A collection of over 40,000 trees in rural Utah is the world’s largest single organism, having all descended from a single seedling. But that’s not all: According to a team of researchers, the grove—collectively known as Pando—may also be the world’s oldest living organism.
Though it consists of over 40,000 individual trees, Pando is a single organism that originated from a single seed. Exactly when that seed sprouted, though, remains up in the air. According to a team that recently estimated the organism’s age, Pando is between 16,000 to 80,000 years old. In other words, sometime between the glaciers receding from Manhattan and the last time the Tsuchinshan-ATLAS comet passed through Earth’s skies, a seedling in what would become Utah began to form Pando. The team’s research on Pando is not yet peer reviewed and is hosted on the preprint server bioRxiv.
The grove that constitutes Pando is the largest, most dense organism yet known, clocking in at nearly 13 million pounds (5.9 million kilograms) and covering 106 acres (43 hectares), according to the U.S. Forest Service. Based on the recent research, Pando may have already been 40,000 years old when Neanderthals disappeared from the fossil record about 40,000 years ago.
“We studied a very iconic organism, whose size has made us wonder about its evolution in time and space,” said Rozenn Pineau, a researcher at the University of Chicago and lead author of the study, in an email to Gizmodo. “We expected close trees in space to be more closely related genetically. We find that that is the case, but to a much lower extent than we were expecting.”
To approximate the age of the clone, the research team genetically sequenced over 500 samples from Pando and its neighbors. The team sampled a range of tree tissues including leaves, roots, and bark, and sorted somatic mutations of the clone from germline mutations. Germline mutations occur in a parent’s reproductive cells and are inherited, while somatic mutations are changes to DNA that occur after conception of a cell. These random mutations occur over the course of an organism’s life, and the rate of these mutations allowed the team to calculate the grove’s approximate age.
“Clonally reproducing organisms may also achieve exceedingly long lifespans, making somatic mutation an important mechanism of creating heritable variation for Darwinian evolution by natural selection,” the research team wrote in the paper. “Yet, little is known about intra-organism mutation rates and evolutionary trajectories in long-lived species.”
The researchers made phylogenetic models that described how mutations were introduced into the Pando clone over time, giving them an age range for the ancient grove. The team clocked Pando’s age somewhere between 16,000 years old and 80,000 years old—an admittedly wide range, though one that is corroborated by the presence of aspen pollen in sediment samples taken from the nearby Fish Lake.
“Despite root spreading being spatially constrained, we observed only a modest positive correlation between genetic and spatial distance, suggesting the presence of a mechanism preventing the accumulation and spread of mutations across units,” the team wrote in the paper. In other words, even though Pando’s roots are limited in terms of spread, its genetic makeup is surprisingly uniform. Some unknown process appears to be limiting mutations from piling up across the grove, the researchers suggest.
“To take into account uncertainty in the mutation calling step, we explored three scenarios, and this is why our range for the age is so wide,” Pineau added. “It is very much possible to come to a narrower window. Indeed, colleagues at UC Berkeley are currently working on getting higher resolution genetic data to help narrow down this window.”
According to the Forest Service, Pando is in decline due to browsing by ungulates including deer, and attacks from bark beetles and disease. Foresters are working to encourage Pando to sprout new trees, lest this ancient living marvel go the way of the dodo. Or the woolly rhino. Or the mammoth. Or any other species that existed alongside Pando, but did not manage to outlive it.
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