Tardigrades, also known as water bears or moss piglets, may well be the most indestructible animals ever to roam the Earth. Though they are only half a millimeter long on average, these tiny creatures are giants when it comes to durability. Water bears can withstand temperatures from minus 458 degrees Fahrenheit on the bone-chilling end of the spectrum, all the way to 300 degrees on the fiery hot extreme. You can even toss a tardigrade out of a spaceship airlock and it would survive in the vacuum of space for well over a week, depressurization and radiation be damned.
As the new adage goes, "water bear don't care."
Now, a new study in the journal Cryobiology has found even more reason to respect the incredible durability of this adorable phylum. Led by Megumu Tsujimoto, a researcher at the National Institute of Polar Research, the research demonstrates that the Antarctic tardigrade species Acutuncus antarcticus can successfully reproduce after decades in frigid conditions, deprived of sustenance.
"In the available studies of long-term survival of micrometazoans, instances of survival have been the primary observation, and recovery conditions of animals or subsequent reproduction are generally not reported," the team wrote in the study's abstract.
"We therefore documented recovery conditions and reproduction immediately following revival of tardigrades retrieved from a frozen moss sample collected in Antarctica in 1983 and stored at minus 20 degrees Celsius [or minus 4 degrees Fahrenheit] for 30.5 years."
So essentially, two full-grown tardigrades and one tardigrade egg were collected from Antarctica's Yukidori Valley on November 6, 1983, and were subsequently put on ice and shelved for over 30 years. During that time, they hung out in suspended animation until Tsujimoto's team thawed them out in the balmy waters of a Petri dish in May of 2014. According to the paper, this is "the longest recorded cryptobiotic duration of survival for tardigrades as animals or eggs."
Understandably enough, it took the two adult water bears—playfully named Sleeping Beauty 1 and 2—a few days to regain their bearings.
The first big breakthroughs came on day six, when SB-1 began to crawl towards an appetizing patch of algae left in its dish. Amazingly, the rehydrated egg sample suddenly hatched on the same day, revealing a perfectly healthy tardigrade larva—a water bear cub, if you will. SB-3, as the newly born critter was called, was conceived in the same year that The Return of the Jedi hit theatres, but did not hatch until 2014.
The findings only got stranger from there. Around day 13, SB-1 was gobbling down its first meal since 1983, and SB-3 was observed developing eggs.
At around the three week point, both SB-1 and SB-3 had laid a new generation of tardigrade eggs via parthenogenesis, which is an asexual form of reproduction. (Depending on the species, water bears can reproduce either sexually or asexually, which is fitting given their general survivalist reputation.)
Sadly, SB-2 didn't weather its long period of dormancy as well as its brethren. It was able to recover somewhat, but it had lost use of some of its limbs, and was only able to eat a small amount of food before it perished on day 20, without producing progeny. This is a good reminder that while water bears are known for their insane hardiness, some individuals still have their limits.
"Tardigrades are not true extremophiles because they are not adapted to live in extreme conditions," evolutionary biologist Jim Garey told Astrobiology magazine. "They can merely survive exposure to such conditions. The longer they undergo such exposure, the greater their chance of dying. Tardigrades are always waiting for something better."
Even so, the fact that SB-1 and SB-3 were able to bounce back enough to begin breeding again is a testament to the resilience of tardigrades as a whole. Having reawoken in a completely new millennia, these two water bears were not only unfazed, they were game to start a family. Truly, tardigrades are the most indefatigable troopers in evolutionary history.