All hail the water bears.
Tardigrades are one of the most fascinating creatures on Earth—and the moon. Last year, the Israeli spacecraft Beresheet crashed on the moon, spilling thousands of the dehydrated tardigrades that scientists loaded onto the lander (along with human DNA samples), according to a WIRED report.
The tardigrades were in “tun” form, a dormant state where they shrivel up into a ball, expel most of the water in their bodies, and lower their metabolism via cryptobiosis until they enter an environment better suited to sustain life. They can exist like this for decades. They’re also pretty hardy and can endure the harshest environments, including subzero temperatures—and crash lunar landings.
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Now, the ever-mysterious, alien-like creatures have presented scientists with another quandary: What’s the deal with the newly discovered tardigrade species that lay spiked eggs?
Various Dactylobiotus ovimutans eggs are shown, each displaying its own custom morphology.
In a new paper published in Scientific Reports, scientists reveal that Dactylobiotus ovimutans, the new species, displayed a “range of eggshell morphologies” despite the fact that “the population was cultured under controlled laboratory condition.”
The researchers believe an “epigenetic factor” could be causing the range of shapes and features seen on the D. ovimutans eggs. But the mystery still remains: Why has D. ovimutans turned to epigenetics (the activation/deactivation of genes that has no affect an organisms DNA sequence) when it comes to their offspring?
The jury is still out. But until we get an answer, here’s everything else we do know about these fascinating, space-faring creatures.
What’s So Special About Tardigrades?
Tardigrades are a class of microscopic animals with eight limbs and a strange, alien-like behavior. William Miller, a leading tardigrade researcher at Baker University, says they are remarkably abundant. Hundreds of species “are found across the seven continents; everywhere from the highest mountain to the lowest sea,” he says. “Many species of tardigrades live in water, but on land, you find them almost everywhere there’s moss or lichen.”
In 2007, scientists discovered these microscopic critters can survive an extended stay in the cold, irradiated vacuum of outer space. A European team of researchers sent a group of living tardigrades to orbit the earth on the outside of a FOTON-M3 rocket for 10 days. When the water bears returned to Earth, the scientists discovered that 68 percent lived through the ordeal.
Although tardigrades are unique in their ability to survive in space, Miller insists there is no reason to believe they evolved for this reason or—as a misleading VICE documentary has implied—that they are of extraterrestrial origin. Rather, the tardigrade’s space-surviving ability is the result of a strange response they’ve evolved to overcome an earthly life-threatening problem: a water shortage.
Land-dwelling tardigrades can be found in some of the driest places on Earth. “I’ve collected living tardigrades from under a rock in the Sinai desert, in a part of the desert that hadn’t had any record of rain for the previous 25 years,” Miller says. Yet these are technically aquatic creatures, and require a thin layer of water to do pretty much anything, including eating, having sex, or moving around. Without water, they’re about as lively as a beached dolphin.
But land-dwelling tardigrades have evolved a bizarre solution to living through drought: When their environment dries up, so do they. Tardigrades will enter a state called desiccation, in which they shrivel up, losing all but around 3 percent of their body’s water and slowing their metabolism down to an astonishing 0.01 percent of its normal speed. In this state, the tardigrade just persists, doing nothing, until it’s inundated with water again. When that happens, the creature pops back to life like a re-wetted sponge and continues onward as if nothing had happened.
What’s even more astonishing is that tardigrades can survive being in this strange state for more a decade. According to Miller, a few researchers believe some species of tardigrades might even be able to survive desiccation for up to a century. Yet the average lifespan of a (continuously hydrated) tardigrade is rarely longer than a few months.
“It sounds quite strange,” says Miller, “that even though these tardigrades only live for a few weeks or months, that lifetime can be stretched over many, many years.”
How Does the Tun State Protect Tardigrades?
In its desiccated state, the tardigrade is ridiculously, almost absurdly resilient. Laboratory tests have shown that tardigrades can endure both an utter vacuum and intense pressures more than five times as punishing as those in the deepest ocean. Even temperatures up to 300 degrees Fahrenheit and as low as -458 degrees F (just above absolute zero) won’t spell the creature’s doom.
But the exact source of its resilience is a mystery, says Emma Perry, a leading tardigrade researcher at Unity College in Maine. “In general, we know very little about how this species functions, especially when we’re talking about the molecular level.”
There are clues. Scientists have learned that when the tardigrade enters its desiccated state, “it replaces some of its cell contents with a sugar molecule called trehalose,” Perry says.
Researchers believe this trehalose molecule not only replaces water, but also in some cases can physically constrain the critter’s remaining water molecules, keeping them from rapidly expanding when faced with hot and cold temperatures. This is important, because expanding water molecules (like what happens when you get frostbite) can mean instant cellular death for most animals.
What About Space Radiation?
Space is deadly, and not just because of the vacuum. Outside our protective atmosphere there is killer radiation caused by distant supernovae, our sun, and other sources. Space radiation comes in the form of harmful charged particles that can imbed in the body of animals, ripping apart molecules and damaging DNA faster than it can be repaired.
But here, too, the tardigrade seems oddly prepared for life in space. According to Peter Guida, the head of NASA’s space radiation laboratory, one of the biggest radiation concerns for astronauts (and space-bound tardigrades) is a set of molecules called reactive oxygen species. Ionizing radiation enters the body and bores into wayward molecules that contain oxygen. In simple terms, those newly irradiated molecules then troll through the body causing all sorts of harm.
Tardigrades during their desiccated state produce an abnormal amount of anti-oxidants (yes, these actually exist outside the health-food world), which effectively neutralize those roaming, evil reactive oxygen species. Partly because of this talent, tardigrades have been found to withstand higher radiation doses with far greater success than researchers would otherwise believe they should.
The reason that tardigrades would have evolved to survive high radiation doses is a mystery, too. However, Miller points to a leading theory: Perhaps tardigrades evolved to be swept up by the wind and survive in the earth’s atmosphere—which would explain not only their hardiness, but also why they’re found all over the world.
A Seemingly Simple Weakness
But there might be one thing tardigrades are not so well-equipped to handle: high temperatures over a prolonged period of time, per a study published in Scientific Reports in January 2020. The study revealed that this temperature-based Achilles’ heel also extends to when tardigrades are in their protective tun states.
Researchers studied Ramazzottius varieornatus, a species of tardigrade, in tun state and noted nearly 50 percent of the tardigrades exposed to 181 degrees Fahrenheit over the course of an hour perished. Active tardigrades—that is, those not in tun state—fared even worse.
These temperature experiments show that given time, most tardigrades can adjust to intense temperature fluctuations: The tardigrades who had an hour to acclimate to intense heat faced higher mortality rates, compared to those who had a full 24 hours.
“Tardigrades can survive pressures that are comparable to those created when asteroids strike Earth, so a small crash like this is nothing to them,” Lukasz Kaczmarek, an expert on tardigrades, told The Guardian.
So what does this mean for us? If humans can replicate cryptobiosis in the way tardigrades do, we’d live far longer than the average life expectancy. According to Kaczmarek, when a tardigrade enters the tun state, it doesn’t age. It becomes dormant at one month old and can wake up years later and still biologically be the same age.
“It may be that we can use this in the future if we plan missions to different planets, because we will need to be young when we get there,” said Kaczmarek.