A polar bear is a brown bear

[brobear]

Oct 21, 2022 0:06:29 GMT -5 brobear said:

Scientists Sequence Genome of 100,000-Year-Old Polar Bear
Jun 17, 2022 by News Staff / Source

www.sci.news/genetics/polar-bear-paleogenome-10914.html

Polar bears (Ursus maritimus) and brown bears (Ursus arctos) are sister species possessing distinct physiological and behavioral adaptations that evolved over the last 500,000 years. In new research, a team of scientists from the United States, the United Kingdom, Canada and Sweden generated and analyzed a paleogenome from an approximately 100,000-year-old polar bear that reveals a massive prehistoric admixture event between these two species, which is evident in the genomes of all living brown bears.

In 2009, the skull of a juvenile polar bear nicknamed Bruno was found on the beach of the Beaufort Sea near Point McLeod in Arctic Alaska.

The geomorphic setting where the skull was found suggests that Bruno lived during the most recent period when the relative sea level was higher than today, possibly between 110,000 and 70,000 years before present when the sea was as much as 10 m higher than today along this portion of the Beaufort Sea coastline.

“The availability of Bruno’s paleogenome has made it possible to detect an ancient admixture event that impacted all living brown bears,” said Dr. Ming-Shan Wang, a postdoctoral researcher in the Howard Hughes Medical Institute and the Department of Ecology and Evolutionary Biology at the University of California Santa Cruz.

In the study, Dr. Wang and colleagues generated the nuclear genome and the high coverage mitochondrial genome using DNA from the root of a tooth extracted from Bruno’s skull.

Their genomic analysis shows that Bruno belonged to a polar bear population that was ancestral to living polar bears.

At some point, probably after around 125,000 years ago, the polar bear lineage leading to Bruno and the brown bear lineage leading to all living brown bears crossed paths and hybridized.

As a result of this ancient admixture, polar bear ancestry accounts for as much as 10% of the genomes of brown bears living today.

“We never would have seen this without Bruno’s genome, because all living brown bears have that admixture as part of their genomes,” said Professor Beth Shapiro, also from the Howard Hughes Medical Institute and the Department of Ecology and Evolutionary Biology at the University of California Santa Cruz.

The study did find some evidence of possible gene flow from brown bears into Bruno’s lineage, but the absence of admixture in polar bears today supports the idea that brown bear ancestry reduces a bear’s fitness for life as a polar bear.

After diverging from brown bears about 500,000 years ago, polar bears evolved into highly specialized hunters of marine mammals on the Arctic sea ice. Brown bears, in contrast, are generalists ranging widely across North America, Europe, and Asia.

Bruno lived during a time of changing climate after the peak of a warm interglacial period when temperatures and sea levels were considerably higher than they are now.

Similar conditions can be expected in the future as a result of rapid climate change driven by the burning of fossil fuels and other human activities.

As Arctic sea ice declines, many polar bear populations are already struggling to survive.

“If the rapid, unnatural, and severe human-caused warming of the Arctic we are documenting today continues unabated, it is uncertain whether polar bears will have a sea ice habitat to return to and survive genetically,” said Dr. Ian Stirling, a researcher in the Department of Biological Sciences and the Environment and Climate Change Canada Department of Biological Sciences at the University of Alberta.

“We shouldn’t be surprised to see admixture happening again today as the climate changes and these species are overlapping and encountering each other again in the wild,” Professor Shapiro said.

“Climate change allows gene flow to occur between what we think of as different species.”

The results appear in the journal Nature Ecology & Evolution.

_____

MS. Wang et al. A polar bear paleogenome reveals extensive ancient gene flow from polar bears into brown bears. Nat Ecol Evol, published online June 16, 2022; doi: 10.1038/s41559-022-01753-8

Quote: “Climate change allows gene flow to occur between what we think of as different species.”

[brobear]

Classification is just that; Classification. A method of listing and separating one animal from another. Categorizing. 
 
