Yakutia in the Siberian Far East is one of the coldest places on Earth. Temperatures can drop below −70°C (-94°F) in the wintertime. But with their hairy winter coats, squat bodies, stubby limbs, and various other adaptations, native Yakutian horses thrive there in the open air year-round. Now, researchers analyzing their genomes reveal that these horses represent one of the fastest cases of adaptation to extreme temperatures. The findings are published in Proceedings of the National Academy of Sciences this week.
About 40 percent of Yakutia’s territory is above the Arctic Circle. Between the 13th and 15th centuries, a group of Turkic-speaking horse-riders migrated into what’s now the Sakha Republic of the Russian Federation. The Yakut people then successfully developed a unique economy based on horse and cattle breeding. Yakutian horses, the most northerly distributed horse on the planet, were sources of both milk and meat. They’re well-adapted for grazing in snowbound vegetation, and in addition to their thick coats and compact bodies, these horses also have seasonal metabolisms.
To better understand their evolutionary origin and the genetic basis of these striking adaptations, University of Copenhagen’s Ludovic Orlando sequenced the complete genomes of nine present-day Yakutian horses and two ancient ones from the early 19th century and from 5,200 years ago. Then they compared these genomes to those of two Late Pleistocene horses, 27 domesticated breeds, and three wild Przewalski’s horses (who were just sequenced a couple months ago).
Contemporary Yakutian horses, they found, don’t come from the native horses that lived in the area up until the mid-Holocene several millennia ago. Instead, they descend from domestic livestock introduced after the Yakut people settled in this subarctic landscape a few centuries ago. That means their metabolic, anatomical, and physiological adaptations emerged on very short time scales, evolutionarily speaking – making them an exceptional example of rapid adaptation to extreme temperatures.
Specifically, the team uncovered variations in regulatory DNA tied to hair density and development, subcutaneous fat storage, body surface-to-mass ratio, and metabolic and hormone signaling pathways that may minimize heat loss and help with cold tolerance.
Furthermore, the researchers also found evidence for convergent evolution with native human populations in the area as well as woolly mammoths. Genes involved in insulin metabolism and blood vessel constriction, for example, evolved independently in these other cold-adapted populations.