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Squirrel DNA, Arctic past
Researchers analyzing permafrost-preserved ground squirrel droppings recovered ancient environmental DNA from multiple animals, insects, plant species, and microbes, with samples dating to about 30,000 to about 700,000 years ago.
“In the long quest to understand what life was like for the saber-toothed cats, bison, and mammoths that roamed North America’s dry tundra during the last Ice Age, scientists have hit on a potent new tool: ancient poop”
The study, published in Nature Communications, reassembled “over 18 mitochondrial genomes” from woolly mammoth, steppe bison, horse, and ground squirrels, and also found evidence of other rodents and larger predators including wolves and big cats.
In the Yukon, the droppings were described as “little pellets, the size of rabbit poo,” and the team said the DNA extracted is among the oldest recovered and sequenced.
The work is aimed at reconstructing the bygone environment of Beringia, an ancient area famous for the Bering Land Bridge, across multiple glacial periods.
Evolutionary geneticist Hendrik Poinar, director of the McMaster Ancient DNA Centre, said the coprolites preserve “remarkably diverse genetic snapshots of ancient Beringia.”
What scientists found
Tyler Murchie, a Hakai Institute paleogenomics researcher and lead author, described the Yukon’s Arctic ground squirrels as acting “kind of like pack rats,” collecting plant material, bones, seeds, and other items into their burrows.
In the Yukon’s Klondike region, the pellets were used to identify an array of plant and animal life, and Murchie said the oldest sample used in the study is about twice as old as humanity, with the oldest sample dating to about 700,000 years ago.
Murchie also said the findings show the DNA can be resistant to degradation, adding, “it turns out in some cases DNA can be quite resistant to degradation,” when combined with being frozen perpetually for all this time.
The research team reported previously unknown genetic diversity among Arctic ground squirrels, including a lineage dating back about 700,000 years with close living relatives in western Siberia.
EurekAlert! quoted Poinar saying the coprolites help reconstruct paleoenvironments “through the deep past,” linking the genetic record to evolutionary and ecological change across glacial periods.
Why it matters now
The researchers said the permafrost-preserved record can preserve ancient DNA even better than bones or surrounding permafrost, and Poinar said the approach can help researchers look at genes under selection due to climate change in the past.
“McMaster University image:Researchers analyzed permafrost samples collected from ground squirrel burrows that span several glacial periods and can remain frozen and sealed for thousands of years”
Murchie said studying the ancient squirrel feces could help researchers understand shifts between interglacial periods and offer insight into the current epoch, the Holocene, which began about 11,700 years ago.
He also pointed to the last interglacial, saying, “this was about 115,000 thousand years ago, when it was warmer than it is today,” and he hoped that period would help researchers understand how anomalous the Holocene is.
The Canadian Press report said scientists are racing against the clock because of the rapid pace of thaw in the north due to human-caused climate change, with Murchie saying there are scientists trying to archive these findings quickly because of how fast they are degrading.
EurekAlert! added that the samples dated back 30,000 to approximately 700,000 years, and that the work opens “the door to many future discoveries” by preserving a high-resolution record of Quaternary ecosystems.
