Breakthrough in paleogenetics
Recently, scientists for the first time extracted and deciphered the nuclear DNA of Neanderthals not from bones and teeth, but from the soil of caves where Neanderthals lived. Now the genomes of bears – VM have been analyzed by the same method.
Scientists have recreated the DNA of a fossil bear preserved in the soil for the first time
For the first time, scientists were able to reconstruct the genomes of two species of bears that lived in the Upper Paleolithic in northern Mexico, using DNA extracted from cave deposits containing the feces of ancient animals. The authors compare this discovery in importance for genomics with the landing of a man on the moon. It confirms that now, in addition to bone remains, other sources can be used to extract ancient DNA. In addition, soil DNA makes it possible to study genetic features in the context of populations, not just individuals.
The results of the study are published in the journal Current Biology (Pedersen et al., Environmental genomics of Late Pleistocene black bears and giant short-faced bears).
The Chiquiuit Cave in the mountains of Northern Mexico, where the samples were obtained, is well known as a place of residence of ancient people. Numerous stone tools and their fragments, known as flakes, found here are 30-25 thousand years old. In addition, scientists found bones and signs of the presence of ancient bears, bats, voles and other rodents in the cave.
Danish scientists from the Lundbeck Foundation Geogenetics Center at the University of Copenhagen, led by Professor Eske Willerslev, in collaboration with colleagues from the USA, Great Britain, China, Mexico, Norway and Canada, isolated the so-called ecological DNA (eDNA) from cave sediments containing feces and urine traces of ancient animals and for the first time in genomics histories have recreated on its basis the genomes of two Upper Paleolithic bears – the American black bear Ursus americanus, which still lives in the forests of the North American continent, and the giant short-faced bear Arctodus simus, one of the largest bears that ever existed, which became extinct at the end of the last ice age about 12 thousand years ago.
"When an animal or a person urinates or defecates, the body's cells are also excreted from the body," the press release says. St. John's College, Cambridge University, words by Professor Willerslev. – And the DNA fragments of these cells are what we can detect in soil samples. Using extremely powerful sequencing methods, we reconstructed genomes – the genetic profiles of animals - based on these fragments for the first time."
The authors believe that their results open a new era in paleogenomic research. Now, in order to judge the most diverse aspects of ancient life on Earth, from evolution to climate change, scientists do not need to rely only on rare finds of fossils of bones or teeth that have preserved DNA. Researchers have proved that highly fragmented DNA from the soil is also suitable for this.
"All over the world, everyone who studies ancient DNA recognizes the need to reconstruct the genome from fragments found in soil or sediments. The opportunity to do this for the first time means that we have opened new horizons," Villerslev notes. "We have shown that hair, urine and feces are genetic material that, under the right conditions, can exist for much longer than ten thousand years."
The researchers compared the genomes of bears from the Chiquiuit cave with the genomes of other bears, including 83 modern black bears from the USA and Canada and three giant short-faced bears that lived on the Yukon in Canada about 22 thousand years ago. It turned out that the black bears from Chiquiuit are genetically closely related to modern black bears North America, but the short-faced bears that lived in the Paleolithic in northern Mexico are very different from the population that lived at the same time in northwestern Canada.
"This is a great example of new knowledge that suddenly becomes available when you reconstruct genomes based on DNA fragments extracted from the soil," explains the first author of the article, associate professor at the University of Copenhagen Mikkel Winter Pedersen (Mikkel Winther Pedersen). – Research on ancient ecological DNA has so far been very limited. Fragmented DNA from the soil could only tell if a particular species lived in a certain area at a certain time, but did not give any specific details."
"I am not exaggerating when I say that the possibility of extracting this kind of information from a soil sample weighing only a few grams will revolutionize our field," the scientist concludes.
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