Where a frozen desert now stretches, arctic life once thrived: DNA traces in sediments have given researchers insight into the plants and animals of an ecosystem that existed in northern Greenland during a warm period around two million years ago. It is the oldest DNA ever recovered and analyzed. The study thus makes it clear that the further development of the method of analyzing environmental DNA makes it possible to gain deeper insights into past living environments than previously thought.
In order to obtain information about animals and plants of the past, researchers were dependent on examining fossil finds for a long time: Bone remains or remains of plant structures gave clues. But now a new technique has found its way into research that can provide insights in an alternative way: the study of fossil DNA. The method is based on the fact that genetic material can be preserved for a long time under certain circumstances. Genetic material obtained from bone finds has already provided important insights into the developmental history of humans and other living beings. The previous age record for fossil DNA was the approximately one million year old genome that researchers extracted from a Siberian mammoth bone.
It had also already been shown that DNA can not only have been preserved in body tissues: So-called environmental DNA can also survive in sediments for a long time. This is genetic material that living beings pass on to their environment in the form of excretions, dander or other substances with genetic content. Fragments of this environmental DNA can be obtained from sediments using modern laboratory methods and then sequenced. Comparisons with known genetic information from animals and plants in databases then enable assignment. In this way, it is possible to shed light on which species existed in certain places in the past and at different climate phases.
On the trail of a bygone world
An international team of researchers has now applied this method to the case of an ecosystem that once existed in a region in the extreme north of Greenland that is now characterized by a polar desert. The impetus for the study was the results of paleoclimatological investigations, which revealed that the area around the Kap-København Formation was once characterized by a comparatively friendly climate: warm phases around two to three million years ago led to temperatures of 11 to 19 degrees Celsius were higher than today. The extent to which this enabled plants and animals to live there has not yet been precisely clarified by fossil finds in the area. As part of their study, the researchers therefore explored whether usable environmental DNA can still be obtained from deposits in the area that are around two million years old.
As the researchers report, they actually succeeded in extracting pieces of environmental DNA from the sediment samples from different places. Apparently they are bound to clay and quartz and have survived the passage of time protected by the low temperatures. The team was then able to compare the obtained sequences with information from DNA libraries that contain genetic information from modern-day animals, plants and microorganisms. “It was only the development of a new generation of devices for DNA extraction and sequencing that made it possible for us to extract DNA fragments from the sediment samples. We were finally able to describe an ecosystem that is two million years old,” says lead author Kurt Kjær from the University of Copenhagen.
Even proboscidea roamed the lush landscape
According to this, a boreal forest ecosystem existed there at that time with a mixed vegetation of poplars, birches and thujas as well as various shrubs and herbs. The DNA traces also showed that rabbits, reindeer, rodents and geese lived there. The researchers were also able to prove that primeval proboscis animals trudged through this landscape at that time. Until now it was assumed that the range of these mastodons did not extend so far north. The researchers were even able to detect traces of marine life in certain sediment samples from the coastal region. Apparently, the water in the area was so warm at the time that Atlantic horseshoe crabs, among other things, could exist there. "Due to the much higher temperatures at that time than today, an ecosystem could exist at Cape København for which there is no equivalent today," says co-first author Mikkel Pedersen from the University of Copenhagen.
In addition to the genetic traces of plants and animals, the researchers also found the sequences of many microorganisms, including bacteria and fungi, in the DNA samples. How the interaction of animals, plants and protozoa once shaped the living environment in the far north of Greenland is what the researchers now want to shed more light on through further investigations. As they point out, the results so far show above all the fundamental potential of analyzing environmental DNA. "We have shown that given the right circumstances, we can look further back in time than anyone could ever have imagined," says senior author Eske Willerslev from the University of Copenhagen. "Having successfully extracted fossil DNA from clay and quartz, it may be possible that similar material also conserved genetic traces in warm, humid environments, for example at sites in Africa. If this is the case, we may be able to gather groundbreaking information about the origins of many different species - perhaps even new insights into the first humans and their ancestors."
Source: St John's College, University of Cambridge, Article: Nature, doi: 10.1038/s41586-022-05453-y