Water bears are probably the hardiest animals in existence, able to live through extreme heat, cold, pressure, radiation, and even the vacuum of space. Now, these water-dwelling critters have set a new personal best, with cryobiologists from Japan successfully reviving a tardigrade after it had been frozen for more than 30 years. What’s more, the defrosted creatures even managed to reproduce; with one laying 19 eggs of which 14 successfully hatched.
The water bears were able to survive this time in the cooler thanks to a process known as cryptobiosis. This is a state of extreme hibernation that many microscopic creatures use to survive difficult environments, such as those lacking water or air. In the tardigrade’s case, the creature’s metabolism slows down to less than 0.01 percent of its normal rate; it sheds nearly all of the water in its body, and curls up into a “tun” state — forming a tiny, indestructible pellet. It’s thought that some tardigrade species replace the water in their cells with natural antifreeze (glycerol) or crystalline sugars to preserve their structure.
In the case of these recently-revived tardigrades, the creatures were originally collected in November 1983 in moss samples from East Antarctica. The samples were stored at −20 °C after collection, and thawed in May last year over several days. Individual tardigrades were collected from the moss, with two of the creatures — nicknamed Sleeping Beauty (SB)-1 and SB-2 — judged to be alive. (Their bodies were still curled up in the “tun” state, while the others had stretched out again in miniature rigor mortis.) These individuals were then placed on a culture plate, immersed in water (Volvic), and left in the dark to think things over.
The tardigrades came to very, very slowly. Imagine taking a 31-year sleep and then instead of a hot cup of coffee when you wake up, all you’re given is a sip of water and a bit of algae to munch on. Here are the scientists from Tokyo’s National Institute of Polar Research (NIPR) describing the process for SB-1:
“SB-1 first showed slight movement in its 4th pair of legs on the first day after rehydration. This progressed to twisting of the body from day 5 along with movement in its 1st and 2nd pairs of legs, but the movements remained slow. After starting to attempt to lift itself on day 6, SB-1 started to slowly crawl on the agar surface of the culture well on day 9, and started to eat the algal food provided the culture plate on day 13.”
After taking nearly two weeks to come around, SB-1 started developing eggs on day 21, depositing them in five clutches by day 45. (Some female tardigrades can reproduce asexually.) SB-2, unfortunately, didn’t make it. It started moving at about the same time as SB-1, but stopped eating around two weeks in and died on day 20. An egg that had also been retrieved from the frozen moss sample was revived as well, hatching into a fully functional tardigrade on day six, which then went on to lay its own eggs just eight days later. This is a species that just doesn’t know how to quit.