the tardigrade

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The tardigrade, champion of survival!

The tardigrade is a small animal ubiquitously not exceeding 2 mm, which is a branch alone as its classification poses problems for biologists, it is now close to the phylum arthropods. We now know several species.

It is a freshwater species whose various studies have shown amazing results that allow us to grant it to date the hotly contested title superchampion Animal resistance.

Indeed, in very adverse conditions, it is able to empty its water, mummify in some way, and passing cryptobiosis. In a state of almost absolute anhydrobiose, suspended almost entirely metabolism to the point that the most powerful tools we have now, can not detect any traces.

The tardigrade in cryptobiosis takes a form very compact keg (almost opaque microscopic) which allows it to reduce surface evaporation and thus limit water losses which could be fatal to the organelles very sensitive to desiccation. The animal then produces a sugar which takes place in the water body which can limit the alteration of the membrane sufficiently for it to be repaired during rehydration. This phenomenon also exists in a toad and a squirrel snow, which produce a kind of glycerol and water which replaces them playing the role of antifreeze. It is known that it is the ice crystals that form during freezing which damage cell membranes, condemning the cell.

The compound which takes place water does not form crystals and allows the cell to survive freezing Only rotifers, nematodes (which encyst), some insects and crustaceans are able to Like tardigrade to enter cryptobiosis. The tardigrade can maintain this quiescent for centuries or millennia, before the conditions again become favorable and he miraculously recovers life.

Exceptional "survival" capabilities

tardigrade of specimens were discovered in an ice cap whose age was estimated at over 2000 years and came back to life.This form of resistance not only to suspend the course of time but also to survive the attacks of the extreme temperatures and many chemicals.

It can indeed withstand enormous thermal amplitudes, exhibitions -272,9 20 ° C for hours, or in the liquefied air -190 ° C for 25 months or otherwise at temperatures over 150 ° c they survive without problems in a vacuum, or, conversely, to a hydrostatic pressure megapascals 600 or 6 times the pressure at the bottom of the ocean -10 000 6000 meters deep or times atmospheric pressure, while normally from 30 megapascals is a pressure to 3000 m depth or 300 times atmospheric pressure, the cell membranes, proteins and DNA irreversible damage.

They also are resistant to extremely hard radiation (ultraviolet, ....) But also the bombing as well as X-rays of toxic chemicals and poisons that would inevitably most body size. Moreover, in this area the tardigrade is far from having revealed all its secrets.
As we have seen, the tardigrade is over-equipped to withstand any animal, it is even overadapted.

Some animals are known to live in extreme environments, such as riftias or thermophilic bacteria, for example, living in close vicinity of hydrothermal vents, under temperatures and enormous pressure.
ice towards meanwhile, can withstand extreme cold and very low oxygen portion. These animals are able to adapt to these extreme environments by a very long and very sensitive evolutionary process. This adaptation is so fine and so developed, that organizations that benefits are very sensitive to even small changes in their environment. They are usually very effectively adapted to the conditions of their environment but not all the conditions to the opposite extreme.

The cold, the heat, the lack or absence of o2, the presence of co2, lack of water, nutrients, toxic substances, all these unfavorable conditions for life have lead to organizations managed to adapt specifically to them. However the specific adaptation, though necessarily very efficient and well developed, can allow the organizations that are developed to withstand different conditions of life from those of their respective biotope, by virtue of their specific adaptation. It joined the Darwinian concept that the more developed ecological niches and are best suited are also the most fragile. The specific adaptation is subject to compromise eternal life, in a way that is effective and another is very limited for the same reasons. The compromise appears to be a great dogma of life that makes each benefit granted is associated with a disadvantage.

The tardigrade meanwhile seems to escape these inevitable compromises. The extreme conditions that we have mentioned above seem very unfavorable to life, but none seems incompatible with the survival of tardigrade.

A more philosophical approach

The tardigrade is able to withstand the conditions that we do not even meet on earth, where they finally seem lenient to scale from those found elsewhere in the universe. Nature never doing anything to chance, then we can ask what is it to be so strong, as on earth is truly amentities. How natural selection has it you could be on the characteristics of tardigrade to allow him to retain the attributes that could not be tested?

Natural selection by its selective action tends to keep all the variations that appear useful to the animal, but for its action to be effective, must still that these variations can be tested by the conditions of an environment and they have any advantage. The tardigrade is resistant to conditions that we can not meet on earth, so either natural selection, made her keep these extreme characteristics without actually able to select, assuming that over-adaptation can not be unfavorable to 'animal. Either natural selection does retain some of its characteristics which are essential, and these super-resistances have been preserved by chance.
One can also think that the tardigrade would undergoes natural selection other than on earth where extreme conditions it is resistant meet.
This reality has prompted some biologists to advance the hypothesis that the origin of the tardigrade could be external to the globe.

The hypothesis of extraterrestrial origin of tardigrade. Anyway, whatever its origin, the tardigrade still remains a gifted animal adaptation, an exceptional organization that still has many secrets to reveal to us and which we do not have at present that very little information in comparison to the interest it can generate in the scientific community. This alone shows the infinite power of nature to design extraordinary beings ingenuity, diversity and adaptability to any conditions that the laws of physics and chemistry were imposed in the universe.

Learn more about the Tardigrade
What is cryptobiosis?


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