Frontiers for Young Minds

Frontiers for Young Minds

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Water Bears—The Most Extreme Animals on The Planet (And in Space!)

research on water bears

Can you imagine that there is an eight-legged bear that tolerates colder temperatures than the polar bears do in the Arctic? Can you imagine that this bear is able to grow older than the grizzly bears in North America? And can you imagine that this bear grows by molting, like spiders or snakes? These so-called water bears, scientifically named tardigrades, are the most extreme animals on our planet. They not only survive in ice, but also in boiling water. Moreover, they can stop breathing for long periods and they have even traveled to outer space, surviving without an astronaut’s suit. Since water bears can withstand the harshest conditions on earth and beyond, they may teach us how we can protect ourselves from extreme environmental conditions.

Are Water Bears True Bears?

What are water bears? Are they really bears? This question is easy to answer: no, the only thing that water bears and bears have in common is the fact that both are animals. The shape of a water bear slightly resembles that of true bears, such as the polar bear or the grizzly, but they are most closely related to the huge group called the arthropods , which includes insects, spiders, millipedes, and crabs. However, you cannot see a water bear with the naked eye, because these animals are very tiny. They usually grow to <1 mm ( Figure 1 ). Water bears were discovered more than 200 years ago [ 1 ]. The German pastor and biologist Johann Goeze initially named them “little water bears,” because of their size and their preference for wet living spaces.

Figure 1 - Water bears, also called tardigrades, are extremely small compared to other animals.

  • Figure 1 - Water bears, also called tardigrades, are extremely small compared to other animals.
  • This image of a water bear was taken with a scanning electron microscope. The water bear micrograph by Bob Goldstein and Vicky Madden ( ). Photographs of the grasshopper and the cat by S. Elleuche.

Water bears love wet or at least humid environments where they can remain covered by a layer of water. They are among the most successful lifeforms known and are widely distributed all over our planet. We can observe water bears in all oceans, rivers, seas, and lakes, and in wetlands , but they are mainly found in mosses or swamps. Water bears have even conquered the highest mountains, rainforests, and Antarctica. Many different types of water bears have been found and described. They even conquered Hollywood, where you may have encountered water bears in the Marvel superhero movies “Ant-Man” and “Ant-Man and the Wasp,” when Scott Lang disappears into the quantum realm.

Water bears have a strange shape—they are of stout build with four pairs of short and stubby legs, ending with four to eight claws, and they appear to lumber along as they move ( Figure 1 ). The first three pairs of legs are used for moving, while the water bears use the last pair of legs to hang on to the surface on which they walk. Even with so many legs, water bears usually do not walk but instead passively slide, using the flow of water or wind. The way they move is also reflected by their scientific name: tardigrades . Tardigradum means “slow walker,” and this name was given to water bears by Loredano Spallanzani, a former Italian biologist, due to the slow and sedate behavior of these animals, which might look like laziness.

How Do Water Bears Grow?

Just like almost any other creature on our planet, water bears must eat food and breathe air to generate the energy needed for their cells to divide and their bodies to grow. In contrast to true bears, water bears are just too tiny to eat salmon or seals. Honey is also not on their menu. Nevertheless, water bears basically eat everything. While they mainly prefer vegetarian foods like plants and algae, they will also eat microscopic animals.

Unlike most other animals, the bodies of water bears are created following a specific plan. Every type of adult water bear even has exactly the same number of cells. Their cells are continuously dividing, but the water bear is covered by a non-growing and non-flexible sheath, or protective outer covering. As soon as the sheath becomes too tight, water bears will shed the sheath in a process called molting , similar to spiders and snakes. Although both humans and water bears need oxygen to survive, water bears do not breathe the way we do. In fact, they do not even possess respiratory organs like lungs. Water bears take up air through the surfaces of their bodies, just like insects. Water bears can even stop breathing and eating for some time, similar to the process of hibernation that allows other animals, such as polar bears, to slow down their bodily processes to survive the winter months. However, water bears are even more impressive, because not only can they sleep for a couple of months, but they can also become extremely old and thrive in the most extreme places on earth.

What Are the Most Extreme Living Spaces for Water Bears?

Water bears are the most extreme animals that we know—they basically tolerate almost every extreme condition that we can think of. They can survive in the Arctic alongside polar bears, or in Antarctica, where penguins feel at home ( Figure 2A ). Water bears even survive in the laboratory at temperatures below −200°C, which is more than twice as cold as the coldest temperature that was ever observed in nature. Under such extreme conditions, the water bears enter a stage that resembles death. During this death-like resting stage, called dormancy , water bears stop all functions that usually define life: they stop breathing, they stop moving and growing, and they even stop digesting their last meal [ 2 ]. Depending on how long they are in dormancy, it can take several hours to wake them up. Some water bears have even been seen to last for a century in dormancy.

Figure 2 - (A) Water bears can survive in extremely cold habitats, like the icy Himalaya mountains, and at temperatures as low as −150°C.

  • Figure 2 - (A) Water bears can survive in extremely cold habitats, like the icy Himalaya mountains, and at temperatures as low as −150°C.
  • (B) Water bears can survive in extremely hot habitats, like the hottest deserts, and at temperatures as high as 100°C. (C) Water bears can even survive in the vacuum of space!

On the other end of the temperature scale, there are microbes that can grow at temperatures around 120°C. These heat-loving microbes are called extremophiles [ 3 , 4 ]. Water bears do not love the extreme heat, but not only can water bears survive in the desert, they can even tolerate temperatures around 150°C ( Figure 2B )—temperatures that would kill most extremophiles. Even more impressive is the fact that water bears can be repeatedly heated up and frozen without dying. These abilities have allowed water bears to become unrivaled in their success over the course of evolution. More than 1,000 different types of water bears are known, with the oldest species dating back more than 500 million years.

Water bears do not only survive the coldest cold or the hottest heat without food and without air to breathe, but they can also go without water and they are resistant to radiation. Since those extreme conditions exist in space, scientists asked themselves whether water bears might even be able to travel in space ( Figure 2C ). Scientists knew that the high pressure present in the deep sea could be tolerated by water bears, but in space there is a vacuum, with lower pressure compared to earth. Nevertheless, several species of water bears were sent into space and all of them returned home in healthy condition. Moreover, more than 1,000 water bears in dormancy were crash-landed on the moon as passengers of a spacecraft in 2019. It is expected that most of these robust animals have survived the crash and could be revived by water and oxygen in the future.

Could Water Bears Be Used to Help Humans?

For a long time, scientists have been trying to understand the water bears’ resistance to radiation. Although radiation in the form of X-rays can be used by doctors to examine broken bones, radiation can also cause the destruction of the body’s instruction manual. This instruction manual is called the genome , and it is similar in every living organism on earth, including water bears. There must be a reason for the immense resistance to radiation seen in water bears, which is more than 1,000 times higher than humans’ resistance.

One part of the genome of water bears has recently been identified and reproduced in a laboratory [ 5 ]. When this factor was added to human cells grown in the same laboratory, the human cells tolerated more intense radiation than did human cells without the water bear factor. These early experiments may lead to future applications of water bear factors that could not only be used to protect the human cells against radiation, but possibly also to stabilize drugs or to increase the resistance of crop plants to environmental conditions like drought.

What We Have Learned From Water Bears

So, now you can see that those little water bears are quite different from the bears we know well. We have learned from these animals that they not only tolerate the most extreme conditions on our planet, they are even capable to survive in Space. Because of these unique properties, water bears are fascinating and among the most interesting model organisms for us to further study.

Arthropods : ↑ This group of animals is characterized by the outer skeleton and includes insects, spiders, millipedes, and crabs.

Wetland : ↑ A living space for multiple organisms that is temporary or permanently flooded by water and inhabited by aquatic plants.

Tardigrade : ↑ A scientific nomenclature for a group of animals that are also known as water bears or moss piglets.

Molting : ↑ Some animals, such as water bears, insects, spiders and snakes do not grow continuously. They have to replace their outer sheath when it became too tight.

Dormancy : ↑ Death-like resting stage during which each kind of activity such as growth or ingestion is temporarily stopped.

Extremophiles : ↑ Microorganisms that love to live in the most extreme environments on the planet. Water bears are no true extremophiles because, although they can tolerate extreme conditions, they do not prefer such environments.

Genome : ↑ A kind of construction plan that is included in every living cell in all organisms (Bacteria, Fungi, Plants, Animals etc.), which determines the look and composition of most cellular compon.

Conflict of Interest

The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


The author thanks Sylvia Wiese and Jan Friesen for critically reading the manuscript.

[1] ↑ Jönsson, K. I. 2019. Radiation tolerance in tardigrades: current knowledge and potential applications in medicine. Cancers 11:1333. doi: 10.3390/cancers11091333

[2] ↑ Fontaneto, D. 2019. Long-distance passive dispersal in microscopic aquatic animals. Mov. Ecol . 7:10. doi: 10.1186/s40462-019-0155-7

[3] ↑ Elleuche, S., Schröder, C., Stahlberg, N., and Antranikian, G. 2017. “Boiling water is not too hot for us!”—preferred living spaces of heat-loving microbes. Front. Young Minds . 5:1. doi: 10.3389/frym.2017.00001

[4] ↑ Schröder, C., Burkhardt, C., Antranikian, G. 2020. What we learn from extremophiles. ChemTexts 6:8. doi: 10.1007/s40828-020-0103-6

[5] ↑ Hashimoto, T., Horikawa, D. D., Saito, Y., Kuwahara, H., Kozuka-Hata, H., Shin, I. T., et al. 2016. Extremotolerant tardigrade genome and improved radiotolerance of human cultured cells by tardigrade-unique protein. Nat. Commun . 7:12808. doi: 10.1038/ncomms12808

Microscopic water bears, also known as tardigrades

Tiny animals survive exposure to space

Scientists recently revealed that tiny creatures called water bears are the first animals to survive exposure to space. Sending water bears into space is one of several ESA experiments looking at organisms which can survive longer periods in open space.

Water bears, also known as tardigrades, are very small, segmented animals. The largest species is just over one millimetre in length. Water bears live in temporary ponds and droplets of water in soil and on moist plants. They are known to survive under conditions that would kill most organisms – they can withstand temperatures ranging from -272 deg C to +150 deg C, they can be without water for a period of 10 years, and they are extremely resistant to radiation.

Knowing them to be so hardy, the Swedish and German scientists behind the ‘Tardigrades in space’ (TARDIS) experiment wanted to find out how the water bears would fare in the harsh space environment. For 12 days in September 2007, some 3000 water bears hitched a ride into space on ESA’s orbital Foton-M3 mission.

The Foton-M3 capsule spent 12 days orbiting the Earth in September 2007

“Our principle finding is that the space vacuum, which entails extreme dehydration and cosmic radiation, were not a problem for water bears,” says TARDIS project leader Ingemar Jönsson, from the University of Kristianstad in Sweden.

That the water bears survived, shows just how robust they are. The next step will be to understand what mechanism makes this possible. Jönsson: “How do their cells stabilise the membrane and DNA when they dry out for example?” Understanding these mechanisms can open the door to many insights both in space bioscience and in other areas.

