We are bombarded every day with media – emails, Instagram, Facebook, WhatsApp, television and newsletters of all kinds. Those who want to attract our attention amid this cacophony of information have to use superlatives – extreme this, or extreme that – it appears that everything is now extreme.
But a genuinely extreme animal can be found all around us. It’s just that they are so small we don’t normally see them. I’m talking about tardigrades.
What are tardigrades?
Tardigrades (meaning ‘slow steppers’) are microscopic eight-legged animals that look a bit like miniature bears – hence the nickname ‘water bears’. There are around 1 300 species of tardigrades worldwide. They are considered aquatic because they require a thin layer of water around their bodies to prevent dehydration.
Tardigrades have been found in all kinds of environments, from deep-sea trenches to mountain tops. Freshwater mosses and lichens are their preferred terrestrial habitat, hence their other nickname, ‘moss piglet’.
Despite looking like inflatable toys, tardigrades are covered in a tough cuticle, similar to the exoskeletons of insects to which they are very distantly related. Like those insects, tardigrades have to shed their cuticles to grow. Interestingly, they hatch from the egg with the same number of body cells as the adult. So they grow, not by multiplying their cells, but by growing the size of each cell.
They have four to six claws on each foot, which helps them cling to plant matter, and specialised mouthparts, which allow them to suck nutrients from plants and micro-organisms.
Tardigrades have been on the planet for about 600 million years – around 400 million years before the dinosaurs.
Tardigrades’ best-known feature is their truly remarkable ability to survive extreme conditions. Forget about what you’ve seen on Survivor; tardigrades win hands down.
A few years ago, the Discovery network show Animal Planet aired a countdown story about the most rugged creatures on Earth. Tardigrades were crowned the ‘Most Extreme’ survivor, topping penguins in the Antarctic cold, camels in the dry oven of the desert, tubeworms in the abyss and even the legendarily persistent cockroach.
Tardigrades are, indeed, the most resilient animals known to science.
Tardigrades are found in saltwater, in freshwater and on land on every continent. It’s the ones that live on land that have to cope with the most extreme conditions. They need a film of water around them – which is why they like to hang out in moss or lichens, both of which act like sponges to hold water.
But sometimes even the best sponges are baked by the summer sun and dry out. Or they freeze in arctic temperatures. Yet the tardigrades live through it all.
No mammal could survive what a tardigrade can tolerate. Under stresses such as dehydration or extremes of temperature, they shrink into a ‘tun’ – a state in which their metabolism all but stops, like extreme hibernation. In this state they can survive without water for decades, tolerate high doses of gamma and X-ray radiation, and survive temperatures from -272°C to 150°C. They have also lived through 10 days in the vacuum and radiation encountered in space.
What are their survivor super-powers?
In most other organisms, the extreme radiation in space would destroy the DNA in their cells. But researchers have found that tardigrades have a damage-suppressor protein (Dsup) that somehow shields the DNA from being damaged.
They discovered that this damage-controlling protein is “intrinsically disordered” and highly flexible, and seems to be able to adjust its structure to precisely fit the shape of the cell’s DNA and to act as an electric shield against radiation. Exactly like “shields up” on the Starship Enterprise.
Tardigrades manage to survive years of complete dehydration. As mentioned before, they assume a shrivelled-up, dormant state called a ‘tun’ for as long as a decade, reviving within an hour when exposed to water.
To pull off this remarkable trick, the animals rely on proteins unique to them, called tardigrade-specific intrinsically disordered proteins (TDPs).
When there is water around, these anti-dehydration proteins are jelly-like and don’t form into well-defined three-dimensional structures like most known proteins do. But when the tardigrades start to dry out, these proteins turn into a kind of glassy ‘sanctuary’ that protects all dehydration-sensitive materials in the animal from harm.
“When the animal completely desiccates, the TDPs vitrify, turning the cytoplasmic fluid of cells into something like glass,” says Thomas Boothby of the University of North Carolina.
“We think this glassy mixture is trapping other biological molecules and locking them in place, physically preventing them from unfolding, breaking apart or aggregating together.”
Tree frogs can also survive dehydration. They produce a special sugar called ‘trehalose’ that works the same way – by taking on a glass-like state.
This is a fascinating example of convergent evolution, in which evolution comes up with a similar solution more than once. What a remarkable adaptation to turn into a stable glassy state when the body dries out!
Now, scientists have discovered yet another reason to be impressed with tardigrades; some of these creatures have a glowing ‘shield’ that protects them from ultraviolet radiation. According to a new study, some tardigrades fluoresce – an ability that protects them like a layer of sunscreen, transforming damaging UV rays into harmless blue light.
Bio-fluorescence differs from bioluminescence, which creates light through a chemical reaction between compounds in the animal’s body; think of the bioluminescent glimmer produced by fireflies, for example. Fluorescent animals have molecules inside their cells that absorb light particles, or photons, from invisible UV rays and emit lower-energy light in a longer wavelength that is visible to us. For example, some jellyfish glow with fluorescent light, as do scorpions.
UV resistance provides these tardigrades with an ability to thrive in environments with a high UV index, such as in deserts or the tropics.
Tardigrades have survived all five mass extinctions. So when Homo sapiens has self-destructed, and the earth becomes uninhabitable due to climate change, tardigrades will survive – and may live to inherit the earth.
Looking for tardigrades
Tardigrade hunt with Whale Coast Conservation and Hermanus Botanical Society
About the Author
Whale Coast Conservation passionately lives by its slogan “Caring for your environment”.
Its small staff and volunteers are dedicated to
- raising community and visitor awareness of the unique, biodiverse natural resources of the Cape Whale Coast region and
- to projects that convert awareness into practical actions that lead towards living sustainably.
WCC ensures expert representation in public participation processes that contribute to environmental and developmental policies and legislation. We monitor regional development; and ensure compliance with legislation and guidelines.
WCC increases general public awareness of sustainability through environmental education, citizen-science research projects, community projects and campaigns.
WCC communicates with its audience through exhibitions, signage, technology demonstrations, workshops, talks, film shows, newsletters and articles.
WCC places emphasis on educating future generations through its Youth Environment Programme (YEP). YEP is offered to 24 schools in its target area with a total of over 10,000 learners.
WCC facilitates schools’ participation in special events such as Earth Day, Walking for Water, Arbor Day and Coastal Clean-ups.
WCC facilitates educator development programmes to improve the capacity of educators to offer informed environmental content in their lessons across all learning streams.