Tiny tardigrades have three claims to fame: their charmingly pudgy appearance, delightful common names (water bear and moss piglet) and stunning resilience in the face of threats ranging from the vacuum of space to temperatures near absolute zero.

Now scientists have identified a key mechanism contributing to tardigrades’ resilience—a molecular switch of sorts that triggers a hardy dormant state of being. The researchers hope that the new work, published on January 17 in the journal PLOS ONE, will encourage further exploration of the microscopic creatures’ ability to withstand extreme conditions.

“It’s opened up a whole huge repertoire of experiments we can now pursue,” says Leslie Hicks, a chemist at the University of North Carolina at Chapel Hill and a co-author of the study. . . .

When Kolling told Hicks about seeing free radicals in a tardigrade, Hicks wondered if these atoms might play a role in the animal’s hardiness. The team devised several experiments to temporarily expose little water bears to stress-inducing, free-radical-producing conditions—including high levels of salt, sugar and hydrogen peroxide.

Under these forms of stress, tardigrades curl up into a temporary protective state of dormancy called a tun. “When there’s a lot of stress, they’re masters of protecting themselves,” Kolling says. The researchers monitored whether the tardigrades entered their protective state and, if so, whether they could bounce back and resume normal activity when conditions improved.

Hicks studies signaling interactions between free radicals and cysteine, a key component of proteins, and she wondered whether the mechanism could play a role in tun formation. So the scientists exposed the tardigrades to different kinds of molecules known to block cysteine oxidation, as scientists call binding by a free radical. Under stressful conditions, with cysteine unavailable to the free radicals being produced, the tardigrades couldn’t form tuns.