Polar bears found to have diverged from brown bears just 70,000 years ago

Credit: Unsplash/CC0 Public Domain

A team of molecular ecologists at the University of Copenhagen, in Denmark, has found that polar bears developed unique features that allowed them to survive in a harsh, cold environment just 70,000 years ago.

In their study published in the journal BMC Genomics, the group analyzed the genomes of more than 100 polar bears, another 100 brown bears and a pair of fossilized polar bears to learn more about the timeline involved in the development of characteristics such as white fur and the ability to subsist on a diet high in cholesterol.

Prior research has shown that polar bears are closely related to brown bears but until now, it was not known when the two species diverged. In this new study, the team in Denmark set themselves the task of finding the answer.

Some of the main differences between brown and polar bears are their fur color, of course, but also their fur types. Brown bears have one layer of fur, polar bears have two—an undercoat of downy fur that helps them stay warm and an overcoat that helps them stay dry. Polar bears have also developed the ability to eat meat containing a lot of blubber. If brown bears ate such a lipid-rich diet, they would develop heart disease and die young.

To learn more about when the two species diverged, the team looked at the genomes of both types of bears, most specifically at those genes involved in fur type and color and cardiovascular functions.

Geographic localities of the polar and brown bears included in this study. CWL shows the bears that were used in the study by Castruita, Westbury, and Lorenzen. Stars indicate the two Late Pleistocene polar bears. Credit: BMC Genomics (2024). DOI: 10.1186/s12864-024-10617-3

By comparing the genomes of 119 polar bears, 135 brown bears and two fossilized polar bears, the researchers found differences going back approximately 70,000 years, suggesting that polar bears have developed their unique characteristics much more recently than previously thought.

More specifically, the team found seven genes related to polar adaptation, four of which were fixed alleles in the polar bears. The comparison also showed that divergence was more gradual than previously thought.

The research team concludes that the gene differences associated with polar bear adaptions may have been influenced by bears living during the end stages of the last ice age.

More information: Yulin Sun et al, Late Pleistocene polar bear genomes reveal the timing of allele fixation in key genes associated with Arctic adaptation, BMC Genomics (2024). DOI: 10.1186/s12864-024-10617-3


Journal information: BMC Genomics

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