NEW YORK (GenomeWeb News) – African village dogs are just as genetically diverse as dogs from East Asia, according to a study appearing online last night in the Proceedings of the National Academy of Sciences, suggesting dogs may not have been domesticated in East Asia as previously believed.
An international research team led by Cornell University computational biologist Carlos Bustamante compared DNA samples from hundreds of African village dogs with samples from Puerto Rican street dogs, and mixed breed dogs from the US. They also drew on information from breed dog genetic studies. Their results suggest that the overall genetic diversity in African dogs is about as high as that reported for East Asian dogs, raising questions whether dog domestication occurred in East Asia or elsewhere.
"I was surprised that there was as much genetic diversity in Africa as we saw," lead author Adam Boyko, a research associate in Bustamante's lab at Cornell, told GenomeWeb Daily News.
Past research indicates that dogs descended from Eurasian wolves between 15,000 and 40,000 years ago, subsequently spreading through Eurasia and into Africa, the Americas, and Oceania. For example, a mitochondrial DNA study published in Science in 2002 found that East Asian dogs had greater genetic diversity than dogs tested elsewhere, suggesting dogs were domesticated somewhere in East Asia. But the new paper by Boyko and his co-workers suggests that may not have been the case.
"We always thought it would be interesting to try to look at domestication," Boyko said.
The team got that opportunity partly by chance, he explained, when his brother and sister-in-law — co-authors Ryan Boyko and Corin Boyko, anthropologists at the University of California at Davis — expressed interest in going to Africa for their honeymoon. The pair was soon collecting dog blood samples in villages across Africa. In exchange, Bustamante funded part of the trip.
Altogether, the researchers assessed DNA samples from 318 dogs living at seven sites in Egypt, Uganda, and Namibia. They typed 206 of these dogs on 89 microsatellite markers or 300 SNP markers, along with 15 Puerto Rican street dogs and two mixed-breed dogs form the US.
Because village dogs — semiferal, indigenous dogs that depend on humans — are under less selection than breed dogs, Boyko and his co-authors explained, their genetics provide clues about dog population history.
The researchers identified five different dog groups: one representing Egyptian dogs, one comprised of dogs on Uganda's mainland, another containing dogs from Uganda's Kome Island, one that included dogs from Northern Namibia, and a final group representing admixed dogs (including those in Puerto Rico, the US, central Namibia, and a few other African locations).
Overall, the African village dogs appeared to have high genetic diversity, while the dogs from shelters in Puerto Rico were genetically indistinguishable from US mixed-breed dogs and dogs in central Namibia, Boyko said.
The team also compared their findings with microsatellite, mitochondrial DNA, and SNP data for hundreds of dogs from 126 breeds, including Afghan hounds, Basenjis, Pharaoh hounds, Rhodesian ridgebacks, and Salukis (considered African breeds).
Among African breeds, Basenjis grouped with Northern Namibian and Ugandan village dogs, while Afghan hounds and Salukis grouped with Egyptian dogs. Pharaoh hounds and Rhodesian ridgebacks, on the other hand, grouped more closely with mixed breed dogs, Boyko said, suggesting these breeds might have been reconstituted outside of Africa.
When the team sequenced 680 base pairs of mtDNA, they found 47 mitochondrial haplotypes among the African village dogs tested and nine haplotypes for the Puerto Rican street dogs. And overall, the mitochondrial diversity detected in the African dogs was similar to that previously observed in East Asian dogs, the researchers noted.
"Surprisingly, we find similar mtDNA haplotype diversity in African and East Asian village dogs, potentially calling into question the hypothesis of an East Asian origin for dog domestication," they wrote.
The team isn't suggesting that dogs were domesticated in Africa. Since there are no gray wolves on the continent, Boyko explained, that explanation is fairly unlikely. Rather, those involved say scientists should re-think the East Asian dog domestication notion.
"Although we do not suggest that Africa is actually the site of dog domestication, we do believe that an East Asian origin of dogs should be further scrutinized," they wrote.
The team plans to continue exploring the origins of various dog breeds and dog domestication by expanding their sampling to Europe, the Middle East, and Asia. Ryan and Corin Boyko are presently collecting samples in Papua New Guinea.
Mitochondrial sequence data from the current study has been deposited into GenBank. In addition, samples collected for the project have been added to Cornell's biobank. Information on the Village Dog Genetic Diversity Project is available online.