The Arctic is not the most hospitable place on Earth. Some animals there, such as reindeer, have several genetic adaptations, thanks to which they can adapt to harsh living conditions. Now it seems that one of the top hunters of the North is not an exception to this rule.
Scientists are calculating when polar bears (Ursus maritimus(maybe some of the genes that separate them from the brown bear)Ursus arctos) have evolved. A new genomic analysis suggests that the polar bear may have changed as recently as 70,000 years ago.
Polar bears are very closely related to brown bears, but have many key adaptations that help them survive in the arctic’s icy conditions; For example, they have two layers of fur that help them stay warm and dry. The first is a large downy layer close to the skin, and the other layer is made up of longer hairs called guard hairs that act like a raincoat.
The bright white color of the fur helps camouflage. Polar bears can also digest large amounts of cholesterol without damaging the heart, which helps them adapt to eating seals and even some species of whales, such as belugas.
Polar bears and brown bears diverged evolutionarily relatively recently, roughly in the last million years.
Scientists believe that polar bears and brown bears diverged evolutionarily relatively recently, about a million years ago. How and when polar bears adapted to the Arctic is still debated.
In the study, the research team analyzed the genomes of 119 modern polar bears, 135 modern brown bears and two fossil polar bears. One of the fossils is the jaw bone of Polpinten from the Norwegian archipelago of Svalbard, which is dated between 130,000 and 100,000 years ago. Another fossil was the skull of an immature polar bear named Bruno, found in Alaska’s Beaufort Sea. Bruno was a female bear that lived between 100,000 and 70,000 years ago, and its genome helped scientists investigate the divergence of brown bears and polar bears.
Michael Westbury“We found variants that may have been selected for in the last 70,000 years (that is, not in fossil polar bears),” study co-author and evolutionary biologist at the University of Copenhagen told Popular Science. It was always assumed that when polar bears diverged from brown bears, they must have quickly adapted to the Arctic in a rapid evolutionary change. “However, our results suggest that this may not have been the case and that adaptation to the Arctic was a more gradual process.”
The research team compared the genomes to determine when seven genes key to arctic adaptations were selected. The team found that for four genes (ABCC6, AIM1, COL5A3, and POLR1A), entire polar bear genomes have a DNA variant. This condition is called a fixed allele, which is the only variant available for a particular gene in a population.
However, the brown bear genome had multiple alleles, suggesting that these genes had already been selected for in some ancient polar bear ancestor, and that polar bears had adaptations to arctic life early in their evolution.
Photographer: Pam Grove
However, three genes, APOB, LYST, and TTN, contained alleles that were fixed in modern polar bear genomes, but not in ancient genomes. APOB, LYST and TTN genes are associated with cardiovascular functions. APOB and TTN are associated with metabolism, and APOB and LYST are associated with pigmentation.
The research team believes that these genes may be related to adaptations that were necessary for the survival of polar bears in more recent history, perhaps as late as the last ice age. It is also unclear whether other arctic animals have similar adaptations on genes that affect fur color, heart health and metabolism.
“I think copies of these genes,” Westbury says[ÛŒ سازگاری با شمالگان] It is found in most animals, but it may be the special variants of the polar bear that allow it to live in the Arctic. We did not investigate whether any other arctic animals have the same variants, but for further study [موضوع] It will be interesting.”
The findings of the study have been published in the journal BMC Genomics.
