January 17, 2014
Dog-Wolf Family Tree More Complex Than Scientists Thought
Brett Smith for redOrbit.com - Your Universe Online
According to popular belief, all of today’s dog breeds are descended from wolves domesticated thousands of years ago. However, a new study published on Thursday in PLOS Genetics has found that today’s dogs are more closely related to each other than they are to wolves – an indication that dogs were domesticated after they diverged from wolves.
"Dog domestication is more complex than we originally thought," said study author John Novembre, associate professor of human genetics at the University of Chicago. "In this analysis we didn't see clear evidence in favor of a multi-regional model, or a single origin from one of the living wolves that we sampled. It makes the field of dog domestication very intriguing going forward."
To reach their findings, the international team generated high quality genome sequences from three gray wolves: one each from China, Croatia and Israel. The team chose these regions because they are thought to be where dogs originated. The researchers also sequenced genomes for two dog breeds: a basenji, which came out of central Africa, and an Australian dingo, from regions that have been historically isolated from modern wolf populations. Geneticists working on the study also sequenced the genome of a golden jackal as an 'outgroup' of earlier canine divergence.
The basenji and dingo genomes, as well as a European boxer genome from a previous study, were found to be most closely related to each other even though they originated in disparate lands. The three wolves from each geographic area were also more closely related to each other than to any of the domestic dog breeds.
Novembre said he was surprised to see that each dog is not most closely related to its nearest geographic counterpart – for example, the basenji and the Israeli wolf. Instead, both dogs and wolves seem to come from an older ancestor common to both species.
"One possibility is there may have been other wolf lineages that these dogs diverged from that then went extinct," he said. "So now when you ask which wolves are dogs most closely related to, it's none of these three because these are wolves that diverged in the recent past. It's something more ancient that isn't well represented by today's wolves."
The study team also found that genetic exchange across canid species is more pervasive than previously believed.
"If you don't explicitly consider such exchanges, these admixture events get confounded with shared ancestry," said study author Adam Freedman, a postdoctoral fellow at UCLA. "We also found evidence for genetic exchange between wolves and jackals. The picture emerging from our analyses is that these exchanges may play an important role in shaping the diversification of canid species."
The team also found major bottlenecks in the historical population sizes of both early dogs and wolves. By analyzing patterns of deviation, the team discovered that both dogs and wolves had a significant drop in population size as they diverged from each other, suggesting that diversity among the animals' common ancestors was greater than that seen in modern wolves.
Novembre said the study conveys a multifaceted picture of early canine domestication.
"We're trying to get every thread of evidence we can to reconstruct the past," he said. "We use genetics to reconstruct the history of population sizes, relationships among populations and the gene flow that occurred. So now we have a much more detailed picture than existed before, and it's a somewhat surprising picture."