For many of Canada’s hibernating animals, surviving winter is a lot tougher than just laying down for a nap. The season is even harder on small northern animals like the arctic ground squirrel, which hibernate in extreme temperatures and are limited in where they can find shelter due to the permafrost.

But the arctic ground squirrel has a unique way of dealing with this problem, according to a new study published in Biology Letters.

“They’re like no other hibernator” says Rudy Boonstra, a professor of Biological Sciences at the University of Toronto Scarborough and one of the authors of the study. Boonstra explains that the temperature in the squirrels’ hibernating environment can get as low as -23 degrees Celsius. The researchers found that in order to keep its body temperature high enough, the arctic ground squirrel burns muscle as well as fat. But that means the creatures must quickly build up large amounts of muscle during the summer months.

The researchers report that the arctic squirrel increases its muscle mass 30 per cent over the summer and does so by producing high levels of testosterone and other anabolic steroids.

Typically animals would face risks like a weakened immune system or altered behaviour from such high steroids levels. Not so for the arctic ground squirrel.

“Their immune system has androgen levels no greater than my control species, which was the Columbian ground squirrel,” says Boonstra. “They’ve been able to de-couple what anabolic steroids normally do.”

The research team did their tests during the summer of 2009. Although only a small sample was tested (seven arctic ground squirrels and six Columbian ground squirrels as a control group) the research team found clear evidence that arctic ground squirrels had large numbers of androgen receptors in muscles tissue and a lack of those same receptors in their immune system, protecting it from damage.

Building large stores of protein in muscle tissues and burning it throughout the winter gives the arctic squirrel access to glucose which is needed to protect important systems like the brain and heart.

This target steroid adaptation allows the arctic squirrel to build the muscle it needs quickly, a key element to the species’ survival while hibernating in arctic conditions.
As the northern climate changes Boonstra wonders if over time that adaption will still be necessary. While it will take thousands of years, he said other species of squirrels may find they are able to survive further north.

“Here we have a highly adapted organism dealing with this particular, very serve environment and climate change is going to alter that,” says Boonstra.