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Cool Creatures, Spineless Wonders

Nature’s Tough Guys

What are the toughest creatures in nature? You might instinctively imagine lions, and tigers, and bears… oh my! With fearsome claws and bone-crushing jaws, these carnivores might seem an obvious choice. Then again, a stampeding elephant is clearly a formidable force of nature, tough enough to trample all in its path – whilst the deadly crocodile is a killing-machine that has remained essentially unchanged since before the demise of the dinosaurs.

These creatures may be dangerous; but does that make them tough? Consider the emperor penguin bracing itself against the bitter Antarctic winter; or the dromedary camel crossing the baking Sahara desert. You’d have to be tough to survive conditions like these. However, nature’s toughest animal is arguably the tardigrade. Although their cute common names – water bear or moss piglet – might suggest otherwise, these microscopic creatures are tougher than Chuck Norris, Arnold Schwarzenegger, and Jean-Claude Van Damme combined.

Nature's tough guys: the Tardigrades

Nature’s tough guys: the Tardigrades – image from wikimedia commons

Although not as famous as their Hollywood tough-guy counterparts, tardigrades are found worldwide, everywhere from mountaintops to the deep sea. They live in water, or in damp places such as moss, lichen and leaf litter. Nearly translucent and averaging about half a millimetre in length, they are only just visible to the naked eye (being about the size of the full-stop at the end of this sentence). However, when viewed under a microscope the charismatic nature of these miniature action heroes becomes apparent.

Resembling tiny bears waddling slowly on eight stubby legs, tardigrades are unlikely to secure the heroic lead in any action blockbuster. However, they can survive things that are too unbelievable for even the most far-fetched of movie plots. Tardigrades are virtually indestructible. Scorching temperatures of 151°C, well in excess of the boiling point of water; or freezing to within one degree of absolute zero (‑273°C) are endured with no ill effects. They’ve also survived pressures six-times those found at the bottom of the Mariana Trench – the deepest point in the world’s oceans. Even exposure to the air-less vacuum of outer space, or being bombarded with bursts of X-rays and burning UV radiation, are all taken in their ambling, stubby, stride.

The tardigrades’ brute, dogged ability to survive such spectacularly extreme conditions is incredible. Even the persistent cockroach – which can remain alive for weeks following decapitation – cannot compete. The secret to the tadigrade’s extreme survival is their ability to enter a dehydrated, hibernation-like state, called cryptobiosis. Metabolic processes grind to a complete stop; the tardigrade loses 97% of its body moisture, and it shrivels to one-third its original size. There are no signs of life, and to all intents and purposes the tardigrade is dead. However, in a feat akin to Lazarus’s resurrection, this death-like state is completely reversible. In this desiccated form they can survive the extremely harsh conditions listed above; however, when rehydrated, they spring back into life. In a sense, they survive as a freeze-dried powder containing all the ingredients for life… just add water!

Tardigrade clambering over moss

Tardigrade clambering over moss by Frank Fox

So, why would these critters need to be so tough? Current thinking is that it is an adaptation to extreme changes in their environment. Not all species are so tough; and those that live in aquatic environments – where conditions are fairly constant – don’t exhibit these extreme survival skills. However, the tough land-living tardigrades are those that usually live in a thin film of water on the surface of some moss or lichen. This water can readily dry up. By entering this dormant state, these critters can survive the dry periods, and resume life as normal when things eventually get wetter again.

Understanding the finer details of the tardigrade’s extreme toughness, could help us to understand how other organisms can adapt to environmental stress. Also their ability to survive harmful doses of radiation suggests a very effective DNA repair system. Understanding this could have big implications for identifying better treatments for cancer. As such research into these little known, but remarkable animals could offer great returns – there’s much that nature’s tough guys can teach us!

References

Jönsson, K. Ingemar, and Roberto Bertolani. “Facts and fiction about long‐term survival in tardigrades.” Journal of Zoology 255.1 (2001): 121-123.

Persson, Dennis, et al. “Extreme stress tolerance in tardigrades: surviving space conditions in low earth orbit.” Journal of Zoological Systematics and Evolutionary Research 49.s1 (2011): 90-97.

Horikawa, Daiki D. “Survival of tardigrades in extreme environments: a model animal for astrobiology.” Anoxia. Springer Netherlands, 2012. 205-217.

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About StuartKing

Hi, I'm Stuart, an Assistant Features Editor at eLife and recent life sciences PhD graduate. I blog about evolution and its weird and wonderful creations.

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