What Makes Tardigrades Immortal?

This episode is brought to you by Skillshare. The first 1,000 people to sign up using the
link in the description will get their first 2 months free. Tardigrades are strange-looking, slow-moving
microscopic animals. They are semi translucent, segmented like
caterpillars, and have eight limbs with claws at the end of each one. They are also called “moss piglets” and
“water bears,” and they are found almost everywhere on the planet. Some of them live completely in water, while
others are terrestrial and exist in damp vegetation and soil. According to Live Science, they “suck the
juices from algae, lichens and moss,” and “some species are carnivores and even cannibals.” What makes them special is their unusual survival
skills, which we will discuss in this episode of The Infographics Show, “What Makes Tardigrades
Immortal.” Tardigrades are not immortal in the sense
that they live forever. However, they can endure extreme conditions
that would kill many other animals. One common problem terrestrial tardigrades
experience is dehydration. They need at minimum a thin film of water
to function, but the long-term absence of water is not necessarily a death sentence
for them the way it is for humans, whitetail deer, and many other animals. Tardigrades can be revived after years of
drought. Just add water and they are good to go! Tardigrades also don’t easily freeze to
death even in subzero temperatures. According to an American Scientist article,
they have survived short-term freezing for 20 hours at functional absolute zero or -459.3
°F (-272.95 °C) and long-term storage for 20 months at -328°F (-200°C ). It can tolerate
temperatures that are even cooler than the red flat bark beetle of Alaska, which has
survived temperatures as low as -238°F (-150°C) according to a Business Insider article. Tardigrades can be thawed and revived in a
short period of time. In addition, tardigrades can withstand high
temperatures. The American Scientist reports that they have
lived after being “exposed to 150 Celsius (302°F), far above the boiling point of water.” To give you an idea of just how hot this is,
Guinness World Records states that the highest recorded temperature on Earth was 56.7 °C
(134.1 °F), which occurred at California’s Death Valley in 1913. This record temperature is less than half
of the scorching temperature the tardigrades were exposed to! If freezing and boiling them weren’t enough,
scientists tested the toughness of the tardigrades in other extreme ways. They tried to crush them with high pressure. A Live Science article reports that “tardigrades
can withstand pressures of up to 87,000 pounds per square inch (600 megapascals) – six
times what you’d experience at the bottom of the sea.” It also noted that “just half this pressure
would kill most other organisms on Earth.” One of those organisms would be humans. We can withstand only about one atmosphere
of pressure according to the American Museum of Natural History. This is a measly pressure of 14.2 pounds per
square inch. And then the scientists hit them with high
levels of X-rays, gamma rays, and other types of radiation. The Mother Nature Network reports that “researchers
found some water bears can survive radiation doses of 5,000 to 6,000 grays.” Once again, tardigrades prevail where humans
easily fail. We sicken and die after exposure to significantly
lower levels of radiation. According to the CDC, it takes only about
0.7 grays of radiation for a human to develop radiation sickness under certain conditions,
and 10 grays is the LD 100 dose that is “necessary to kill 100% of the exposed population.” These tough tiny animals have also faced the
final frontier – outer space. “Tardigrades in space” may sound like
the title of a science fiction B-movie, but it actually happened in 2007. Popular Mechanics briefly described the tardigrades’
off-planet experience: “A European team of researchers sent a group of living tardigrades
to orbit the earth on the outside of a FOTON-M3 rocket for ten days. When the water bears returned to Earth, the
scientists discovered that 68 percent lived through the ordeal.” Up to that point, no known animal on Earth
had accomplished such a feat, and there are good reasons why. One source describes outer space as “the
closest physical approximation of a perfect vacuum.” The very low pressure of outer space would
suck out the air of animals with lungs. There are also the dangers of ionizing radiation. Among the open space conditions described
in a Space.com article are “deadly levels of solar UV radiation, which are more than
1,000 times higher than on the surface of the Earth.” And then there is the extreme cold. The temperature in outer space is -454 °F
(-270°C). How are tardigrades able to survive in conditions
that are inhospitable to most life on Earth? If necessary to save their lives, tardigrades
enter a state that ironically mimics death called cryptobiosis. A Live Science article reports that in this
reversible near-death condition, the “tardigrades’ metabolic activity gets as low as 0.01 percent
of normal levels.” What happens to them next depends on what
extreme conditions they are subjected to. If the problem they face is the absence of
water, tardigrades can undergo a form of cryptobiosis called anhydrobiosis, which the American Scientist
defines as the “metabolic suspension brought on by nearly complete desiccation.” The tardigrades curl up, dry out, and shrivel
into smaller structures called tuns. They enter a “dry state of suspended animation”
called anabiosis, and they are essentially reduced to a “powder comprised of the ingredients
of life.” Popular Mechanics notes that this desiccated
state also allows them to endure “utter vacuum and intense pressures.” They can be rehydrated back to life in a short
period of time with some form of moisture such as rain or dew. If they are submerged in water with dangerous
levels of salinity, tardigrades can undergo a form of cryptobiosis called osmobiosis. They can contract into a tun in this situation
as well to avoid what the American Scientist calls “destructive osmotic swelling,”
but it may not be necessary “since active animals can survive high salinity” according
to one source. When faced with extreme freezing conditions,
tardigrades can undergo a form of cryptobiosis called cryobiosis. This state also involves a dramatic slowdown