The tardigrades join a fairly select group of organisms which are able to cope with the extreme conditions in space. Over the past 10 years, other ESA experiments have shown that lettuce seeds and lichen were also able to survive exposure to space. If shaded from direct sunlight, bacterial spores are also known to survive for many years under space conditions.

Space exposure experiments are carried in Biopan on the outside of the Foton capsule

“The water bears are something new. Nobody knew about that capability” says René Demets, ESA project biologist. “The question is why are terrestrial organisms prepared to survive exposure to space conditions? Is there a rationale? Nobody knows at the moment.”

Survival in space is often linked to a much wider theory about how life originated here on Earth. “Perhaps the starting point for life was not even here on Earth,” says Demets. “Could life as we know it have started elsewhere, to be carried later for instance on a meteorite and delivered here on Earth? Favourable conditions meant that it could further propagate, develop, grow and live on. Now we have actually found some organisms that can survive under harsh space conditions.”

If these organisms were to travel on board a meteorite, they would also have to survive the entry through Earth’s atmosphere. ESA’s series of Stone experiments, also conducted on the Foton missions, show that in the upper layer of the meteorite, up to 2 cm depth, nothing could survive the atmospheric entry because of the high temperature and pressure. Only an organism that could live inside deeper cracks or pores in the rock could perhaps survive.

Expose hardware

These space exposure experiments have so far been limited to one or two weeks in mission duration. ESA is now also testing longer duration exposure with an suite of experiments on the International Space Station called Expose. Several trays filled with terrestrial organisms are already installed on the outside of the European Columbus laboratory as one of the nine payloads of the European Technology Exposure Facility (EuTEF). Another Expose unit, scheduled for launch on a Russian Progress cargo carrier in November, will be attached to the Russian segment of the Space Station.

“After about one and a half years we will get the Expose trays back and see what the situation is after long duration exposure,” explains Martin Zell, Head of ESA's ISS Utilisation Department. “We could have a brilliant result with survival of the organisms as we have seen with the water bears, or we could have a quite negative result and know for sure that long-duration exposure will never work. With these experiments we are probing the alterations of organisms in space and their ultimate limits of survival.”

For more information please contact:

Martin Zell ESA Head of ISS Utilisation Department Directorate of Human Spaceflight Martin.Zell[@]

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7 Fascinating Facts About the Tardigrade, the Only Animal That Can Survive in Space

All hail the toughest organism on Earth.

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 for sustaining life. They can exist like this for decades. They’re also pretty hardy and can endure even the harshest environments, including subzero temperatures—and, you know, lunar crash landings.

💫 The universe is amazing! Let’s nerd out over it together.

We talked to leading researchers to find out what makes these little “water bears” so amazing. Here are our seven favorite facts about tardigrades, according to the latest research.

1) Tardigrades are everywhere .

tardigrades, illustration

Tardigrades are a class of microscopic animals with eight limbs and 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.

2) Tardigrades can pause their biological clock.

water bear tardigrades

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 three percent of their body’s water and slowing their metabolism down to an astonishing 0.01 percent of its normal speed—a metabolic state known as cryptobiosis. 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 than 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.”

Similarly, tardigrades can also survive being frozen. A new study published in Journal of Zoology in September 2022 shows that tardigrades exposed to freezing temperatures entered cryptobiosis and lived longer than those who never entered this state during their lives.

Out of a total of 716 tardigrades, those that were periodically frozen became “sleeping beauties,” living around twice as long as the control group. The oldest tardigrade stuck around for 169 days, with 94 days at room temperature. In the control group, which stayed warm, the oldest tardigrade lived for 93 days.

“During inactive periods, the internal clock stops and only resumes running once the organism is reactivated,” explains zoologist Ralph Schill, one of the researchers. “So, tardigrades, which usually only live for a few months without periods of rest, can live for many years or even decades.”

3) Tardigrades probably can’t see in color.


Recent research from the Genome Biology and Evolution journal reports that the resilient little critters don’t have the same opsins (light-sensitive, photoreceptive proteins) as animals who use their eyes to see color. One of the tardigrade species ( Ramazzottius variornatus ) that was analyzed in this study didn’t have eyes at all but did have active opsins. Another species ( Hypsibius exemplaris ) did have eyes, but their opsins didn’t respond to light stimuli—a necessary feature for color vision . It’s technically still possible that tardigrades can see some color, but it’s more likely that they see things in black and white. Their eyes are very simple, after all. Further research is needed to determine how their vision works.

4) Tardigrades can survive the harshest atmospheres.

tardigrade, sem

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 minus 458 degrees Fahrenheit (just above absolute zero) won’t spell out 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.

5) Even space radiation is no match for tardigrades.

water bear, sem

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, in their desiccated state, produce an abnormal amount of antioxidants (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.

6) Still, tardigrades aren’t completely invincible.

water bear

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 could 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.

7) Some tardigrades lay spiked eggs.

various dactylobiotus ovimutans eggs are shown, each displaying its own custom morphology

The ever-mysterious, alien-like creatures have presented scientists with yet another quandary: What’s the deal with a newly discovered tardigrade species that can lay spiked eggs?

In a June 2020 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 on an organism’s DNA sequence) when it comes to their offspring?

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Princeton University

Princeton engineering, tiny, squishy, water bears walk just like insects 500,000 times their size.

By Patricia Waldron

September 17, 2021

After analyzing hundreds of hours of water bears plodding along under a microscope, researchers at Princeton and Rockefeller University discovered that the steps of the tiny, ultra-resilient animals are surprisingly similar to insects, despite vast differences in their size, habitat and body type.

The new study , published online Aug. 31 in the Proceedings of the National Academy of Sciences, is the first investigation into the mechanics of how water bears walk. Exactly how they developed this insect-like gait is still unknown, but the new understanding may help scientists develop miniature or soft-bodied robots that walk.

“We thought water bears might have an uncoordinated gait because the media has portrayed them as slow and clumsy critters, or that they would have some really wacky patterns because they are so small and needed different strategies,” said Daniel J. Cohen , an assistant professor of mechanical and aerospace engineering and senior author of the study. “And then it turns out they happily charge along, doing something remarkably similar to creatures 500,000 times larger than they are.”

Water bears are eight-legged animals, the size of a few strands of hair, that live almost everywhere on Earth they can find water. Despite their aquatic lifestyle, they are poor swimmers and walk more like land animals. Their official name, tardigrade, means “slow stepper.” The hardy animals can survive radiation, starvation and freezing temperatures and endure almost complete dehydration by entering a state of suspended animation. Walking may represent a vital survival skill for water bears because it allows them to seek out damp environments or find slowly drying spots that let them transform into their dormant state.

In their standard stepping pattern, water bears move diagonal pairs of legs, one set at a time, as shown in this underside view of a water bear.

Illustration by Neil Adelantar from an image by Nirody et al.

Cohen collaborated with  Jasmine Nirody , an independent joint fellow at Rockefeller University and Oxford University who specializes in animal locomotion to investigate how water bears walk. The two researchers met as graduate students at the University of California, Berkeley and have since been waiting for an opportunity to study these fascinating creatures.

As perhaps the smallest animal with legs, water bears face unique challenges to walking. “We know a lot about how larger things walk, but when things get really small, the physics of their interactions with the environment naturally change a lot,” said Nirody. “At their size, they are fighting the viscous forces of water. It’s like if we were walking through honey or peanut butter.”

Also, water bears have neither the internal skeleton of a mammal, nor the rigid exoskeleton of an insect. Animals use their skeletons to push off the ground and propel themselves forward. Instead, water bears use their claws like grappling hooks. When they can’t gain traction, like in this video of a water bear on a glass microscope slide , they just flail—ironically, waterbears cannot swim.

To figure out how water bears get around, co-authors Lisset Duran , a graduate student in molecular biology, and Deborah Johnston, a former high school student now at the University of Rochester, raised a species of water bear typically found on wet moss. They placed the animals under the microscope on a thick gel that they could dig their claws into and recorded hundreds of hours of water bears ambling by at about one-third of an inch per minute. The entire team pitched in to track the water bears’ footsteps on the videos, and Nirody analyzed the results to develop a model of their stepping patterns.

Water bears use their front six legs to walk, moving diagonal pairs of legs, one set at a time, in a pattern that is surprisingly similar to stick insects. To go faster, they simply let each foot rest on the ground for less time in between steps. The stepping pattern remains the same regardless of speed, so the researchers suspect that a single neural circuit controls this behavior.

When the researchers placed the water bears on a softer gel, they were surprised to see them switch from stepping to galloping. They had to coordinate all their legs simultaneously to move across the squishy ground. “Interestingly, that kind of coordination scheme was recently characterized in a desert-dwelling beetle that moves on shifting sand,” said Nirody.

There are two potential explanations for why water bears walk in this completely familiar, not-at-all clumsy way. One possibility is that they inherited the neural circuit that controls the stepping pattern from a common ancestor they share with insects. Water bears are cousins to the arthropods—the wildly successful group that includes insects, millipedes, crustaceans and spiders. Another possibility is that both groups independently evolved the same walking strategy, even though they live in vastly different environments and scales.

“We can’t answer that from this study, but it seems like it’s one of those two things, which is pretty neat either way,” said Cohen.

“It’s a very nice paper – I’m jealous I didn’t do it!” said Daniel Goldman, the Dunn Family Professor of Physics at the Georgia Institute of Technology. “I am fascinated by the questions it raises regarding the neural circuits and mechanics that control these gaits, and why these animals use the diverse gaits they do.”

These findings may be useful for engineering new types of robots. Soft-bodied robots are more flexible and adaptable that rigid ones, but scientists know less about how to control them. The work also suggests it’s possible to build microrobots at that scale that move around on legs rather than by swimming.

For the next steps, Cohen wants to study how water bears generate forces and use their claws in the hopes of bio-inspired solutions to future microbots. Nirody is interested in how the water bears adapt their walk to different conditions, like scaling an incline or traversing a rough surface. She also hopes to investigate other species. “There are about 1,000 species of tardigrades out there,” she said. “I would expect that there are some interesting adaptations in the marine and freshwater ones that we haven’t yet seen.”

Funding for this project came from a School of Engineering and Applied Science Innovation Grant from the Helen Shipley Hunt Fund. Co-authors on the paper received support from the James S. McDonnell Foundation, the University of Oxford, Rockefeller University, and a Jonas Salk Award.

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research on water bears

Daniel J. Cohen

research on water bears

Bioengineering and Health

research on water bears


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Tardigrades in Space Research - Past and Future

Erdmann weronika.

Faculty of Biology, Department of Animal Taxonomy and Ecology, Adam Mickiewicz University in Poznań, Umultowska 89, 61-614 Poznań, Poland

Kaczmarek Łukasz

To survive exposure to space conditions, organisms should have certain characteristics including a high tolerance for freezing, radiation and desiccation. The organisms with the best chance for survival under such conditions are extremophiles, like some species of Bacteria and Archea, Rotifera, several species of Nematoda, some of the arthropods and Tardigrada (water bears). There is no denying that tardigrades are one of the toughest animals on our planet and are the most unique in the extremophiles group. Tardigrada are very small animals (50 to 2,100 μm in length), and they inhabit great number of Earth environments. Ever since it was proven that tardigrades have high resistance to the different kinds of stress factors associated with cosmic journeys, combined with their relatively complex structure and their relative ease of observation, they have become a perfect model organism for space research. This taxon is now the focus of astrobiologists from around the world. Therefore, this paper presents a short review of the space research performed on tardigrades as well as some considerations for further studies.

