Ruth Rivkin, Kiersten King, Jon Aars, Kristin Laidre, Alexandra Langwieder, David McGeachy, Levi Newediuk , Stephen D Petersen, Nicholas Pilfold, Aryn P Wilder, Geoff York, Evan S Richardson, Colin Garroway

The extent to which species might be able to evolutionarily respond to rapid environmental change relies strongly on their genetic diversity. Accurate knowledge of both patterns of evolution and genetic variation across the species range is important for determining appropriate conservation and management strategies. The Arctic is the fastest-warming region on the planet, with the rest of the world expected to reach temperature increases currently experienced in the Arctic by the turn of the century. Here, we review and synthesize research on evolutionary processes in polar bears. Polar bears are perhaps the best-studied species living at the forefront of climate-mediated habitat change, so patterns of evolutionary change in this species should be instructive for understanding the consequences of warming that are expected to occur elsewhere in the near future. Global warming has led to significant sea ice loss that has altered patterns of gene flow across the Arctic and contributed to declines in genetic variation in some, but not all, polar bear populations. Natural selection due to warming may be driving the evolution of smaller body sizes in polar bears. However, evidence of adaptive change remains limited, despite considerable behavioural plasticity in the species in response to changing sea ice conditions. Following our review, we suggest ways that identifying the effects of warming on evolution and genetic variation in polar bears could improve strategies for locally supported conservation and management decisions. Our results point to variable responses to warming that we can expect to occur across different genetically distinct populations in the same species and the general complexity of predicting the consequences of warming for wide-ranging species.