No brown bear family tree is complete without the polar bear. One brown bear subspecies, Sitka brown bear - Ursus arctos sitkensis, even though in appearance looks like any other brown bear, is no less than 50% polar bear.

The two, categorized as separate species, continue to breed freely producing what is called grolar bears. Grolar bears are a product of nature. IMO, it should be against the law for a hunter, with permit to hunt bears, to shoot a grolar bear. 

The polar bear is nothing more than a population of brown bears which have adapted perfectly into his pure-arctic environment. -In essence, during the last 150,000 years polar bears have diverged from their grizzly bear cousins under the intensive pressure from their environment to select for traits geared toward hunting seals from the ice. If ever there was a specialist, this is it.

                       

[brobear]

Oct 25, 2020 20:27:01 GMT -5 OldGreenGrolar said:

Modern polar bears are derived from an ancient Irish brown bear.




A female grizzly [brown] bear who lived in Ireland less than 50,000 years ago was an ancestor of all modern polar bears, suggesting “grolar” hybrids were an important part of polar bear history.

The unexpected DNA evidence suggests that interbreeding between polar bears and brown bears — usually known as grizzly bears in North America — is not unusual at times when climate change caused the range of the two species to overlap, such as around the beginning of the last ice age.

“It’s something that’s part of the history of the polar bear,” said Daniel Bradley, a genetics researcher at Trinity College Dublin who co-authored the study published Thursday in the journal Current Biology.

Grizzly-polar bear hybrids are rare, but a number have been seen in Canada in recent years. A bear in the Northwest Territories in April 2010 is believed to be the first second-generation hybrid — the offspring of a female grizzly-polar bear hybrid and a male grizzly bear — ever found in the wild.

Bradley and his colleagues wrote that their results suggest that hybrid bears should be protected, as both polar bears and grizzly bears currently are.

“They may play an underappreciated role in the survival of species,” the paper said.

Previous DNA studies had suggested that polar bears became a separate species about 800,000 to 150,000 years ago, and were most closely related to brown bears in the Admiralty, Baranof and Chichagof Islands near Alaska.

Bradley and his colleagues uncovered the evidence about the bears’ ancestry by looking at mitochondrial DNA extracted from the bones of museum specimens of Irish brown bears, which became extinct around 3,000 years ago. They compared it to mitochondrial DNA from other brown bears around the world as well as two ancient polar bear specimens from over 100,000 years ago.

“What was interesting was that the sequences from our brown bears were closer to modern polar bears than those ancient polar bears were,” he said in a phone interview Thursday.

In fact, the results, which Bradley said were unexpected, suggest that all polar bears share a female Irish brown bear ancestor from within the last 50,000 to 20,000 years — not that long ago on the evolutionary time-scale.

Based on the similarity between modern polar bear DNA and that of the Irish brown bear around the last ice age (between 100,000 and 10,000 years ago), they may have interbred multiple times.

About 22,000 years ago, an ice sheet covering most of Britain and Ireland was at its largest. That would have provided habitat for polar bears and may have forced brown bears into lowlands near the sea, where they could have encountered and mated with polar bears, the researchers suggested.

Bradley said he’s not sure how polar bears would have arrived in Ireland, but they may have crossed over the ice from Scandinavia.

The large differences between the mitochondrial DNA of ancient and modern polar bears is due to the fact that many polar bear lineages have died out, Bradley said. Modern polar bears are all very closely related to one another and may belong to a lineage that is different from that of the ancient specimens in the study.

The research team involved in the study included scientists from Ireland, the U.S., Belgium, England, Spain, Denmark, Russia, Scotland and Sweden.

When I first heard about the grolar bears, I thought that this could possibly the future for the polar bear species. The polar bear really isn’t a good species. It is really just a modified form of brown bear, and this study strongly indicates that there has always been some gene flow between the two animals.