What are Tardigrades?

Water bears (Tardigrada), discovered in 1773, are a phylum of small invertebrates belonging to the supertype Articulata. They can be found all over the Earth and can inhabit very diverse environments (from the deepest oceans to mountain tops). Water bears are small, cylindrical invertebrates, up to 2.1 mm in length, and are divided into five segments. The first segment contains the head and the next four each have one pair of unsegmented legs ending (most often) in claws. The tardigrade body is covered with a flexible cuticle, which is smooth or covered with gibbosities, spines or plates. Despite being so small, they have a very complicated internal structure. Water bears have a complete digestive system adapted, depending on the species, to consume algae, bacteria, fungal cells or small invertebrates such as rotifers, nematodes and other tardigrades. They have a well developed nervous system consisting of rings around mouth (brain) and an abdominal chain with segmental ganglia. They also have various sensory organs like papilla, chemoreceptors and eyes. Water bears can be dioecious and bisexual; in the second case, sexual dimorphism is sometimes present (especially in Heterotardigrada). In many species, the phenomenon of parthenogenesis is also present. Fertilisation can be external or internal. The eggs are covered with an additional shell, the smooth or ornamented chorion, and are laid freely (directly into the environment) or in old exuviae. After hatching, tardigrades moult between two to seven times. The young resemble the adults, and they reach sexual maturity after the second or third moult, which takes several days. Adult tardigrades live approximately two to several months (Nelson et al. 2015 ). Currently, approximately 1,200 tardigrade species are known (Degma et al. 2009–2016 ; Vicente and Bertolani 2013 ), although it is estimated that the real number of species is much higher. At present, this phylum is divided into two classes, Eutardigrada and Heterotardigrada. Eutardigrada consists mainly of freshwater and terrestrial species (marine species are extremely rare). The body of eutardigrades is translucent or milky white (but sometimes has different colouration) and is covered with a flexible cuticle and devoid of plates. Among Heterotardigrada, both marine and terrestrial species are present. Their body is covered with a cuticle that produces various kinds of plates (Nelson 2002 ; Nelson et al. 2015 ).

What Makes Them so Special?

As mentioned above, tardigrades live not only in freshwater and marine environments but also in terrestrial habitats. Terrestrial species can be found in mosses, lichens and soil where they are threatened by drying. In this situation, terrestrial species need a thin water film around their bodies in order to stay active. These species have also developed a special skill that protects them against the effects of dehydration: the ability to enter into a cryptobiotic state. There are several types of cryptobiosis: a) anoxybiosis, a reaction to lack of sufficient oxygen, b) cryobiosis, a reaction to freezing temperatures, c) osmobiosis, a reaction to excessive salinity, and the best known type of cryptobiosis, d) anhydrobiosis, a reaction to a lack of liquid water in the environment (Kinchin 2008 ). In the anhydrobiotic state, the metabolic activity of tardigrades drops to a very low level (Pigoń and Węglarska 1955 ). This latent state can occur at the egg stage as well as in adults and can be repeated multiple times (Kinchin 2008 ). Anhydrobiosis gives tardigrades resistance to a lack of water, but also to a number of physical factors such as high temperature, radiation or different kinds of chemicals, such as ethanol, hydrogen sulphide and carbon dioxide (Kinchin 1994 ; Ramlov and Westh 2001 ; Wełnicz et al. 2011 ; Guidetti et al. 2012 ). Not all Tardigrada species show equal resistance to drying out, as there are differences in drying tolerance even between populations of the same species (Jönsson et al. 2001 ; Horikawa and Higashi 2004 ). The entrance into anhydrobiosis is preceded by a preliminary phase, during which the tardigrade body undergoes a series of metabolic and anatomical changes that are necessary to survive the unfavourable conditions. The changes are easiest to observe as a shrinkage of the body (forming numerous folds which reduce the body’s surface area), namely the adoption of the tun formation (Baumann 1922 ). The tun form reduces the surface for evaporation and thus slows down the loss of liquid water (transpiration is reduced by about 50 %) (Wright 1989 ). The tun state also prevents the destruction of the internal and external organs during the drying process (Crowe 1975 ). When all free water evaporates from the tardigrade body, it begins the process of replacing the water bound to macromolecules. The lost water is replaced with bioprotectants such as trehalose, which protects macromolecules, such as nucleic acids and proteins, from losing their proper structure (Kinchin 2008 ). If the macromolecule structure is damaged, the cell dies. It is not certain how trehalose contributes to the protection of membrane proteins. It is also possible that the trehalose hydroxyl groups interact with hydrogen atoms replacing the same evaporating water (Kinchin 2008 ). In summary, trehalose is responsible for stabilising proteins, membrane lipids and nucleic acids (Webb 1964 ; Crowe 2002 ). However, it should be also emphasised that some tardigrades synthesise trehalose on a very low level (Wang et al. 2014 ). The other molecules involved in tardigrade cell protection during anhydrobiosis are LEA (late embryogenesis abundant), HSP (heat shock proteins), CAHS (cytoplasmic abundant heat soluble), SAHS (secretory abundant heat soluble) and aquaporin proteins (Förster et al. 2009 ; Yamaguchi et al. 2012 ; Grohme et al. 2013 ; Guidetti et al. 2011 , 2012 ; Wełnicz et al. 2011 ). The LEA proteins have similar functions to trehalose, but in addition to protecting the cell membranes and proteins, they can also act as a hydration buffer and sequester ions. They can also be responsible for cell structure protection through renaturation of unfolded proteins (Tunnacliffe and Wise 2007 ). In turn, the HSPs could work as molecular chaperons (Goyal et al. 2005 ) and participate in protein folding, and inhibiting protein aggregation. So far, it has been proven that this type of protein (presumably the Hsp70-90 proteins family) are produced and stored in organisms going into anhydrobiosis, but their role during desiccation is still uncertain (Ramlov and Westh 2001 ; Reuner et al. 2010 ; Wełnicz et al. 2011 ). The CAHS and SAHS proteins probably form a molecular shield in water-deficient conditions (Yamaguchi et al. 2012 ). Aquaporin proteins may play a minor role during anhydrobiosis by fine-tuning water transport and greatly increasing membrane permeability (Grohme et al. 2013 ). Also, possession of the ROS (Reactive oxygen species) scavenging enzymes could represent a crucial strategy to avoid damages during desiccation in anhydrobiotic tardigrades (Rizzo et al. 2010 ; Rebecchi 2013 ). However, most of the bioprotectants and mechanisms that protect tardigrade cells during cryptobiosis are still poorly understood or completely unknown.

Toughest Animals on Earth

The ability to enter into a state of anhydrobiosis (which distinguishes water bears from most other organisms) lets tardigrades resist many unfavourable environmental factors (Rebecchi et al. 2007 ). Moreover, tardigrades are able to survive in an inactive form for many years (from nine to 20 years in natural conditions) (Guidetti and Jönsson 2002 ; Rebecchi et al. 2006 ; Guidetti et al. 2012 ). Interestingly, the death of individuals that are in a long anhydrobiotic state is mostly caused by the drying process itself and not by the aging process. This phenomenon can be explained by the so-called “Sleeping Beauty” model, first reported in rotifers (Ricci 2001 ; Segers and Shiel 2005 ). At the time when the model was confirmed for rotifers, this kind of shift in the age of anhydrobiotic animal was also supposed for tardigrades (Hengherr et al. 2008 ). On the other hand, it was also proven that during anhydrobiosis, cell damages accumulate with time (Rebecchi et al. 2009a ). It is possible that such damages are accumulated in proportion to the time spent in anhydrobiosis and lead to animal death, even though desiccation itself does not seem to have an effect on tardigrade longevity and ageing (Guidetti et al. 2011 ). Water bears are also very resistant to extreme temperatures, and they can survive from −272.8 °C (Becquerel 1950 ) to about 150 °C (up to 15 min) (Rahm 1923 , 1924 , 1926 ). Resistance to low temperatures was investigated repeatedly during research on anhydrobiosis and on cryobiosis. One of the first studies showed that many different species of Tardigrada withstand immersion in liquid air ( ca. -190 °C), liquid nitrogen ( ca. -253 °C) and liquid helium ( ca. -272 °C) (Rahm 1923 , 1924 , 1926 ). Other studies demonstrated that some species inhabiting the Arctic soil can survive up to six years (74 months) at −80 °C (Newsham et al. 2006 ). These small invertebrates also exhibit significant resistance to low and high atmospheric pressures (from 200 to 280 hPa to 7,500 MPa) (Jönsson et al. 2008 ; Ono et al. 2008 ). Tardigrades in an anhydrobiotic state are also resistant to high doses of ionising radiation and X-rays ( ca. 5000 GY) (May et al. 1964 ; Horikawa et al. 2006 ). Some individuals are even able to survive very high doses of ultraviolet radiation (between 75 and 88 kJ m 2 ) (Altiero et al. 2011 ). Water bears are resistant to physical stressors as well as some chemical stressors such as hydrogen sulphide, carbon dioxide, ethanol (for ca. 10 min) and 1-hexanol (Baumann 1922 ; Ramlov and Westh 2001 ).

Unlike the other multicellular extremophiles, water bears are not only resistant in the anhydrobiotic state but also in the active state. Active tardigrades are able to survive in temperatures of about 38 °C (Li and Wang 2005 ; Rebecchi et al. 2009b ) and −196 °C (Ramlov and Westh 2001 ). They also exhibit a significant resistance to high atmospheric pressures (up to 100 MPa) (Seki and Toyoshima 1998 ). It is also known that tardigrades in the active state are almost as resistant to radiation as in anhydrobiosis (Jönsson et al. 2005 ; Horikawa et al. 2006 2009 ; Altiero et al. 2011 ).

Tardigrades in Space Research and Space Missions

All of the above mentioned features of tardigrades caused scientists to consider them in the context of space research. In 1964, in the article “Actions différentielles des rayons x et ultraviolets sur le tardigrade Macrobiotus areolatus ”, it was suggested for the first time that tardigrades, due to their enormous resistance to radiation, could be model animals for space research (May et al. 1964 ). Thirty-seven years later, in the article “Tardigrades as a potential model organism in space research”, Bertolani et al. ( 2001 ) suggested a similar concept. At the same time, studies focused on the phenomenon of cryptobiosis in tardigrades were conducted, revealing still greater resistance of this amazing animal to many unfavourable factors encountered in outer space. In 2007, Jönsson, based on knowledge resulting from these studies, showed that tardigrades can be suitable model organisms for astrobiological studies because of their ability to dehydrate, extreme temperature tolerance and radiation resistance (Jönsson 2007 ). Since that time, numerous articles suggesting that tardigrades can be used in space research have been published (Horikawa et al. 2008 ; Rebecchi et al 2010a ). The latest paper from early 2012 indicated that tardigrades are an excellent model for space research (Guidetti et al. 2012 ). While that paper emphasises the previously known extraordinary resistance of tardigrades, it also suggests that there is a greater complexity to tardigrade organisms. The authors repeatedly emphasise that the complex structure of tardigrades allows extrapolation of the results of such studies to vertebrates (including humans). In conjunction with their small body size, their relative ease to culture and obtain offspring further enhances their importance as a potential model species (Guidetti et al. 2012 ). In 2008, Horikawa et al. proposed Ramazzottius varieornatus Bertolani & Kinchin, 1993 as a model species in astrobiology research. In their paper they described a methodology for breeding this species under laboratory conditions. They also described the life history of this species and identified characteristics required to consider this particular species of tardigrade as a model (Horikawa et al. 2008 ). In the same year, it was also suggested that tardigrades could travel through space in a large meteorite and could probably confirm the theory of panspermia (Ono et al. 2008 ).

