In the stomach of a mummified wolf pup, scientists find DNA from a woolly rhino

Two ancient wolf cubs discovered buried in Siberian permafrost more than a decade ago are revealing new stories, thanks to the rich DNA clues preserved inside their bodies.

For the first time, researchers have discovered a piece of meat from a woolly rhino – a creature similar in size to the modern white rhino, but with a shaggy coat – preserved in the stomach of one of the pups. The DNA from this flesh and fur survived under Siberian ice for more than 14,000 years, allowing scientists to sequence the entire genome. They shared their findings in a study published Wednesday in the journal Genome Biology and Evolution.

“This is the first time that an entire genome has been reconstructed from an Ice Age animal that was inside another Ice Age animal,” said Camilo Chacón-Duque, study author and evolutionary biologist at Uppsala University in Sweden. “It’s a high-quality, high-resolution genome.”

The woolly rhino in question died out around 14,400 years ago, just a few hundred years before the species disappeared from the fossil record. This means that researchers now have a snapshot of the species’ genome just before it was wiped out.

“This sample is by far the youngest woolly rhino that has been sequenced – with the youngest, I mean the closest to the extinction of the species,” Chacón-Duque said.

Evolutionary biologists have long wondered whether hunters or climate change ultimately doomed the woolly rhino. The new genomic data suggests that the population may have been healthy until the end – before something caused it to collapse.

A group of ivory hunters searching for mammoth tusks found the first of two pups in Siberia about 15 years ago. Four years later, they discovered each other.

Hunters could not have known that these mummified animals – known today as “Tumat puppies” – would help scientists elucidate the fate of a different species.

The pups, both female, were likely littermates: They were found about 6 feet apart and shared some DNA characteristics, according to research published last year in Quaternary Research.

“They died quite young, around nine weeks,” said Anne Kathrine Wiborg Runge, co-author of the Quaternary Research paper. “They still had their baby teeth.”

This earlier study suggested that thawing permafrost could have triggered a landslide that buried the wolves in ice or snow. It’s also possible that the pups died after their den collapsed, he adds.

“They are immediately buried and frozen in a freezer – a deep freezer – for 14,000 years,” said Nathan Wales, Runge’s co-author and senior lecturer in the department of archeology at the University of York in the UK.

Because the puppies were found near a site where ancient humans had slaughtered woolly mammoths, researchers wondered whether they were domestic dogs, as opposed to wolves. But no mammoth DNA was found in their stomachs, which could have been a clue linking the pups to humans. Instead, researchers believe a pup’s last meal was the woolly rhino. The other had recently eaten a bird, which left some feathers in the permafrost, as well as some rhino meat.

In the study published Wednesday, Chacón-Duque sequenced a hard, thick piece of flesh from that last meal.

“This piece has basically been sitting in the stomach for many, many years,” Runge said. “It’s just incredible.”

Complete woolly rhino genomes are rare, but the researchers were able to compare the genome to two other high-quality genomes that died about 18,000 and 49,000 years ago, respectively.

Chacón-Duque and his colleagues found no evidence of inbreeding or harmful mutations that would have doomed the population – it appeared healthy.

“They don’t find any signs that the population is collapsing, which is strange given that the species is disappearing,” said Wales, who specializes in ancient DNA but was not involved in the new research.

A few hundred years after this rhino set foot on Earth, the Northern Hemisphere began a period of brutal warming that would end the ice age. The study authors believe the newly sequenced DNA provides evidence that climate change was the driving factor in the extinction of the woolly rhino.

Chacón-Duque said warming has likely put a strain on the cold-adapted population. It could also have allowed humans to expand into the woolly rhino’s geographic range and spread disease.

“All of these things will act in synergy to probably cause the permanent disappearance of the species,” Chacón-Duque said. “But we are convinced that climate change is the key factor. »

Mick Westbury, an associate professor and evolutionary biologist at the Technical University of Denmark who did not contribute to the research but has studied ancient rhinos, said the theory was plausible.

But Westbury added that rare and ancient DNA can be difficult to interpret and it can sometimes take several generations to see the impacts of population decline on a species’ genetics. The woolly rhino could have been in peril even if that creature’s genes didn’t show it, he said.

“Sometimes genomics alone isn’t enough to sell the whole picture,” Westbury said.

Yet as human-caused climate change intensifies and threatens modern species, Westbury said this research could offer conservationists an important lesson.

“Based on these results, the woolly rhino does not appear very vulnerable to extinction,” Westbury said. “Just because a living species on the surface appears genetically healthy doesn’t mean it isn’t vulnerable.”