Of course, they don’t normally live in the same areas, so opportunities for cross-breeding are not as common as one might suppose.

This study found that after the polar bear population evolved fromn the ancient brown bear species, the only surviving lineage of polar bear still in existence is derived from hybridization with the Irish brown bear.

Hybridization between very closely related species is much more common in the wild that we have realized, and in the case of the polar bear, the only surviving form is derived from a brown bear ancestor.

I certainly think that grolar bears should be protected, but we’re going to have to come up with some way of classifying brown and polar bears that recognizes their close relationship.

I don’t know whether we should call them a single species or if we should call it the “brown and polar bear species complex.”

But we have such a narrow typological definition of species that it may be impossible to find some way to legally protect grolars.

This is one of those weird situations, which we humans have a very hard time understanding. Being the only surviving member of your genus means that we have a hard time realizing how two members of the same genus can have a gene flow. And just because one species has the genes of another doesn’t mean that one species is “polluting” the other. These gene flows are not necessarily bad things. They maintain genetic diversity, and they have the potential to spread beneficial traits from one species to another.

But when we blind ourselves to narrow typologies, we can’t see how crossbreeding can have some merit.

The world for the polar bear won’t end if we find a polar bear with a grizzly bear ancestor three generations away. It didn’t end when a polar bear mated with an Irish brown bear all those years ago. Indeed, that crossbreeding may have conferred certain advantages onto the ancestors of modern polar bears, allowing that lineage to survive while all the other polar bear lineages died out.

Polar and brown bears exist within a dynamic that includes some gene flow between populations. It isn’t as extensive as it is between wolves and dogs or between wolves and coyotes. But it isn’t insignificant.

We just like to think that species are unchanging. We like to think that once they have evolved, nothing more will happen.

But there is no “once they have evolved.” Species will continue to evolve and adapt to new conditions.

One way they are able to adapt is to receive new genes from hybridizing with related species– if we want to think of polar and brown bears as distinct species.

Hybridization isn’t always species killer. In this case, it might be a species saver. And it may have been one in the past.

But this is so difficult to grasp.

We are the species that does all the classifying. But we, as a species, are an unusually genetically depauperate species of ape, which is also the only surviving member of our genus.

We just don’t understand that other species can have greater genetic diversity than we do and can augment their genetic diversity through crossbreeding with a related species.

So we like to split species.

But we really ought to be lumpers.

retrieverman.net/tag/grolar-bear/

Quote: Hybridization isn’t always species killer. In this case, it might be a species saver. And it may have been one in the past.

[brobear]

Mar 26, 2017 12:35:10 GMT -5 brobear said:

www.pbs.org/wnet/nature/arctic-bears-how-grizzlies-evolved-into-polar-bears/777/

The icon of the Arctic, the polar bear, is the ultimate survivor in one of the harshest areas on Earth. Reigning over a world of ice, tundra, and snow, this carnivore would seem to have a lineage that traces back to some mammoth creature of the icy regions.

But in fact, the polar bear’s closest ancestor is a land carnivore we associate more strongly with our forests. Over the years, scientists have uncovered an evolutionary path suggesting that polar bears are a relatively new species, and actually a subspecies, of Ursus arctos, more widely known as the brown bear. Scientific evidence has found that the brown bear, a species that also includes grizzly bears, was a “precursor” to polar bears, which then went on to develop specializations for inhabiting the harsh Arctic.

Proving their genetic compatibility, brown bears and polar bears can mate and produce viable, or fertile, offspring. It is this reproductive viability that establishes that an animal belongs within a given species. In 2006, a hybrid grizzly/polar bear, which some call a “pizzly,” was discovered in the Canadian Arctic, providing researchers proof that polar bears and grizzly bears can interbreed, even in the wild. And when researchers in Alaska compared the DNA of brown bears from around the world, looking for genetic links, they made an interesting discovery about one population of brown bears in particular. Analysis of the DNA of a distinct population of brown bears living on Alaska’s ABC islands, 900 miles south of the nearest polar bear, revealed that the ABC bears were even more closely related to polar bears genetically than they were to other brown bears.

