World’s toughest animal frozen for 24,000 years, can still reproduce

Bdelloid rotifers may be the toughest, tiniest animal you’ve never heard of.

The microscopic, multicellular creatures are one of the planet’s most radiation-resistant animals. They can withstand extreme acidity, starvation, low oxygen and years of dehydration.

“They’re the world’s most resistant animal to just about any form of torture,” said Matthew Meselson, a molecular biologist at Harvard University.

Bdelloids can also come back to life after tens of thousands of years in deep freeze, according to a study published on Tuesday AEST in the journal Current Biology. Bdelloids are one of a handful of teensy creatures, including tardigrades, that are known to survive incredibly inhospitable conditions. The new findings also show such robust micro-animals can endure lengthy durations of suspended animation as well.

These microscopic creatures have complex systems with brains and muscles and guts. Credit:Diago Fontaneto, Plos Biology, 2007

For the study, scientists collected samples by drilling about 3 metres below the surface of permafrost in north-eastern Siberia. They discovered living bdelloid rotifers locked in the ancient permafrost, whose average temperature hovers around -10 degrees Celsius.

Radiocarbon-dating revealed the bdelloids were 24,000 years old. Once thawed, they twere still capable of reproducing.

“We revived animals that saw woolly mammoths, which is quite impressive,” said study co-author Stas Malavin, a scientist at Russia’s Institute of Physicochemical and Biological Problems in Soil Science.

Scientists have previously regrown Antarctic moss and whole campion plants from samples and seeds frozen for hundreds or thousands of years. In 2016, a group of Japanese scientists successfully revived another resilient animal — the tardigrade, also known as a water bear — after 30 years of cryptobiosis, or suspended animation prompted by freezing, desiccation or other adverse conditions.

Until this paper, prior research on rotifers suggested they could survive deep freezes for up to a decade.

“We know for sure now it can withstand tens of thousands of years of cryptobiosis,” Malavin said.

Bdelloid rotifers are all around us — on moist strands of moss, in rain puddles and bird baths, and across freshwater bodies spanning arctic and tropical regions and everything in between. They have been studied by scientists since the invention of microscopes. In 1702, Antony van Leeuwenhoek described them as “little round animalcules,” after spotting the creatures in gutter water from his house.

In the intervening centuries, scientists have carefully examined the complex organisms, which — despite the smallest being only a few dozen microns wide — are equipped with brains, guts, muscles and reproductive systems.

But scientists still don’t understand exactly how bdelloid rotifers are able to shield their cells and organs from seemingly catastrophic conditions and patch up broken DNA. Scientists have also been baffled about how the life-form has been able to diversify to more than 450 species over millions of years seemingly by asexual reproduction alone, which is often considered an evolutionary disadvantage.

“I guess now we have more questions than answers,” said study co-author Nataliia Iakovenko, a zoologist at the Czech University of Life Sciences Prague who studies polar microscopic animals.

Unlocking these micro-animals’ super-resilient biological strategies could help us to someday preserve other animal cells, tissues and organs here on Earth, and beyond — which is why scientists have sent both tardigrades and rotifers to space.

“They’re probably the only animals we know that could do pretty well in outer space,” Meselson said.

The New York Times

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