The ground squirrel has adapted to be less sensitive to cold than its non-hibernating cousins, according to a new study published in the journal Cell Reports. This new finding comes from researchers at Yale University, who found that the unique tolerance is linked to a specific cold-sensing protein in the sensory nerve cells of the ground squirrels and another hibernator, the Syrian hamster.
In the study, the group took mice — which do not hibernate — and put them on one of two hot plates. One of the plates was 86 degrees Fahrenheit, while the other was much colder. Almost all of the rodents strongly preferred the warmer plate. However, when the team ran the same experiment with ground squirrels and Syrian hamsters, they found the mammals did not notice any difference in plate temperatures until one dipped below 50 degrees Fahrenheit.
Further analysis of the rodents showed that a cold-sensing protein known as TRPM8 activated much more easily in mice than it did in hamsters and squirrels. The molecule is found in the sensory nerve cells of vertebrates and sends a cold sensation to the brain when temperature drops.
Though the team is not sure, they believe this resistance is directly linked to hibernation. Falling asleep when you are cold is not easy to do. While hibernation is different than normal sleep, the team speculates cold tolerance could help squirrels and hamsters transition to the long slumber. If an animal feels chilly, its body will expend a lot of energy trying to warm up, which then makes it harder to sleep.
“If these animals were to feel cold, they would not be able to hibernate because their sensory system would tell the rest of the body that they need to warm up first,” said study co-author Elena Gracheva, a physiologist and neuroscientist at Yale University, in a statement. “They would not be able to survive as a species.”
Scientists are not yet sure how TRPM8 gets activated by cold, but researchers recently published a detailed structure of the protein. The team hopes that structure will allow them to expand on their research by linking genetic adaptations for cold tolerance in TRPM8 with specific structural changes in the protein.