Wolves survived the Ice Age as a single global population

Wolves survived the Ice Age as a single global population

Image of a single wolf.
Enlarge / An eastern gray wolf is a mix of Siberian ancestry and coyote DNA.

Man’s best friend was the first of many animals man domesticated. But there was no clear before and after moment when dogs were suddenly a separate population from wolves. While some ancient skeletons are clearly dogs, there are plenty of ambiguous skeletons before that. It is possible to get an idea of ​​what happened using the genomes of modern and ancient dogs. But this analysis is highly dependent on what you think the wolf populations the dogs came from look like.

Now researchers have generated a much clearer picture of the last 100,000 years of wolf evolution. The picture it paints is of a population that has remained a single unit despite being spread across the Arctic continents, with the population sporadically refreshing from a core centered in Siberia. Many dog ​​breeds seem to originate from an East Asian wolf population. But others seem to have also received a significant contribution from a population in the Middle East, but it is not clear whether this population was wolves or dogs.

Wolves around the north

The ability to sequence ancient DNA was key to this new work, which involved obtaining DNA from 66 wolf skeletons that collectively span around 100,000 years of evolution, including most of the last ice age. Wolves are found in the Northern Hemisphere, and the skeletons used here tend to be closer to the Arctic (probably in part because DNA survives better in colder climates). But they are widely distributed, with Europe, Asia and North America represented. The researchers also included five ancient wolf genomes that others had analyzed, as well as some modern wolf genomes.

Typically, you’d expect to find regional populations that don’t mingle often with their more distant relationships. If you map the most closely related genomes, you will usually find that they cluster together. That’s not the case here; instead, ancient wolf genomes clustered together over time. That is, a given wolf was more likely to be closely related to other wolves living around the same time, no matter where those wolves lived on the planet.

Studies of modern wolves have indicated that local populations expanded after the last peak of the last Ice Age. But all of these populations are more similar to each other than the wolves around before the peak of the Ice Age.

How did these animals retain genetic continuity over the immense distances that separated them? Apparently, by repeated population expansions in Siberia. There was a distinct European population of wolves somewhere before 100,000 years ago. But continued arrivals from Siberia have gradually reduced the ancestral European presence by between 10 and 40 percent, depending on the animal. In North America, on the other hand, all current wolves are mainly from Siberia, the rest being a contribution from interbreeding with coyotes.

One of the consequences of having a global population is that favorable mutations spread rapidly around the world. The researchers found 24 areas of the genome that appear to carry useful adaptations, and all of these useful stretches of DNA appear in all wolf populations examined.

Gone to the dogs

So what about dogs? They also resemble the Siberian wolves that were alive just before the last peak of the Ice Age. But when all wolves older than that point were tested for a close relationship with dogs, the connection was not strong. This suggests that if dogs came from a specific wolf population, we don’t have DNA from that population.

But the researchers found there was a good match if you had a population of mostly Siberian wolves with a fraction of its DNA (between 10 and 20 percent) coming from a different canid, the dhole, which happens to be also in Asia. Some East Asian dog breeds appear to have retained this ancestry to the present day.

But other breeds in Europe and Africa seem to have a large contribution from a wolf population that is more closely related to a current wolf from Syria. Researchers estimate that a Middle Eastern dog from about 7,500 years ago had about half of its genome from this local source and the other half from Siberian ancestors. Many dogs in Africa and Europe have between 20 and 60% of their genomes from this additional ancestor.

Overall, their data favors a model where dogs were first domesticated in East Asia, where most of the breeds present are solely descended from Siberian ancestors. But as our best friend spread across Asia with us, he came into contact with another population, probably close to the Middle East. This population could have been wolves, could have been a population of dogs that had been domesticated separately, or it could have been somewhere in between – there’s no way to tell with genetic data.

In any case, the wolf data provides context for why dog ​​ancestry has been so difficult to sort out: Genetically, wolves are unique in having a worldwide population that is regularly increased by a way that disrupts long-term stable regional populations. . One consequence of this is that there is little point in researching a wolf population to which the dogs are closely related to identify where the dogs were domesticated. Even if this population of wolves existed at the time, it would likely end up mixing with other populations soon after.

Nature2022. DOI: 10.1038/s41586-022-04824-9 (About DOIs).

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