How did a brown bear and a polar bear hybridize? What do their babies look like?

On April 23, 2012, the temperature was -25 degrees Celsius. In Viscount Melville Sound in Canada's Northwest Territories, Evan Richardson and his colleagues flew a helicopter to search for polar bears from the air.

"What's that?" someone asked on the intercom.

Richardson leaned out the window and saw what looked like a grizzly bear chasing a smaller polar bear on the ice. The helicopter got closer. They found that the "polar bear" looked unusual: it had a brown stripe on its back, a pair of dark circles under its eyes, and long claws.

It is not a polar bear, but a hybrid of a polar bear and a grizzly bear - a grizzly polar bear .

In April 2012, scientists first spotted a suspected "grizzly polar bear" in the wild | Jodie Pongracz, Environment and Natural Resources, Government of the Northwest Territories

The hybrid "Grizzly Polar Bear"

Scientists have long heard that the Inuit have encountered such "grizzly polar bears", but this phenomenon was not officially reported in the literature until 2012. In 2016, a Canadian hunter shot and killed a gray polar bear, which attracted widespread attention.

Hunter Didji Ishalook with the polar bear he shot | Didji Ishalook, Facebook

The grizzly polar bear is half polar bear (Ursus maritimus) and half grizzly bear (Ursus arctos horribilis), a subspecies of the brown bear.

Grizzlies usually have gray or brown fur, with darker legs. Grizzlies living along the Alaskan coastline can fish for a living, so they grow large; inland grizzlies mostly live in forests and grasslands, where they don't have much food, often eat berries, and grow smaller (but they still weigh more than 130 kilograms!). Not only are they strong, they can run up to 70 kilometers per hour ...

It is not easy to identify a grizzly bear by its fur color, so you can look at its back. There is a hump-like bump on the back of a grizzly bear. | Dwayne Reilander, Wikipedia, CC-BY-4.0

How come polar bears, whose main activity range is in the Arctic Ocean, have cubs with grizzly bears in the south?

As the climate warms, polar bears move south and grizzly bears move north

In northern Canada, near the Arctic Circle, grizzly bears and polar bears used to keep to themselves, but climate change has made this line increasingly blurred .

Generally speaking, polar bears migrate south to land when the ice melts in the summer , survive on their fat reserves, and get through the fasting period, waiting until the sea freezes in the winter before heading north to hunt.

However, research has found that due to climate change and melting ice, polar bears that cannot find food are landing earlier and earlier and leaving later and later .

Polar bear skinny as a bag of bones | Paul Nicklen

Hungry polar bears are moving south, while grizzly bears are expanding their territory northward.

Global warming has turned some tundra areas into grasslands , attracting grizzly bears to settle down. On the other hand, humans have occupied some important habitats of grizzly bears, which has also prompted them to move north to find living space.

Both polar bears and grizzly bears breed in the spring. When the breeding season arrives, adult males leave their birthplaces and wander around, looking for new territories to mate with females in the territories. The overlapping living spaces of polar bears and grizzly bears increase the likelihood of contact and even mating .

Research evidence shows that the time when grizzly bears end hibernation is also related to the weather. As spring temperatures rise, grizzly bears wake up from hibernation earlier and earlier , 10 days earlier in ten years.

Males generally wake up earlier than females, and the female estrus cycle is mainly triggered by the extension of daylight hours, so early-awakening males may have difficulty finding mates. Some of these individuals have gone all the way north, into polar bear territory, and interbred with female polar bears to have cubs.

Has the “Hybrid Bear” become stronger?

Polar bears and brown bears diverged about 500,000 years ago, a short period of time in evolutionary history, so they were able to interbreed and produce fertile offspring. Can the hybrid gray polar bear inherit the advantageous characteristics of both parents?

There are indeed rumors that grizzly polar bears are more agile and aggressive than polar bears. But Richardson believes: " Grizzly polar bears will either grow into vulnerable polar bears or vulnerable grizzly bears ." In nature, the mixed characteristics of hybrid offspring usually do not bring survival buffs, but may put them in an awkward situation.

The physical characteristics of polar bears and brown bears are highly adapted to their respective environments . Polar bears have long, narrow skulls to help them pull seals out of the sea. They also have smaller molars because seals are rich in fat and are less tiring to chew. In addition, they have broad, short claws to help them walk on ice.

Polar bear | Arturo de Frias Marques, Wikipedia, CC-BY-4.0

In contrast, grizzly bears have a much wider diet , eating both vegetarian food such as berries and leaves, and preying on large animals such as reindeer and musk oxen. They also have long and sharp claws, which are suitable for attacking prey and digging caves for hibernation .

A grizzly bear's claws can be 5-10 cm long | Pierre5018, Wikipedia, CC BY-4.0

Scientists do not yet know what physical characteristics and behavioral patterns grizzly polar bears will exhibit. Currently, there are only a few confirmed grizzly polar bears, and they are often identified after being hunted.

According to existing observations, the claws of the grizzly bear are longer than those of the polar bear, which may be disadvantageous for walking on the ice ; its mottled hair is also more conspicuous in the ice field environment, making it easier for prey to find it . If it goes south to the grizzly bear's hometown, its fighting power seems to be inferior to those "pure blood" grizzly bears.

There are only temporary winners in the climate crisis

However, due to climate change, there may be more polar bears in the future. Such stories are happening in many places on Earth: climate change changes the activity patterns of animals , disrupts their courtship and reproduction rhythms, or allows species that were originally distributed in different time and space to meet and compete for survival resources.

Male dragonflies use melanin patches on their wings for courtship displays, but this absorbs more heat and causes their body temperature to rise, endangering their lives. Making the melanin patches smaller would make them less attractive to females.

The problem of hybridization in polar bears is just one aspect of the impact of climate change. In contrast, the more pressing problem they face is the destruction of their habitat caused by the melting of sea ice . The reduction of sea ice will make it more difficult for polar bears to hunt seals, and they will be forced to eat unsuitable food such as bones, carcasses of other animals and even garbage.

Polar bears are highly specialized animals, meaning they have developed exaggerated features to adapt to their particular environment, making them particularly vulnerable to climate change . A 2016 study predicted that polar bear populations could decline by 30 percent over the next 30 years.

In contrast, species such as brown bears, raccoons, and coyotes may adapt better to climate change because they have a diverse diet and can adapt to a variety of environments, but they are only temporary winners in the climate crisis.

Some people may say, why not just treat climate change as a form of natural selection? However, compared with the time scale of evolution, climate change is too fast. Perhaps a few species can rise in this process, but there will be many more species that cannot adapt, and the entire ecosystem will become more homogeneous and more fragile . In the face of the increasingly severe climate crisis, such an ecosystem may be vulnerable.

References

[1]"Pizzlies, Grolars – Why Hybrid Grizzly Polar Bears Aren't The Answer | Polar Bears International". 2023. Polarbearsinternational.Org. https://polarbearsinternational.org/news-media/articles/pizzlies-grolars-polar-bear-grizzly-hybrid.

[2]"'Pizzly' Bear Hybrids Are Spreading Across The Arctic Thanks To Climate Change". 2021. Livescience.Com. https://www.livescience.com/pizzly-bear-hybrids-created-by-climate-crisis.html.

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[8] Petherick AS, Reuther JD, Shirar SJ, et al. Dietary ecology of Alaskan polar bears (Ursus maritimus) through time and in response to Arctic climate change[J]. Global Change Biology, 2021, 27(13): 3109-3119. https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.15573

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[10]hes grizzly bears north https://www.nationalobserver.com/2019/12/15/news/climate-change-pushes-grizzly-bears-north

Author: Maya Blue

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