Mammoth migrations

The last woolly mammoths in Siberia weren’t Siberian — they were North American, researchers report in the Sept. 9 Current Biology.

The finding suggests evolutionary biologists need to revise their classical view of mammoth history, says study coauthor Hendrik Poinar, a molecular evolutionary geneticist at McMasterUniversity in Ontario, Canada.

“There was not just one, big mammoth mumbo jumbo all the way across Eastern Europe and throughout Canada,” Poinar continues. Instead, bits of sequenced mitochondrial DNA from 160 mammoth fossils showed that there were two, genetically different mammoth groups, one on “each side of the pond,” he explains. These populations could be two distinct species of mammoth, but scientists need more evidence to confirm this.

Using computer modeling based on the mitochondrial DNA sequences, scientists determined that members of the North American group started to migrate back to its presumed Siberian origins roughly 400,000 years ago. Along the way, the group appears to have broken into two subgroups that crossed the Bering land bridge. The two subgroups then replaced the mammoths that never left Siberia, says Régis Debruyne, a McMasterUniversity molecular ecologist who led the new study.

“It’s an interesting story,” comments Webb Miller of PennsylvaniaStateUniversity in University Park. The story confirms an earlier finding by Miller and colleagues that two distinct woolly mammoth groups roamed Siberia at the same time thousands of years ago.

“We couldn’t explain it,” Miller says about the apparent genetic split. Now, by analyzing many more samples, “an amazing amount,” from both Siberia and North America, he says, “Poinar’s team has started to piece together at least some scenario that would explain that genetic split.”

The scientists used a record number of mammoth samples, Miller says, but did not sequence a substantial number of the DNA base pairs, which leads him to question the study’s conclusions. Still, “it’s nice research, a first step,” he notes.

Determining whether the North American mammoths, climate change, or something else, such as human hunting, caused the Siberian natives to go extinct is a possible next step, Poinar says.

“Right now, all we know is that those native Siberian mammoths basically fell off the face of the planet, and the North American guys just took over,” he says.

That’s also what happened to bison, notes Beth Shapiro, a molecular evolutionary biologist also at PennState.

“That this pattern has now been observed in two different species is pretty exciting,” she says. And, the new study confirms that, rather than hang around in the same place, bison and mammoths seemed to have moved more and to have experienced much more dynamic population changes than expected, Shapiro adds.

Only by pairing traditional fossil studies with analyses of DNA from those fossils, can evolutionary biologists begin to understand how predators, climate and competition within species may have caused these movements and population changes, she says.

And, “a better idea of all of these things can give us a handle on how habitats and communities respond to climate change,” Shapiro says. “We can then use that data to make predictions about what might happen as a consequence of climate change today.”