How did dogs get to America? Old bone fragment contains clues
The history of dogs since ancient times has been intertwined with that of the people who domesticated them.
But how far back does this story go in America and how did dogs enter this part of the world?
A new study from the University of Buffalo provides insight into these questions. The research reports that a bone fragment found in Southeast Alaska belongs to a dog who lived in the area about 10,150 years ago. Scientists say the remains – a piece of a femur – represent the oldest confirmed remains of a domestic dog in America.
DNA from the bone fragment contains clues to early canine history in this part of the world.
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The researchers analyzed the dog’s mitochondrial genome and came to the conclusion that the animal belonged to a line of dogs whose evolutionary history differed from that of the Siberian dogs as early as 16,700 years ago. The time of this split coincides with a time when people may have immigrated to North America along a coastal route that included southeast Alaska.
The research was published in the Proceedings of the Royal Society on February 24. B. Charlotte Lindqvist, a UB evolutionary biologist, was lead author on the study, which included scientists from UB and the University of South Dakota. The results contribute to a growing knowledge of the migration of dogs to America.
“We now have genetic evidence from an old dog found on the Alaskan coast. Since dogs are a proxy for people’s employment, our data provides not only a point in time but also a place for dogs and people to enter America. Our study supports the theory that this migration occurred precisely when the coastal glaciers retreated during the last Ice Age, ”says Dr. Lindqvist, Associate Professor of Life Sciences at the UB College of Arts and Sciences. “There have been several waves of dogs immigrating to America, but one question was when the first dogs would arrive. And did they follow an inner ice-free corridor between the massive ice sheets that covered the North American continent, or was it their first migration along the coast? “
“The fossil record of ancient dogs in America is incomplete, so any new remains found provide important clues,” says Flavio Augusto da Silva Coelho, a UB PhD student in life sciences and one of the first authors of the paper. “Before our study, the earliest ancient American dog bones were found in the American Midwest and their DNA had been sequenced.”
A surprising finding from a large collection of bones
Lindqvist’s team did not set out to examine dogs. Scientists came across the femoral fragment while sequencing DNA from a collection of hundreds of bones excavated years earlier in Southeast Alaska by researchers such as Timothy Heaton, PhD, professor of earth sciences at the University of South Dakota.
“It all started with our interest in how climate changes during the Ice Age affected the survival and movements of animals in this region,” says Lindqvist. “Southeast Alaska could have served as some sort of ice-free breakpoint, and now – with our dog – we think early migration of people through the region may be a lot more important than some previously suspected.”
The bone fragment, which was originally believed to have come from a bear, was quite small, but when the DNA was examined, the team found it came from a dog, Lindqvist says.
Photo credit: Bob Wilder / University of Buffalo
After this surprising discovery, the scientists compared the mitochondrial genome of the bone with those of other ancient and modern dogs. That analysis showed that about 16,000 years ago, the Southeast Asian dog shared a common ancestor with American dogs that lived before the arrival of European colonizers, Lindqvist says. (Mitochondrial DNA inherited from the mother represents a small fraction of the total DNA of an organism. Sequencing a complete nuclear genome could therefore provide further details if this material can be extracted.)
Interestingly, the carbon isotope analysis of the bone fragment reveals that the ancient Southeast Alaska dog likely had a marine diet that may have consisted of foods like fish and remains of seals and whales.
The research adds depth to the complex story of how dogs came to America. As Lindqvist notes, canines did not arrive all at once. For example, some Arctic dogs later arrived from East Asia with the Thule culture, while Siberian Huskies were imported into Alaska during the gold rush. Other dogs were brought to America by European colonizers.
The new study sharpens the debate over the migration of dogs and humans to America.
“Our early Southeast Alaska dog supports the hypothesis that the first migration of dogs and humans was via the coastal route in the northwest Pacific rather than the central continental corridor, which is believed to have only become viable about 13,000 years ago.” notes Coelho.
The research was funded by the National Science Foundation. In addition to Lindqvist, Coelho and Heaton, Stephanie Gill and Crystal Tomlin were among the authors of the new paper in Proceedings of the Royal Society B.