Wed July 10, 2013
Barking Up The Family Tree: American Dogs Have Surprising Genetic Roots
Originally published on Wed July 10, 2013 8:58 pm
America is as much of a melting pot for dogs as it is for their human friends. Walk through any dog park and you'll find a range of breeds from Europe, Asia, even Australia and mutts and mixes of every kind.
But a few indigenous breeds in North America have a purer pedigree — at least one has genetic roots in the continent that stretch back 1,000 years or more, according to a new study. These modern North American breeds — including that current urban darling, the Chihuahua — descended from the continent's original canine inhabitants and have not mixed much with European breeds.
"There is ... archaeological and historical evidence that the native peoples of the Americas had dogs," says Peter Savolainen, an evolutionary geneticist at the KTH-Royal Institute of Technology in Stockholm and an author of the new study. When humans first came to the Americas from Asia, they're thought to have brought with them dogs, whose descendants populated North and South America for centuries.
But those dogs didn't fare too well once Christopher Columbus got here. "It's known that most of these dogs were eradicated when Europeans arrived in America," says Savolainen. Pathogens the Europeans brought killed humans and dogs alike, he says.
Any canines that survived are thought to have interbred with European dogs over time. Most researchers have assumed that today's dogs would have little trace of their ancient American ancestry.
To find out if that was indeed the case, Savolainen and his colleagues looked at the mitochondrial DNA of a handful of modern breeds with indigenous origins. Mitochondrial DNA is inherited from the mother and remains relatively unchanged over generations. By looking at the mitochondrial DNA sequence, one can get a peek at the ancient maternal ancestry. "You can go back in time as far as tens of thousands of years," Savolainen says.
He and his colleagues looked in particular at the maternal lineage of the Inuit sled dog, the Alaskan malamute, the Greenland dog, the Chihuahua, the Xoloitzcuintli (Mexican hairless dog), Perro Sín Pelo del Peru (Peruvian hairless dog) and a range of strays from North and South America. The scientists compared the DNA sequences of these dogs with those of hundreds of dogs from Europe and Asia.
Savolainen expected to find a strong European influence on these breeds, but he was surprised.
Except for some of the stray dogs and the Alaskan malamute, "they have very little influence of European dogs in these breeds," he says. "So they have been kept pretty pure."
When he and his team compared the sequences of the relatively unchanged breeds with those of 19 ancient dog sequences found across the two American continents, he was even more surprised. One breed — the Chihuahua — had a portion of DNA that was an exact match to that of an ancient dog.
"We have exactly the same unique DNA type in Mexico 1,000 years ago and in modern Chihuahua," Savolainen says. This suggests that at least this particular breed had genetic roots stretching back before the arrival of Europeans.
In addition, most American breeds in the study had a lot in common with present-day dogs from East Asia, he says. This genetic similarity is because the indigenous American breeds descended from the first dogs that traveled from Asia to the Americas.
Maternal ancestry, of course, can't tell the whole story, Savolainen says, and mitochondria trace the genetic lineage only through mothers.
But the evidence does show many modern North American dogs continue to carry a significant genetic signature from their distant past, he says. And that means that, like distinct languages, they're very much the products of the indigenous human cultures that created the breeds.
"These are [a] remaining part of the indigenous cultures — the Indian and Inuit culture — in America," Savolainen says. "And that makes it more important that these populations ... are preserved."
ROBERT SIEGEL, HOST:
People in North America trace their ancestry back to places all over the world - Asia, Africa, Europe. Many of our canine friends do, too. A new study finds that at least some dogs have been here a very long time.
As NPR's Rhitu Chatterjee reports, some modern breeds may have descended from animals that accompanied the very first groups of people who migrated from Asia to America.
(SOUNDBITE OF A BARKING DOG)
RHITU CHATTERJEE, BYLINE: A quick visit to a dog park can tell you a lot about American dogs. When I visit Lincoln Park in Washington, D.C., there are a range of breeds running around.
UNIDENTIFIED WOMAN #1: Teddy, (unintelligible).
CHATTERJEE: There are the popular purebreds, like this beautiful white labrador retriever.
UNIDENTIFIED WOMAN #1: Come here, buddy.
CHATTERJEE: And then there are mixed breeds, like Lola.
UNIDENTIFIED WOMAN #1: She is a Schnoodle, a schnauzer-poodle mix.
CHATTERJEE: But these dog breeds are relatively recent arrivals. Peter Savolainen is an evolutionary geneticist at the KTH-Royal Institute of Technology in Sweden. He says there've been dogs in America for far longer.
PETER SAVOLAINEN: There is both archaeological and historical evidence that the native peoples of America had dogs.
CHATTERJEE: He's the lead author of the new study published this week in the British journal Proceedings of the Royal Society B. No one really knows what happened to these ancient dogs. Some must have interbred with all the European dogs that came later. Savolainen wanted to know if any of the ancient dog genes could still be found in modern American dogs. To find out, he and his team decided to look at mitochondrial DNA. Now, that's the DNA inherited only through the mother and changes very little across generations.
SAVOLAINEN: And this means that you can go back in time as far as tens of thousands of years.
CHATTERJEE: They analyzed samples from several of the most traditional types of dogs in North and South America.
SAVOLAINEN: Inuit sled dogs, Greenland dog, Alaskan Malamute, Chihuahua, Mexican hairless dogs, and Peruvian hairless dogs.
CHATTERJEE: All these dogs are associated with cultures that go back way beyond the arrival of Europeans. And when they compared their DNA with that of dogs in Europe, they were very surprised.
SAVOLAINEN: These breeds are indeed almost pure indigenous breeds. They have very little influence of European dogs.
CHATTERJEE: Then they compared the modern dog DNA with that of ancient dogs found in archaeological sites in Alaska and South America. And in the case of the Chihuahua, they found a close match.
SAVOLAINEN: So, we have exactly the same unique DNA type in Mexico 1,000 years ago and in modern Mexican Chihuahua.
CHATTERJEE: They also found that most of these indigenous dogs had a strong genetic resemblance to present day East Asian dogs. Now, he admits that the picture may get more complicated if one looks at the paternal side of inheritance. But he says his findings do show a direct connection between some modern American breeds and the very first dogs that migrated to the Americas from Asia. Adam Boyko of Cornell University College of Veterinary Medicine agrees.
ADAM BOYKO: Gives us sort of the clearest picture to date as to, you know, whether or not we see any contribution of pre-Columbian Native American dogs in today's dogs.
CHATTERJEE: He says it also shows why scientists should look beyond recognized breeds for signs of ancient DNA. The team also looked at the DNA of feral dogs.
BOYKO: There is a significant component of genetic diversity retained in these semi-feral street dog populations, as well as indigenous breed populations.
CHATTERJEE: And studying that genetic diversity, he says, may tell us more about the history of dogs in America. Rhitu Chatterjee, NPR News. Transcript provided by NPR, Copyright NPR.