Based on researcher suggestions, a few space programmes focused on tardigrades were started and finished in recent years. In 2007, three projects were conducted during the FOTON-M3 mission studies. The Tardigrade Resistance to Space Effects (TARSE) Project was the first one involved in the mission of FOTON-M3. Its aim was to analyse the impact of environmental stress, life history traits and DNA damages in space (on board the spacecraft) on eutardigrade Paramacrobiotus richtersi (Murray, 1911). In this project active and anhydrobiotic tardigrades were exposed to radiation in microgravity conditions. Both active and inactive individuals had high survival rates with no induction of HSPs while showing an induction of the antioxidant response (Rebecchi et al. 2009c , 2010b , 2011a ). The next project involved in the mission of FOTON-M3 was TARDIS (Tardigrada In Space). The main goal of this project was to check whether tardigrades from two species, Milnesium tardigradum Doyère, 1840 and Richtersius coronifer (Richters, 1903), were able to survive conditions of open space. The experiments showed that tardigrades can survive exposure to the space vacuum, but the addition of factors such as ultraviolet solar radiation, ionising solar radiation and galactic cosmic radiation significantly reduced their survival rate (Jönsson, et al. 2008 ). In the third project from the FOTON-M3 mission, RoTaRad (Rotifers, Tardigrades and Radiation), scientists examined effects on initial survival, long-term survival and fecundity of selected species of limno-terrestrial tardigrades in extreme stress conditions (mainly cosmic radiation) (Persson et al. 2011 ). Next was the Endeavour mission in 2011 and the project TARDIKISS (Tardigrades in Space). The main aim of this project was to broaden our knowledge of life history traits and mechanisms of repairing structural DNA damage during exposure to space flight stresses (Rebecchi et al. 2011b ; Vukich et al. 2012 ). The first results showed that microgravity and cosmic radiation did not significantly affect the survival rate of tardigrades (Rebecchi et al. 2011b ; Vukich et al. 2012 ). However, Rizzo et al. ( 2015 ) showed a significant difference in activities of ROS scavenging enzymes, the total content of glutathione and the fatty acid composition between tardigrades sent into space and control animals on Earth. The last space research project involving tardigrades was the Phobos Life Project. It was a part of the Phobos Ground Mission. The goal of this project was to study how the living organisms survive during space flight conditions. Scientists wanted to test the viability of selected organisms during an interplanetary flight lasting approximately 34 months and verify the theory of panspermia (;wap2 ). For this mission, the same organisms already used in other space experiments, and well-known to be radiation resistant, were used. They represented all three domains of life (Bacteria, Eukaryotes and Archaea). A total of 10 different taxa were used (species or strains), including three species of tardigrades: M. tardigradum , R. coronifer and Echiniscus testudo (Doyère, 1840). Unfortunately, the experiments were not successful because the spacecraft carrying the whole apparatus crashed and burned over the South Pacific Ocean on January 15th 2012.

Further Perspectives

As demonstrated above, we already know quite a lot on the limits of endurance of tardigrades regarding various stress factors. However, we still do not know the exact mechanisms of action that protect and repair their bodies in unfavourable conditions. The understanding of these mechanisms and knowledge of the responsible genes is an important step in astrobiological studies, especially if it can be extrapolated to vertebrates (including humans).

There are many possible future directions of astrobiological research regarding tardigrades. For example, one experiment could evaluate the ability of tardigrades to survive in a simulated atmosphere of certain celestial bodies in our solar system (such experiments simulating Martian conditions were conducted on bacteria, cyanobacteria, lichens and also tardigrades (Cockell 2005 ; Johnson et al. 2011 ; Rebecchi et al 2010b ; Smith et al. 2009 ; Vera et al. 2010 ; 2014 ). This is interesting because a few of the celestial bodies in our solar system may periodically exhibit micro-environmental conditions appropriate for the survival of certain extremophiles. For example, it is well known that Martian soil contains water (Mitrofanov et al. 2014 ), and in some regions of Mars, in the summer periods, temperatures up to 20 °C were recorded (NASA, official webpage). Even if all environmental conditions are not entirely favourable for life, tardigrades are quite resistant in both the anhydrobiotic and the active state. Moreover, organisms which provide nourishment for tardigrades (e.g. bacteria, algae, rotifers or nematodes) are just as resistant as water bears (Guidetti and Jönsson 2002 ; Rettberg et al. 2002 ; Islam and Schulze-Makuch 2007 ; Meeßen et al. 2013 ). However, these relatively beneficial life periods are interrupted by periods of very unfavourable conditions for living organisms. This is where cryptobiosis has a potential and very important role. The ability to enter into cryptobiosis is helpful not only for travelling for long cosmic distances, but also for providing a possibility of surviving long periods when environmental conditions are unfavourable. This could enable researchers to determine whether tardigrades can survive and live on other planets in the solar system or on their moons. We should also continue studies on tardigrade resistance to combined stress conditions such as the combined effects of cosmic radiation and microgravity, or low temperature and the presence of harmful chemicals. Such studies would help determine the limits of survival of Earth’s multicellular organisms. This is very interesting especially in the context of searching for life on other planets and moons.


The studies were conducted in the framework of activities of the BARg (Biodiversity and Astrobiology Research group). The authors also wish to thank Cambridge Proofreading LLC ( ) and ( ) for help in improving the English in the manuscript.

This paper is part of the Special Collection of Papers from EANA 2013: The 13th European Workshop on Astrobiology, 22–25 July 2013, Szczecin, Poland (Franco Ferrari and Ewa Szuszkiewicz Guest Editors)

Contributor Information

Erdmann Weronika, Email: lp.nnamdre@akinorew .

Kaczmarek Łukasz, Email: lp.ude.uma@ramzcak .

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By william randolph miller.

These ambling, eight-legged microscopic “bears of the moss” are cute, ubiquitous, all but indestructible and a model organism for education

Biology Microbiology

Current Issue

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September-october 2011, volume 99, number 5.

DOI: 10.1511/2011.92.384

The young woman in my office doorway is inquiring about the summer internship I am offering. What’s a tardigrade? she asks. Tardigrades, I reply, are microscopic, aquatic animals found just about everywhere on Earth.

research on water bears

Figure 1. In this colorized electron micrograph (EM), which has the feel of a museum diorama, a tardigrade emerges from under a moss leaf to hunt for food or a companion. EMs are produced by layering a molecular film of metal on a sample. The technology gives a false sense of the “hide” of this tardigrade. In actuality, tardigrades are translucent and display a variety of colors—white, green, orange, red. In the microenvironments made by water that coheres in the fissures of mosses and lichens due to surface tension, tardigrades thrive by feeding on smaller organisms and by sucking contents out of plant cells. Their moist realm is transient, and in response tardigrades have evolved an array of strategies based on induced cryptobiosis—the suspension of metabolism by drying or freezing. In their cryptobiotic state, desiccated or frozen, they are astonishingly durable. These organisms survive extreme conditions—of temperature, pressure and radiation—to a degree unparalleled in nature.

Eye of Science/Photo Researchers

Terrestrial species live in the interior dampness of moss, lichen, leaf litter and soil; other species are found in fresh or salt water. They are commonly known as water bears, a name derived from their resemblance to eight-legged pandas. Some call them moss piglets and they have also been compared to pygmy rhinoceroses and armadillos. On seeing them, most people say tardigrades are the cutest invertebrate.

At one time water bears were candidates to be the main model organism for studies of development. That role is now held most prominently by the roundworm Caenorhabditis elegans , the object of study for the many distinguished researchers following in the trail opened by Nobel Prize laureate Sydney Brenner, who began working on C. elegans in 1974. Water bears offer the same virtues that have made C. elegans so valuable for developmental studies: physiological simplicity, a fast breeding cycle and a precise, highly patterned development plan. Some species may, like C. elegans, be eutelic , meaning that the organisms retain the same number of cells through their development. Tardigrades have somewhere over 1,000 cells. I and others use water bears as a model educational organism to teach a wide range of principles in life science.

Tardigrades are nearly translucent and they average about half a millimeter (500 micrometers) in length, about the size of the period at the end of this sentence. In the right light you can actually see them with the naked eye. But researchers who work with tardigrades see them as they appear through a dissecting microscope of 20- to 30-power magnification—as charismatic miniature animals.

Most tiny invertebrates dart about frantically. Tardigrades move slowly as they clamber around on bits of debris. They were first named tardigrada in Italian from the Latin meaning “slow walker.” Tardigrades walk on short, stubby legs located under their bodies, not sticking out to the sides. These stout legs propel them unhurriedly and deliberately about their habitat.

Tardigrades have five body sections, a well-defined head and four body segments, each of which has a pair of legs fitted with claws. The claws vary in different species from familiarly bearlike to strangely medieval fistfuls of hooked weaponry. The hindmost legs are attached backwards, in a configuration unlike that of any other animal. These legs are used for grasping and slow-motion acrobatics rather than for walking.

research on water bears

Figure 2. Tardigrades’ appearance is not their only aspect that is reminiscent of macrofauna. A light-microscope image of the anterior end of a tardigrade ( left ) shows the mouth; stylets, strutures that help them feed; the buccal apparatus, part of the digestive tract; and the pharynx at the top of the alimentary system. A cross section of a generic water bear ( right ) shows the relative positions of the organ systems. Lacking are circulatory and respiratory systems. At this tiny scale, an open hemocoel cavity is sufficient to distribute oxygen and nutrients through the organism.

Dr. David J. Patterson/Photo Researchers. Illustration at bottom by Tom Dunne, adapted from a figure by the author.

Inside these tiny beasts we find anatomy and physiology similar to that of larger animals, including a full alimentary canal and digestive system. Mouth parts and a sucking pharynx lead to an esophagus, stomach, intestine and anus. There are well-developed muscles but only a single gonad. Tardigrades have a dorsal brain atop a paired ventral nervous system. (Humans have a dorsal brain and a single dorsal nervous system.) The body cavity of tardigrades is an open hemocoel that touches every cell, allowing efficient nutrition and gas exchange with no need for circulatory or respiratory systems.

Taxonomists divide life on Earth into three domains: Bacteria, Archaea (an ancient line of bacterialike cells without nuclei that are likely closer in evolutionary terms to organisms with nucleated cells than to bacteria), and Eukarya. Eukarya is divided into four kingdoms: Protista, Plantae, Fungi and Animalia. Phylum Tardigrada is one of the 36 phyla (roughly, depending on whom one asks) within Animalia—making water bears a significantly distinctive branch on the tree of life.

