THE CURIOUS CASE OF THE HORSES WHO “HIBERNATE”

The Yakut horses of northern Siberia may provide lessons in how animal populations can respond to environmental extremes.

These days, when many of us protect our horses from winter chill with blankets and cozy stalls, consider the diminutive Yakut horses of Siberia. Researchers say that this hardy breed not only has the capacity to achieve a physical state akin to hibernation during periods of extreme cold, but it developed this adaptation with surprising swiftness.

The Yakutia region of the Russian Federation, also known as the Sakha Republic, is one of the coldest inhabited places on earth. Temperatures of -40 degrees Celsius (-40 degrees Fahrenheit) are common during the winter, and in the portion of Yakutia that sits above the Arctic Circle, temperatures may go as low as -70 degrees Celsius (-94 degrees Fahrenheit). Nonetheless, horses and humans continue to live and thrive in the region. Today Yakut horses are used for riding and pulling sleds, and as sources of milk and meat—as they have been for centuries.

An international group of researchers headed by Ludovic

Orlando, PhD, of the Centre for GeoGenetics at the Natural History Museum of Denmark, investigated the origins of the Yakut horses and the qualities that enable them to survive and thrive despite their inhospitable environment.

Although archaeological evidence suggests horses were present in the region 5,200 years ago, the researchers used DNA analysis to determine that modern Yakut horses descend from those brought by people who migrated to northern Siberia during the 13th and 15th centuries.

What’s more, the researchers say, the Yakut horse population quickly developed adaptations to its frigid environment. Specifically, modern Yakut horses are small in stature with compact bodies and short

legs, conformation that helps conserve body heat. They also grow thick winter coats, which help insulate them from cold.

Finally—and perhaps most interesting—Yakut horses appear to adjust metabolically to extreme cold. The researchers observed that the horses enter a “restful” state characterized by low body temperature, slow heart rate and reduced metabolic activity for hours at a time during winter. This response, called torpor, is used by bears, squirrels and other animals to cope with periods of cold and low food availability, but it had not previously been documented in horses.

Extended torpor, lasting for several days or weeks, is sometimes described as hibernation. Even as their metabolism slows during the harsh winters in their region, Yakutian horses remain active, entering a state that some researchers call “standing hibernation.”

Normally, an evolutionary response to environmental pressure plays out over thousands of years. However, the international research team determined that the Yakut horses made these adaptations in about 100 equine generations, one of the most rapid adjustments to extreme environmental conditions documented in animals.

These findings, say the researchers, could help to improve our understanding of how animals adapt to climate change and aid in the development of selected breeding programs that produce animals better suited to cope with extreme environments.

Reference: “Tracking the origins of Yakutian horses and the genetic basis for their fast adaptation to subarctic environments,” Proceedings of the National Academy of Sciences, December 2015