The researchers sequenced the oldest known DNA in the world. Using materials from the early and middle Pleistocene subepochs, the analysis of ancient DNA destroys the record for the oldest sequenced DNA in the world. It comes from mammoth remains that were discovered in Siberian permafrost and proves that under the right conditions ancient DNA can survives more than a million years.
But the analysis of that very old DNA depends on the fact that researchers also have the right technology. Fortunately, an international team led by researchers at the Center for Paleogenetics in Stockholm, Sweden, had advanced sequencing and bioinformatics technologies at their disposal. A The nature The news report for the new paper says researchers have pushed current technology close to its limits to allow the extraction of old strands of DNA from mammoth teeth that had been stored in Siberian permafrost. The lead author of the Nature study, Love Dalén, a professor of evolutionary genetics at the Center for Paleogenetics, notes that the scientific team was lucky, saying:
“It’s not like everything in permafrost always works. The vast majority of samples have poor DNA. ”
How Ancient Mammoth DNA set records
The discovery is truly amazing, because after an organism dies, its chromosomes gradually become smaller and smaller, and in most cases, the extremely old DNA strands have become so small that they have lost all their informational content. But a new article published in the journal The nature shows that the team managed to obtain 49 million base pairs of nuclear DNA from a 1.65 million-year-old tooth found near a village called Krestovka (the tooth was also nicknamed Krestovka). They also extracted 884 million base pairs of ancient DNA from a 1.3 million-year-old tooth called Adycha and 3.7 billion base pairs of DNA from a tooth. 600,000-year-old woolly mammoth they called Chukochya. The three mammoth remains were discovered in the 1970s and are part of the collection of the Russian Academy of Sciences in Moscow.
Love Dalén and lead co-author Patrícia Pečnerová with a mammoth corner on Wrangel Island. (Credit: Gleb Danilov)
The nature The news report explains that the old mammoth DNA study did not find the oldest biomolecular information from fossil records – this is the protein sequenced in 2016 from 3.8 million-year-old ostrich eggshells in Tanzania. In second place is a protein sequence from a 1.77 million-year-old rhinoceros tooth from Georgia, which was analyzed in 2019. However, although proteins are more resistant and can survive in extremely fossil fuels. From ancient places without permafrost, it is not as useful as DNA for researchers who want to study the ancestors of an organism.
This is just one of the reasons why the new mammoth DNA study is so important – it contains genetic information that was not available in older protein samples.
A second reason the study makes headlines is that it beat ancient DNA from a genome in a 560,000- to 780,000-year-old horse’s foot bone found in Canada’s Yukon Territory for the oldest sequence. Ancient DNA. Putting the mammoth evidence in context, Dalén said:
“This DNA is incredibly old. The evidence is a thousand times older than the remains of the Vikings and even precedes the existence of humans and Neandertal. ”
The first example of hybrid speciation in ancient DNA
The new study also amplified the ability of researchers to track the evolutionary process of speciation – the formation of new and distinct species. A The nature the press release states that this process generally takes place “in periods of time that are believed to exceed the limits of DNA research.”
A corner of a woolly mammoth discovered in a creek bed on Wrangel Island in 2017. (Credit: Love Dalén)
However, scientists’ study of mammoth DNA suggests that there was not one, but two different mammoth descendants alive during the early Pleistocene, in the region of what is now Eastern Siberia. Adycha and Chukochya are believed to be members of a species that gave birth to the woolly mammoth, but Krestovka seems to have come from an unknown and possibly entirely new offspring of the mammoth. Tom van der Valk, lead author of the study and bioinformatics scientist at Uppsala University in Sweden, explains the researchers’ shock at this discovery:
“It was a complete surprise for us. All previous studies have indicated that there was only one mammoth species in Siberia at that time, called the steppe mammoth. But analyzes of our DNA now show that there were two different genetic lines, which we refer to here as the mammoth Adycha and the mammoth Krestovka. We can’t say for sure yet, but we believe that they can represent two different species “.
In their study, researchers suggest that the Krestovka genome may have departed from other mammoths 2.66-1.78 million years ago. They also believe that this mammoth line “was ancestral to the first mammoths to colonize North America.” It seems that Colombian mammoths in North America ( Mammuthus columbi ) can trace half of their ancestors to woolly mammoths and half to previously unrecognized Krestovka mammoth offspring.
The nature The news report states that this means that the new study also provided the first evidence of “hybrid speciation” – a new species that is formed by mixing – found in ancient DNA. The study’s co-lead author, Patrícia Pečnerová, an evolutionary biologist at the Swedish Museum of Natural History, says the team believes that “the Colombian mammoth, one of the most iconic species of the North American ice age, evolved through a hybridization that took place about 420 thousand years ago. ”
How far can researchers go?
Finally, the ancient mammoth DNA study inspired Dalén to analyze several samples of permafrost animals dating back more than a million years. Next on his list? Oxen muscles, moose and lemming. But the professor of evolutionary genetics knows that there is an age limit that he will not be able to cross when analyzing ancient DNA – 2.6 million years – “This is the permafrost limit. Before that, it was too hot, “he says.
Mammoth wool mushrooms coming out of the permafrost on the central island of Wrangel, located in northeastern Siberia. (Credit: Love Dalén)
Image above: The illustration is a reconstruction of the steppe mammoths that preceded the woolly mammoth, based on the genetic knowledge we now have from the Adycha mammoth. Source: Beth Zaiken / Center for Paleogenetics
By Alicia McDermott