Genetic spotlight thrown on a hardy, high-altitude horse breed

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A horse in Tibet. Photo: Jan Reurink (originally posted to Flickr as T251) CC BY 2.0 via Wikimedia Commons

The Tibetan horse has been of economic importance to the region for hundreds, if not thousands, of years, yet little is known of its origins.

Did the breed originate in Tibet or did it enter the area via ancient migratory routes?

Tibetan horses currently number a little over 270,000 individuals and are mainly distributed in the Qinghai-Tibet Plateau, the highest ecosystem in the world, with an average elevation greater than 4000 meters.

Tibetan horses have shown outstanding adaptability to extreme, high-altitude environments, according to researchers, and to this day they play a critical role in transportation, stock farming, and trade.

They were crucial in the horse-silk trade with Han Chinese during the Tang and Song dynasties, from around 618 to 1279 AD).

Archaeological records indicate that horses have been present in Tibet at least since the Neolithic period more than 4000 years ago, but what of the Tibetan horses we see today?

Now, researchers have undertaken extensive testing of maternal DNA to paint a much clearer picture of its origins.

Lin Yang, Xiaoyan Kong and their colleagues, writing in the journal PLOS ONE, have described a study in which they analysed maternal DNA in 2050 horses, comprising 290 from five Tibetan populations and 1760 from other areas across Asia.

Their work revealed multiple maternal lineages in the Tibetan horse.

Their results indicate that the Tibetan horse migrated first from Central Asia to Mongolia, moved south to eastern Tibet (near Deqen), then finally westward to other regions of Tibet.

Analysis of population genetics showed that the Deqen horse of eastern Tibet is more closely related to the Ningqiang horse of northern China than to other Tibetan horses or the Yunnan horse.

The study team also identified a novel lineage that mainly comprises Tibetan and Yunnan horses, suggesting an indigenous domesticated origin for some Tibetan horse breeds from local wild horses.

The findings indicate that that modern Tibetan horse breeds originated from the breeding of local wild horses with exotic (introduced) domesticated populations from the broader region, including lineages from outside China, despite its dominance of the trade routes.

“We found that the five Tibetan horse populations can be clustered into most previously reported lineages, suggesting a complex origin,” the study team wrote.

“Most Tibetan haplotypes were present in the originating Kazakhstan lineage, indicating that ancestors of Tibetan horses generally immigrated from other regions.”

Generally, livestock, such as horse and sheep, moved with nomadic tribes as they were important transport tools and food resources for people.

“Historical records provide some clues regarding the likely path of gene flow. Notably, the South Silk Road of the Tang dynasty (618~907 AD) connected central China with the Tibetan plateau, beginning from Xi’an of Shanxi province, then passing through Gansu, Qinghai, Qamdo, Deqen, westward to Xigazê, and finally reaching Nepal.

“Furthermore, the Mongolian westward expansion on horseback during the Yuan dynasty likely exerted a direct genetic influence on Tibetan horses.

“Considering this evidence, we propose that the migratory route of some ancestral Tibetan horses began in Central Asia, moved up to Inner Mongolia, then south to eastern Tibet (Deqen), and finally spread throughout the entire Tibet Autonomous Region.”

The full study team comprised Lin Yang and Hao Zhang, from China Agricultural University in Beijing; and Xiaoyan Kong, Shuli Yang, Xinxing Dong, Jianfa Yang and Xiao Gou, from Yunnan Agricultural University in Kunming.

Yang L, Kong X, Yang S, Dong X, Yang J, Gou X, et al. (2018) Haplotype diversity in mitochondrial DNA reveals the multiple origins of Tibetan horse. PLoS ONE 13(7): e0201564. https://doi.org/10.1371/journal.pone.0201564

The study, published under a Creative Commons License, can be read here

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