What Is a Water Bear? All about the Amazing Tardigrade!

When I was younger, I was amazed at the hardy nature of the cockroach. They are able to survive up to a month without food and even the glue from a postage stamp contains enough nutrition to sustain them for longer. They thrive in warm temperatures and can survive in temperatures as low as -8 degrees Celsius for up to twelve hours by hibernating. They can even withstand losing their heads and survive for a week or longer. And yet, compared to the tiny animal that I will be introducing to you today, they are positively puny.

I would like to introduce to you the tardigrade. Tardigrades are an eight-legged aquatic invertebrate. There are some four hundred species of these guys, and they can thrive just about anywhere on this planet where there is a surface layer of moisture. Although they can be found all over the globe, from dense rainforests to your own backyard, there is a good chance you have never seen one. The larger species of Tardigrades only reach about one millimeter long and are nearly impossible to see without a microscope. These micro-animals are also known as water bears, and once you get the little guys under a microscope you can see why. Upon initial inspection, they look a bit like an eight-legged bear wearing a partially deflated balloon. This “partially deflated balloon” is actually a cuticle made up of lipids, proteins, and chitin. If you look closely at their faces you will see something a little strange. There are no visible eyes or ears, or recognizable facial features of any sort. Instead, there is a small cylinder that shoots out ever so often. This is the tardigrade’s mouth, and it contains many stylets, which work like exceptionally sharp little teeth. They also have claws on the end of each of their legs, which seems to help in locomotion. Although most Tardigrades dine on plants and bacteria there are some predatory species which use these stylets as spears to actively hunt other microscopic invertebrates.

These little animals are part of a group known as extremophiles, which means that they can survive and even thrive in extreme environments. Other examples of extremophiles are the Pompeii worm, which live their lives attached to hydrothermal vents on the ocean floor, and the Antarctic krill, who feed off of the algae that lives on the underside of pack ice in the Antarctic. In the case of tardigrades, they can survive in just about any environment that you throw at them. They have survived experiments including extremes such as being boiled in 300 degree F water and frozen to -328 degrees F, being dehydrated for nearly ten years, being exposed a thousand times the radiation it would take to kill a human, and even being exposed to the vacuum of deep space.

These hardy little guys are not new animals. As a matter of fact, they are one of the oldest living groups of animals on this planet. There is evidence of tardigrades living as far back as mid- Cambrian times, back when Trilobites were the dominant life form. Most of the animals were still aquatic, and this was long before any dinosaurs made their appearance. Because they are so tiny, it was difficult to find evidence of them, even where they are plentiful, so there is the distinct possibility that they were in existence long before the mid- Cambrian times. We do know that they have managed to survive through every extinction level event since the Cambrian age.

The big question on about these little guys was how exactly they managed to survive so many extreme environments. It appears that the tardigrade is able to reversibly suspend their metabolism in several different ways. They can survive extended periods of dryness constricting and folding their bodies and covering it with a waxy extrusion of a sugar called trehalose, a process known as Tun formation. This can allow survival of desiccation up to zero percent relative humidity for an extended amount of time. This process is also critical in how they handle changes in the salinity of their environments. They handle the extreme cold by an ordered freezing of the water inside their cells known as cryobiosis and a lack of oxygen by moving into a suspended state of turgid immobility. Even though they have been around for quite some time we still have a lot to learn about these little water bears.

Oddly enough, this little animal turned out to be very difficult to grow to adulthood in the lab. They do have males and females in their populations. Females lay anywhere from one to thirty eggs at a time, and the males then fertilize those eggs. They go straight from egg to water bear with no larval stage in between. The number of cells in the tardigrade body is fixed from the time that they are hatched. Tardigrade eggs are exceptionally light and are easily dispersed by the wind. Bob Goldstein, a biologist from the University of North Carolina at Chapel Hill, has had some luck in raising them. It started with some guy in a shed in England who learned how to breed them successfully to sell to local schools for scientific experiments. It is their descendants that Goldstein now raises. Because of this breakthrough we may be able to learn a great deal more from these little guys. We will now be able to study them in similar ways to the fruit fly. Some of the applications of research with these little guys are in the areas of cryogenics, suspended animation, and also in a way to more safely and effectively transport vaccines around the world.

[1] Maeve McDermott, “5 Reasons Why The Tardigrade Is Nature’s Toughest Animal”, National Geographic, Published March 19, 2014, retrieved December 29, 2014.

http://tvblogs.nationalgeographic.com/2014/03/19/5-reasons-why-the-tardigrade-is-natures-toughest-animal

[2] Karen Lindahl and Professor Susie Balser “Species Distribution Project, Tardigrade Facts.” Illinois Wesleyan University, Last revised 2 Oct. 1999, retrieved December 29, 2014.

http://sun.iwu.edu/~tardisdp/tardigrade_facts.html#anooxybiosis

[3] Matt Simon, “Absurd Creature of the Week: The Incredible Critter That’s Tough Enough to Survive in Space”, Wired, Published March 21, 2014, retreived December 29, 2014.

http://www.wired.com/2014/03/absurd-creature-week-water-bear