Multicellular invertebrates called Bdelloid rotifers are a class of rotifers entirely made up of females. These microscopic worm-like creatures are labeled an “evolutionary scandal” by biologists for having thrived for millions of years without having sex. Recently, researchers have discovered Bdelloid rotifers can persist for at least 24,000 years in Siberian permafrost and then reproduce.
Rotifers are well-known for their extreme resistance to radiation and ability to endure unwelcoming environments, such as low oxygen, drying, and starvation. They’ve existed for at least 35 million years and can be found today in freshwater ponds, lakes, streams, and moist terrestrial habitats such as soil, lichen, tree bark, and moss.
These tough little creatures– which have a complete digestive tract that comprises a mouth and an anus – can survive hostile environments by halting all activity and almost wholly arresting their metabolism. This behavior is called cryptobiosis, or “hidden life.” Tardigrades can also suspend their metabolism and fall into cryptobiosis for nearly a decade, allowing them to survive extreme conditions.
Soil Cryology Laboratory researcher Stas Malavin at the Institute of Physicochemical and Biological Problems in Soil Science in Pushchino, Russia, describes cryptobiosis:
It’s a state, kind of, between life and death.
After samples salvaged from remote Arctic locations via a drilling rig were recovered, Malavin and his colleagues used radiocarbon dating to determine that the rotifers were about 24,000 years old. Earlier evidence had revealed the creatures could survive for up to ten years when frozen.
The researchers note that the rotifers found in the permafrost would have been under giant woolly creatures’ feet, like the woolly rhino, which is now extinct. Impressively, once the team thawed the samples in the lab, the rotifers were able to reproduce. The findings are published in Current Biology.
However, scientists are yet to understand the biological mechanisms that allow these tiny organisms to survive on ice for such a prolonged period. “The outcome of this paper is more questions than answers,” commented Malavin.
Studying these creatures could help researchers find ways to improve the cryopreservation of cells, tissues, and organs. “Humans cannot preserve organs and tissues for such a considerable time. These rotifers, together with other organisms found in the permafrost, represent a result of a big natural experiment that we can’t replicate, so they are good models to study further,” Malavin suggested.
Zoology professor Matthew Cobb from the University of Manchester, who wasn’t involved in the study, believes that all kinds of animals frozen in the permafrost could awake as global warming temperatures melt the permafrost. “That doesn’t mean that terrifying things are going to come out and eat us, but it gives scientists the possibility of studying how the rotifer has adapted to resist the bad effects of freezing and the opportunity to explore the difference between existing species and their predecessors,” he pointed out.
Cobb added:
This is particularly significant in the case of bdelloid rotifers that reproduce by parthenogenesis (the females’ clone themselves). One of the advantages of sex is that you shuffle up the genes every generation – here, they are all copied down, so there is less variability for natural selection to operate on.
Now we have the possibility of comparing the genome of this group of animals with their modern equivalents, which are known from Belgium. That will shed light on a key biological curiosity and may reveal why some animals have given up sex altogether.
In February 2020, scientists at the University of Colorado at Boulder found that abrupt permafrost thawing in the Arctic could double carbon emissions, thus, speeding up climate change. However, by March 2020, scientists in Hamburg concluded that resettling massive herds of large herbivores, including reindeer, horses, and bison, could curb this effect and save up to 80% of the world’s permafrost soils until 2100.
