A reconstruction of the steppe mammoths that preceded the woolly mammoth, based on the genetic knowledge gained the Adycha mammoth. CREDIT Beth Zaiken Centre for Palaeogenetics

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World’s oldest DNA reveals how mammoths evolved

An international team, including the Museum’s Prof Adrian Lister, has sequenced DNA recovered from mammoth remains that are up to 1.2 million years old

The analyses show that the Columbian mammoth that inhabited North America during the last ice age was a hybrid between the woolly mammoth and a previously unknown genetic lineage of mammoth. In addition, the study provides new insights into when and how fast mammoths became adapted to cold climate.

Around one million years ago there were no woolly mammoths, as they had not yet evolved. This was the time of their predecessor, the ancient steppe mammoth. Researchers have now managed to analyse the genomes from three ancient mammoths, using DNA recovered from mammoth teeth that had been buried for 0.7-1.2 million years in the Siberian permafrost.

This is the first time that DNA has been sequenced and authenticated from million-year-old specimens, predating the existence of humans and Neanderthals. Extracting the DNA from the samples was challenging. The scientists found that only minute amounts of DNA remained in the samples and that the DNA was degraded into very small fragments.

Prof Adrian Lister, Merit Researcher at the Natural History Museum and author on this study says, ‘Until now ancient DNA has rarely probed beyond a few tens of thousands of years, limiting what we can learn about the process of evolution.  With million-year-old DNA we extend beyond the date of origin of many iconic species like the mammoth, so we can track how species evolve and how their adaptations have arisen.’

The age of the specimens was determined using both geological data and the molecular clock. Both these types of analyses showed that two of the specimens are more than one million years old, whereas the third is roughly 700 thousand years old and represents one of the earliest known woolly mammoths.

Analyses of the genomes showed that the oldest specimen, which was approximately 1.2 million years old, belonged to a previously unknown genetic lineage of mammoth. The researchers refer to this as the Krestovka mammoth, based on the locality where it was found. The results show that the Krestovka mammoth diverged from other Siberian mammoths more than two million years ago.

Until now, all previous studies indicated that there was only one species of mammoth in Siberia at that point, the steppe mammoth, so the team were surprised to see that their DNA analyses now show that there were two different genetic lineages, referred to as the Adycha mammoth and the Krestovka mammoth.

The researchers also suggest that it was mammoths that belonged to the Krestovka lineage that colonised North America some 1.5 million years ago. In addition, the analyses show that the iconic Columbian mammoth that inhabited North America during the last ice age, was a hybrid. Roughly half of its genome came from the Krestovka lineage and the other half from the woolly mammoth.

The second million-year-old genome, from the Adycha mammoth, appears to have been ancestral to the woolly mammoth. The researchers could therefore compare its genome with the genome from one of the earliest known woolly mammoths that lived 0.7 million years ago, as well as with mammoth genomes that are only a few thousand years old. This made it possible to investigate how mammoths became adapted to a life in cold environments and to what extent these adaptations evolved during the speciation process.

The analyses showed that gene variants associated with life in the Arctic, such as hair growth, thermoregulation, fat deposits, cold tolerance and circadian rhythms, were already present in the million-year-old mammoth, long before the origin of the woolly mammoth. These results indicate that most adaptations in the mammoth lineage happened slowly and gradually over time.

Prof Lister concluded ‘This collaboration between palaeontologists and geneticists has been immensely rewarding. Earlier studies by myself and colleagues had suggested an origin of North American mammoths from Siberian steppe mammoths, based purely on their tooth morphology, but we could never have guessed that it was a genetic lineage that had separated off in Siberia a million years previously, nor that it hybridised with woolly mammoths well before the last ice age. We also saw the steppe mammoth’s teeth and skull as adapted to the arctic environment, and it is great to have this confirmed, with so much more detail, by the genetics’.

These findings are published in Nature.

ENDS

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