Tardigrades
Boil them, deep-freeze them, crush them, dry them out or blast them into space: tardigrades will survive it all and come back for more
13 March 2015
If you go into outer space without protection, you'll die.The lack of pressure would force the air in your lungs to rush out. Gases dissolved in your body fluids would expand, pushing the skin apart and forcing it to inflate like a balloon. Your eardrums and capillaries would rupture, and your blood would start to bubble and boil. Even if you survived all that, ionising radiation would rip apart the DNA in your cells. Mercifully, you would be unconscious in 15 seconds.
How do these seemingly insignificant creatures survive in such extreme conditions?
But*one group of animals can survive this: tiny creatures called tardigrades about 1mm long. In 2007, thousands of tardigrades were attached to a satellite and blasted into space. After the satellite had*returned to Earth, scientists*examined them*and found that*many of them had survived. Some of the females had even laid eggs in space, and*the newly-hatched young were healthy.
It's not just the harsh environs of outer space that tardigrades can survive in. The little critters seem adept at living in some of the harshest regions of Earth. They have been discovered*5546m (18,196ft) up a mountain in the Himalayas,*in Japanese hot springs,*at the bottom of the ocean*and*in Antarctica. They can withstand huge amounts of radiation, being heated to 150 °C, and being frozen almost to absolute zero.
How do these seemingly insignificant creatures survive in such extreme conditions, and why have they evolved these superpowers? It turns out that tardigrades have a host of tricks up their sleeves, which would put most organisms to shame
View image of Tardigrades are tiny animals (Credit: Science Photo Library/Alamy)
Tardigrades, at first glance, are intimidating. They have podgy faces with folds of flesh, a bit like a*Doctor Who*monster. They have eight legs, with ferocious claws resembling those of great bears. Their mouth is also a serious weapon, with dagger-like teeth that can spear prey.
Fossils of tardigrades have been dated to the Cambrian period over 500 million years ago
But there's no need to worry. Tardigrades are one of nature's smallest animals. They are never more than 1.5 mm long, and can only be seen with a microscope. They are commonly known as "water bears".
There are 900 known species. Most feed by sucking the juices from moss, lichens and algae. Others are carnivores, and can even prey on other tardigrades.
They are truly ancient. Fossils of tardigrades have been*dated to the Cambrian period over 500 million years ago, when the first complex animals were evolving. And ever since they were discovered, it has been clear that they are special.
View image of Tardigrada macrobiotus (Credit: Kim Taylor/NPL)
Tardigrades were discovered in 1773 by a German pastor named Johann August Ephraim Goeze. Three years later, the Italian clergyman and scientist Lazzaro Spallanzani discovered that they had superpowers.
Spallanzani added water to sediment from a rain gutter, and looked under a microscope. He found hundreds of little bear-shaped creatures swimming around. In his book "Opuscoli di Fisica Animale, e Vegetabile", he named them "il Tardigrado", meaning "slow-stepper", because they moved so slowly.
In 1995, dried tardigrades were brought back to life after 8 years
In truth, this wasn't a first. Back in 1702, the Dutch scientist Anton van Leeuwenhoek sent a letter to the Royal Society in London, entitled "On certain animalcules found in the sediment in gutters on the roofs of houses". He took dry, apparently lifeless dust from a gutter and added water. Using a microscope of his own devising, Leeuwenhoek found that within an hour many small "animalcules" became active, and began swimming and crawling around.
These animals were*rotifers, tiny aquatic creatures that look like they have wheels on their heads. They could seemingly survive months without water.
However, tardigrades may be able to survive without it for decades. In 1948, the Italian zoologist Tina Franceschi claimed that tardigrades found in dried moss from museum samples over 120 years old could be reanimated. After rehydrating a tardigrade, she observed one of its front legs moving.
This finding has never been replicated. But it does not seem impossible. In 1995,*dried tardigrades were brought back to life after 8 years.
View image of The tardigrade Hypsibius dujardini (Credit: blickwinkel/Alamy)
For most animals, life without water is completely impossible.
"When a typical cell dries out its membranes rupture and leak, and its proteins unfold and aggregate together, making them useless," says extremophile researcher*Thomas Boothby* of the University of North Carolina in Chapel Hill. "DNA will also start to fragment the longer it is dry."
The tardigrade curls up into a dry husk
Somehow tardigrades avoid all this. "Since water bears can survive drying, they must have tricks for preventing or fixing the damage that cells like ours would die from," says Boothby
How do they do it? One of the key discoveries came in 1922, courtesy of a German scientist named H. Baumann. He found that when a tardigrade dries out it retracts its head and its eight legs. It then enters a deep state of suspended animation that closely resembles death.Shedding almost all the water in its body, the tardigrade curls up into a dry husk. Baumann called this a "Tönnchenform", but it is now commonly known as a "tun".*Its metabolism slows to 0.01% of the normal rate. It can stay in this state for decades, only reanimating when it comes into contact with water.
View image of Paramacrobiotus richtersi in its tun state (Credit: Eye of Science/SPL)********
Besides tardigrades, some nematode worms, yeast and bacteria can also survive desiccation. They do this by making a lot of a particular sugar called trehalose. This sugar forms a glass-like state inside their cells that stabilises key components, such as proteins and membranes, which would otherwise be destroyed.
Tardigrades might have unique tricks for surviving desiccation.
Trehalose can also wrap itself around any remaining water molecules, stopping them from rapidly expanding if the temperature rises. Rapidly expanding water molecules are dangerous because they can rupture cells, which can be fatal.
You might expect that tardigrades would use this trick to survive drying, but according to Boothby, only some species seem to make trehalose. "Some species do not appear to contain trehalose, or make it at such low levels that the sugar is undetectable," he says.
"This suggests that tardigrades might have unique tricks for surviving desiccation," says Boothby. "We know that, as they start to dry out, tardigrades make protectants that allow them to survive becoming completely dry. But what exactly these protectants are is still a mystery."
Full article here:
http://www.bbc.com/earth/story/20150...imals-on-earth
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