Ecology and life history
Most tardigrades are phytophagous (plant eaters) or bacteriophagous (bacteria eaters), but Most tardigrades are phytophagous (plant eaters) or bacteriophagous (bacteria eaters), but some are predatory (e.g., Milnesium
some are predatory (e.g., Milnesium tardigradum).tardigradum).
Physiology
Physiology
Scientists have reported tardigrades in hot springs, on top of the Himalayas, under layers of Scientists have reported tardigrades in hot springs, on top of the Himalayas, under layers of solid ice and in ocean sediments. Many species can be found in a milder environment like solid ice and in ocean sediments. Many species can be found in a milder environment like lakes, ponds and meadows, while others can be found in stone walls and roofs. Tardigrades lakes, ponds and meadows, while others can be found in stone walls and roofs. Tardigrades are most common in moist environments, but can stay active wherever they can retain at are most common in moist environments, but can stay active wherever they can retain at least some moisture.
least some moisture.
Tardigrades are one of the few groups of species that are capable of reversibly suspending Tardigrades are one of the few groups of species that are capable of reversibly suspending their metabolism and going into a state of cryptobiosis. Several species regularly survive in a their metabolism and going into a state of cryptobiosis. Several species regularly survive in a dehydrated state for nearly ten years. Depending on the environment they may enter this dehydrated state for nearly ten years. Depending on the environment they may enter this state via anhydrobiosis, cryobiosis, osmobiosis or anoxybiosis. While in this state their state via anhydrobiosis, cryobiosis, osmobiosis or anoxybiosis. While in this state their metabolism lowers to less than 0.01% of normal and their water content can drop to 1% of metabolism lowers to less than 0.01% of normal and their water content can drop to 1% of normal. Their ability to remain desiccated for such a long period is largely dependent on the normal. Their ability to remain desiccated for such a long period is largely dependent on the high levels of the non-reducing sugar, trehalose, which protects their membranes. In this high levels of the non-reducing sugar, trehalose, which protects their membranes. In this cryptobiotic state the tardigrade is known as a tu
Tardigrades are able to survive in extreme environments that would kill almost any other Tardigrades are able to survive in extreme environments that would kill almost any other animal. The following are extremes states Tradigrades can survive:
animal. The following are extremes states Tradigrades can survive:
TemperatureTemperature –– Tardigrades can survive being heated for a few minutes to 151 °C Tardigrades can survive being heated for a few minutes to 151 °C
(424 K or 304 F), or being chilled for days at −200 °C (73 K or
(424 K or 304 F), or being chilled for days at −200 °C (73 K or -328 F), or some can-328 F), or some can survive temperatures for a few minutes at −273 °C (~1 degree above absolute zero/0 survive temperatures for a few minutes at −273 °C (~1 degree above absolute zero/0 Kelvin or -458 F).
Kelvin or -458 F).
PressurePressure –– they can withstand the they can withstand the extremely low pressure of a vacuum and also veryextremely low pressure of a vacuum and also very
high pressures, more than
high pressures, more than 1,200 times atmospheric pressure. Tardigrades can survive1,200 times atmospheric pressure. Tardigrades can survive the vacuum of open space and solar radiation combined for at least 10 days. Some the vacuum of open space and solar radiation combined for at least 10 days. Some species can also withstand pressure of 6,000 atmospheres, which is nearly six times species can also withstand pressure of 6,000 atmospheres, which is nearly six times the pressure of water in the
the pressure of water in the deepest ocean trench, the Mariana trench.deepest ocean trench, the Mariana trench.
DehydrationDehydration –– although there is one report of a leg movement in a 120-year-old although there is one report of a leg movement in a 120-year-old
specimen from dried moss, this is not generally considered "survival", and the longest specimen from dried moss, this is not generally considered "survival", and the longest tardigrades have been shown to survive in a dry state is nearly 10 years. When tardigrades have been shown to survive in a dry state is nearly 10 years. When exposed to extremely low temperatures, their
exposed to extremely low temperatures, their body composition goes from 85% waterbody composition goes from 85% water to only 3%. As water expands upon freezing, dehydration ensures the tardigrades do to only 3%. As water expands upon freezing, dehydration ensures the tardigrades do not get ripped apart by the freezing ice.
not get ripped apart by the freezing ice.
RadiationRadiation –– tardigrades can withstand 1,000 times more radiation than other tardigrades can withstand 1,000 times more radiation than other
animals, median lethal doses of 5,000 Gy (of gamma-rays) and 6,200 Gy (of heavy animals, median lethal doses of 5,000 Gy (of gamma-rays) and 6,200 Gy (of heavy ions) in hydrated animals (5 to 10 Gy could be
ions) in hydrated animals (5 to 10 Gy could be fatal to a human). The only explanationfatal to a human). The only explanation found in earlier experiments for this ability was that
found in earlier experiments for this ability was that their lowered water state providestheir lowered water state provides fewer reactants for the ionizing radiation. However, subsequent research found that fewer reactants for the ionizing radiation. However, subsequent research found that tardigrades, when hydrated, still remain highly resistant to shortwave UV radiation in tardigrades, when hydrated, still remain highly resistant to shortwave UV radiation in comparison to other animals, and that one factor for this is their ability to efficiently comparison to other animals, and that one factor for this is their ability to efficiently repair damage to their DNA resulting from that exposure.
repair damage to their DNA resulting from that exposure.
Environmental toxinsEnvironmental toxins –– tardigrades can undergo chemobiosis tardigrades can undergo chemobiosis——a cryptobiotica cryptobiotic
response to high levels of environmental toxins. However, these laboratory results response to high levels of environmental toxins. However, these laboratory results have yet to be verified.
have yet to be verified.
Outer spaceOuter space –– Tardigrades are the first known animal to survive in Space. Since Tardigrades are the first known animal to survive in Space. Since
September 2007, Tardigrades were taken into low Earth orbit on the FOTON-M3 September 2007, Tardigrades were taken into low Earth orbit on the FOTON-M3 mission and for 10 days were exposed to the vacuum of space from which they mission and for 10 days were exposed to the vacuum of space from which they returned alive. After being rehydrated back on Earth, over 68% of the subjects returned alive. After being rehydrated back on Earth, over 68% of the subjects protected from high-energy UV radiation survived and many of these produced viable protected from high-energy UV radiation survived and many of these produced viable embryos, and a handful had survived full exposure to solar radiation. In May 2011, embryos, and a handful had survived full exposure to solar radiation. In May 2011, Italian scientists sent tardigrades into space along with other extremophiles on STS- Italian scientists sent tardigrades into space along with other extremophiles on STS- 134, the final flight of Space Shuttle Endeavour. Their conclusion was that 134, the final flight of Space Shuttle Endeavour. Their conclusion was that microgravity and cosmic radiation "did not significantly affect survival of tardigrades in microgravity and cosmic radiation "did not significantly affect survival of tardigrades in flight, confirming that tardigrades represent a useful animal for space research." In flight, confirming that tardigrades represent a useful animal for space research." In November 2011, they were among the organisms to be sent by the US-based November 2011, they were among the organisms to be sent by the US-based Planetary Society on the Russian Fobos-Grunt mission's Living Interplanetary Flight Planetary Society on the Russian Fobos-Grunt mission's Living Interplanetary Flight Experiment to Phobos; however, the launch failed.