The tardigrade can withstand being plonked in boiling hot springs or being buried under layers of ice.
The tardigrade can withstand being plonked in boiling hot springs or being buried under layers of ice.
They're little battlers, the greatest survivors on the planet and you may have them in your garden, writes Lana Hart.
They've been boiled, frozen, put in vacuums, starved, and exposed to unbearable pressures and radiation - but scientists can't kill this creature.
They are the only animal to have survived all five of earth's mass extinctions. This incredible feat is due to their development of unique survival mechanisms not seen in other parts of the animal kingdom.
Extraordinary as they are, they are ubiquitous, found around the world almost everywhere that there is water: in mosses, carparks, sewers, glaciers, sand, the deepest parts of the oceans - from Antarctica to the Arctic Circle and on the highest mountains on Earth.
Scientists have found them in boiling hot springs and buried under layers of ice in the Himalayan mountains, withstanding temperatures ranging from –200C to 150C.
The mighty tardigrade; nearly microscopic with an average length of half a millimetre, it is headless, has eight legs, bulky segments, and a mouth tube that telescopes outward revealing sharp teeth. It looks like a fat caterpillar.
Outside of the world of zoology, not much is known about it.
Tardigrade literally means "slow walker" due to its side-to-side lumber, but it is also known as the "water bear" or "moss piglet", giving us some idea of what early scientists thought the creature looked like. Discovered in 1773 by the German zoologist Johann August Ephraim Goeze, there are now over 1000 different species of identified tardigrades, with varying features that have adapted over time to the wildly diverse environments that they live in.
As extremophiles, tardigrades can thrive in conditions that are detrimental to most life forms.
A tardigrade character features on the TV series Star Trek: Discovery. Pictured with Michael Burnham (actress Sonequa Martin-Green)
In 2007, a group of scientists led by Sweden's Kristianstad University exposed tardigrades to the vacuum and solar radiation of outer space. Some of the specimens survived and some even went on to produce viable offspring. The researchers concluded "only lichens and bacteria have been reported to survive the combined exposure to space vacuum and solar/galactic cosmic radiation… Our results, therefore, represent the first record of an animal surviving simultaneous exposure to space vacuum and solar/galactic radiation".
Another group of scientists, from the Universities of Oxford and Harvard, considered in 2017 how three different astrophysical events – supernovae, gamma-ray bursts, and large asteroid impacts – might bring about global extinction via the boiling of the Earth's oceans. Organisms "such as tardigrades would be the only kind of life that could survive long-term in such conditions". Thanks to the tardigrade, they concluded "complete global sterilisation (is) an unlikely event".
How do they do it? What makes these creatures nearly indestructible and more tolerant of harsh environments than any other known animal on earth?
In two words: dehydration, sugar.
Tardigrades have the ability to change themselves into a lifeless cyst, called a tun, if life gets too tough. The process is called anhydrobiosis and enables tardigrades to live for long periods in a sort of deep hibernation without being harmed by most environmental dangers.
By alternating through active and anhydrobiotic stages, some tardigrades can survive more than 100 years. One specimen was found in dried moss that was 120 years old. Once it had been soaked in water, the tardigrade sprang back to life.
During anhydrobiotic or dried-out periods, not much is known about what actually happens to the tardigrade. Scientists agree that metabolism slows to slightly above zero or can sometimes cease altogether. Some tuns survive longer without oxygen, suggesting that oxygen could be harmful to some species. But tardigradologists admit that the biochemistry and the molecular pathways of these animals is largely unknown.
Although nature has not reserved anhydrobiosis solely for tardigrades – some parasitic nematodes and microscopic marine animals also claim this survival trick – it is the chemical way tardigrades protect themselves from damage that gets microbiologists excited.
Dr Siouxsie Wiles, Associate Professor of Microbiology at the University of Auckland, explains that a sugar called Trehalose is found in many invertebrate animals. It is used as a blood sugar, or source of energy, by many insects for flight, for example.
"What is unusual for the tardigrades is how they use Trehalose. When they dry out, Trehalose helps convert their bodies into a glass-like substance, keeping their organs and membranes in place. With this hardening, the tun is less likely to get damaged and allows them to survive for a long time. Tardigrades are the only animals that we know of to use Trehalose in this way."
Dr Siouxsie Wiles, Associate Professor of Microbiology at the University of Auckland. Photo / Sarah Ivey
The animals are capable of different types of transformations that allow them to survive in all sorts of extreme conditions. For instance, if the oxygen content of the water around them becomes too low, they stretch out into a long, relaxed shape, reducing their metabolic rate, and allowing as much water and oxygen to enter their cells as possible.
If the temperature falls below freezing, the tardigrade forms a cold-resistant tun using molecules that prevent the formation of ice crystals that could damage cell membranes.
With all these special stunts to respond to their environments, it is no wonder that scientists are looking for ways to utilise tardigrade's features to improve the lives of humans.
