Polar Bears’ Evolutionary Journey into the Arctic
The Arctic, with its harsh conditions, is home to some of the most resilient animals on Earth. Among them, polar bears (Ursus maritimus) stand out as top predators with genetic adaptations that set them apart from their brown bear relatives. Recent genomic analysis suggests that these adaptations may have emerged as recently as 70,000 years ago, shedding light on the evolutionary timeline of these Arctic giants. The study, published in the journal BMC Genomics on September 15, delves into the genetic changes that have allowed polar bears to thrive in their icy habitat.
Polar bears, closely related to brown bears (Ursus arctos), have evolved key features to survive in extreme Arctic conditions. Their dual-layered fur, consisting of a dense undercoat and longer guard hairs, provides insulation and waterproofing. The bears’ distinctive white fur serves as camouflage in their snowy surroundings, while their ability to digest high amounts of cholesterol from blubber enables them to sustain themselves on a diet of seals and even whales like belugas.
The divergence between polar bears and brown bears is estimated to have occurred within the last one million years, with the exact timeline of polar bear adaptation to the Arctic still under debate.
In a recent study, researchers analyzed the genomes of modern polar bears, modern brown bears, and two fossilized polar bears, including the Poolepynten jawbone from Svalbard and a juvenile polar bear skull named Bruno. By examining genetic variants associated with Arctic adaptations, the team uncovered clues about the gradual evolution of polar bears’ unique traits over time.
The study’s findings indicate that certain genetic variants associated with Arctic adaptations were selected in polar bears over the last 70,000 years. This suggests a more gradual process of adaptation to the Arctic environment, rather than a sudden evolutionary leap. By comparing the genomes of polar bears and brown bears, researchers identified specific genes linked to Arctic survival, shedding light on the genetic changes that have shaped polar bears’ unique characteristics.
Genes such as ABCC6, AIM1, COL5A3, and POLR1A were found to have fixed alleles in modern polar bear genomes, indicating their role in Arctic adaptation. On the other hand, genes like APOB, LYST, and TTN showed fixed alleles in modern polar bear genomes but not in ancient ones, suggesting a more recent evolutionary shift related to cardiovascular functions, metabolism, and pigmentation.
These genetic insights offer a glimpse into the intricate process of polar bear evolution and adaptation to the Arctic environment. The study highlights the ongoing exploration of how these iconic Arctic predators have thrived in one of the world’s harshest ecosystems.
