How did dogs get to the Americas? Ancient bone fragment contains clues

The history of dogs is intimately linked, since Antiquity, to that of the humans who domesticated them.

But how far back does this history go in the Americas, and what route did dogs take to enter this part of the world?

A new study by the University of Buffalo provides insight into these questions. Research reports that a bone fragment found in Southeast Alaska belongs to a dog that lived in the area around 10,150 years ago. Scientists say the remains – a piece of femur – represent the oldest confirmed remains of a domestic dog in the Americas.

The DNA from the bone fragment contains clues to the beginnings of dog history in this part of the world.

The researchers analyzed the dog’s mitochondrial genome and concluded that the animal belonged to a line of dogs whose evolutionary history differed from that of Siberian dogs 16,700 years ago. The timing of this split coincides with a period when humans were able to migrate to North America along a coastal route that included southeast Alaska.

The research will be published on February 24 in the Proceedings of the Royal Society B. Charlotte Lindqvist, an evolutionary biologist from UB, was the lead author of the study, which included scientists from UB and the University of South Dakota. The findings add to a growing body of knowledge about dog migration to the Americas.

“We now have genetic evidence from an ancient dog found along the Alaskan coast. Because dogs are an approximation of human occupation, our data not only helps determine when but also indicates when. entry point for dogs and people into the Americas. Our study supports the theory that this migration occurred just as the coastal glaciers retreated during the last ice age, ”says Lindqvist, Ph.D. ., associate professor of biological sciences at UB College of Arts and Sciences. “There have been several waves of dogs that migrated to the Americas, but one question has been: when did the first dogs arrive? And did they follow an ice-free interior corridor between the enormous ice caps that covered the North American continent, or their first migration along the coast? “

“The fossil record of ancient dogs in the Americas is incomplete, so any newly discovered remains provide important clues,” says Flavio Augusto da Silva Coelho, UB Ph.D. student of biological sciences and one of the first authors of the article. “Prior to our study, the first bones of ancient American dogs whose DNA was sequenced were found in the American Midwest.”

A surprise discovery of a large collection of bones

The Lindqvist team did not set out to study dogs. Scientists discovered the femur fragment while sequencing the DNA of a collection of hundreds of bones excavated years earlier in Southeast Alaska by researchers such as Timothy Heaton, Ph.D., professor of earth sciences at the University of South Dakota.

“It all started with our interest in how Ice Age climate changes impacted the survival and movement of animals in this region,” says Lindqvist. “Southeast Alaska could have served as an ice-free stopping point, and now, with our dog, we believe the early human migration through the region could be much greater than some previously suspected.

The bone fragment, originally thought to be from a bear, was quite small, but when DNA was studied, the team realized it was from a dog, Lindqvist says .

After this surprise discovery, scientists compared the mitochondrial genome of bone to that of other ancient and modern dogs. This analysis showed that the Southeast Alaskan dog shared a common ancestor around 16,000 years ago with American dogs that lived before the arrival of European colonizers, Lindqvist says. (Mitochondrial DNA, inherited from the mother, is a small fraction of an organism’s complete DNA, so sequencing a complete nuclear genome could provide more detail if this material can be extracted.)

Interestingly, the analysis of carbon isotopes on the bone fragment indicates that the ancient dog of Southeast Alaska likely had a marine diet, which may have consisted of foods such as fish and the remains of seals and whales.

The research adds depth to the layered story of how dogs came to populate the Americas. As Lindqvist notes, the canines did not come all at once. For example, some Arctic dogs later arrived from East Asia with the Thule culture, while Siberian huskies were brought to Alaska during the Gold Rush. Other dogs were brought to the Americas by European colonizers.

The new study sharpens the debate on the migration of dogs and humans to the Americas.

“Our primitive Southeast Alaska dog supports the hypothesis that the first dog and human migration occurred via the Pacific Northwest Coastal Highway instead of the Central Continental Corridor, which would have become viable. only 13,000 years ago, ”notes Coelho.