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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.”
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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!