Unraveling the History of Polar Bears and Brown Bears • Earth.com

A new study led by the University at Buffalo has explored the intertwined evolutionary history of polar bears and brown bears. Experts estimate that polar and brown bears started becoming separate species 1.3 to 1.6 million years ago, but they continued to mate for some time. So, rather than simple divisive events, the histories of polar and brown bear species hide convoluted stories of divergence and interbreeding, similar to those that complicate the story of human evolution.

“The formation and maintenance of species can be a messy process,” said the study’s lead author, Professor Charlotte Lindqvist. “What happened with polar bears and brown bears is a good analog to what we learn about human evolution: that the division of species can be incomplete.”

“As more and more ancient genomes have been recovered from ancient human populations, including Neanderthals and Denisovans, we find that there was ongoing multidirectional genetic mixing as different groups of archaic humans were mating with ancestors of modern humans. Polar bears and brown bears are another system where you see this happening.

By analyzing the genomes of 64 modern polar and brown bears, as well as that of a polar bear that lived 115,000 to 130,000 years ago in the Norwegian archipelago of Svalbard – its DNA was extracted from a tooth attached to a subfossil jaw – Prof Lindqvist and his colleagues discovered a complicated and intertwined evolutionary history in brown and polar bears, with the main direction of gene flow from polar bears to brown bears.

Additionally, after becoming a separate species, polar bears suffered a dramatic population decline and prolonged genetic bottleneck, leaving them with far less genetic diversity than brown bears.

The discovery that Arctic-adapted polar bears continued to capture genetic material from brown bears long after their species diverged could be of great interest to scientists studying the impact of climate change on endangered species. . Since global warming and subsequent decline in Arctic sea ice could cause polar and brown bears to meet more frequently in places where their ranges overlap, a better understanding of their tangled evolutionary histories could help researchers scientists to predict how climate change could affect these species in the near future. coming.

“Population genomics is an increasingly powerful toolkit for studying the evolution of plants and animals and the effects of human activity and climate change on endangered species,” the co concluded. –study author Luis Herrera-Estrella of Texas Tech University. “Bears provide no more simple speciation stories than human evolution. This new genomic research suggests that groups of mammalian species may hide complicated evolutionary histories.

The study is published in the journal Proceedings of the National Academy of Sciences.

By Andrei Ionescu, Terre.com Personal editor

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