Tardigrades can survive frozen oblivion by stopping their biological clocks: ScienceAlert

Reminiscent of the title character in the classic fairy tale “Sleeping Beauty,” famous tomboys can stop their biological clocks when they’re in a deep, cold sleep, new research suggests.

These ridiculously durable beasts already have a variety of superpowers that they use to withstand the harshest conditions, including armor to protect their important DNA from radiation and a special protein coating that prevents their cells from collapsing over long periods of time dehydration.

With this bag of tricks and more they can survive even in the vacuum of space.

To withstand freezing to death, sweet water bears enter an extreme form of hibernation called cryobiosis. In this state their metabolic activity essentially stops.

Now it turns out that their metabolism is not the only process that has been put on “pause”.

University of Stuttgart biologist Jessica Sieger and her colleagues exposed a bunch Milnesium inceptum delayed in alternating weekly periods of freezing at −30 °C (−22 °F) and feeding at 20 °C (68 °F), until they die. Another group was kept at room temperature.

Amazingly, out of a total of 716 latecomers, those who were periodically frozen lived twice as long as the control group. The oldest lived for 169 days, 94 of which were spent at room temperature, while the oldest late in the control group reached 93 days.

Overall, both groups spent the same amount of time actively alive, demonstrating that the biological aging of argon was dramatically slowed, if not completely stopped, by cryobiosis. This, the researchers say, confirms the “sleeping beauty” cryolife model of the animal’s biological clock, in contrast to other models that have suggested that aging either slows down or continues normally.

“During inactive periods, the internal clock stops and resumes once the organism is reactivated,” explains zoologist Ralph Schill, also from the University of Stuttgart. “Therefore, latecomers, which normally only live for a few months without periods of rest, can live for many years or even decades.”

These adorable near-immortals also go into a state of suspended animation under extremely dry conditions—a process called anhydrobiosis. Previous research by Schill has shown that snails inhibit their aging during this state as well, but this is the first time it has also been confirmed while they are in a frozen state.

This elegant trick allows the millimeter-sized beasts to wait out dangerous conditions and spring back into action when their environment is more favorable. For example, the return of rain after decades of drought, in place of the true loves kiss that woke Sleeping Beauty.

Tardigrades have been recovered after being frozen for over 30 years, still alive and fertile. But their suspended animation is not a foolproof system.

Safe freezing is a complex physiological process. Instead, death can occur if freezing happens too quickly — without allowing certain biochemical processes to complete quickly enough, the researchers explain.

Insufficient energy storage can be another factor that can go very wrong. Previous studies have shown that entering and exiting their deep sleep state uses energy stored in cells within the chonky animals’ body cavity.

“The severity, seasonality, unpredictability, and variability of environmental conditions determine invertebrate life cycle patterns,” Sieger, Schill and team summarize in their paper.

This research was published in Journal of Zoology.

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