The oldest DNA ever discovered shows the paradise that was the current arctic desert | Sciences

Kap København is located in the far north of Greenland so it directly faces the North Pole. Today it is what they call a polar desert, with a few days a year free of ice that make use of lichens and mosses to survive. But a study has just shown that two million years ago it was almost heaven on earth. The authors found evidence that hundreds of species live there. In a forest of birch, poplar and pine trees, fragrant and floral plants related to roses abounded. Small herbivores, such as mice, lemmings, and rabbits, thrived on these plants. But it is also large, like the current reindeer. There were even megafauna, such as the now-extinct mastodons. The amazing thing is that they haven’t found fossils of such biodiversity. Scientists discovered this because they were able to extract the DNA of much of the life associated with Earth.

The recovery of increasingly ancient genetic material is rewriting the history of life. DNA is a fragile substance that deteriorates when exposed to the environment for many reasons (corrosion, enzyme action, temperature, pressure, oxidation…). The best place to keep it is the better-preserved fossil remains, such as teeth and bones. Advancements in retrieval and sequencing technologies in the past two decades have allowed us to go back further and further. 20 years ago, science believed it You cannot recover ancestral DNA that is more than 100,000 years old. A decade ago, Spanish scientists were able to extract mitochondrial DNA (which is inside the cell, but outside the cell’s nucleus) from Humans who lived in Atapuerca 400,000 years ago. In 2013, they succeeded in sequencing its genome An ancestor of horses that lived 700,000 years ago. But last year, another group of researchers scored a milestone with the ability to extract Huge genetic information Preserved in the Siberian permafrost for over a million years. Now, DNA found in København doubles the marker, which dates it to between 2.1 and 1.9 million years ago. This time it was not a fossil. This time they retrieved it from Earth, literally.

Work published in Scientific journal nature, led by Eske Willerslev, a researcher both at the University of Cambridge (UK) and director of the Center for GeoGenetics at the University of Copenhagen (Denmark). “This is the longest story I’ve ever been involved with, because we started in 2006 when we went to Greenland to collect samples,” he said in an online presentation to several journalists. With the traditional techniques of paleontology, in the coastal arid lands of Cap Copenhaven, they have barely found a few dozen pollen grains from plants from the past and one fossil, which they believe to be a hare or a hare. So there were no fossils from which DNA could be extracted. However, they were piecing together layers of the Earth in hopes of extracting some information from it as the technology advanced. Each time there have been improvements in extraction issues [de material genético] Or in sequencing technologies, we would review the samples again, but we failed, and we failed, and we failed again,” he adds. But everything changed a few years ago.

One of the new things we discovered here was to look at how DNA binds to minerals.

Karina Sand, researcher at the Center for GeoGenetics at the University of Copenhagen

Barely five years ago, various scientific groups were examining the possibility of extracting genetic information not from the organism to which it belonged, but from the environment in which it was found. The new system focuses entirely on environmental DNA, specifically ancient DNA in sediment (sedaDNA, for its English acronym). In one such group was Karina Sand, now also at the University of Copenhagen and co-author of the study. “One of the new things we’ve discovered here is to see how DNA binds to minerals,” he says. Once the organism it belongs to has decomposed, the genetic material sticks to the substrate. Thus, they verified that some sediments absorb more DNA than others. “Clay minerals can preserve DNA much better than quartz minerals, for example,” Sands details. One problem they found is that clay absorbs it so well that removing it later costs a lot, even four times more than quartz. Finding genetic material in a geological substrate is already a breakthrough, but being able to extract and analyze it is what deserves a Nature publication.

Spanish scientist Antonio Fernández Guerra, also from the Danish Center for Genetics and one of the authors of the paper, tells in a telephone conversation what it was like to work with the environmental DNA discovered at Cap Copenhaven: “You have to think about what it was like two million years ago. You had the kind of forest that We described it, with trees, plants and streams that carry all kinds of substances out to sea. DNA accumulates in the mouth, especially from plants. With animals it’s more difficult. Any organism that lived on the coast two million years ago will also be in the environmental DNA. When you take a sample “Of genetic sequences, there’s a bunch of bacteria and archaea, so you have to go through all that noise to try and find the DNA that’s been out there waiting to be found for so long. There are times for every million sequences we retrieve, only one is valid.”

So, by counting needles among stacks of hay, researchers have identified more than a hundred genera of vegetable plants. Genus is one of the categories into which life is organized (the taxonomic categories are domain, kingdom, phylum, class, order, family, genus and finally species). Identifying specific species in environmental DNA from two million years ago shouldn’t have been easy, but they did. Under genus, they identify specific trees, such as arctic willow or dwarf birch. With animals, it was much more complicated. As in any ecosystem, there are fewer animals than there are plants, so they identified fewer animal DNA. They could not go down to the family or genus level, although they did find genetic remains of vertebrates still extant in Greenland, such as the lemon near the North Pole or the Arctic hare, the only animal for which fossil remains have been found. They also identified the genera of fleas, ants, and extinct relatives of today’s elephants and reindeer.

What was not found was carnivores. It has its own logic, following the hierarchical structure of life, the higher the scale, the lower the number. Researchers are convinced that, as in other ecosystems in arctic latitudes, there must be wolves, bears, and even saber-toothed tigers. “Obviously, plants are more common than herbivores and herbivores, and they are more common than carnivores,” says Willerslev, lead author of this research. “Maybe that’s why we haven’t found omnivores. However, I would say that if we As we continue sequencing and sampling and as we continue sequencing, my prediction is that at some point we’ll catch some carnivores.”

The fact that we are able to detect the presence of species in ecosystems for which we have no fossil evidence is remarkable.

David Diez del Molino, a researcher at the Center for Paleogenetics in Stockholm

David Diez del Molino is a researcher at the Center for Paleogenetics in Stockholm (Sweden) and one of those who have recovered the DNA of those million-year-old mammoths. Unrelated to the current study, it highlights the novelty of its techniques and the fruits it can bear. “Ancient DNA from sediments is one of the hottest topics and one of the hottest areas in paleobiology right now,” he says. “It could allow us to reconstruct the DNA of an entire ecosystem from the past at a given site, which is basically impossible using DNA from bones and other materials,” he adds. But its strength also lies in its weakness: “The amount of DNA recovered from each species is very small compared to DNA from bones. For this reason, most of the analyzes that are allowed for each species are a bit primitive,” he continues. In the case of their giant molars, for example, they were able to recover millions of nuclear sequences from three samples, allowing them to perform complex phylogenetic analyzes and discover previously unknown lineages of mammoths. But he goes on to consider the “fascinating” fact that it is possible to “discover the presence of species in ecosystems for which we have no fossil evidence and, therefore, were not known at that location.”

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