Tardigrades have been named the most resilient animal both
in and out of this world. You read
right, these creatures, also known as water bears, can happily survive in space
as well for a period of time. The only
way to see these tiny, water-dwelling creatures, is under a microscope. A scanning electron micrograph shows the
water bear up-close and personal, which in my opinion looks less like a bear
and more like a headless Heimlich, the caterpillar from A Bug’s Life.
These
invertebrates have four pairs of stumpy legs which allow them to move very
slowly. Water bears only reach half a
millimeter on average, yet research shows these creatures have anatomy and
physiology similar to larger animals. Its
tube-like digestive system begins with a pharynx which leads to an esophagus,
stomach, intestine and anus. Below is a
picture that shows more internal structures, indicating the water bear is much
more complex than what meets the eye.
Many
water bears have been found to live in areas with dense moss and ferns, where
they feed off of plant cells, algae, and other microscopic animals. Yet, because water bears are able to adapt
and survive almost any environment on earth, it shouldn’t come as a surprise
that these creatures have been discovered all over the world, from the arctic
poles to the equator, the deep ocean and the top of forest canopies.
These
extremophiles can also withstand a lack of oxygen, exposure to harmful
chemicals and pollution, temperature extremes, even in chilled liquid helium
that approaches absolute zero, high levels of radiation, and no food or water
for a decade. The unique characteristic
that contributes to the resiliency of the water bear is known as
cryptobiosis. This is considered to be a
state which shows no signs of life and limited or ceased metabolism, yet they
are not dead. This adaptation is
reversible and protects the water bear from extreme conditions. Anhydrobiosis is the best understood type of
cryptobiosis, and is triggered in an environment of extreme dryness. During this period, the water bear dehydrates
itself while synthesizing proteins and sugars that serve to protect its
cells. Once these preparations have been
implemented, the water bear stops metabolism and is practically
indestructible. When the time is right
and the water bear comes into contact with even a drop of water, they are able
to resume normal metabolism and mosey along on their stubby legs.
Current
research involves the water bear’s role in extraterrestrial exploration. Astrobiologists and molecular biologists are
particularly fascinated in discovering how their genetic information stays
intact even under harsh conditions, such as the high levels of radiation that
exist in space. Some scientists even
believe understanding the survival tactics of the water bear could be the key
to unlocking a way to protect humans from space as well.
References
Brennand, E.
(2011, May 17). Tardigrades: Water bears in space. BBC Nature. Retrieved from http://www.bbc.co.uk/nature/12855775
Clegg, J.S.
(2001, April). Cryptobosis: A peculiar state of biological organization. Comp Biochem Physiol B Biochem Mol Biol. 128(4):
613-624. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/11290443
Miller, W.R.
(2011, October). Tardigrades. American
Scientist. Retrieved from http://www.americanscientist.org/issues/pub/2011/5/tardigrades/1
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