correlation between pairwise maternal geographic distances and MtDNA-HVRll sequence differences (Table 2) yielded statistically significant negative correlation (-0.1951 p=0.05).
The results of the present study could be utilized to infer the possible demographic scenario of ancient migration of Austro-Asiatic tribes in Central India. Korku and Nihal were distributed in the same geographic space and number around 30,000 and 10,000 respectively. No written records exist as to their settlement. They were the southern most extension of Austro-Asiatic tribes in central India, was based on their language and genetic inferences. The route of their migration was further exemplified by the existence of various endogamous Austro-Asiatic tribes in the contiguous areas extending from eastern to central India. The possible demographic scenarios regarding migrationary history of Austro-Asiatic tribes from eastern to central India could be 1. Migration on familial lines, over a long period 2. Initial migration on familial lines and further local population expansion and 3. Mass migration. Migration on familial lines could have given a strong spatial structure with respect to maternal MtDNA sequences. Local population expansion is also unexplainable with a trend of negative correlation values at narrower distances between pairwise maternal geographic distances and MtDNA-HVRll sequence differences. The most probable migrationary event could have been mass migration, which is further exemplified by wide geographical distribution of common haplotypes among Korku. This interpretation needs to be considered with caution. Female gene flow also could have contributed to the spatial structure presented. To what extent gene flow played a role will be discernible with the exposition of further data on lineages comprised of MtDNA and non-recombinant Y chromosome SNPs. However given the limitations, It is possible to visualize a demographic scenario wherein Korku and Nihal were two sections of the extant Austro-Asiatic tribes in eastern India, who migrated in large numbers and occupied same geographical area in central India. This is evident from the core elements in the form of dominant haplotypes found among the two endogamous groups. Obviosuly, the present habitat is not their place of expansion. Finally, it is very pertinent to note that Korku and Nihal represent extant Austro-Asiatic populations in central India, and for any medical epidemiology or intervention studies, they need to be considered as independent populations.
Copyright 2003 - the Indian Society of Human Genetics
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