Amazing World

Tardigrades: Nature’s survivors

If you thought the cockroach was the Earth’s hardiest creature, think again! There is an animal even tougher, far smaller and, if you believe it’s possible, even stranger looking: the tardigrade, am eight-legged micro-animal most commonly found in watery environments – however, beyond that, they show up just about everywhere!

Better known as “moss piglets” and “water bears”, tardigrades are minute but near-indestructible creatures; measuring in at only 0.05 – 1.2mm, these tiny animals can survive almost anything, including being boiled, frozen, crushed, dried out and even exposed to the vacuum of space! In fact, fossils of these stubborn tardigrades have been found from over 500 million years ago, suggesting that the species has survived through the planet’s exposure to five mass extinctions.

Of course, surviving for half a billion years does not mean that tardigrades have never changed or developed. There are currently 1,018 individual species of tardigrade, each with slightly different approaches to feeding and reproduction. That said, these amazing critters have a list of incredible features in common.

Tardigrades were first discovered in 1773 by German zoologist and pastor Johann August Ephraim Goeze. They acquired their name Tardigrada (“slow stepper”) three years later, from Italian biologist Lazzaro Spallanzani. The ‘water bear’s’ mouth can telescope outward to reveal sharp teeth that are used to grab onto food. As water dwellers, tardigrades obviously swim, preferring to live in sediment at the bottom of lakes, on moist pieces of moss or in other wet environments.

However, these little commandoes can survive anywhere. Sightings of tardigrades have been reported in hot springs, on top of the Himalayas, deep below the sea, and even in the polar regions. In fact, tardigrades have been found to survive extreme cold as low as –272.8 C (-459 F) and extreme heat as high as 148 C (300 F). This isn’t all: they can also survive, extreme desiccation – drying out. Despite living in and consuming liquids (tardigrades suck juice from algae, lichens and moss, although some also prey on other tardigrades), ‘water bears’ are able to survive far dryer conditions than most creatures. After all, a large percentage of all living things is made of water! Despite this, drying to a near-dead state doesn’t stop a tardigrade – instead, they go into a ‘tun’ state, dropping their metabolic rate down to as low as 0.01% of its usual levels.

Surviving this state is made possible by anti-dehydration proteins that are exclusively unique to the tardigrade, found in no other creature. Scientists have dubbed these proteins Tardigrade-Specific Intrinsically Disordered Proteins (TDPs). When water is present, the proteins exist in a jelly-like form, but in its extreme absence, they transform, taking on a glass-like structure that protects material in the cells from harm. In 1995, dried tardigrades were brought back to their usual state after eight full years in this state.

This isn’t the only usually-cell-damaging experience a tardigrade can survive. Whilst in a tun state, they can withstand up to 600 megapascals of pressure, a vast amount that is six times greater than the deepest part of the ocean! In other words, pressure that would kill almost all creatures. As for extreme cold. their key to withstanding these low temperatures is found in a chemical they produce dubbed ‘ice nucleating agents’. Essentially, these agents allow crystals to form outside of their cells rather than inside when they freeze, again protecting important molecules from damage. Crazier still, a 2007 a space mission found that they could survive vacuum of space!

However, the most exciting of these creatures’ abilities is one that has already yielded promising results in medical research. Thanks to yet another unique protein, called Dsup, tardigrades are even protected from the damage of x-rays. In test conditions, this same resilience was applied to human cells using the protein, allowing said cells to suppress 40% of x-ray damage. If this study continues, it could one day protect patients undergoing radiation therapy, turning these marvels of nature into a potential miracle-cure. Of course, as studies and testing continue, scientists must strive to treat these creatures with respect; imagine the irony if, after surviving so much, the tardigrade ran into peril from our own laboratories! However, as it stands, those who work with tardigrades do so out of fascination and seem to hold a genuine love for the little anomalies – and who could blame them?