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| Sometimes one expresses their enthusiasm for science with naff embroidery. |
When you think of a tough animal you may turn your mind to the image of a proud silverback, the vicious tiger or the tank-like rhino. Go a little smaller and perhaps you could come to respect the seemingly sadistic wasp or the strong worker ant. But the real badass of the animal kingdom is far smaller than that: the tardigrade, also known as the water bear or, even more adorably, the 'moss piglet.'
So what is a water bear?
Tardigrades are microscopic animals (usually about 1mm across) that primarily eat moss and other small plant matter. They're endearingly cute with chubby bodies and 8 stubby legs, which is a large reason behind their popularity with geeky sorts on the internet, though they do suffer from the all too common hellbeast-mouth-syndrome. They have a mouse, digestive tract and nervous system so are most definately animals. There are male and female versions that mate via eggs and on the whole they live rather quiet normal lives sucking on plant juices.
However when you look closer, the water bear is quite remarkable. Recent studies have shown that 17.5% of water bear's genome is made of foreign DNA (that is, where their genes come from outside creatures). While all animals - ourselves included - have some foreign DNA in us, often from the microorganisms that live inside us, this is often less than 1% of our total makeup. Tardigrades can acquire genes from plants, fungi and bacteria 'horizontally'. What this means is that these genes aren't passed down through parents to children, but instead are part of a genetic swap with other species. Scientists think that part of the reason for why tardigrades have such a high number of foreign genes is due to how they survive even the harshest conditions...
What makes it so tough?
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| Photo by Sinclair Stammers |
When water bears are subject to the harshest of environments they don't just curl up and die like us lesser mortals. Instead, their DNA reforms and adapts to survive, often pushing out almost all the water in its body and going into a state of suspended animation. Getting rid of the water is essential, as it's often how water reacts with cells that cause the greatest damage. This process is a tough one and often the DNA itself is broken apart in the stresses. In order to 'revive' the water bears rehydrate themselves and it is thought that at this time the DNA is 'leaky' and more likely to absorb genetic information from other nearby items. As tardigrades repair their DNA they use these chunks of other molecules as building materials, propping up their own DNA with these foreign, often bacterial, genes. *
What do we classify as the harshest of environments? Well, water bears have been known to survive deep freezes as low as -200 degrees C, extreme heat of over 150 degrees C, and extreme radiation of 570,000 roentgens (just 570 roentgens would kill a human 150 miles downwind of a nuclear blast). They can survive 1,000 atmospheres of pressure and even the vacuum of space!
One of the most famous examples was the 2 water bears that were recovered from frozen moss samples in antarctica in 1983. These samples were stored at -20 degrees C for some 30 years before the scientists, judging the water bears still to be alive, attempted to revive them by taking them out of freeze and putting them in water. Over a process of 2 weeks the hardy tardigrades 'woke up': one unfortunately stopped eating and died after 20 days, but the second named SB-1 (Sleeping Beauty - 1) thrived and even successfully laid eggs.
Most remarkably, during the FOTON-M3 space mission the European Space Agency took a handful of 'hibernating' water bears and exposed them to the vacuum of space and all the X-ray and ultraviolet radiation that entails. They were brought back to the lab and rehydrated to see the effects. Those that has ben exposed to the vacuum of space alone had survived very well, with no difference to the survivability of average water bears that had been kept as a test sample. However, when affected by the combined forces of the radiations - especially solar radiation -and vacuum combined, they finally started to struggle. 68% revived, but did not survive long, with only a slim number surviving the whole brutal process. They concluded that the vacuum of space did not in any way affect survival or reproduction, and even though the other combined radiations (like unfiltered UV radiation) they fared far better than any other anima. Previously only lichens and bacteria have been reported to survive the combined exposure of the space vacuum and solar/galactic cosmic radiation, so the water bear is the very first animal to ever have been shown that it is possible survive the combination of all three at once.Either way, they're the Chuck Norris of the animal kingdom.
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* It's worth noting that this theory is still under dispute, as the scientists involved have been accused of using contaminated samples. But it certainly suggests a theory as to why water bears are so resilient.
Sources
-Wikipedia - Tardigrade
-The water bear - the most extreme animal on our planet
-Water bears: genome sequence says it has the most foreign DNA of any animal on our planet
-Scientists revive microscopic water bears after 30 years of deep freeze
-Tardigrades return from the dead
-First animal to survive in space
-How does the tiny water bear survive in outer space?
-Tardigrades survive exposure to space in low Earth orbit.
-Tardigrade diagram
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