Wiles explains: "Tardigrades are able to protect their bodies from all sorts of potential damage. If we can better understand how they do this, we could be able to stop damage to other things that we want to preserve. Vaccines, for example, can be sensitive to changes in temperatures and yet need to be transported across many different temperatures. It would be really useful if we could learn to make proteins stable in different conditions.
"Considering how hearty tardigrades are, understanding this could also be used to make crops more tolerant to temperature. This could involve modifying genes in the plant so that we can grow them in more extreme weather conditions resulting from climate change."
She also notes that with tardigrades' experience of space travel in some experiments, we know that they can survive against space's damaging rays and vacuums. This knowledge could help us understand what life forms we might be looking for in space. For example, in our exploration of Mars.
But in order to learn from the evolutionary brilliance of tardigrades in these ways, she says, we need to know more about this little creature. "We still don't know where tardigrades fit in the tree of life. Their genome has not been sequenced and until this happens, we can't fully understand this animal."
There are many gaps in scientific knowledge about the tardigrade, especially in New Zealand. The NZ Inventory of Biodiversity explains why it is difficult to discuss the distribution of the hundreds of tardigrade species across the planet, reporting there is a "paucity of collecting in many areas of the world, especially in the Southern Hemisphere. Distributions are really a reflection of where tardigradologists have collected."
In 1978, microbiologists reported 58 different species or tardigrades from areas including the Three Kings Islands. Photo / Northern Advocate
Dr Donald Horning was one of the few scientists in New Zealand to have studied tardigrades closely. In 1978, he and other microbiologists conducted a comprehensive survey of tardigrades in New Zealand, reporting 58 different species from areas including the Three Kings Islands near Cape Reinga, Kaikoura, and D'Urville Island in the Marlborough Sounds. Much taxonomic work was done in the years following: grouping individual specimens into species, arranging and naming species into larger groups, and considering how different biological characteristics related to known tardigrade species from other continents.
Despite the highly-detailed work, New Zealand tardigrade specimens were not always indisputably categorised, with some species becoming the focus of controversies and misunderstandings amongst international tardigradologists. One species, for example, "was based on a general and potentially inadequate definition of the taxon (organism class)", according to the NZ Inventory of Biodiversity.
By 2010, tardigrade classifications were being agreed upon as more species were discovered, but most of this work was done overseas. There are currently no resident New Zealanders who work specifically on the tardigrade; experts on the NZ tardigrade hail from Europe, the UK, and North and South America.
The tardigrade "hotspot" of New Zealand is Arthur's Pass National Park. Two creeks in the Park, Halpins and Kellys, have yielded more species of tardigrades than any other place in New Zealand. But these are just the areas that scientists have so far discovered – there could be many other tardigrade-rich locations.
The tardigrade "hotspot" of New Zealand is Arthur's Pass National Park. Photo / NZPA
And you don't have to get on your hiking boots to find tardigrades. They're probably hanging out in your garden right now. Lichens and moss are the most common habitats for the NZ tardigrade, and they also reside in soil, sediment and leaf litter.
With all the extraordinary characteristics of the commonly-found tardigrade, you'd think that more people knew about this little critter. Why hasn't the tardigrade been anthropomorphised in modern culture like ants, spiders and butterflies? Why don't we teach kids about tardigrades in science class? Where are the songs and pictures about the only animal on Earth that has survived since the dawn on life on our planet?
Modern culture could be just starting to catch on. The American adult animated sitcom South Park began featuring a "Moss Piglet" in 2017 and a subsequent episode concerned "Water Bears". The TV series Star Trek: Discovery has an oversized tardigrade with thick, rounded body armour called Ripper, inflated to a massive size due to a science experiment gone wrong.
But it will take more than a bit of animation and sci-fi to escalate the terrific tardigrade to its rightful position in our understanding of the biological world we live in. Wiles believes that first, "we need to get teachers interested in them. Once they start teaching kids about the tardigrade, they'll be much more interest."
One of the problems is of course their size. Microscopic that they are, you wouldn't exactly spot one on the bonnet of your car. But Wiles assures us that backyard scientists are become more common as scientific technology becomes more available to everyone.
"There are now microscopes that you can attach onto your smartphone. They are low cost and anybody can do this. You only need a little moss or water, it could take a bit of searching, but the tardigrade is almost everywhere and is very distinctive under a microscope.
"Go find a tardigrade and see what they look like. Do they really move like that? Yes, they do."
This kind of enthusiasm for the world's most indestructible animal will start to shine a light on the amazing, albeit tiny, world of the tardigrade, inspiring more students of science – and their teachers - to take an interest in NZ's own species. This will bring about more research, more scientists specialising in NZ tardigradology, more fascinating facts, and more opportunities to learn what tardigrades have to offer us.
If you don't have your smartphone microscope and a bit of moss already, it's time you got them.
How to Find Tardigrades
1. Collect a clump of moss or lichen (dry or wet) and place in a shallow dish, such as a Petri dish.
2. Soak in water (preferably rainwater or distilled water) for 3-24 hours.
