One of the world's oldest turds has been given the royal science treatment, with ancient Arctic ground squirrel droppings offering a smorgasbord of DNA from other animals and plants dating back up to 700,000 years.
The well-preserved poop, recovered from ancient burrows in preserved permafrost in the Yukon, has allowed researchers from McMaster University, the Hakai Institute and the University of Alberta to get an extremely rare glimpse into the diverse world these ground squirrels inhabited, when animals like woolly mammoths still roamed the land.
From evolutionary biology to ecology, poop plays a big role in how we understand life. Whether it's sifting through pungent seal feces to identify diet and feeding habits, to using turds to track elusive wildlife species, it's a critical tool for gathering knowledge.
However, given the nature of poop, its rare in the fossil form – known as coprolites – as they're fragile, organic and are quickly broken down by microbes.
So these squirrel nuggets, packed full of ancient environmental DNA (aeDNA), left by the mammals 30,000 to 700,000 years ago, are gold in the animal-science world.
“The research shows us that ground squirrel coprolites, or droppings, preserve remarkably diverse genetic snapshots of ancient Beringia, making them exceptional repositories for understanding evolutionary and ecological change through the deep past,” says evolutionary geneticist Hendrik Poinar, one of the study’s senior authors, Director of the McMaster Ancient DNA Centre.
“It helps reconstruct paleoenvironments in much deeper time, providing insights into environmental change, megafaunal evolution, dispersal and ultimately extinction,” he adds.
The small, round pellets, about the size of an average-sized rabbit's poop offered the scientists a window into a time long past; once the aeDNA was extracted and reassembled, more than 18 mitochondrial genomes were identified. Overall, the scientists detected an incredible range of plants, microbes, insects and animals, including megafauna like woolly mammoths, horses, American cheetahs and steppe bison.
The team identified other rodents and predators, including gray wolves, and more than 200 groups of plants.
One sample uncovered the extent of the Arctic ground squirrels' lineage, with scientists estimating it had been preserved for 700,000 years and was from an ancient species no longer in the Yukon. Its closest relatives are now found in western Siberia.
Present-day Arctic ground squirrels (Urocitellus parryii) are known to be opportunistic feeders with a diverse diet of plants and animals – and it seems their ancestors were very much the same. And, thanks to their hibernation habits, their ancient icy burrows kept their feces intact.
“The Arctic ground squirrels that are in the Yukon today act kind of like pack rats,” says Tyler Murchie, a Hakai Institute paleogenomics researcher and lead author of the paper. “So they’ll go into the landscape, and they’ll collect a whole bunch of different bits of plant material and bones, seeds, and they’ll bring it back to their burrow.”
The poop now opens the door to future discoveries, with the researchers believing that these unassuming droppings preserve aeDNA even better than bones. While some DNA may have come into contact with the droppings at a later point in time, these findings show that permafrost coprolites are nonetheless treasure troves of ancient life.
And the past can also help inform the future.
“We can look at genes under selection due to climate change in the past and that may help us think about how animals today may, or may not, adapt to our current warming climate,” says Poinar.
The research was published in Nature Communications.
Source: McMaster University
