What Polar Bear Genomes May Reveal About Life in a Low-Ice Arctic

The one of Shapiro Ecology of nature The study also focused on what could have happened to other polar bear genomes during periods of low ice, in this case about 120,000 or 125,000 years ago when, according to Shapiro, Arctic ice levels were similar to the current ones. But here, he looked at the relationship between polar bears and brown bears.

His team built a phylogenetic tree, such as an evolutionary map showing how bears separated from a common ancestor over time, using the genome of Bruno and those of polar bears, brown bears and a black bear that they currently live. (Shapiro was able to use one of Laidre’s Southeast Greenland polar bear genomes in his analyzes, although the time gap between his life and Bruno’s is huge. The set of samples, he says , “100,000 years of evolution are missing.”)

From this and other analyzes, scientists obtained some evidence that about 20,000 years before the birth of Bruno, brown bears and polar bears mixed to generate hybrid offspring. Scientists hypothesized that during this warm period, polar bears may have reached the coast. The carcasses of hunting marine mammals could have attracted rough bears, leading to mating opportunities. As a potential result of this ancient cross, Shapiro says, up to 10 percent of the modern brown bear genome comes from the polar bear’s ancestry.

Finding out how and when polar bears and brute bears mixed, specialized more, or diverged is a difficult task, given the limited fossil record and complexity of evolution. “Evolution is a messy process,” says Andrew Derocher, a polar bear researcher at the University of Alberta who was not affiliated with the studies. He compares the process of evolutionary speciation with a “massive bunch of vines that crawl down the base of a tree,” intertwine, and entangle. “Finally, some of these vineyards could have their own trajectory, and that’s what our species are,” he says. “But in this process, they can cross, they can reconnect and merge, and it’s certainly impossible to separate it, because they’re very interconnected.”

Still, these two studies are related, says Laidre, “in the sense of: where did polar bears persist when the sea ice was low and how?” Research can provide insight into how bears from the past, and bones from southeastern Greenland today, have survived in warmer climates with less ice.

But how genetic changes manifest in physical form and how those changes may have helped bears survive past warming events are still open questions, scientists say. And the results of these studies should not make us feel that the problem of Arctic warming is solved, or that current bears can easily adapt to rapidly declining sea ice levels. “It looks like global warming is happening too fast,” Lindqvist says. He wonders if polar bears “can keep up.”

After all, polar bears depend on seals as a food source, and these depend on sea ice. “There are parts of the Arctic that used to be excellent seal habitats and excellent polar bear habitats,” Derocher says. “But there is no more sea ice there. And as a result, there are virtually no bears. There are very few seals and the ecosystem has basically disintegrated.”

So what could really help? “Global action on climate change,” Laidre says. “This is.”

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