Just 70,000 Years Ago, Polar Bears Diverged From Brown Bears And Developed Key Characteristics To Help Them Survive In Harsh Arctic Conditions
As recently as 70,000 years ago, polar bears developed key features to help them survive in extreme arctic conditions.
A team of molecular biologists from the University of Copenhagen in Denmark analyzed the genomes of three groups of bears—modern polar bears, modern brown bears, and fossilized remains of polar bears—to determine how they evolved to have certain adaptations, such as white fur and the ability to live off of a diet high in cholesterol.
Polar bears have two layers of fur to keep them warm and dry. The first is a large, downy undercoat, and the other is an overcoat made of longer hairs that act like a raincoat. Brown bears, on the other hand, only have one layer of fur.
Polar bears can also digest high amounts of cholesterol from meat containing a lot of blubber. They can thrive while eating seals and even some whale species like belugas. But if brown bears ate such a diet, they would develop heart disease and die at an early age.
Previous research has shown that polar bears are closely related to brown bears, but until now, it has not been clear when the two species diverged.
The scientists believe that polar bears and brown bears diverged within roughly the past one million years.
In the study, they compared the genomes of 119 modern polar bears, 135 modern brown bears, and two fossilized remains of polar bears to learn more about when they diverged from each other.
One of the fossilized polar bears helped the team pinpoint the divergence. The first fossil was a Poolepynten jawbone from the Norwegian archipelago of Svalbard.
It dates back between 130,000 and 100,000 years ago. The other fossil was the skull of a juvenile polar bear nicknamed Bruno.
Rixie – stock.adobe.com – illustrative purposes only, not the actual polar bear
Bruno was a female bear that lived in Alaska’s Beaufort Sea somewhere between 100,000 and 70,000 years ago.
Her genome helped the scientists spot differences going back approximately 70,000 years, indicating that polar bears developed their unique characteristics more recently than previously thought.
“We found some variants that may have been selected in the last ~70,000 years (i.e. they were not in the fossil polar bears),” said Michael Westbury, a study co-author and an evolutionary biologist from the University of Copenhagen.
“It was always assumed that when polar bears diverged from brown bears, they must have quickly adapted to the Arctic in one rapid evolutionary change. However, our results suggest that may have not been the case, and the adaptation to the Arctic was a more gradual process.”
The team found seven genes related to polar adaptation. Four of the genes were fixed alleles, meaning that they had the same DNA variant present for a specific gene within a population.
The research team concluded that the gene differences in polar bears may have been influenced by the environmental conditions toward the end of the last ice age.
The study was published in BMC Genomics.
Sign up for Chip Chick’s newsletter and get stories like this delivered to your inbox.
More About:Animals