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Ancient Wolf Study Points to Early Split Between Wolf, Dog Lineages

NEW YORK (GenomeWeb) – An American and Swedish team has found new genomic evidence for an earlier split between wolves and domestic dogs than was previously envisioned.

As they reported online today in Current Biology, the researchers sequenced mitochondrial and genomic DNA from the 35,000-year-old remains of an ancient wolf, known as Taimyr 1 that was discovered in northern Siberia's Taimyr Peninsula.

By comparing these sequences to those from ancient and living wolves and dogs, the team found clues that the Taimyr 1 wolf belonged to a lineage that diverged from the ancestors of dogs and existing wolves at roughly the same time that dog and wolf lineages split from each other.

If so, that would put the start of dog domestication as far back as roughly 27,000 to 40,000 years ago, the study's authors explained.

"[O]ur results provide direct evidence for a longer timescale for the divergence of the dog and wolf lineages than previously assumed, and thus suggest that dogs may have originated much earlier than commonly accepted," senior author Love Dalén, a bioinformatics and genetics researcher at the Swedish Museum of Natural History, and colleagues wrote.

Though the gray wolf is widely regarded as domestic dogs' closest living relative, there has been much debate over when the lineages split, the researchers noted. According to some recent analyses of wolf and dog genomes, the lineages likely diverged after the last Ice Age, sometime within the last 16,000 years.

Still, such dating events encompass mutation rate uncertainty. And archaeological evidence hints that canines with features resembling domestic dogs may have been around as far back as 36,000 years ago.

In the latest attempt to unravel the timing of dog domestication — as well as the wolf population(s) involved — researchers took advantage of an ancient wolf rib bone that had been radiocarbon dated to around 34,900 years old.

Using the Illumina HiSeq instrument, Dalén and his team sequenced DNA libraries from the Taimyr 1 wolf to produce one-fold coverage of its genome, on average, and 182-fold average coverage of the mitochondrial genome.

To assess the Taimyr 1 wolf's relationship to other canines, the team considered these sequences in the context of previously sequenced dogs and wolves, including mitochondrial DNA sequences from ancient canine samples found in Europe and the New World.

When they put together phylogenetic models and mutation rate estimates that fit all of this available sequence data, the researchers saw a three-way split between the Taimyr 1 wolf group, dogs, and other wolves that took place between 27,000 and 40,000 years ago.

Co-corresponding author Pontus Skoglund, a genetics and archeology researcher affiliated with Harvard University, the Broad Institute, and Stockholm University, pointed out that early domestication may have involved yet-to-be-tamed wolves that ran in parallel with humans for long stretches prior to domestication as we know it.

He and his colleagues also noted that the data could conceivably fit with more recent dog domestication, but only under a model that assumes a large proportion of domestic dog ancestry from an extinct or untested wolf population.

In a study published in PLOS Genetics last year, an international team led by investigators in the US sequenced gray wolves from three proposed sites of dog domestication. Because the investigators did not see closer-than-usual ties to domestic dogs in any of these wolf populations, they argued that domestic dogs might have arisen from a yet-unknown wolf population.

On the other hand, authors of the current analysis concluded that domestication was likely a lengthy process that involved multiple events — a notion supported by the higher-than-usual proportion of Taimyr 1 wolf sequences in breeds such as the Siberian husky or Greenland Sledge dog.

Dalen, Skoglund, and colleagues estimated that roughly 3.5 percent of the ancestry in the Greenland Sledge dog came from the ancient Siberian wolf group, for example, though the proportion of sequences may be as broad as 1.4 percent to around 27 percent.

Based on such findings, they argued that "the ancestry of present-day dogs is derived from multiple regional wolf populations."