How a species of ground squirrel manages to go without food and water over the winter months

A team of molecular and physiology specialists at the Yale University School of Medicine has uncovered some of the hibernating secrets of thirteen-lined ground squirrels, and have partly explained how it manages to avoid thirst during its long winter layover. Their paper is published in the journal Science.

Prior research has shown that the thirteen-lined ground squirrel, which lives on the North American plains, hibernates from six to eight months every year during the winter. Research has also found that the squirrels do not eat or drink for the entire time they are in hibernation, even when they stir occasionally. In this new effort, the research team sought to determine how this is possible.

The researchers followed up on their previous work that showed that during their hibernation, the squirrels maintain ion levels in their blood close to the levels seen in active squirrels. They do so, the team found, by both conserving water in the body and by moving ion reserves into parts of their bodies where it would not be absorbed into the bloodstream.

They also found that some of the squirrel’s hormones were acting as antidiuretics, helping to hold onto water. They noted that the parts of the squirrel brain that signaled for the production of such hormones remained high during torpor states.

What the researchers really wanted to know was how the squirrels turned off feelings of thirst. They found that if the squirrels were offered water when awakened from torpor, or during one of their short waking times during hibernation, the squirrels would refuse to drink. And it did not appear they had to fight any desire for it. They tried offering the squirrels salt and found they were willing to take it, suggesting it was used as part of the hibernation process.

They next looked at protein expression in the brain, neural activity and the response of neurons to thirst-triggering hormones. They found that such neurons did respond as they would during times when the squirrels were not hibernating. Thus, some brain mechanism was preventing the neuronal signals from reaching the parts of the brain that responded with the sensation of thirst.

Unfortunately, the team was not able to find the mechanism, but they plan to keep looking. They suggest fully understanding how a mammal like a squirrel can survive hibernation, when its body temperature falls to near freezing, could help with efforts to send humans on long space missions or better survive long surgeries.

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