Gut bugs help squirrels survive the winter

For many animals that hibernate through the winter, a 6-month fast inevitably results in a loss of muscle mass, despite dramatically lower metabolic rates in hibernation. Not so for the 13-lined ground squirrel Ictidomys tridecemlineatus. A group of researchers at the University of Wisconsin–Madison have worked out how these animals prevent muscle wastage during hibernation: nitrogen management in their guts (Science 2022, DOI: 10.1126/science.abh2950).

Hannah V. Carey and Fariba Assadi-Porter led the work, which involved using stable isotopes to track the path of nitrogen and carbon through the squirrels during wakefulness and hibernation. As expected, the animals broke down their proteins for fuel during hibernation, producing urea.

Scientists had previously proposed that critters like these squirrels might salvage this nitrogen waste as part of their sleepy survival. The new research proves it. Gut bacteria in the hibernating squirrels take the urea and remodel it into amino acids that the rodents resorb and use to produce fresh proteins. The gut microbiome in hibernating squirrels has more urea-munching microbes than that of active ones, the team found.

Muscle wasting is not just a problem for hibernators, of course. Muscle loss is an issue in humans, especially in old age or when malnourished. Maybe, the researchers say, we could learn a thing or two from these little mammals.