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Polar bears, between hybridization and risk of extinction

Mirjana Binggeli 27. June 2024 | Arctic, Science

Les huit hybrides identifiés proviennent tous de la même famille, déjà connue des scientifiques. Une femelle ours polaire née en 1989 s’était accouplée avec deux grizzlis donnant naissance à quatre petits. L’un de ces rejetons s’est ensuite à son tour accouplé avec les deux grizzlis. Ce phénomène, appelé rétrocroisement par les biologistes, a généré une nouvelle génération d’hybrides. Photos (de gauche à droite) : Julia Hager / Jean Beaufort, Wikipedia

While one study shows that hybrids between polar bears and grizzly bears are extremely rare, another is sounding the alarm about the possible disappearance of Hudson Bay polar bears.

Eight grolars, all descended from the same family. This is the total known population of hybrid bears, the result of a mix between polar bears and grizzlies. Such are the conclusions of a study published on June 13 in the journal Conservation Genetics Resources.

To achieve these results, a research team analyzed DNA samples collected from 371 polar bears, 440 grizzly bears and the 8 hybrids between 1975 and 2015, from Greenland, Alaska and Canada, using a new tool, an 8K genotyping chip. Dubbed Ursus maritimus V2 SNP, this chip reads genetic samples and delivers a genome analysis with 100% accuracy. The result: with the exception of the eight existing members already known to scientists, no new hybrids have been identified.

Although hybridization is not an adaptive trait of polar bears, scientists expect to discover more hybrids in the future. As sea ice shrinks and polar bears move to new territories, the chances of meeting and breeding with grizzly bears increase. Both species are genetically close, which makes mating possible, as polar bears and grizzlies share the same ancestor.

Pizzly, grolar, grolaire, grizzbear. Various names exist for this hybrid. To make sense of the different names, the name depends on the paternal lineage. If the father is a grizzly, it’s a grolar, and if the father is a polar bear, it’s a pizzly. In any event, hybridization between the two species is rare in the wild. However, it can occur in zoos, as here at Osnabrück Zoo. Photo: Stefan David

Hudson Bay polar bears threatened with extinction?

Released on the same day, another study paints a darker picture for polar bears. A research team of climatologists and biologists studied polar bear populations in Hudson Bay. Their conclusions are unequivocal: if the objectives of the Paris Agreement are not met, the polar bears of this region are likely to become extinct.

Published in the journal Nature Communications Earth and Environment, the study shows that the Hudson Bay has warmed by more than 1°C over the past 30 years, creating a difficult situation for polar bears. With such a temperature increase , sea ice melts earlier and reforms later, leaving polar bears on land for longer. With no opportunity to hunt seals, the bears have to draw on their fat reserves or feed on occasional, less nutritious prey while waiting for the ice to return.

In the absence of sea ice, polar bears have no access to their preferred prey, seals. A difficult situation for those cold-adapted hunters, who must then try to feed themselves as best they can or fast on land. Photo: Michael Wenger

Drawing on the latest information from climate models, the authors had produced the first holistic look at the future of the Hudson Bay ecosystem. By analyzing sea ice thickness, the researchers concluded that polar bear survival had been overestimated in previous studies which only assessed sea ice, thus presenting a bleaker picture. According to the researchers, the Hudson Bay polar bear population could disappear by 2030 if emissions are not cut drastically.

“If we fail to limit global warming to less than two degrees Celsius, we will lose Hudson Bay’s populations of polar bears,” states Professor Julienne Stroeve, polar climate scientist and lead author of the study, in a press release issued by the University of Manitoba on June 13. “The disappearance of the Southern Hudson Bay polar bears is imminent, with Western Hudson Bay not far behind. Our research underscores the rapid changes human activity imparts to our climate. It’s incumbent upon us to understand the impending impact on our natural world, so that we can make policy decisions informed by science.”

Links to studies :

Miller, J.M., Malenfant, R.M., Rivkin, L.R. et al. Development of an 8K SNP chip to assess adaptive diversity and hybridization in polar bears. Conservation Genet Resour (2024). https://doi.org/10.1007/s12686-024-01359-1

Stroeve, J., Crawford, A., Ferguson, S. et al. Ice-free period too long for Southern and Western Hudson Bay polar bear populations if global warming exceeds 1.6 to 2.6 °C.Commun Earth Environ 5, 296 (2024). https://doi.org/10.1038/s43247-024-01430-7

Mirjana Binggeli, Polar Journal AG

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