Tardigrades : evolutionary explorers in extreme environments

• Tardigrades have long been recognized for their ability to survive the most extreme environmental conditions. In particular, the widespread ability of tardigrades to dehydrate and enter a state ofarrested metabolism (cryptobiosis) has allowed these aquatic animals to persist in habitats regularly deprived of water. The evolutionary strategy to allow metabolic arrest during periods of hostile conditionshas several advantages, including arrest of the biological clock and energy consumption, but since all cryptobiotic animal taxa have very small body size there must be physical or physiological constraints preventing this strategy to evolve in larger animals. Our understanding of the molecular mechanisms of cryptobiotic tardigrades has improved considerably over the last decade, much due to the genome and transcriptome sequencing of some species. Although we are still far from a comprehensive understanding of how tardigrades maintain cellular structure under complete dehydration, it is clear that multiple molecular mechanisms with carbohydrates and proteins are involved, and that different adaptive mechanisms have evolved within tardigrades. Based on their documented tolerances, tardigrades made their entrance into astrobiology with the FOTON-M3 mission in 2007, and were the first animals to survive a combined exposure to space vacuum, cosmic radiation and UV radiation. With their ancient adaptations for coping with environmental extremes, tardigrades are excellent animals for studies of how early metazoan life evolved, and for understanding the constraints of cryptobiotic adaptations. Most tardigrades do not fit within the traditional definition of extremophiles, but rather belong to the category of extremotolerant organisms, surviving extreme conditions but with optimal performance under more normal environmental conditions. However, tardigrades have been reported from some permanently extreme environments, such as deep sea and hot and radioactive springs, and more studies of these populations would be of great interest.

Ämnesord

NATURAL SCIENCES  -- Biological Sciences -- Zoology (hsv//eng)

NATURVETENSKAP  -- Biologiska vetenskaper -- Zoologi (hsv//swe)

NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

Nyckelord

Tardigrada

cryptobiosis

anhydrobiosis

extremotolerants

extremophiles

evolutionary adaptations

desiccation tolerance

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