Tardigrades are encased in a rugged but flexible cuticle that must be shed as the organism grows. Thus they have been placed among the phyla on the ecdysozoa line of evolution between animals such as nematodes and arthropods that also shed their cuticles to grow.

I can see in my drop-in student’s eyes that she remembers the ecdysozoan way of being from introductory biology but she does not really understand it.

Animals grow in either of two ways, by adding more cells or by making each cell larger. Tardigrades generally do the latter. If an animal has a hard cuticle or exoskeleton, it must break out of that shell in order to grow. For example, in summer in many parts of the world, one encounters the shed exoskeletons of locusts on trees everywhere.

Tardigrades are divided into two classes, Eutardigrada and Heterotardigrada. As a general rule, the members of Eutardigrada have a naked or smooth cuticle without plates, whereas the Heterotardigrada boast a cuticle armored with plates.

Tough Customers

Tardigrades’ best-known feature is their brute, dogged ability to survive spectacularly extreme conditions. A few years ago, the Discovery network show Animal Planet aired a countdown story about the most rugged creatures on Earth. Tardigrades were crowned the “Most Extreme” survivor, topping penguins in the Antarctic cold, camels in the dry oven of the desert, tube worms in the abyss and even the legendarily persistent cockroach.

research on water bears

Figure 3. Tardigrades ( left ) were for a time considered competitors with the round worm Caenorhabditis elegans ( right ) and the fruit fly Drosophila melangaster as major invertebrate model organisms. Tardigrades have played that role less over the years, but research attention is increasing as new genetic research tools allow deeper inspection of their extreme durability and adaptivity in response to changing environmental conditions. Tardigrades are predators of nematode worms such as C. elegans . Under the microscope, tardigrade researchers occasionally encounter a water bear grabbing a nematode around the middle. The nematode wriggles furiously all over the dish, with the tardigrade hanging on like a bronco rider, until the drained nematode surrenders.

Photograph courtesy of Bob Goldstein and Vicky Madden of the University of North Carolina at Chapel Hill.

But extreme survivorship applies only to some species of terrestrial tardigrades. Marine and aquatic tardigrades did not evolve these characteristics because their environments are stable. It appears that the extravagant survival adaptations have been selected in direct response to rapidly changing terrestrial microenvironments of damp flora subject to rapid drying and extreme weather.

Terrestrial tardigrades have three basic states of being: active, anoxybiosis and cryptobiosis . In the active state, they eat, grow, fight, reproduce, move and enact the normal routines of life. Anoxybiosis occurs in response to low oxygen. Tardigrades are quite sensitive to oxygen tension. Prolonged asphyxia results in failure of the osmoregulatory controls that regulate body water, causing the tardigrade to puff up like the Michelin Man and float around for a few days until its habitat dries out and it can resume active life.

Cryptobiosis is a reversible ametabolic state—the suspension of metabolism—that has inevitably been compared to death and resurrection. In cryptobiosis, brought on by extreme desiccation, metabolic activity is paralyzed due to the absence of liquid water. Terrestrial water bears are only limnoterrestrial—aquatic animals living within a film of water found in their terrestrial habitats. Moss and lichens provide spongelike habitats featuring a myriad of small pockets of water and, like sponges, these habitats dry out slowly. As its surroundings lose water, the tardigrade desiccates with them. It has no choice. The creature loses up to 97 percent of its body moisture and shrivels into a structure about one-third its original size, called a tun . In this state, a form of cryptobiosis called anhydrobiosis—meaning life without water—the animal can survive just about anything.

research on water bears

Figure 4. Tardigrades have evolved a suite of survival tactics to escape the vagaries of their localized and vulnerable environments. Anoxybiosis and encystment, described in the upper part of this figure, are responses one might see in a variety of organisms. The bottom half of the chart shows three states of cryptobiosis, in which metabolism is suspended—an act usually diagnostic of death. Cryobiosis occurs in response to freezing, and anhydrobiosis in response to drying. During the latter, an organism surrenders its internal water to become a desiccated pellet. Both result in the formation of a durable shrunken state called a tun . More rarely, a tun is created to resist osmotic assault, which requires water. In the tun state, tardigrades can survive for many years, impervious to extremes far beyond those encountered in their natural environments.

Illustration by Tom Dunne.

Tardigrades have been experimentally subjected to temperatures of 0.05 kelvins (–272.95 degrees Celsius or functional absolute zero) for 20 hours, then warmed, rehydrated and returned to active life. They have been stored at –200 degrees Celsius for 20 months and have survived. They have been exposed to 150 Celsius, far above the boiling point of water, and have been revived. They have been subjected to more than 40,000 kilopascals of pressure and excess concentrations of suffocating gasses (carbon monoxide, carbon dioxide, nitrogen, sulfur dioxide), and still they returned to active life. In the cryptobiotic state, the animals even survived the burning ultraviolet radiation of space.

Challenging student scientists to ponder the astonishing durability of tardigrades brings their understanding of physics, chemistry and biology into play. They recall that water expands as it approaches the freezing point, which is why ice floats. At 4 degrees celsius the expansion of water exerts sufficient force to split boulders, rupture metal containers and explode living cells. A cell is more than 95 percent water. The rupturing forces and icy microshards that form in frozen cells are the same that cause frost bite.

How can water bears survive all that? my new student and, perhaps, future colleague asks.
Really, deep down, we’re still puzzled about a lot of it, I respond.

The survival attributes of tardigrades are in fact quite appropriate for an organism that makes its home in mosses and lichens (bryophytes), which provide them with just a thin layer of protection. Bryophytes are subject to the environmental extremes experienced on a planet bathed in solar radiation. They may receive varying periods of direct ultraviolet exposure and are never far from drying out as ambient conditions change.

Improvise, Adapt and Overcome

Tardigrades exhibit distinctly different responses, grouped under the general name of cryptobiosis, to different sources of stress. Anhydrobiosis and cryobiosis lead to the formation of tuns, but they are not equivalent—they are different mechanisms for protection against different environmental assaults.

research on water bears

Figure 5. Eutardigrades lack armor, which appears to have done little to inhibit their evolutionary success. Larger eutardigrades—such as those of the genus Macrobiotus (shown above in active form and tun state)—are found in many habitats, where they consume smaller tardigrades as well as nematode worms and rotifers. Their large appetite for nematodes (they may consume many per day), and their resulting controlling role on the nematode population, indicates a significant role in the food web for tardigrades at the micro scale.

Anhydrobiosis—metabolic suspension brought on by nearly complete desiccation—is a common state for tardigrades, which they may enter several times a year. To survive the transition, water bears must dry out very slowly. The tun forms as the animal retracts its legs and head and curls into a ball, which minimizes surface area. When nearly all of its internal water has been surrendered, the tardigrade is in anabiosis, a dry state of suspended animation. It is almost as if the animal preserves itself by becoming a powder comprised of the ingredients of life. When rehydrated by dew, rain or melting snow, tardigrades can return to their active state in a few minutes to a few hours.

In cryobiosis, another form of cryptobiosis, the animal undergoes freezing yet can be revived. Any temperature below the cell cytoplasm’s freezing point suppresses molecular mobility and therefore suspends metabolism. Deep-freeze temperatures could be expected to cause additional structural disruptions, yet tardigrades, as noted above, have survived the most drastic chills. It seems likely that survival is conferred by the release or synthesis of cryoprotectants. These agents may manipulate tissue freezing temperature, slowing the process and allowing an orderly transition into cryobiosis, and they may suppress the nucleation of ice crystals, resulting in an ice-crystal form that is favorable for subsequent revival with thawing.

Osmobiosis is a response to extreme salinity, which can cause destructive osmotic swelling. Some tardigrades exhibit strikingly effective osmoregulation, maintaining stasis in the face of steep osmotic gradients. Some others escape via formation of a tun that is impervious to osmotic transfer.

In 2007, tardigrades became the first multicellular animal to survive exposure to the lethal environs of outer space. Researchers in Europe launched an experiment on the European Space Agency’s BIOPAN 6/Foton-M3 mission that exposed cryptobiotic tardigrades directly to solar radiation, heat and the vacuum of space. While the experimental vessel orbited 260 kilometers above the Earth, the researchers triggered the opening of a container with tardigrade tuns inside and exposed them to the Sun. When the tuns were returned to Earth and rehydrated, the animals moved, ate, grew, shed and reproduced. They had survived. In summer of 2011, Project Biokis, sponsored by the Italian Space Agency, ferried tardigrades into space on the U.S. space shuttle Endeavor . Colonies of tardigrades were exposed to different levels of ionizing radiation. The damage is now being assayed to learn more about how cells react to radiation and, perhaps, how tardigrade cells fend off its damage.

My student’s mind is turning.
How far is the nearest solar system? Could cryptobiotic tardigrades make it to Earth? she asks.
I saw a post recently on a listserv that says it might be only about 10 light years away, I answer. So if tardigrade tuns were transported here on a meteor or asteroid at just one tenth the speed of light, they could conceivably make the trip within the known survival capability of the animal. Theoretically. But the likelihood is awfully small. And think of the poignancy of arriving after that great journey but having no way to make it through the fiery descent through an atmosphere. Even tardigrades can’t survive that.

Surviving intense radiation suggests an especially effective DNA repair system in an active organism. Effective osmoregulation in extreme salinity implies a vigorous metabolism—osmoregulation in the face of high environmental salinity is energetically extremely expensive as metabolic transactions go, requiring the pumping of ions against steep osmotic and ionic gradients. Thus, we see in tardigrades two opposing responses to environmental extremes: the passive response of dormancy in the form of cryptobiosis, balanced by the hyperactive responses of impressive DNA repair and high-performance osmoregulation. As practitioners of adaptive evolution, tardigrades are virtuosos.

Getting Around

Tardigrades have been discovered just about everywhere that anyone has looked, from the Arctic to the equator, from intertidal zones to the deep ocean, and even at the top of forest canopies. Their ubiquity is intimately linked to their survivorship. I am often asked how tardigrades manage to find their way to the canopy of towering trees. Most likely, wind carries them. In the tun state they are barely distinguishable from dust particles. But like spores, pollen and seeds, the tuns have a preference for where they land. Many microenvironments will be unsuitable habitats for freshly arrived tardigrades. Yet an unhappily placed tun can simply wait for a change in precipitation or perhaps a change in season. When conditions improve, life can begin again.

research on water bears

Figure 6. The armored Heterotardigrade of the genus Echiniscus in the active state ( top ) and in the cryptobiotic tun state ( bottom ). The armor of these tiny predators contains chitin, the same material incorporated in the cuticle of insects. The armor may slow the process of drying. In drier environments, heterotardigrades are predictably represented in larger numbers than are naked species. The armor plates may supply some degree of protection to the vulnerable active form.

Images courtesy of the author.

