We may think it's cold and miserable here in the UK in winter, but it's nothing compared to what polar bears have to put up with in the Arctic.
Although their black and brown bear cousins hibernate for the winter, and pregnant female polar bears hide out in dens during the coldest months, other polar bears brave the Arctic winter.
So how do these bears cope? New research from scientists, led by a team at the University at Buffalo in the US, suggests that the answer lies in their genes – specifically genetic adaptations that control the production of a chemical in the body called nitric oxide, which cells use to convert the nutrients in food into energy and heat.
Comparing DNA from 23 polar bears, three brown bears and a black bear, the researchers discovered key differences between polar bears and their cousins in the genes that control nitric oxide production.
The chemical is thought to help cells switch between generating energy from food, to keeping warm, or storing energy as fat, suggesting that this is helping the polar bears adapt to life in the freezer.
But what about animals living in other types of extreme climates? Interestingly, a related story was published this week from a team of Chinese, US and Canadian researchers who've been looking at Tibetan Mastiffs – dogs that are adapted to living up in the mountains at very high altitudes, which were originally domesticated from native dogs living on the Chinese plains.
Led by Dong-Dong Wu, the researchers scanned through the genomes of 32 Tibetan Mastiffs, and compared them to 20 Chinese native dogs and 14 grey wolves.
They identified 16 key gene variations that seemed to be particular to the mastiffs, and found that around 12 of them were relevant to life at high altitude.
While the genes identified in the polar bear were involved in keeping the animals warm, the dog genes seem to be focused on how to generate energy in the low oxygen conditions you get up at high altitude.
Similar gene signatures have been found in other high-altitude animals, suggesting that similar gene pathways evolve independently to cope with the extreme conditions.
Intriguingly, one gene found in the Tibetan Mastiffs, called EPAS1, has also been implicated in adaptation to low oxygen by Tibetans themselves. So maybe the dogs and their owners have evolved together to cope with life up the mountains, although this needs to be explored further to be sure.