Over several decades, sea ice has gradually been receding from the areas around Svalbard. New research shows that this has led to loss of genetic diversity and an increasing degree of isolation in the local polar bear population.
Although the polar bear is a good swimmer, it depends on sea ice for hunting, eating and resting.
“The polar bear spends most of its life on sea ice,” says Snorre Hagen, head of research at NIBIO Svanhovd. In collaboration with the Norwegian Polar Institute, NIBIO has investigated how the genetic diversity of the polar bear population around Svalbard has changed in recent years.
Extensive DNA analyses
Researchers have analysed the DNA of 626 polar bears. The samples were collected by the Norwegian Polar Institute in the 1995–2016 period, from four different locations on Svalbard.
The results show that the genetic diversity of the polar bears on Svalbard was reduced by 3–10 percent during the study period. In addition, the researchers found an increase of almost 200 percent in genetic differentiation across regions, as well as an increase in the average genetic relationship between individuals.
“In other words, we can say that the polar bears across the entire area are becoming more and more genetically similar, while the polar bears in each individual area are becoming increasingly genetically isolated from one another,” says Hagen.
Sea ice is receding
These effects are best explained by the fact that the polar bear’s habitat is being divided into smaller and smaller fragments, while the ice-free season is growing longer.
“When the sea ice disappears, the polar bears become less mobile. This leads to the bears becoming more similar to one another on a local level, and the local gene pool grows smaller as the polar bears in a given location increasingly mate with polar bears from the same area,” Hagen concludes.
Loss of Arctic sea ice owing to climate change is predicted to reduce both genetic diversity and gene flow in ice-dependent species, with potentially negative consequences for their long-term viability. Here, we tested for the population-genetic impacts of reduced sea ice cover on the polar bear (Ursus maritimus) sampled across two decades (1995–2016) from the Svalbard Archipelago, Norway, an area that is affected by rapid sea ice loss in the Arctic Barents Sea. We analysed genetic variation at 22 microsatellite loci for 626 polar bears from four sampling areas within the archipelago. Our results revealed a 3–10% loss of genetic diversity across the study period, accompanied by a near 200% increase in genetic differentiation across regions. These effects may best be explained by a decrease in gene flow caused by habitat fragmentation owing to the loss of sea ice coverage, resulting in increased inbreeding of local polar bears within the focal sampling areas in the Svalbard Archipelago. This study illustrates the importance of genetic monitoring for developing adaptive management strategies for polar bears and other ice-dependent species.