Spotlight on the genetics of a robust, high-altitude horse breed

A horse in Tibet. Photo: Jan Reurink (originally posted on 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, but little is known about its origins.

Does the breed originate from Tibet or did it enter the region through ancient migratory routes?

Tibetan horses currently number just over 270,000 individuals and are mainly distributed on the Qinghai-Tibet Plateau, the world’s highest ecosystem, with an average altitude of over 4,000 meters.

Tibetan horses have shown exceptional adaptability to extreme and high-altitude environments, researchers say, and to this day they play a vital role in transportation, herding and trading.

They were essential in the horse silk trade with the 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 over 4,000 years ago, but what about 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 diary PLOS ONE, described a study in which they analyzed the maternal DNA of 2,050 horses, including 290 from five Tibetan populations and 1,760 from other parts of Asia.

Their work revealed multiple maternal lines in the Tibetan horse.

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

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

The study team also identified a new line that mainly includes Tibetan and Yunnan horses, suggesting a domesticated indigenous origin for some Tibetan horse breeds from local wild horses.

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

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

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

In general, cattle, such as horses and sheep, moved with the nomadic tribes as they were important tools of transportation and food resources for the people.

“Historical documents provide some clues as to the likely path of gene flow. Notably, the Southern Silk Road of the Tang Dynasty (618 ~ 907 AD) linked central China to the Tibetan plateau, starting from Xi’an of Shanxi province, then passing through Gansu, Qinghai, Qamdo, Deqen, west to Xigazê, and finally arrive in Nepal.

“Moreover, Mongolian expansion westward on horseback during the Yuan Dynasty probably exerted a direct genetic influence on Tibetan horses.

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

The full study team included 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) The diversity of haplotypes in mitochondrial DNA reveals the multiple origins of the Tibetan horse. PLoS ONE 13 (7): e0201564.

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

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