Yakutian horses adapted to the extreme cold of eastern Siberia in less than 800 years, according to researchers.
The study team said the change happened almost overnight in evolutionary terms, covering only 100 or so generations. The process involved changes in the expression of a raft of genes, including some also selected in human Siberian groups and the extinct woolly mammoth.
The researchers, in a new scientific study, compared the complete genomes of nine living and two ancient Yakutian horses from Far-East Siberia with a large genome panel of 27 domesticated horses.
The analysis shows that the current population of Yakutian horses was founded after the migration of the Yakut people into the region in the 13-15th century AD. Yakutian horses thus developed their striking adaptations to the extremely cold climate of the region in less than eight centuries.
This represents one of the fastest examples of evolutionary adaptation yet seen within mammals.
The international team of researchers, whose findings have been published in the early edition of PNAS (Proceedings of the National Academy of Sciences of the USA), said horses have been essential to the survival and development of the Yakut people, who migrated into the Far-East Siberia, probably from Mongolia.
There, Yakut people developed an economy almost entirely based on horses. Horses were crucial for communication and keeping the population in contact within a territory slightly larger than Argentina, and with 40% of its surface area situated north of the Arctic Circle.
Horse meat and hides have also been revealed as crucial for surviving extremely cold winters, with temperatures occasionally dropping below -70 degrees Celsius.
Horses have been present in Yakutia for a long time, as 30,000 year-old Late Pleistocene fossils from the region show. Yet, the study team, led by the University of Copenhagen’s Dr Ludovic Orlando, showed that ancient horses of this region were not the ancestors of the present-day Yakutian horses.
The genome sequence obtained from the remains of a 5200 year-old horse from Yakutia appears within the diversity of a now-extinct population of wild horses that the team discovered last year in Late Pleistocene fossils from the Taymir peninsula, in Central Siberia.
This new finding extends by thousands of kilometres eastwards the geographical range of this divergent horse population, which became separated from the lineage leading to modern horses some 150,000 years ago. It also extends its presence up to 5200 years ago – a time when woolly mammoths also became extinct.
“This population did not appear on any radar until we sequenced the genomes of some of its members,” said Dr Orlando, who is with the Centre for GeoGenetics at the Natural History Museum of Denmark, which is part of the University of Copenhagen.
“With 150,000 years of divergence with the lineage leading to modern horses, this makes the roots of this population as deep as the origins of our human species.”
Interestingly, the new genome analyses show that the horses Yakut people now ride, and probably rode throughout history, as shown by the genome of a horse that lived about 200 years ago, are not related with this now-extinct horse lineage, but rather with the domesticated horses from Mongolia.
“We know now that the extinct population of wild horses survived in Yakutia until 5200 years ago.
“Thus, it extended from the Taymir peninsula to Yakutia, and probably all across the entire Holarctic region. In Yakutia, it may have become extinct prior to the arrival of Yakut people and their horses. Judging from the genome data, modern Yakutian horses are no closer to the extinct population than is any other domesticated horse.”
The new genome analyses show that the founders of the modern Yakutian horse population probably entered the region with Yakut horse-riders in the 13-15th Century AD.
“This is truly amazing as it implies that all traits now seen in Yakutian horses are the product of very fast adaptive processes, taking place in about 800 years.
“This represents about a hundred generations for horses. That shows how fast evolution can go when selective pressures for survival are as strong as in the extreme environment of Yakutia.”
The team set out to identify the genes underlying such adaptations. Strikingly, they found that a large fraction of the selection signatures were not located within the coding region of genes, but within their upstream regulatory regions. It thus suggests that the adaptation of Yakutian horses to their environment took place through a massive reprogramming of gene expression.
“The founder group of the current population was quite reduced in size,” he said.
“The genetic variation standing within gene bodies was, thus, probably limited in comparison to that present within regulatory regions. These regulatory variants probably offered as many possibilities to rapidly modify horse traits in a way that was compatible with their survival.”
Focusing on the genes and their regulatory regions showing evidence of selection, the team identified key biological functions involved in the adaptive process. These concern physical changes, hormonal responses involved in heat regulation and even the production of anti-freezing compounds.
The list of selective signatures also include genes, such as TGM3, which is involved in hair development and might be responsible for the extremely hairy winter coat of Yakutian horses.
Fellow researcher Dr Pablo Librado, who is also with the university, said: “In addition to unveiling their evolutionary origins, our approach helped narrow down the genetic basis of adaptations that are unique to Yakutian horses. In one word, their genetic makeup.
“We also found genes that were reported to have undergone selection in other Arctic populations, such as indigenous Siberian humans, and even the woolly mammoth. It provides a compelling example of evolutionary convergence, where unrelated groups exposed to similar environments end up independently developing similar adaptations.”
Colleague Dr Clio Der Sarkissian, who also took part in the study, said the work showed the power of ancient DNA. “We would have never been able to discover the existence of the now extinct ancient population of horses by analyzing the genome of modern horses.
“With ancient genomes, we can now understand the dynamics of past populations at unprecedented levels and track, through space and time, how these became adapted to changing environments.
“Applied to pre-industrial museum specimens, our approach can therefore help following how extant populations have been affected by ongoing climate changes and recent human activities. This can help develop tailor-made conservation programs, which will be ultimately essential for preserving endangered populations.”
The study group has already implemented such approaches for preserving the Przewalski’s horse, which represents the last truly wild horse living in the planet.
Tracking the origins of Yakutian horses and the genetic basis for their fast adaptation to subarctic environments.
Pablo Librado et al, doi: 10.1073/pnas.1513696112
The abstract can be read here.