Ice Age mammoth and horse DNA found in soil samples left in freezer

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Researchers take a soil sample in the Canadian Yukon.

Researchers take a soil sample in the Canadian Yukon.
Photo: Tyler murchie

Fieldwork conducted about a decade ago is only now changing researchers’ understanding of large mammal extinctions during the Ice Age. Analysis of DNA trapped in frozen soil samples reveals charismatic species like woolly mammoths and wild Yukon horses have stayed longer than previously believed.

Soil samples were collected from the Klondike region of Yukon, Canada in the early 2010s, but no work on them has been published. Unlike traditional DNA samples, which can be taken from the bones or hair of some organisms, soils (even older ones) contain environmental DNA, which is genetic material locked in the microscopic residue left behind by them. animals as they move through an environment.

The Klondike ice cores were later found in a freezer at McMaster University by Tyler Murchie, an ancient DNA archaeologist at the university, who began to reexamine them. The work of Murchie and his team has been published today in Nature Communications.

“I found them in freezers while researching a new project during my PhD,” Murchie, lead author of the new article, said in an email. “One of my responsibilities at the old DNA center is freezer maintenance, so I had a good idea of ​​what was cool about it while I waited for someone to study.”

One mystery the team sought to unravel was the circumstances under which the large North American species of the last Ice Age became extinct. Animals like woolly mammoths, steppe bison and wild horses have roamed the continent for thousands of years, but the former two have disappeared from the planet. (Modern horses are directly related to the horses of the Ice Age.)

What killed the animals is usually attributed to one of two things: a global warming who have wiped out their food sources, or excessive hunting by mankind. Recent research usually pointed the finger first.

Saber-toothed mammoths, horses and cats in an artist illustration.

Imagination of an artist from the Pleistocene ecosystem.
Drawing: Julius Csotonyi

“I think a combination of climatic, ecological and human-made pressures best explains the losses, but more research is needed to really address this problem that Quaternary scientists have faced for some 270 years,” Murchie said.

In DNA contained in ancient permafrost, the team found evidence that large mammal species were not doing well even before climate change. In other words, the abundance of DNA in samples began to decline long before climate change. (The team used radiocarbon dating of plant material in the soil samples to determine their age.) But the animals did not disappear quickly; woolly and north american mammothhorse DNA remains present in samples until 5,000 years ago, in the middle of the Holocene, some 8,000 years later that the animals were once thought to have become extinct.

“The rich data provides a unique window into the dynamics of the megafau populationna and nuance the discussion around their extinction through more subtle reconstructions of past ecosystems, ”said Hendrik Poinar, evolutionary geneticist at McMaster University and also lead author of the paper, at a university Release.

Indeed, but this information is disappearing. As the climate warms, this time at an alarming rate due to human causes, permafrost loses its permanence. Vast ponds appear in the north of the planet, causing the collapse of whole swathes of the ground in massive chasms. The thaw also threatens genetic information that has been stored in the cold in the frozen earth. At the same time, however, the loss of permafrost has given rise to incredible discoveries as preserved remains emerge from the ice, including a still hairy cave lion and one 30,000 year old wolf head.


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