Genetic proof for domestication of sheep in Indian subcontinent
Researchers at the Central University of Kerala (CUK) have found that domestication of sheep had taken place in the Indian subcontinent, especially in the Indus Valley civilisation regions in the 6th or 7th millennium BC.
The study, led by M. Nagarajan, Assistant professor, Department of Genomic Science, CUK, found genetic evidence that sheep had been domesticated in the region in contrast to the general belief that they were domesticated then in West Asia alone, and that they had arrived in the Indian subcontinent through migration.
Even though India ranks second in terms of sheep population, represented by as many as 44 well-described breeds in addition to several nondescript species, genetic diversity and phylogeography of Indian sheep breeds remained poorly understood, particularly the south Indian breed, Dr. Nagarajan told The Hindu.
However, the study, which examined the south Indian breeds, provided strong genetic evidence that the Indian subcontinent was one of the domestication centres of the lineage A sheep.
When DNA sequences were compared with other breeds across the world, it was found that the Indian sheep haplotypes were unique and highly diverse. The high genetic diversity and statistical analysis suggest that sheep was domesticated in the country.
“We are proposing that wild Sheep, O. vignei blanfordi in Mehrgarh [Pakistan], may be a potential progenitor of domestic sheep lineage, and detailed genome sequencing of this wild sheep may further contribute to our understanding of the genetics of domestic sheep,” said Dr. Nagarajan.
He added that the study also found that the introduction of sheep ‘lineage B’ into the Indian subcontinent had been through sea route, and not from the Mongolian plateau, as proposed by researchers in China.
Researchers also retrieved the mitochondrial DNA sequences of another 11 breeds for analysis, which further strengthened their study, he added.
When the researchers analysed these sequences along with published data of domestic and wild sheep from different countries, including India, the haplotype diversity was relatively high in Indian sheep, which were classified into the three known major mitochondrial DNA lineages namely A, B, and C.
It was found that lineage A was predominant among Indian sheep, whereas lineages B and C were observed at low frequencies, particularly lineage C was restricted to the breeds of northern and eastern India.
He said among the south Indian breeds, except for Mandya, all others, notably Bellary, Coimbatore, Hassan, Katchaikatty Black, Nilgri, Ramnad White, and Vembur, were fully encompassed with lineage A, while Kenguri Kilakarsal, Madras Red, Mecheri, and Tiruchy Black breeds, had very low occurrences of lineage B mitochondria.
In contrast, a majority of individuals of Mandya and Sonadi breeds carried a relatively high frequency of lineage B.
“Our study will be useful in understanding the history of agriculture in Indus Valley Civilisation,” Dr. Nagarajan said.
In terms of practical applications, the study shows that two breeds of Indian sheep, Sonandi and Mandya, carry lineage B mitochondria at very high frequency as compared to other Indian breeds. In terms of conservation of sheep genetic resources, these two breeds are important with respect to maternal lineages, he added.
The research titled ‘Evidence for independent domestication of sheep mtDNA lineage A in India and introduction of lineage B through Arabian Sea route’ has been published in the journal Scientific Reports. The researchers included Ranganathan Kamalakkannan, Satish Kumar, Karippadakam Bhavana, Vandana R. Prabhu, Carolina Barros Machadi, Hijam Surachandra Singha, Dhandapani Suresh Gopi, and Vincy Vijay.