“WATER BEARS ARE MINI ASTRONAUTS“
What will be the last creature on Earth?
A tardigrade expert answers
Three people, one big question. In this edition: apocalypse critters.
Jan Beccaloni‘s 3-minute noodles
“Tardigrades are out of this world. They are the first known animals to survive after exposure to the hard vacuum of outer space. In 2007, some tardigrades were taken on a spin around the Earth where they were also exposed to UV solar radiation. Although some of these mini-astronauts died and some had reduced egg-laying capacity, many lived to tell the tale and to produce viable offspring. They have also been aboard the International Space Station in 2011, and cosmic radiation wasn’t too much of a problem.
They’re chill! Tardigrades have become a perfect model organism for space research because they have a high resistance to the different kinds of stress factors associated with cosmic journeys. There is even speculation that they might be sent to Mars. In 2019, it was thought that tardigrades might have started living on the Moon because they were in a lunar lander which crashed there, but they most likely did not survive the impact.
Tardigrades are *so* cool that there are heaps of songs written about them… like ‘Walking on The Moon’ (The Police), ‘Intergalactic’ (Beastie Boys) and ‘Out of Space’ (The Prodigy).
They are not ‘penises with teeth’, like the naked-mole rat. Instead of having a dubious moniker, their common names include water bears and moss piglets. That’s because they look as if they have been inflated with a bicycle pump, as they have plump keg-like bodies with four pairs of unjointed stubby legs that either have claws or suction disks at the tips. They have a tubular mouth that is flat-ended, giving it the appearance of pig snout, and are often found in mosses and lichens where they feed on small invertebrates, algae and plant cells, hence the name moss piglets. Some larger species feed on smaller tardigrades. They are also known as water bears because of their slow, lumbering gait and bear-like appearance.
Not young kids on the block. Tardigrades are certainly old-timers. It is likely that they evolved more than 500 million years ago. There are specimens with modern forms found in amber from the Cretaceous period (66 -145 mya). There are currently around 1,300 known species of these super-cute microscopic invertebrates, which are distantly related to arthropods. They grow by shedding their skin.
They’re cosmopolitan critters. Tardigrades can be found in regions all over the world and have evolved to colonise a vast array of environments such as the deep sea, hot springs, mountains, the Antarctic, tropical rainforests and in coastal dunes. However, they can also be found in more temperate environments. They basically can remain active wherever there is some moisture.
They’re Wim Hof! Tardigrades are capable of withstanding temperatures from to -276°C to 150°C. Their super cold tolerance is due to cryobiosis, which is essentially the ability to suspend their metabolism. The water content of their body drops down to 3% and this prevents them from going pop when their tissues freeze and expand. Although tardigrades have a short life span from between 3-4 months and two years, depending on the species, they can last for 30 years at −20 °C!
Tardigrades have their own matrix. They can withstand prolonged periods of dehydration, going without water or food for up to ten years. This is because a glass-like matrix forms within cells to protect them upon desiccation. They can also withstand extreme low and pressures, depths of 4,700m up to an altitude of 6,000m, and 1,000 times more radiation than other animals, partly because they have an amazing ability to repair damage to their DNA.
Not actually extremophiles. As J.K. Ingemar stated in ‘Extremophiles as Astrobiological Models’, most tardigrades do not fit within the traditional definition of extremophiles, but rather belong to the category of ‘extremotolerant’ organisms, surviving extreme conditions but with optimal performance under more normal environmental conditions.
These beasties are super iconic. Tardigrades are *way* more iconic than cockroaches or mole-rats. Why? Because not only they have featured in Family Guy and South Park (where they dance to the music of Taylor Swift), they have also been in several films including Star Trek: Discovery, have been in a comic – and in a video game! Actually, I do love roaches, as I have them as pets and have discovered a new species of hissing cockroach in Madagascar, so I don’t want to diss roaches too much, but I’m Team Tardigrade here.
Not just binary female and male. Tardigrades may be ‘gonochoric’ (sexually reproducing species in which individuals have one of at least two distinct sexes), ‘unisexual’ (the condition of an organism or species capable of producing only male or female sex cells but never both), or ‘hermaphroditic’ (the condition of having both male and female reproductive organs).
Hanging onto poop. As amazing as tardigrades are, I’m not sure that I would like to be a tardigrade – as some species only defecate when they molt.
Game, set and match to tardigrades. A deathmatch between a naked mole-rat, tardigrade and cockroach is somewhat size-ist and clearly not a good measure of the toughness of a tardigrade. Of course, my little dudes wouldn’t be able to eat a mole-rat or a cockroach. Size isn’t everything, it’s what you do with it that counts. But… if you scaled a tardigrade up to the size of a mole-rat, things could be drastically different. In answer to the question of “Who will be the last survivor on Earth?”, it is unequivocally the small, humble but fantastically awesome tardigrade!
What’s so good about this?
Are you curious about the amazing superpowers of the tardigrade? You can find out more about Jan Beccaloni’s work at the Natural History Museum. She is currently researching abnormalities in horseshoe crabs. Now, don’t get us started on lichen, fungi or the mummichog fish.
Meet the writer
Lisa Goldapple is the brain behind the world of TOPIA, and a wise-cracking detective somewhere in the multiverse. She might not behave as good as gold, but thinks good is golden. To understand her rare brain, a bit, follow @lisagoldapple and read Mind Blown: “If life splinters and you hallucinate triangles, make a kaleidoscope”. And sign up to the TOPIA newsletter, A World of Good.