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 What are tardigrades? |
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| Tardigrades are invertebrate animals (those without a backbone) that compose a taxonomic phylum Tardigrada. More than 1,000 species of tardigrades have been recorded so far. Their body length ranges from 0.1 to 1.0 millimeter. They are found all over the world and live in a variety of environments from the ocean depths to high mountains. Terrestrial tardigrades are usually found in mosses, lichens, or soils. All tardigrade species need water surrounding them to be active, even the terrestrial species. |
| photo by D.D. Horikawa and F. Yukuhiro |
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Cryptobiosis in tardigrades |
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| Tardigrades characteristically form an ametabolic state called gcryptobiosish when they encounter certain environmental stresses. Cryptobiosis in tardigrades are divided into four forms according to environmental stress types. For example, anhydrobiosis (induced by desiccation), cryobiosis (induced by freezing temperatures), osmobiosis (induced by high osmotic pressure) or anoxybiosis (induced by lack of oxygen). The animals resume their activity when favorable environments are return. |
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Anhydrobiosis in tardigrades |
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Among cryptobiosis in tardigrades, anhydrobiosis induced by desiccation have interested many biologists for hundreds of years. This is because anhydrobiotic tardigrades can survive almost complete dehydration indicating that even multicellular organisms have the potential to maintain their biological function under dry conditions.
Tardigrades turn into a contracted form called gtunh when they enter into anhyrobiosis. Their body water content is reduced from about 80% in the active state to 1-3% in the anhydrobiotic state. When tardigrades are in the active state through their whole life their longevity is generally about one month to one year. On the other hand, tardigrades in anhydrobiotic state are known to be able to survive for up to 9 years. Therefore, it is expected that the study of tardigrade anhydrobiosis will provide insight into dry preservation techniques concerning biological materials such as cells, foods, organs, or whole bodies. |
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Tolerance of tardigrades to extremes |
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Anhydrobiotic tardigrades can survive considerable environmental extreme conditions. So far, they has been shown to survive temperatures ranging from -273 to 151, vacuum at 5 x 10-5 Pa, high pressure at 6000 atm, chemicals such as alcohol, and one thousand times of dose of irradiation killing human. Furthermore, even non-anhydrobiotic active tardigrades show tolerance to some extreme environments such as extreme low temperature and irradiation. Extreme low temperature tolerance of active tardigrades is known as gcryobiosish as mentioned above.
On the basis of the tardigrade high tolerant capacities, some scientists consider that they may survive even in outer space. We may be able to estimate the possibilities that there exists extraterrestrial life by flyingtardigrades to outer space and evaluating whether they can
survive or not. |
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