Polar bears in southern Greenland are 'using jumping genes to rapidly rewrite their own DNA' to survive melting sea ice

Temperature stress may be driving genetic mutations in polar bears in southern Greenland, a new study reports.

The species is struggling in the face of a changing global climate. Global sea ice levels dropped to a record low in February, and the warming planet is pushing up sea levels. These changes threaten polar bears, which live and hunt on the shrinking ice sheets.

But a group of polar bears (Ursus maritimus) in southern Greenland may be evolving to cope with their challenging environment. Researchers have found a link between changes in polar bear DNA and rising temperatures.

The study, published Dec. 12 in the journal Mobile DNA, "shows, for the first time, that a unique group of polar bears in the warmest part of Greenland are using 'jumping genes' to rapidly rewrite their own DNA, which might be a desperate survival mechanism against melting sea ice," lead author Alice Godden, a senior research associate at the University of Anglia in the U.K., said in a statement.

Jumping genes, also known as transposons or transposable elements, are pieces of DNA that move from one location on the genome to another. Depending on where they insert themselves into the organism's genetic code, transposons can change how other genes are expressed. More than one-third of the polar bear genome is made up of transposable elements, while in plants it can be as much as 70%. By contrast, transposons make up about 45% of the human genome.

Transposons appear to be helping polar bears adapt to climate change, the authors of the new study argue.

A 2022 study published in journal Science described an isolated population of polar bears in southern Greenland that was less reliant on sea ice. The group split from a community of bears in northern Greenland about 200 years ago, and their DNA was different from that of bears in the North. The new research builds on these earlier findings.

The researchers analyzed the DNA of 17 adult polar bears in Greenland — 12 from the cooler northeast and five from the group in the warmer southeast. They compared transposon activity in the two populations, and then linked that with climate data.

In the Southeastern population, there were changes to genes linked to heat stress, aging, and metabolism, as well as fat processing, which is important when food is scarce. According to the study, this suggests the bears "might be adjusting to their warmer conditions."

"By comparing these bears' active genes to local climate data, we found that rising temperatures appear to be driving a dramatic increase in the activity of jumping genes within the southeastern Greenland bears' DNA," Godden said. "Essentially this means that different groups of bears are having different sections of their DNA changed at different rates, and this activity seems linked to their specific environment and climate."

Despite the bears' potential ability to adapt to warmer climates and less ice, Godden warned that climate change remains a real threat to polar bears.

"We cannot be complacent; this offers some hope but does not mean that polar bears are at any less risk of extinction," she said. "We still need to be doing everything we can to reduce global carbon emissions and slow temperature increases."