in metabolism and the formation of tuns. According to the American Scientist, some
researchers believe that tardigrades also produce “cryoprotectants” that slow down
the tissue freezing process to the point where the most damaging ice crystallization is prevented
and revival from thawing is possible. However, researchers still struggle to understand
how tardigrades protect themselves from cell death caused by the expansion of water at
extreme temperatures. Some of them think this protection comes from
a sugar called trehalose. A Popular Mechanics article notes that trehalose
“replaces water” and prevents “remaining water molecules . . . from rapidly expanding
when faced with hot and cold temperatures.” According to a Wired article, others became
skeptical that trehalose is an extreme temperature protectant after the discovery that “not
all water bear species produce the sugar under stress” and the ones that did produced only
a small amount of it – about 2 percent of their body weight. A new theory is that tardigrades produce special
proteins to protect themselves from the ravages of extreme temperatures. The same Wired article reports these proteins
are made exclusively by tardigrades and are called “intrinsically disordered proteins.” These proteins bring on vitrification, a process
that turns the tardigrade into a “frozen glass figurine.” Vitrification is a way for the tardigrades
to bypass the most damaging effects of desiccation, which normally “crystallizes living cells,
shredding up proteins and DNA in the process.” Tardigrades may not live forever, but an amazing
by-product of cryptobiosis is that it extends their lives way beyond their normally short
lifespans, which range between 3 months and about 2 years depending on the species. Tardigrades don’t age while they are in
cryptobiosis. They can live in a state of suspended animation
for years or even decades until they are revived. A Live Science article reports that scientists
were able to bring back to life “two tuns and an egg that had been in cryptobiosis for
more than 30 years” in a 2016 experiment. There are also stories about a tun that was
over 120 years old being revived in a 1948 experiment, but “this research has never
been duplicated, according to the BBC.” However, tardigrades don’t always need to
undergo cryptobiosis and form tuns to endure extreme conditions. In a BBC article, researcher Thomas C. Boothby
says that “’Tardigrades can survive freezing, radiation, and low-oxygen conditions without
forming a tun.” Experiments have also revealed that tardigrades
can “cope with excessive amounts of alpha, gamma and ultraviolet radiation – even if
they’re not in the tun state.” Tardigrades have other tricks they can turn
to in order to survive. For instance, they produce high levels of
antioxidants to reduce “harmful chemicals” created by desiccation and high radiation. They also produce another special protein
that counteracts DNA damage. The science journal Nature reported the recent
discovery of “a protein known as Dsup” that “prevented the animal’s DNA from
breaking under the stress of radiation and desiccation.” It is important to keep in mind that there
are some limitations to the tardigrades’ impressive resiliency. First, not all tardigrades are extreme survivors. American Scientist reports that “marine
and aquatic tardigrades did not evolve these characteristics because their environments
are stable.” The tardigrades that live in hot springs,
Antarctica, and other places with highly variable and harsh environmental conditions are the
ones that possess the extreme survival abilities. Second, tardigrades can’t handle oxygen
deprivation as well as they can handle other extreme conditions. One source states that a lack of oxygen can
trigger a cryptobiotic state called anoxybiosis. During anoxybiosis, the tardigrades become
“immobile, transparent, rigid, and very extended due to water absorption resulting
from loss of osmotic control,” and they can’t live very long in this condition. Depending on the species, they can survive
a few hours to up to 5 days in anoxybiosis. They will die if oxygen is not restored within
that time frame. Third, the tardigrades’ ability to undergo
cryptobiosis does not mean that they can come back from the dead. Tardigrades are still alive even though they
may seem dead in cryptobiosis. There is still some metabolic activity going
on during cryptobiosis even though it is very low. One source notes that death differs from cryptobiosis
because it involves the “cessation of metabolic activity.” Unlike cryptobiosis, death is also “considered
an irreversible state.” Tardigrades may not be immortal as individual
organisms, but they have a kind of immortality as a group. According to Live Science, they “have survived
five mass extinctions over the course of around a half a billion years.” Volcanic eruptions, sudden climate change,
and possibly even a comet or an asteroid impact may have wiped out ancient life forms like
trilobites and dinosaurs, but tardigrades lived on. Given the tardigrades’ great track record
of survival, scientists are optimistic that these cute but hardy creatures will continue
to exist after the next mass extinction event. A 2017 study cited in a Telegraph article
predicts that the “astonishing abilities” of the tardigrade will make it “the only
creature that will survive until the Sun dies.” If you want to be immortal like the tardigrade,
why not learn how to write, produce, and animate your own online videos like us here at The
Infographics Show? After all, they say the internet is forever-
so check out Skillshare for the skills you need to make high quality content. With classes like Creative Personal Writing:
Write the Real You and The Beginner’s Guide to Animating Custom GIFs, you can be on your
way to online immortality today! You can learn about these and many other topics
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months of skillshare absolutely free. Join skillshare and start learning today! Do you know of any other animals with amazing
survival skills like those of the tardigrades? Do you think humans can ever become immortal? Let us know in the comments! Also, be sure to check out our other video
called Why Would a Scientist Inject Himself with 3.5 Million Year Old Bacteria?! Thanks for watching, and, as always, don’t
forget to like, share, and subscribe. See you next time!

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