Polar Bears Could Turn Brown, And They’ve Done It Before

The polar bear’s backstory may not be exactly what we thought, and the iconic snow-white predator may be getting browner. And it isn’t the first time. A study released on Thursday in PLOS Genetics tracked the DNA of various arctic bear species including the enigmatic brown bears of Alaska’s so-called ABC Islands.

The team, led by University of California Santa Cruz researchers, said that the bears on Admiralty, Baranof, and Chicagof Islands clearly look and act like modern brown bears. However, they share an unusual amount of DNA with their close relatives, the polar bears.

UC Santa Cruz’s Beth Shapiro, one of the authors of the study, explained that the ABC brown bears have 6.5 percent of their X chromosome from polar bears, while only 1 percent of their other genes come from a polar bear ancestor. In other words, they share a lot more DNA from polar bear females than from males.

Also it’s clear that the bears’ ancestors were hybrids, allowing the reseachers to work out what happened to create the population. They theorize that the ABC islands were inhabited by polar bears at the peak of the last ice age. As the climate warmed up and the ice retreated, they were thenleft stranded on the islands or nearby ice floes.

The brown bears, mostly young male bears in search of their first territory, would push north as warmed lands opened in that direction. The young males would seek out healthy young females to be their mates — even though the available females would not be of their species.

Over time, the ABC island bears would be transformed into a population of brown bears that still had a rich heritage of DNA from their polar bear mothers.

The end of the ice age was a natural change and left habitat in the high arctic for the polar bears. But more recent climate change is threatening even that.

We know that polar bears will hybridize with other bears in the wild if they meet. Public awareness got a jolt in 2006 when hunter Jim Martell shot a bear in Canada’s Northwest Territories that DNA analysis proved to be the first known wild polar bear and grizzly bear hybrid.

Since then, the so-called pizzlies or grolar bears have been reported in growing numbers. Some observers have expressed concern that the possible hybrids might not be fertile, threatening both species.

However, the new study from the ABC islands strongly suggested that brown bear/polar bear hybrids are in fact perfectly capable of reproducing themselves and handing down their mixed heritage.

Animal lovers have to ask: If the Arctic continues to warm, will the beloved polar bear turn brown?

[top photo polar bear family courtesy Scott Schliebe and Wikipedia]
[swimming polar bear photo by Elaine Radford]