A recently-discovered species of tardigrade glows blue under ultraviolet light and uses fluorescence as a protective shield, according to a new study published in Biology Letters.
New tardigrade glows blue, resistant to lethal ultraviolet light levels
Tardigrades are named after water bears or moss piglets — and are microscopic animals with incredible resiliency to conditions like radiation, dehydration, freezing temperatures, and even the deadly vacuum of space. In 2016, scientists in Japan brought a tardigrade frozen for more than 30 years back to life. Roughly 1,300 separate species of these eight-legged animals are known to scientists, and they hail from around the planet.
The latest tardigrade "superpower" stems from the newly-discovered one — of the Paramocrobiotus genus — which features a natural fluorescence that creates an eerie blue glow under ultraviolet light. Additionally, this fluorescent effect shields tardigrades from UV radiation levels known to be lethal for other microorganisms — like viruses and bacteria, Gizmodo reports.
The biochemist Sandeep Eswarappa of the Indian Institute of Science in Bangalore co-authored the new study.
Mysterious tardigrade group survived 30 days after lethal UV light dose
Eswarappa and his colleagues extracted the tardigrade of interest along with others from moss growing around a concrete wall in Bangalore. With the help of a germicidal lamp, scientists exposed the specimens to a blast of ultraviolet light to test the critters' tolerance levels.
Fifteen-minute durations of exposure at 1 kilojoule per square meter killed most of the tardigrade species called Hysibius exemplaris — with all dead after a day had passed.
However, a strange group of tardigrades with reddish-brown spots survived for 30 days after receiving a dose capable of killing bacteria and nematode worms (Caenorhabditis elegans) in a mere five minutes.
Strange tardigrades survived at 60 percent chance
During a follow-up test, Eswarappa and colleagues raised the UV radiation dose up to 4 kilojoules per square meter — bur for an entire hour.
Amazingly, 60% of the mysterious tardigrades survived for 30 days after this devastating blast — leaving the scientists unsure if they'd discovered a new species, which is why they came up with a provisional name: Paramacrobiotus BLR.
"After UV radiation treatment, tardigrades were observed daily for signs of life — active movement and egg laying," wrote the authors in the recent study. "There was no significant change in the number of eggs laid, their hatchability and the hatching time, between UV-treated and untreated Paramacrobiotus BLR specimens."
Fluorescent compound creates 'shield,' protects from UV light
Next, the scientists used an inverted fluorescence microscope to study the creatures, which caused the reddish-brown tardigrades to emit a blue light. The scientists imagined the tardigrades' fluorescent skin pigments could be linked to UV resistance, so they carried out a novel experiment: Covering the H. exemplaris specimens (and some nematode worms) with the pigments, they exposed creatures they knew couldn't survive the blast to the same UV lamp.
The results clearly showed the fluorescent compound created a "shield" capable of helping organisms survive at nearly twice the lethal rate for unprotected creatures.
"[I]t is possible to transfer the UV tolerance property from Paramacrobiotus BLR strain to the UV sensitive H. exemplaris and C. elegans using the fluorescent extract," read the study, which added that this gives a "direct experimental demonstration of photoprotection by fluorescence."
Evolution empowers small creatures in odd ways
While the precise mechanism at work behind this protective quality remains an unknown, Eswarappa's team thinks the fluorescent shield absorbs lethal UV radiation and somehow converts it into harmless blue light. Paramacrobiotus BLR probably evolved this biological trick to "shield" itself from the high UV radiation levels found in tropical southern India — which sees the UV index rise up to 10, the authors say.
We often have a vague feeling about the life on Earth as having reached a final stage — drawing up a narrative from the viewpoint of the present, as if the shape, behavior, abilities, and distribution of life was always going to be this way. But every time a new fantastic ability — like that of the newly-discovered tardigrades' power to absorb, convert, and deflect UV radiation into blue light — we discover more evidence of evolution at work, everywhere we look.