Ancient dog cancer still around today after 10000 years

A 10,000-year-old dog burial at the Koster site in western Illinois.    
        
        Del Baston courtesy Center for American Archeology

A 10,000-year-old dog burial at the Koster site in western Illinois. Del Baston courtesy Center for American Archeology

The findings - published this week in the journal Science Advances - were made possible by the first genomic study of ancient dog DNA.

"It's quite incredible to think that possibly the only survivor of a lost dog lineage is a tumour that can spread between dogs as an infection", co-lead author Maire Ní Leathlobhair, a researcher from the Department of Veterinary Medicine at the University of Cambridge, said in a statement.

The new findings reinforce the idea that early human and dog inhabitants of the Americas faced numerous same challenges after European contact, Malhi said. This defies the popular notion that American dogs had evolved from North American wolves.

"This suggest something catastrophic must have happened, but we do not have the evidence to explain this sudden disappearance yet". Scientists found that the ancient dogs came first from Siberia, and that modern American breeds share few common genetic connections.

By comparing the ancient and modern genomes, the researchers confirmed that the earliest American dogs were not descended from North American wolves, but likely originated in Siberia, crossing into the Americas during early human migrations. Bizarrely, their nearly total disappearance means that the closest living relative of these bygone dogs is now CTVT, an opportunistic, sexually-transmitted dog cancer that has hitchhiked around the world at least two times over.

"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", said Kelsey Witt, an author of the study and the one who led the analysis of the sample DNAs.

When they compared it to the genetic makeup of modern pooches, they confirmed what other scientists have long suggested: The first dogs of North America, similar to Arctic dogs like Siberian huskies or Alaskan malamutes, were brought to the continent when people crossed the land bridge that formed between Russian Federation and Canada.

The evolutionary journey of how dogs came to occupy millions of human living rooms is a complicated one, filled with detours and false starts. The domesticated canines probably followed humans across the land bridge connecting Asia and North America. "There were millions and millions of dogs all over the continent (that) died out after the Europeans arrived".

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. They could also be killed purposely by the Europeans like what they did with the indigenous people. He noted that we had only sequenced the nuclear DNA of three other ancient dogs until now.

Oddly enough, scientists found that the closest surviving trace of pre-contact dogs' DNA is found in a sexually transmitted canine cancer. "This cancer has its own genome", Perri said.

The analysis revealed that the pre-contact dogs had not a single genetic link with modern American dogs, neither do they have any genetic similarity with the Chihuahuas, Labradors, and Xoloitzcuintli which are supposedly the famous American dog breeds.

There is a type of cancer called canine transmissible venereal tumours (CTVTs) and this was present, genetically, in the North American dog lineage that is all but extinct except for their tumour cells.