Genome sequencing of several ancient and present-day wild and domesticated horses reveals the origin of horses in the Yakutia region, Russia, as well as their rapid genetic adaptations to persistent cold temperatures.
Yakutia, located in eastern Siberia, is one of the coldest regions in the northern hemisphere, with winter temperatures dipping below -70C and permafrost covering nearly its entire area.
Despite these extreme conditions, between the 13th and 15th centuries a group of horse-riders migrated north into the area to escape Mongol expansion. These people brought with them their horse-faring way of life, and their descendants and domesticated livestock are still living in the Yakutia today.
There are also wild horses living in Yakutia, with adaptations such as compact bodies and short limbs, extremely hairy coats, and seasonal differences in metabolic activities that allow them to endure the frigid territory. The origin of these wild horses is still unknown and there are a few contending hypotheses in the literature today.
To understand the origin of wild Yakutian horses and investigate the genetic basis of their adaptations, an international group of scientists sequenced complete genomes of nine living horses and two ancient specimens dating from the early 19th century and ∼5,200 years ago. They then compared these DNA sequences with the genomes of two Late Pleistocene, 27 domesticated, and three wild Mongolian horses.
The researchers’ extensive analysis confirmed the leading hypothesis about the origin of wild Yakutian horses and revealed the nature of their genetic adaptations to extreme cold. The study had three major findings.
First, the present-day wild Yakutian population is not related to the region’s ancient horses, as evidenced by their discontinuity from the ~5,200 year old and Late Pleistocene genomes. In fact, wild and domestic Yakutian horses are much more related to other domesticated horses around the world, and the DNA evidence suggests that they both descended recently from domesticated Mongolian horses.
Second, since historical, and now DNA, evidence suggests that wild Yakutian horses were likely introduced after the human migrations six to eight centuries ago, their rapid adaptation to the climate of Yukutia is extremely surprising.
Genes involved in hair development, body size, and metabolic and hormone signaling pathways were a major part of the Yakutian horse adaptive genetic toolkit. Surprisingly, however, the “coding regions” (the region of a gene that actually translates into a physical protein) were not the main sites of the genetic adaptation – rather it was the regulatory regions, which are responsible for controlling the timing and magnitude of gene expression.
Third, and perhaps most interestingly, the authors found evidence for convergent evolution with native human populations and woolly mammoths. In other words, the patterns of genetic adaptation to cold climate seen in the Yakutian horses were very similar to adaptations seen in humans and mammoths that migrated into the Arctic. This suggests that there may be relatively few evolutionary strategies for adapting and surviving in the cold.
In conclusion, the emergence of wild horses in Yakutia likely began with a founding population of domestic horses that were transported by humans, and the major adaptations of these horses to the harsh environment emerged on very short evolutionary time scales, on the order of about 100 generations.