Collaborative Research: Genetics of Polar Bear Hair, Skin Color: Adaptations to the Arctic Environment

Polar bears have numerous traits that not only give them their iconic appearance but are also adaptations to living in the Arctic environment. These include their large body size with thick fat layer, streamlined head to help dive after prey, and most-noticeable their white fur. While other species of bears live in tropical or temperate environments, polar bears adapted to the extreme low temperatures of the Arctic with novel ways to absorb solar radiation or retain internal body heat.

Three of these thermoregulatory adaptations within the skin or hair include: light hair color, dark skin color, and insulating hollow hair. To identify the genes responsible for these traits, DNA, RNA, proteins, and tissue structure of polar bears will be compared to both the brown/grizzly bear and American black bear. Further, the rate of hair heating and cooling, and energy transfer at the hair-skin boundary will be measured and modeled with the aim of developing novel nanoscale materials.

Thus, the project will yield new insights into how mammals remain warm in extreme cold environments. Similar pigmentation and hair structural variation have evolved in other Arctic mammals; thus, understanding the molecular and cellular mechanisms of these traits will provide a starting point to investigate convergence. Research results will be translated into educational materials appropriate for K-12 students and distributed to zoos with polar bears, as zoos are often the only opportunity people have to observe these animals.

Finally, the project will train scientists in effective science communication and reach non-expert audiences through public outreach.

Arctic species must adapt to the extreme temperatures of their environment. This research focuses on skin and hair traits associated with thermoregulatory adaptation. Comparative genomics, transcriptomics, and histological staining of skin tissue between polar bears and two temperate species, brown and American black bears, will determine the cellular basis for light hair and dark skin.

Specifically, the abundance and location of melanocytes will be characterized, then changes in gene expression among bear species that can account for differences in cellular location will be identified. Beyond pigmentation differences, polar bear hair has a hollow center thought to increase the insulating capacity of the fur. To identify the genes that underly this trait, protein abundance within hair will be compared among species.

Ancestral recombination graphs will be constructed to quantify when during the evolutionary history of polar bears this adaptation arose. As the hollow hair has distinct applications in creating novel heat retaining nanomaterials, this research will quantify and model thermodynamic properties of the hair and hair-skin interface over a range of environmentally relevant temperatures.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.