Contributing to their success as travelers is the fact that many tardigrades of moss, lichen and leaf litter are parthenogenetic, able to produce eggs without mating, and in a few cases are hermaphroditic, able to self-fertilize. A lone tardigrade on an ill wind—active, tun or egg—may be able to establish a population where it lands if the habitat is suitable. We may be under tardigrade rain right now.

research on water bears

Figure 7. These images of tardigrade claws are magnified 3,000 to 5,000 times. Even at so fine a scale, structures have developed that are distinctive to each genus, suggesting adaptations for different lifestyles. Tiny hooks suitable for spearing tiny hors d’oeurves contrast with bristling claws seemingly optimized for a raking, tearing attack. Little studied, tardigrades are far from understood. The diversity of claw types may have roles in mating, tun formation and other tardigrade activities that have not yet been discovered.

Images courtesy of the author and Clark W. Beasley of McMurry University.

At present there are about 1,100 described species of water bears, but not all are valid. Some descriptions are repeats and some are just plain flawed. Around 1,000 species have been properly identified and described. We have about 300 marine, 100 freshwater and 600 terrestrial species. But the land species are much easier to find and have been pursued by many more researchers over many more years. Still, my students have discovered and described four new species so far, and we are working to confirm another half dozen, including one found on the campus of Baker University in Kansas, where I am a faculty member. We believe there is an abundance of species yet to be discovered, especially in the nonterrestrial environments.

I might discover a new species? she asks.
Yes, sitting at a microscope, you might observe an animal nobody in the world has ever seen before. That is pure exploration. In the blink of an eye, you might find a clue to the evolution of the phylum or identify the animal that holds the cure for cancer, I say. Then again, you might not. It took me 16 years to find my first new species.

Finding a New One

Last summer, the student who inquired at my office, Rachael Schulte, became an intern working on our National Science Foundation grant under the Research at Undergraduate Institutions (RUI) program designed to teach research by exploring and expanding the biodiversity of the phylum Tardigrada in North America.

research on water bears

Figure 8. A light-microscope image reveals the dorsal plates and cirri, cuticular extensions, of what one day could be known officially as Multipseudechiniscus raney i. While working with the author, Baker University undergraduate Rachael Schulte found the organism in samples her teacher had collected in California. They have submitted a paper describing the organism for publication.

Image courtesy of the author and Rachael Schulte.

After a couple of weeks of practice on lichen from local trees, Rachael had become proficient with the tools of the tardigrade trade—the dissecting scope, the wire Irwin loop, slide preparation, imaging, record keeping and identification to the level of genus. She was ready to work on actual research material, so we set her up with samples collected a couple of years before on a transect from more than 9,000 feet up in the Sierra Nevada Mountains down to Fresno, California.

Just a week later, she came to me with a finely made slide.

I think it is a Pseudechinsicus but it has many small, plates across its back, lateral filaments on the edge of each segment, and a toothed collar on the last legs, she says.
This was a teaching and a learning moment. I put the slide on the stage of our computer-imaging microscope to take a look.
Do you have other specimens?
Eight, all from the same sample, she replies.
I have seen this before, it is Pseudechinsicus because of this pseudo, or false, segmental plate. But it appears to also have a pseudosegmental plate on each segment. Let’s see how it keys out in Ramazzotti and Maucci, I say.

In 1983, Giuseppe Ramazzotti and Walter Maucci published the monograph The Phylum Tardigrada. It was translated from Italian into English by Clark Beasley in 1985. It is now 27 years out of date and includes only half of the described species. But it remains the reference of first resort. We started with the genus Pseudechinsicus. As I read the diagnostic questions in the key, Rachel worked the microscope to answer them.

The animal looked like Pseudechinsicus raneyi, as described by Gragrick, Michelic, and Schuster in 1964. We pulled up a copy of the paper from the files (we have PDF files of 95 percent of all tardigrade papers) and read. The description matched our animal. We then looked at the 1994 list of species, along with the relevant research papers and geographic distributions, prepared by McInnes. There were only two listings for our species—the original description from California and Schuster and Gragrick’s entry in their 1965 classic work on the western North American tardigrades, which added Oregon to Pseudechinsicus raneyi’s known range. Searching through the more recent literature in our database, Rachael discovered that I had also found the creature in Montana during my master’s work at the University of Montana, Missoula, in the late 1960s, although I did not publish the record until 2006. Now after 40 years we had a fourth record and a new location for an uncommon regional animal.

During our literature review, we learned that the genus was described by Gustav Thulin in 1911, who gave high taxonomic value to the presence of the pseudosegmental plate. Then in 1987, Kristensen revised the family Echinsicidae, redescribed the existing genera and added four new ones to the list. Because this occurred after our creature was described, we needed to confirm the genus assignment by reviewing its characteristics against the amended, more detailed description.

We started down the list of characteristics under the genus Pseudechiniscus I read the first line:

Echiniscidae with black eyes: rigid buccal canal, stylet supports may be present, but very tiny and located close to the margin of the pharyngeal bulb.
Looking through the microscope, under oil immersion at 1,000-times magnification, Rachael says:
Black eyes, yes, but the buccal canal is long and bent. Flexible. No visible stylets.
I continue, … unpaired scapular plate. Typical tiny basal secondary spurs.
No, it is paired. And the spurs are not tiny, nor basal, she says.
I look up and say, No mention of the extra pseudosegmental plate.

Our specimens did not match the description of the genus Pseudechinicus. So we checked the other generic descriptions within the family the same way and concluded that our specimens matched none of them. We now thought there were enough significant deviations from the existing descriptions to merit describing and naming a new genus.

Over the next several months we borrowed the original type specimen of Pseudechiniscus raneyi from the Bohart Museum at the University of California at Davis and confirmed that it was the same as our specimens. Rachael and I made images of the slides, measured multiple characteristics on each specimen and developed a comparative table. We checked and double checked our specimens. As we started to pass the draft of a manuscript back and forth, I asked Rachael whether she wanted to be a coauthor describing the new animal or to have it named after her.

I get to choose?
You found it, helped detect the differences, and contributed to the new description, I say.
What is the difference? she asks.
Both are a bit of immortality. But you can’t be an author and namee, I say. Normally, we would name a new genus after some unique characteristic of the organism, or to commemorate a fellow researcher. We could name the genus after you, but the species would remain raneyi because our specimens match the already described Pseudechiniscus raneyi . We are simply moving an existing species into a new genus, so the species name does not change, I explain. But if you are an author of the paper describing the new genus, your name goes after the genus name, before the date, every time the genus is listed, I say.
So what do we name it? she asks.
What is the most distinctive feature of the critter?
The elongated buccal tube? she says.
True, but that is very difficult to see. What else have you seen?
The extra pseudosegmental plates? she suggests.
Okay, how about Multi pseudechiniscus ? I ask.

Rachael presented a poster about the discovery at the November 2010 Sigma Xi International Meeting and Student Research Conference in Raleigh, North Carolina, with 250 other undergraduate researchers. The new genus of water bear is shown in Figure 8. Our manuscript reporting the find is under review at a peer-reviewed journal.


  • Glime, J. M. 2010. Bryophyte Ecology. Online monograph in two volumes. Chapter 5: Tardigrades. Sponsored by Michigan Technological University and the International Association of Bryologists.
  • Guil, N., S. Snachex-Moreno and A. Machordom. 2009. Local biodiversity patterns in micrometazoans: Are tardigrades everywhere? Systematics and Biodiversity 7:259–268.
  • Kinchin, I. M. 1994. The Biology of Tardigrades. London and Chapel Hill, N.C.: Portland Press.
  • Kristensen, M. A., et al. 2011. Survival in extreme environments—on the current knowledge of adaptations in tardigrades. Acta Physiologica 202:409–420.
  • Kristensen, M. A. 1987. Generic revision of the Echiniscidae (Heterotardigrada), with a discussion of the origin of the family. In Biology of Tardigrades, R. Bertolani (ed.). Selected Symposia and Monographs. Union Zoologia Italia, Mucchi Modena. 1:261–335.
  • McInnes, S. J. 1994. Zoogeographical distribution of terrestrial/freshwater tardigrades from current literature. Journal of Natural History 28:257–52.
  • Miller, W. R. 1997. Tardigrades: Bears of the moss. The Kansas School Naturalist. Emporia State University. 43:1–16.
  • Persson, D., et al. 2011. Extreme stress tolerance in tardigrades: Surviving space conditions in low earth orbit. Journal of Zoological Systematics and Evolutionary Research 49(suppl 1):90–97.
  • Welnicz, W., et al. 2011. Anhydrobiosis in tardigrades—the last decade. Journal of Insect Physiology 57:577–583.

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Thomas Boothby, assistant professor for the Department of Molecular Biology at the University of Wyoming, teaches us about tardigrades, more commonly known as water bears, that are headed up to the International Space Station for a scientific study to learn how these extremophiles adapt to microgravity. HWHAP Episode 197

Water Bears in Space

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Water Bears in Space

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On Episode 197, Thomas Boothby, assistant professor for the Department of Molecular Biology at the University of Wyoming, teaches us about tardigrades, more commonly known as water bears, that are headed up to the International Space Station for a scientific study to learn how these extremophiles adapt to microgravity. This episode was recorded on May 6, 2021.

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Gary Jordon (Host): Houston, we have a podcast. Welcome to the official podcast of the NASA Johnson Space Center, Episode197, “Water Bears in Space.” I’m Gary Jordan and I’ll be your host today. On this podcast we bring in the experts, scientists, engineers, and astronauts, all to let you know, what’s going on in the world of human spaceflight. Water bears are about to head to the International Space Station. If you’re not familiar with water bears, or tardigrades, they are super-tiny animals that are best known for their ability to survive in some of the harshest conditions: extreme heat, extreme cold, bottom of the ocean, near volcanoes, highly radioactive environments, and even the vacuum of space. Exactly how they survive in these conditions is something that Dr. Thomas Boothby has been studying for years. Thomas is an assistant professor at the University of Wyoming Department of Molecular Biology, and he’s taking his research to the International Space Station as the principal investigator for Cell Science-04, which is, you guessed it, sending water bears to space to study how they adapt to microgravity. I got a chance to chat with Thomas about water bears and this investigation that will be making its way to the space station aboard the SpaceX Dragon on the upcoming CRS-22 mission, so let’s get right to it. Enjoy.

Host: Dr. Thomas Boothby, thanks for coming on Houston We Have a Podcast today.

Thomas Boothby: Absolutely, my pleasure to be here.

Host: Hey, this mission that’s going to be carrying your experiment to the International Space Station is right around the corner, about to launch. How are you feeling in anticipation of this, of this launch coming up?

Thomas Boothby: Me, personally, I’m extremely excited. We’ve been working on this since 2015, so a lot of hard work and time has gone into this, and really exciting that the launch is right around the corner.

Host: Well, let’s get right into it, Thomas. We’re going to be talking about water bears today and I got to say, I am a huge fan. I discovered them like a, I think it was back, man, it was a couple years ago. “Animal Planet” did this, did this show called “The Most Extreme,” and they did one on like the most extreme survivors, and that’s where they just went deep into the survivability of a water bear. And I was like absolutely fascinated, I could not believe what these things were capable of surviving in. So, let’s just start there, understanding water bears, tardigrades, because that will sort of help us transition into this specific science investigation that’s going to space station. So, let’s start with Tardigrades 101, Thomas, take us through what these things are.

