Water Bears Survive Outer Space
Tardigrades Revived After Days in Vacuum
The phylum Tardigrada contains some of the toughest animals on the planet.
Tardigrade Biology
There are over 800 known species of Water Bear, and probably many more awaiting discovery. They are all very small (most are less than a millimetre long), and live in almost all environments – from the deepest ocean bottom to the highest mountaintop, and from the equator to the poles. They have four pairs of stumpy legs with hook-like ends, and very complicated mouthparts. Oh yes – and they come in a variety of colours!
- Most live in marine and freshwater sediments (among other meiofauna) and feed on small microorganisms or bacteria.
- A few species have managed to escape from life between the sand grains, but they have not got far away since they creep slowly among the mosses and liverworts that grow on rocky surfaces, or in the cracks and fissures in the rocks themselves.
- Unlike other meiofaunal animals the tardigrades have developed the ability to stay with their sand when it heats up, dries out, or otherwise become unable to support life. They simply go into a state of suspended animation and wait for better times. (The rotifers also suvive hard times in this way.)
Toughest Animals Alive
When in ‘suspended animation’ (largely brought about by dehydration) tardigrades can endure extreme conditions:
- At least ten years as dried out ‘tuns’ (the name for a tardigrade that has stopped walking about), losing up to 99% of their water – yet still able to revive when they get wet again.
- Short exposure to temperature of over 150 °C, or brief time close to absolute zero, does not seem to bother them.
- High pressures (far greater than those experienced at the bottom of ocean trenches), and low pressure (right down to a perfect vacuum) are also survivable.
Presumably these abilities originally evolved to allow tardigrades to remain with their environment (the sediment) when it dried out, heated up, or was carried deeper in the sea. Once evolved these survival mechanisms proved remarkably robust – giving the Water Bears the ability to endure conditions they will never meet on earth.
Water Bears in Space
In 2007 the TARDIS (Tardigrades In Space) project exposed 3,000 Water Bear tuns to more than ten days in the vacuum of space. Most were shielded from cosmic rays, but otherwise unprotected, while a few got the radiation as well. They survived the vacuum very well indeed, and even a few of those zapped by cosmic radiation made it back to earth alive.
This ability to survive high levels of radiation is very surprising because it is known to damage DNA. It has been suggested that Water Bears might have very efficient mechanisms to repair their own DNA, and if this turns out to be the case then much could be learnt.
Water Bear Molecular Studies
DNA analysis suggests that the tardigrades are related to the arthropods and RNA analysis indicates a further possible affinity with the nematodes and Nematomorpha (while the traditional view was that they and the arthropods were closer to the annelids).
Main reference: Tardigrade Newsletter
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