Newswise — ITHACA, N.Y. — Dogs were domesticated between 9,000 and 34,000 years ago, most likely while humans were still hunting and gathering – before the advent of agriculture, according to an analysis of individual genomes of modern dogs and gray wolves.
Cornell University researchers Ilan Gronau, Adam Boyko, Adam Siepel and an international team of researchers published their report in PLOS Genetics, Jan. 16. The researchers studied genomes of three gray wolves, one each from China, Croatia and Israel – all areas thought to be possible geographic centers of dog domestication. They also studied dog genomes from an African basenji and an Australian dingo; both breeds come from places with no history of wolves.
Their findings revealed the three wolves were more closely related to each other than to any of the dogs. Likewise, the two dog genomes and a third boxer genome resembled each other more closely than the wolves. This suggests that modern dogs and gray wolves represent sister branches on an evolutionary tree descending from an older, common ancestor. The results contrast with previous theories that speculated dogs evolved from one of the sampled populations of gray wolves.
“This is an incredibly rich new dataset, and it has allowed us to carry out the most detailed analysis yet of the genetic history of dogs and wolves,” said Adam Siepel, associate professor of biological statistics and computational biology at Cornell and a co-author of the paper. “There are still many open questions, but this study moves the ball forward,” Siepel added.
Computer methods for analyzing complete genome sequences developed by Ilan Gronau, the paper’s second author and a postdoctoral associate in Siepel’s lab, played a key role in the collaboration. Gronau’s computer program, called G-PhoCS, was previously applied with success in a 2011 Nature Genetics study of early human history and demographics.
In this case, G-PhoCS provided a detailed picture of the demographic changes that occurred during the divergence of dogs from wolves. The analysis revealed that domestication led to sizable pruning in population of early dogs and wolves. Dogs suffered a sixteenfold cut in population size as they diverged from an early wolf ancestor. Gray wolves also experienced sharp drops in population, suggesting that the genetic diversity among both species’ common ancestors was larger than represented by dogs and modern wolves. In addition, there was considerable gene flow between dogs and wolves after domestication. Accounting for gene flow was a major challenge in the analysis, and Gronau’s research on this topic proved valuable in obtaining an accurate model of canid demography.
The picture emerging from this study will allow researchers to better interpret genetic differences observed between dogs and wolves and to identify differences driven by natural selection. “This paper sets the stage for the next step in the study of dog domestication that tries to determine the genetic changes that enabled this amazing transformation,” Gronau said.
The study’s senior authors included geneticists John Novembre at the University of Chicago and Robert Wayne at the University of California, Los Angeles. Adam Freeman, a postdoctoral fellow at UCLA, was the paper’s first author. The study was funded by various sources, including the National Science Foundation, National Institutes of Health and Life Technologies.
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