Thomas Boothby: Well, so, tardigrades, or water bears as they’re sometimes commonly referred to as, are a group of microscopic animals that are capable of surviving some of the harshest conditions that we know of. So, despite being these like teeny, tiny, little microscopic organisms that you need a microscope to see, they’re extremely robust, so they can survive a number of extremes that we typically think of as being restrictive to life. So, some examples of sort of extreme environments or conditions that tardigrades can survive include being dried out to the point where they essentially have no water left inside their body or cells; they can be frozen down to just above absolute zero, they can be heated up, in some cases, past the boiling point of water, they can survive thousands of times as much radiation as you or I could; they can go days or weeks with little or no oxygen, and maybe the sort of most remarkable feat that they’ve been shown to perform is that they can actually survive in the vacuum of outer space. They’re the only animal that we know of that can, that can do this, so they’re really, they’re really quite amazing and unique.

Thomas Boothby: So, if I were to, if you were to have a picture of a tardigrade, how would you, how would you describe sort of what they look like?

Thomas Boothby: Yeah, so, what I tell people is think about the little, like gummy bear candy, and imagine that, but with eight legs instead of four. They look like these kind of chubby, little eight-legged gummy bears. Yeah, I think, you know, they’re pretty adorable. If people have seen pictures of them, they’re pretty charismatic, but that’s usually how I describe them.

Host: Yeah, and they’re, I mean the pictures I’ve seen of them, they kind of look clear, right?

Thomas Boothby: Yeah, so depending on what kind of microscope you’re using to look at them, if you’re using like a light microscope, many tardigrades are transparent, so you can, you can see through them. Others aren’t, so different species of tardigrades actually, like morphologically, like how they look, is pretty distinct. You have some that, yeah, as you said, there’s kind of clear. You have others that almost look like they have like armored plates on their backs; they look like little tanks, and those are a little bit harder to see through, but yeah, there’s actually quite a bit of a sort of a morphological diversity within the group of animals.

Host: So, in the beginning of this chat you talked about all of these different, very extreme conditions that the water bears can survive in. So, if I were to go hiking around planet Earth, where could I find them?

Thomas Boothby: So, tardigrades have actually been found almost any, anywhere and everywhere that folks have looked for them. They’ve been found, you know, on the tops of mountains, like in the Himalayas, in the deep ocean, in mud volcanoes, tropical rainforests, in Antarctica, but amazingly, if you just go in your backyard, they’re probably living back there.

Host: Oh, wow, I didn’t realize they were, they were so widespread.

Thomas Boothby: Absolutely.

Host: So, really, when it comes to the extreme stuff, right, I guess, my backyard, I wouldn’t really consider that very extreme, but let’s just say, you know, like near a volcano or in like a very high-pressure environment, you know, what are they doing? Are they just sort of swimming around or do they go into some sort of process to help them survive these extreme conditions?

Thomas Boothby: Yeah, so one of, one of the tardigrade’s sort of greatest tricks is this ability to go into an ametabolic state, so a state where, essentially, they shut down all the sort of life processes that are going on inside of them. And when they do this, they pull their eight little legs and head inside their cuticle, that’s sort of like their exoskeleton that surrounds their body. And they curl up in this little ball-like structure known as a tun. So, have you ever seen like one of these little like roly-poly bugs?

Host: Yeah.

Thomas Boothby: They’re kind of like a tiny, little, microscopic version of that, where they curl up in this little ball, they shut down all their life processes that are going on and, you know, for all intents and purposes, you know, they sort of, it’s almost like they’re dead, but they’re in this state, they’re extremely resilient, and they’re able to ride out the, the sort of rough, harsh, extreme conditions. So, you know, if that’s a desiccating environment where water is being lost, you know, they’ll curl up in this little ball-like structure, dry out, and then, you know, when water returns to the environment, they uncurl. They come out of this ball-like structure and within an hour or so, you’ll see them scrambling around, eating, reproducing like nothing happened to them.

Host: Unbelievable. I’m sure you’ve been studying this for a long time, so, you know, you talk about when water is reintroduced to environment, or they’re, you know, they’re in a better environment where they can get out of this tun. How long have you seen some of these water bears in this state, before they return back to, you know, kind of frolicking through, and eating, and reproducing and all that?

Thomas Boothby: Yeah, so, tardigrades are able to enter this ametabolic state, and many species are extremely stable and viable in that, in that state. So, kind of an average would be about a decade or so in this, in this ametabolic state, but there are reports that tardigrades have been shown to survive, you know, for like over a hundred years; these were experiments going into herbariums, where they had preserved plant material, and people gathered tardigrades off that preserved plant material, which, you know, was documented and cataloged, when it was gathered and preserved. And they’ve been able to purportedly revive tardigrades that are, you know, hundreds of years old.

Host: Unbelievable. Now, I mean, it’s, this is a very unique trait for an animal. You know not everyone, not every—every one —every animal can do this. So, what is it about the tardigrade? What unique quality do they possess to be able to do this sort of thing?

Thomas Boothby: Well, that’s a really excellent question, and that’s something that my lab and other labs are trying to uncover. We’ve found some hints and clues, but certainly there’s a lot more to learn. But one of the really interesting features of tardigrades that we found was, that when they start to dry out or enter these sorts of extreme environments, they start to produce a very special class of protein. And this is actually a type of protein that is unique to tardigrades. So, so no other organisms that we’ve, that we’ve looked at possess similar, similar proteins. And what these proteins do is something very interesting: they build up in their concentration. So, the tardigrades just start making more and more and more of these things. And what these proteins seem to do is they make the environment inside the tardigrade, so like inside the tardigrade cells, really, really viscous. So, imagine, you know, as opposed to water, which is very liquid, imagine it more like becoming like honey, where it’s very sort of gooey and viscous. And what this sort of increased viscosity does is it slows down all the bad things that are happening. So, you know, parts of cells start to break down, or unfold, or fuse together, normally, when a cell is drying out, but in this sort of super-viscous environment all those things are still happening, they’re just happening very, very slowly. And when this super, sort of super-viscous environment gets even drier, it, what it does is it forms a glass, so like glass in a windowpane, and this is really important because glass has a very different molecular makeup than say something like a crystal. So, if tardigrades made something that filled their cells with crystals, that would be really bad because crystals are very sharp and pointy, they can puncture cells or crush, you know, sensitive material inside of the tardigrade cells, but these glasses are much smoother and sort of more amorphous, and they’re actually able to encapsulate these sensitive molecules inside of tardigrade cells, and actually preserve them within this sort of glass-like matrix or structure. And what’s really amazing is, when water returns to the system, when you rehydrate a tardigrade, that glassy material just kind of melts away, and it goes back into solution, it dissolves into the, into the water, and it releases all those sensitive molecules that were stabilized inside of it back into the tardigrade cell, where they can perform their normal biological functions.

Host: Thomas, this is, this is amazing. I mean, I, my next question I feel like is a genuine one, but I feel like just everything you’ve just described sort of answers it for me, just how interesting this is, but what got you interested in this fascinating world of researching tardigrades?

Thomas Boothby: Yeah, that’s a great question. So, so besides tardigrades just being, you know, at least to me, like really fascinating, you know, wanting to understand kind of the, the outliers in biology, right, like, you know, tardigrade biology is quite unique, and in my opinion, understudied, and so, you know, just from a purely, from a place of pure intellectual curiosity, understanding how these little creatures are able to do something that, you know, for us, would be so sort of mind-bogglingly impossible to achieve is, was really, really of interest to me. And then, beyond sort of the fundamental biology of tardigrades, I was really attracted to studying them because of some of the potential applications, you know: what we could do in terms of taking the fundamental biological findings that we made studying tardigrades, and sort of the promise of applying that knowledge to trying to solve real world problems was really, really sort of attractive to me.

Host: So, tell me about, you’re, you’re at the University of Wyoming, right? So, you sort of went and described a little bit more about this protein, and you mentioned that you’re still doing a lot more research to figure out exactly what’s going on to allow the tardigrade to have this sort of unique process. So, tell me about some of your research that you’re doing over there.

Thomas Boothby: Absolutely. So, we’ve got, we’ve got quite a bit of sort of diverse research going on here. On sort of the fundamental biological side, we’re really interested in understanding how these tardigrade proteins are working. So, like, what are the building blocks that make up these proteins that make them so special and so protective? We’re also really interested in understanding whether or not these proteins and other tricks that tardigrades use to, say, survive when they dry out, we’re really interested to know if those are the same tricks that tardigrades use when they’re faced with other extremes, like freezing, for example. So, do tardigrades have sort of one, one way of surviving many different extremes or do they have many different tricks for surviving all these different extremes? And then on the more applied side, we’re really interested in how we can take that knowledge and adapt it to addressing real world problems, like stabilizing pharmaceuticals, or developing crops that are more resistant to extreme environments, so that’s kind of our research, in a nutshell.

Host: So I imagine, you mentioned there are tardigrades all over the world and you want to understand more about the, some of these different processes, or at least when they hibernate, or I guess, go into this, you said, I forget the exact state, something about metabolism, but essentially, into this state, and in this tun, do you get to travel to some of those locations as part of your research, like to, you know, volcanoes, or to whatever, deep sea, and understand, like pressure, or are you bringing them to the lab and doing everything in the, at your university?

Thomas Boothby: Yeah, so, so a little bit of both. So, a couple years ago, as part of a NSF (National Science Foundation) training, training grant, I was able to go down to Antarctica, and we were finding tardigrades down there, along with doing some experiments. One of the reasons that our lab located to Wyoming was to be closer to some of these extreme environments that we study organisms from. So, Wyoming has a number of really diverse extreme environments. You know, people typically think of, you know, sort of the hot springs out in Yellowstone, but then there’s also Wyoming’s Red Desert, which is an immense, high-elevation desert, so, so very cold and very dry, with sort of Martian-like environments. And then, of course, you have the Bighorn Mountains, the Snowy Range Mountains, so, you know, we kind of have all different types of environments out here in Wyoming where we go in and collect organisms from.

Host: That’s pretty cool. Yeah, you got to enjoy those kinds of trips then, you got to enjoy the harsh environments.

Thomas Boothby: Absolutely. Yeah, it helps, it helps to be a little bit tough if you want to go and study these little critters out there.

Host: Well, look, the space station is only 250 miles from Wyoming, you just got to go straight up. So, how did it happen where you were looking at all these different extreme environments and you thought, ah, you know, where we should go is the space station?

Thomas Boothby: Yeah, so, you know, how that kind of came about was, I was just really curious in this observation that tardigrades actually survive a number of extremes that they would never have been exposed to, so it’s kind of this perplexing question of, you know, how could an organism evolve to tolerate a condition that it, it didn’t evolve in? And spaceflight and space environments are probably some of the sort of most foreign or alien environments that you can think of for an organism that evolved on Earth. And so, there have been some space studies using tardigrades before. In particular there was a, there was a Russian capsule that went up in 2007, which actually exposed tardigrades to the vacuum of space, and they were left out there for about ten days in low-Earth orbit, and they were shown to be viable after that exposure. There was another mission involving some Italian scientists, which showed that tardigrades could survive and reproduce without any negative effects during spaceflight. And so, yeah, I got really interested in trying to understand how, right, not just, can they do this, but how are they able to do this? And so, that’s really, kind of the, kind of main driving scientific question for Cell Science-04 mission, is understanding how tardigrades adapt to being exposed to outer space, or to space conditions, rather. And then under those prolonged spaceflight conditions, how do they change and adapt after that initial exposure, you know, say over multiple generations?

