POLAR BEARS TAKING HEAT BY INBREEDING: Loss of sea ice means Svalbard’s bears are keeping things ‘in the family,’ putting health and adaptability to changing conditions at risk

polarbearincest

Whether you call it “polar bear incest” (tabloids) or “reduction of genetic differentiation” (scientists) it means the same thing: more inbreeding among bears in Svalbard due to less sea ice is threatening their health and ability to adapt to things such as climate change.

inbreeding graph

The distribution of polar bears sampled in a study of breeding habits across four geographical areas of Svalbard is shown in the top map. At bottom, a graph shows global surface-air temperature trends since 1979 Images by the Norwegian Institute of Bioeconomy Researc

The genetic diversity of polar bears in Svalbard is up to 10 percent lower than 20 years ago, according to a new study published study of polar bears in the journal Proceedings of the Royal Society B.

“Both the magnitude and rate of loss of genetic diversity were alarming and worrisome given that polar bears already have low levels of genetic diversity and are facing increasingly strong climatic pressure,” said Snorre Hagen, of the Norwegian Institute of Bioeconomy Research. “A decrease in genetic diversity and likely inbreeding depression can lead to further reduced survival and productivity, resulting in elevated risks of extinction.”

Genetic variations affect the risk of various diseases, along with the ability to adapt to changes to the environment – such as temperature increases, according to the study. Inbreeding also increases the risk of genetic disorders and weakens the bears in general.

Other concerns about impacts of climate change on polar bears – such as an inability to hunt seals that is the bulk of their traditional spring diet due to lack of ice – have been expressed by researchers for many years. However, recent census counts in Svalbard show bears are generally still well-nourished and breeding in normal numbers, due in part to their finding new sources of food such as bird eggs on land.

But those findings frequently are accompanied by warnings the species faces near-term and rapidly accelerating threats as climate change impacts increase beyond the bears’ ability to adapt to multitude of challenges.

The threat posed by inbreeding predictably got somewhat more than the usual amount of media coverage lately in terms polar bears being affected by climate change. While “inbreeding” appears to be the most conmon headline term overall, plenty of tabloid and other popular websites used the more eye-grabbing “incest” classification.

That led to reader comment sections like this one whose first postings, in order, referred to Donald Trump, anti-vaxers, climate change as a hoax and “a year from now some of these bears will probably be playing banjos.”

But Hagen noted that, scientifically and legally speaking, keeping things in the family when it comes to polar bear breeding is not incest.

“Strictly speaking, incest is a concept of inbreeding pertaining to humans, which has legal implications,” he said. “For animals and plants, we simply refer to the mating between genetically closely related individuals as inbreeding.”

“As a general rule, mating between close kin, like brother and sister, is prevented by various biological mechanisms, and in polar bears the generally high migration rate ensures that relatives rarely meet and mate with each other under normal circumstances. However, there is a question how good they really are at recognising each other. Especially if they were born from different litters as half- or full-siblings, there is a chance that they may inbreed locally if there is no ice for movement in isolated areas.”

Another shade of grey was spurted by Susan Cockford’s Polar Bear Science, notorius for being foremost among climate change skeptic media websites. She asserts predictions of future harm are based a models looking a century ahead and “apparently never bothered to look at species that have actually suffered dramatic loss of genetic diversity.”

“As far as I can see, it’s all meaningless number-crunching without relevance to the real world of polar bears,” she wrote.