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Ancient Wolf Genomes Reveal Ice Age Population Connections, Clues to Origins of Dogs

Ancient Wolf

NEW YORK – By analyzing DNA sequences from ancient gray wolves, an international research team has come closer to revealing the roots of dog domestication, while painting a picture of genetically connected wolf populations that tended to fare well during the Ice Age.

"We can no longer view dogs and present-day wolves as two completely independent evolutionary branches — instead, dogs are to some extent nested within wolf diversity in a more complex way," co-first and co-corresponding author Anders Bergström, a postdoctoral researcher in senior author Pontus Skoglund's group at the Francis Crick Institute's Ancient Genomics Laboratory, explained in an email.

As they reported in Nature on Wednesday, the researchers assessed ancient wolf samples stretching back around 100,000 years from sites in Europe, Siberia, and northwestern North America, generating 66 new genome sequences for ancient wolves and improving coverage for an existing ancient wolf sequence.

"The question of dog origins has remained contentious, and the previous literature contains many different hypotheses for where dogs underwent domestication," Bergström said. "We think that what has been missing is ancient wolf genomes, and that with our new dataset, we are able to make some real progress on this question."

By analyzing these new data alongside five published ancient wolf genomes and new sequences from an ancient dhole canine in the Caucasus that represented an outgroup species, they detected closer genetic ties between domestic dogs and ancient wolves in eastern Eurasia. Even so, the team saw variable relationships between dogs and different wolf populations, consistent with a more complex evolutionary history for dogs than that proposed in the past.

"The widespread ancestry asymmetries observed between wolves and dogs today have been interpreted as reflecting recent, local admixture," the authors noted. "Our findings that dogs have variable proportions of two distinct components of wolf ancestry may provide a unifying explanation for many of these asymmetries."

Although the specific wolf populations giving rise to domestic dogs are yet to be identified, for example, the latest findings suggest that early dogs found in East Asia, Siberia, the Americas, and northeastern portions of Europe tended to have ancestry from "eastern dog progenitor" wolves in eastern Eurasia.

The investigators also uncovered a smaller component of wolf ancestry from western Eurasia — dubbed "western dog progenitor" wolves — in dogs from the Near East and Africa. The western wolf ancestry also appeared to account for 5 percent to one-quarter of Neolithic and later European dog ancestry, they reported.

"[D]ogs in the Near East and Africa derive up to half of their ancestry from a distinct population related to modern southwest Eurasian wolves, reflecting either an independent domestication process or admixture from local wolves," the authors explained. "None of the analyzed ancient wolf genomes is a direct match for either of these dog ancestries, meaning that the exact progenitor populations remain to be located."

When it came to ancient wolf population features and relationships, meanwhile, the team saw signs that the animals fared surprisingly well during the Ice Age, maintaining genetic connections between far-flung populations that made it possible to pick out two dozen genomic regions that have been subjected to natural selection over tens of thousands of wolf generations.

"We show that wolf populations were genetically connected throughout the Late Pleistocene, probably because of the high mobility of wolves in an open landscape," the authors reported, adding that "the reason Pleistocene wolves appear basal to present-day diversity is not that they went extinct, but that continued gene flow homogenized later ancestry."

While the current findings focused on ancient wolf samples from sites where DNA tends to remain preserved relatively well, the researchers noted that future analyses on larger and broader sets of ancient wolf genomes will likely offer more refined views of wolf history, while making it possible to edge closer to seeing specific dog progenitor populations.

"In our study, we were able to reject sampled ancient wolves as being the ancestors of dogs, which means that the regions that we have sampled are unlikely to be the centers of domestication," Bergström explained, adding that "[i]n future studies, we would therefore like to extend our sampling to other regions — including more southernly ones where DNA preserves less well — to hopefully be able to narrow down the origin of dogs further."