Host: So, let’s get into it, let’s get into the experiment that’s going on the International Space Station, you called it Cell Science-04. So, what’s the, what’s this experiment that’s going up?

Thomas Boothby: Yeah, so what we’re really interested in doing is looking at what the initial changes in gene expression, so, so how tardigrades are adapting to spaceflight environments, is initially, and then how that changes over multiple generations. So, essentially, what we’re going to be doing is sending tardigrades up from the Kennedy Space Center to the ISS, and we’re going to basically have two different pools of tardigrades. One pool is going to be our sort of founding generation, where after a week of being in space, we’re going to preserve them in a special chemical preservative, but then the second pool we’re going to let culture, and grow, and reproduce for two months, and that’ll represent about four generations of tardigrades. So, they’ll have time to reproduce, and their offspring will reproduce, and so on, and so forth, for four generations. And then we’re going to preserve those multigenerational tardigrades. And when we get these preserved tardigrades back to our lab here in Wyoming, what we do is we extract a certain molecule called RNA, and this is kind of an intermediate molecule between the tardigrade’s DNA, their genes, and the final products that those genes are sort of the blueprint to make. And so, by looking at these molecules that we can extract, we can tell what changes in gene expression tardigrades are inducing when they’re exposed to space initially, and when they’re exposed to spaceflight conditions over the long term. And our hope is that by understanding how these tough little organisms are able to survive spaceflight conditions, that this will give us hints and clues into, you know, how we might safeguard astronauts during prolonged space missions.

Host: See, that’s going to be a big deal, especially for NASA’s plans to go to the Moon and Mars, just one extra step to help out in that process, very, very fascinating stuff.

Host: I’m curious to hear about how you’ve been preparing to get this experiment going. You know, you, I guess had to start with the initial process of figuring out how to get the tardigrades into space, but what’s been the process from the initial concept, to getting everything packed, and basically, ready to go on a rocket?

Thomas Boothby: Yeah. So, so initially, kind of the biggest consideration was just trying to figure out how we’re going to grow these little animals in space. So, in the lab, we normally grow them in these sorts of big glass petri dishes filled with a liquid medium, but in space that wouldn’t work so much because the, in microgravity the liquid media that the tardigrades grow in would just sort of float away. So, yeah, initially, it was validating a bioculture system that had been developed by some NASA engineers and adapted to this project. And then, it was really just going through a number of sort of dry runs and seeing, you know, in ground-based experiments, how our experimental plan for the actual flight experiment went. You know, it was a lot of optimizing things that don’t sound very exciting, like how fast a pump moves water through the system, or how much oxygen we need to deliver to the media. But, you know, all that sort of nitty-gritty detail has been worked out and we’re now, actually, this, just this week, in the process of prepping our samples that will go up to the ISS, so that basically involves loading the tardigrades into syringes that will be frozen and can be stored frozen and delivered to the ISS in this sort of inactive state. And then along with that we’re packaging up a lot of the food that the tardigrades eat because, over multiple generations, they’re going to need to be fed a couple times to stay healthy. So, the species of tardigrade that we use, they eat unicellular algae, so little, little algal cells, so we’re also getting those loaded into syringes, and ready to be sent up to the space station.

Host: So, actually, running the experiment on station, it sounds like this, whatever setup you have is going to be installed on a facility on space station, and every once in a while, is it going to require astronaut interaction to go ahead and use this syringe and feed the water bears, over generations?

Thomas Boothby: Absolutely. So, yup, when the, when our samples get up to the space station, they’ll be in syringes, and the astronauts will need to thaw out the tardigrades to sort of reactivate them, and then inject them into this bioculture system. Once they’re in the bioculture system, it’s pretty hands-off. We have telemetry, so we can sort of monitor the temperature and the flow rates and everything, inside the bioculture system. But then, yeah, you’re exactly right, at sort of two-week intervals an astronaut is going to need to attach an algal syringe to the bioculture system and inject fresh algae into it for the, for the tardigrades to eat, but, and then, and then at the end of the experiment they’re going to need to essentially sort of dismantle a portion of that bioculture system, which will be frozen and stored until we can get it back at our lab in Wyoming. So, there will definitely be some astronaut interaction with this, with this experiment, but there are also sort of large portions that are, that are automated.

Host: Yeah. Honestly, it sounds pretty easy in terms of the astronaut crew time needed, just, you know, feed it, it sounds like not even that often. You said once every two weeks was the feeding schedule?

Thomas Boothby: Yup.

Host: Yeah, see, it’s not even that bad. When it comes to measuring though, you said you’re going to, it is going to return, that’s part of the plan is it returns back to Earth, you go to the lab, and you have a number of things that you’re going to be looking at. Is there anything on orbit that will be, that you have in terms of measuring tools? It sounds like you have the, in the facility, you have the ability to control climate and watch all data coming in, but are you going to be doing any data gathering from the facility while it’s in orbit?

Thomas Boothby: So, the only sort of measurements that we’re making on orbit are environmental measurements. So, you know, what the, what the environment that the bioculture system is in. And we’re going to be using that telemetry, so, you know, the temperature, and whatnot, to replicate those experiments back here on Earth, and so we call those our near-synchronous ground controls. So we’re basically going to be doing the exact same experiment, but here on Earth, almost in real time with the, with the flight mission. But yeah, all the, all the sort of biological data that will be gathered is going to be done once we get the samples back from the space station, then we’ll process them here, here in the lab in Wyoming.

Host: So, you said — you said we, right? So, it’s not just, it’s not just you sending the water bears up and looking at everything. It sounds like you got, you got a decent support team that’s helping to bring all of this together.

Thomas Boothby: Yeah, absolutely. And yeah, it’s really great that you bring that up because, you know, I’m just one person in a team of really amazing folks. So, here, in the lab, in Wyoming, specifically, we have Cherie Hesgrove and Ryan Bettcher are working on this project. But then, on the NASA and the KBR side of things, we have a lot of people who really, sort of deserve some credit. So, specifically, Medaya Torres is our CS-04 mission scientist, Natayla Dvorochkin is our contract support scientist, and then on the KBR side there’s a bunch of people that I’d just like to acknowledge really quickly: Daniel Nolan, Kevin Sims, Oscar Roque, Christina Lim, Crystal Kumar, Kris Vogelsong, Brandon Schmitt, and Jamie Bales, Susan Markey, Meghan Feldman. And then on the NASA engineering side, Peter Zell and David Pletcher. And I’m sure I’m forgetting some other folks, but it’s been a, it’s been a huge team and group effort to get to this point, and yeah, I think it’s worth taking a couple minutes just to acknowledge all these folks.

Host: Absolutely. Yeah, and that’s part of the whole deal, right, is it’s not just, you know, it’s not just, “hey, Thomas, let’s get your experiment on the International Space Station,” it does really take a team, not only to get it up there, but to do all the work, to monitor it, make sure it’s working fine, and then of course, what you, what you’re all anticipating is when you get the water bears back from space into the lab in Wyoming and you get to conduct some fascinating research from that, from that group of water bears that went up there.

Host: Yeah. Now, one of the things I’m thinking of, Thomas, is, you know, there’s, well, I think what we’re all anticipating is when you’re starting that research, you know, what are the potential applications that you are thinking of in terms of maybe something we can learn, that we can bring back to benefit us here on Earth, or something that we can use to further space exploration. What are some of the things that you’re looking at that might have potential benefits to this experiment?

Thomas Boothby: Yeah. Well, definitely, part of the sort of stated goal of this mission is, you know, to start to build a foundation for developing therapies or countermeasures that might better safeguard astronauts in the future during prolonged space missions. So, you know, as I sort of mentioned before, spaceflight can be a really challenging sort of environment for organisms, including humans, who have evolved to the conditions on Earth. So, in space, you have much less gravity, you’re in microgravity, and you’re also exposed to a lot more radiation. So, for humans who spend a lot of time in space, you know, there can be detrimental effects to being in these environments. And so, one of the things we’re really keen to do is understand, you know, how are tardigrades surviving and reproducing in these environments, and can we learn anything about the tricks that they’re using that might be adapted to safeguarding astronauts. So, for example, if we see that tardigrades, when exposed to sort of this increased radiation in space, which produces a lot of reactive oxygen species, which are these sort of damaging chemical moieties that are really bad for cells, if tardigrades are producing a lot of reactive oxygen species scavengers, which basically kind of negate those negative effects, then that might be something that we would consider either through, you know, like a dietary supplement, or something like that, providing astronauts with increased antioxidants or reactive oxygen species scavengers. That would just help them stay healthier in space for longer.

Host: See, this makes me think about this experiment and this, like you said, you want to, you want to set a foundation, right, that’s what you were talking about whenever you were thinking of potential application. And I think that’s a very exciting thing to say because what makes me, it makes me think that this is scalable, right? You can continue the research, maybe, maybe bringing next cell science investigations up to the International Space Station. And you were just mentioning the radiation environment, which in low-Earth orbit is a little bit different from say, the Moon. And with the Artemis program, with NASA returning to the Moon, there are potential, there are potential options to have investigations like this, where you can study water bears in an even higher radiation environment and gather even more unique data. So, it, to me it sounds like this is something that you can continue for a while.

Thomas Boothby: Absolutely, we hope so. I think, you know, there’s a lot more to learn about tardigrades and a lot of, you know, continuing potential benefits to society.

Host: And that’s a, that’s such a big deal and it’s all happening on board the International Space Station coming here real soon. So, Dr. Thomas Boothby, thank you again for coming on Houston We Have a Podcast. And really, best of luck to you and your team as you gear up for this launch of a, on a SpaceX Cargo Dragon to the International Space Station. Best of luck to you as your, as your journey just begins for Cell Science-04.

Thomas Boothby: Great. Thanks very much.

Host: Hey, thanks for sticking around. I hope you learned something about water bears and you’re as excited as I am for this launch of CRS-22. You can watch these water bears launch from Florida, travel to the International Space Station. Just check out our website has the latest on our TV schedule when you can see the launch live. If you like this podcast, we are one of several NASA podcasts across the entire agency; you can check all of them out at . We, Houston We Have a Podcast, are on the Johnson Space Center pages of Facebook, and Twitter, and Instagram. So, if you want to talk to us, just use the hashtag #AskNASA on your favorite platform, you can submit an idea or ask us a question, just make sure to mention it’s for us at Houston We Have a Podcast. This episode was recorded on May 6, 2021. Thanks to Alex Perryman, Pat Ryan, Norah Moran, Belinda Pulido, Jennifer Hernandez, Rachel Barry, and the International Space Station Program Research Office for helping to set us up with Thomas. And, of course, thanks again to Dr. Thomas Boothby for taking the time to come on the show. Give us a rating and feedback on whatever platform you’re listening to us on and tell us what you think of our podcast. We’ll be back next week.


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