A new analysis of modern dog, wolf and golden jackal genomes suggests that dogs and wolves evolved from a common ancestor between 11,000 and 16,000 years ago (or 9,000-34,000 years ago with mutation rate uncertainty). The study also shows that dogs are more closely related to each other than wolves, regardless of geographic origin.
Eurasian wolf, Canis lupus lupus. Image credit: Jan Nijendijk / CC BY-SA 3.0.
In this study, an international team of researchers from the United States, Israel and five European countries generated the highest quality genome sequences to date from three Gray wolves (Canis lupus): one each from China, Croatia and Israel, representing three regions where dogs are believed to have originated.
The scientists also produced genomes for two dog breeds: a basenji, a breed which originates in central Africa, and a dingo from Australia, both areas that have been historically isolated from modern wolf populations.
In addition to the wolves and dogs, they sequenced the genome of the Golden jackal (Canis aureus) to serve as an outgroup representing earlier divergence.
This image depicts wolf and dog lineages as they diverge over time. Image credit: Freedman AH et al.
“Dog domestication is more complex than we originally thought. 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,” said Dr John Novembre of the University of Chicago, who is the senior author of a paper published in the open-access journal PLoS Genetics.
The analysis of the basenji and dingo genomes, plus a previously published boxer genome from Europe, showed that the dog breeds were most closely related to each other.
Likewise, the three wolves from each geographic area were more closely related to each other than any of the dogs.
Geographic distribution of sampled lineages. Image credit: Freedman AH et al.
“This tells a different story than we anticipated. Instead of all three dogs being closely related to one of the wolf lineages, or each dog being related to its closest geographic counterpart, they seem to have descended from an older, wolf-like ancestor common to both species,” Dr Novembre said.
Dog domestication apparently occurred with significant bottlenecks in the historical population sizes of both early dogs and wolves.
The team was able to infer historical sizes of dog and wolf populations by analyzing genome-wide patterns of variation, and show that dogs suffered a 16-fold reduction in population size as they diverged from wolves. Wolves also experienced a sharp drop in population size soon after their divergence from dogs, implying that diversity among both animals’ common ancestors was larger than represented by modern wolves.
The researchers also found differences across dog breeds and wolves in the number of amylase (AMY2B) genes that help digest starch.
Recent studies have suggested that this gene was critical to domestication, allowing early dogs living near humans to adapt to an agricultural diet.
But the scientists surveyed genetic data from 12 additional dog breeds and saw that while most dog breeds had high numbers of amylase genes, those not associated with agrarian societies, like the Siberian husky and dingo, did not.
They also saw evidence of this gene family in wolves, meaning that it didn’t develop exclusively in dogs after the two species diverged, and may have expanded more recently after domestication.
______
Freedman AH et al. 2014. Genome Sequencing Highlights the Dynamic Early History of Dogs. PLoS Genetics 10 (1): e1004016; doi: 10.1371/journal.pgen.1004016
