Frozen squirrel poop is doing serious scientific work in Yukon permafrost.
A study published in Nature Communications found Arctic ground squirrel coprolites, preserved in deep permafrost, held an unusually rich collection of ancient DNA dating from about 30,000 to 700,000 years ago. Researchers analysed 13 permafrost samples spanning several glacial periods and found DNA from plants, insects, microbes and animals, including hares, bison, horses and mammoths.
The study says Arctic ground squirrels are “opportunistic feeders”. In a statement, lead author Tyler Murchie said the squirrels, much like pack rats, collect a “whole bunch” of plant material, bones and seeds as they prepare for hibernation that can last up to seven months.
“They have little latrine areas and tunnel networks and caches of food,” Murchie told Science News.
Researchers said they had not previously thawed and tested the rabbit-dropping-sized coprolites with advanced DNA analysis because the material degrades easily. Murchie told Science News he expected the DNA would “mostly just be the squirrel plus their gut microbiome.”
Instead, the sequencing turned up a much broader record of ancient life. A detailed classification of the DNA produced 18 unique mitochondrial genomes, which the team is compiling in a separate forthcoming report.
According to the study, some DNA linked to gray wolves or a big cat may reflect squirrels feeding on the carcass of a predator. The paper also warned that some genetic matches may be less conclusive because of limited available datasets for ancient animal DNA.
The droppings also revealed previously unknown genetic diversity among the squirrels, including one lineage that now lives far from the Yukon.
In a statement, co-senior author Hendrik Poinar, an evolutionary geneticist at McMaster University in Canada, said the material “helps reconstruct paleoenvironments in much deeper time, providing insights into environmental change, megafaunal evolution, dispersal, and ultimately extinction”.
The team said the poop fossils “appear to preserve ancient DNA even better than bones or surrounding permafrost.”
“Science is sometimes at its best when it takes something ordinary, weird, or even funny and shows that it contains a much larger story,” Murchie told Popular Science.
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