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The most common water bear, Hypsibius exemplaris, under the microscope.

Newly discovered water bear is the undisputed king of sunbathing

– Nov. 25, 2020

We already knew for some time that the water bear is a very tough creature. He laughs at extreme heat and cold, survives 30 years without water, and even survives a ride through space. But a newly discovered species of water bears can now add an extreme characteristic: survive a large dose of ultraviolet (UV) radiation. Where we humans get dazed by sunburn in summer, this little sun king comes with a built-in UV protection. But how does he actually do that?

Tracking down tardigrades

To answer that question, the new species of course first had to be discovered. That turned out to be a matter of coincidence, paying attention and a good dose of luck. A group of scientists at the Indian Institute of Science in Bangalore, India searched at their university campus for tardigrades to conduct research into surviving extreme conditions. After collecting water bears from various places, they were subjected to various tests. One of the most random of these tests was placing tardigrades under a strong UV lamp to see how long they can survive.

Ultimate survivor

The UV test had a surprising result. Bacteria and roundworms died after five minutes, and the well-known bear species Hypsibius exemplaris (which is also cultured in Micropia) survived for 15 minutes. However, a reddish-brown species was also spotted among the collected water bears, which easily survived the UV bombardment. Even a dose of four times the previously used UV radiation was no problem for 60% of these tardigrades. Following these results, the reddish-brown water bears were further examined, after which it turned out that it was an undiscovered species within the genus Paramacrobiotus. A new and special water bear!

Blue UV-shield

When conducting further research into the new water bears, it was noticed that this species seemed to glow up in blue under UV light, while other species did not. Fluorescent pigments under the tardigrades skin seemed to be the cause of this glow. The new water bear's pigments convert UV radiation into weaker blue light that we can see. To confirm the suspicion that these pigments protect against UV radiation, it was isolated from the water bears and applied to the "common" Hypsibius water bears as well as to roundworms. After this treatment, these microbes were found to survive under the UV lamp at least twice as long as the specimens without an artificial UV shield.

Unique feature?

Whether the new tardigrade species is the only one that has this property is still unknown. It has previously been suggested that certain corals and some species of comb jellyfish may use a similar mechanism. However, this new species is the only species where it has actually been proven in the laboratory that its fluorescent shield protects against UV radiation. The researchers think that he evolved this feature to protect itself against the harsh Indian sun.

Would you like to admire a water bear in real life? Search for water bears yourself in our experiment “ Tracking down water bears ”. Would you rather view water bears with a real microscope? Then come to Micropia and check out our "Ultimate survivor" exhibit.

Sources
https://royalsocietypublishing.org/doi/full/10.1098/rsbl.2020.0391?af=R