Published: Mon, July 09, 2018
Medical | By

America's first dogs vanished after Europeans arrived, study finds

America's first dogs vanished after Europeans arrived, study finds

Researchers have still not been able to fully pinpoint the exact reasons for their disappearance, and it is something which may remain shrouded in mystery pending further research, but modern American dog populations have nearly nothing in common with their descendants - except one, the canine transmissible venereal tumor (CTVT), a sexually transmitted form of cancer that has spread globally.

The results seem to undercut the popular narrative that breeds such as chihuahuas are descended from ancient American dogs, since their mitochondrial DNA had less than two per cent in common with the ancient dogs in this study.

Researchers from around the globe collaborated to compare sequences of mitochondrial DNA from 71 ancient specimens of North American and Siberian dogs, as well as nuclear DNA from a further 7 sets of remains. These dogs thrived for thousands of years, but mostly vanished after contact with Europeans.

"By looking at genomic data along with mitochondrial data, we were able to confirm that dogs came to the Americas with humans, and that almost all of that diversity was lost - most likely as a result of European colonization", coauthor Kelsey Witt, a graduate student who led the mitochondrial DNA testing, says in a press release from the University of IL.

Benjamin Sacks, a mammalian genetics professor at the University of California, Davis, who was not part of the research, said that while the ideas proposed in the study aren't new, "this study used the most extensive ancient and modern dog DNA sample to date ... to conclusively confirm" these hypotheses. "We suspect that a lot of the reasons [ancient] dogs were wiped out, were similar reasons that Native American populations were destroyed", Perri said. "There were millions and millions of dogs all over the continent (that) died out after the Europeans arrived".

Preserved in every single CTVT tumour is ancient DNA from the long-dead founder.

Instead, the dogs form a monophyletic lineage that likely originated in Siberia and dispersed into the Americas alongside people.

But it was the European wave of immigrants that spelled doom for American dogs, the study found. Perri said historical accounts suggest various possibilities for the demise.

An analysis of the DNA of these ancient dogs revealed that they had unique genetic signatures never found from any other dog breed at present, not even from any other breeds around the world.

Looking closely at the analysis of the genomes, the researchers discovered that the ancient dogs died out when Europeans colonized the Americas. Although there is intriguing evidence that during this time these dogs interbred with wild canids endemic in North America, like coyotes and grey wolves. The ethnographic records and hard evidence suggests they were the constant companion of the Indigenous populations of North America, and yet, very little trace of them exists today in the genomes of modern dogs. "Although this cancer's DNA has mutated over the years, it is still essentially the DNA of that original founder dog from many thousands of years ago".

"I just find it really surprising, " says geneticist Elinor Karlsson from the University of Massachusetts Medical School in Worcester, who did not participate in the study. If that happens, she added, researchers can "work our way further back in time".

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