So just when did polar bears arise as a separate subspecies? Genetic models show that the emergence of the polar bear could have taken place as recently as 70,000 years ago or as many as 1.5 million years ago. For many years, a fossil found at Kew Bridge in London was considered the oldest polar bear specimen. The fossil then placed the evolution around 70,000 years ago. But recently, scientists uncovered a fossilized jawbone from an island in the Arctic Ocean midway between Norway and the North Pole, dated to be at least 100,000 years old. Scientists believe this jawbone may represent the remains of the oldest-known polar bear, thus marking the appearance of the polar bear earlier than previously thought.

Relying on the fossil record and DNA analysis, scientists have been able to arrive at a clearer picture of the polar bear’s evolutionary path over the millennia. Some 200,000 years ago, when glaciers covered much of Eurasia, the Arctic Ocean was completely frozen. It was during this challenging period that brown bears began to wander in search of food. Approximately 125,000 years ago a population of brown bears in the far north of their range was likely split off from their brown bear ancestors, perhaps because of competition for food. The population likely became isolated by massive glaciers and, while most died in the harsh environment, those bears with an evolutionary advantage — ideal coat color and thickness for extreme cold — survived and bred. Over thousands of years, this population of bears underwent further evolutionary change, adapting even more specialized traits for surviving the harsh polar environment. When life in the North demanded teeth better shaped for ripping apart seals than munching berries, the polar bear’s molar teeth changed significantly from those of the brown bear. The bears also grew white fur, which camouflaged them in their snow-covered surroundings and gave them a hunting advantage. Scientists believe that at first these bears scavenged seal carcasses that had washed ashore, and gradually began to hunt the seals by waiting at the water’s edge as the seals surfaced to breathe. This is believed to be an important step in the evolution of a new subspecies of bear — Ursus maritimus or the polar bear.

Nature once exerted such extreme pressure on the brown bear that it eventually gave rise to a new, better-adapted subspecies, the polar bear. Now, once again, evolutionary forces are acting on this long-enduring species. As the Arctic warms, the polar bear’s unique specializations that once lent it an evolutionary edge, may now be the creature’s downfall. A changing climate may name a new king of the Arctic — the fierce and opportunistic brown bear.

Quote: Scientists believe that at first these bears scavenged seal carcasses that had washed ashore, and gradually began to hunt the seals by waiting at the water’s edge as the seals surfaced to breathe. This is believed to be an important step in the evolution of a new subspecies of bear — Ursus maritimus or the polar bear.

[brobear]

Mar 26, 2017 12:39:35 GMT -5 brobear said:

evolution.berkeley.edu/evolibrary/news/100401_polarbears

What is a polar bear?
Evolutionarily speaking, polar bears (Ursus maritimus) are brown bears (Ursus arctos). That might seem counterintuitive, but modern biologists classify species according to their evolutionary history. Organisms that are more closely related are grouped together. In this system, only clades — groups of organisms that contain all the descendents of an ancestor — are named. When we look at the family tree of bears, we can see that not only are polar bears most closely related to brown bears, but they actually fall within the brown bear clade. There is no clade that includes all the brown bears and excludes the polar bears. From an evolutionary perspective, polar bears are simply a unique and highly specialized sort of brown bear!

Quote: Evolutionarily speaking, polar bears (Ursus maritimus) are brown bears (Ursus arctos).

[brobear]

The Bear Tree: 
domainofthebears.proboards.com/thread/902/polar-bear-evolution?page=2  
Polar Bear Evolution - Reply #20

[OldGreenGrolar]

Reply 2: In this case the polar bear merging with the grizzly bear might actually be a process of saving it. Perhaps they should remove the polar bear and call it Ursus Artos Maritimus/ Brown sea bear.

[brobear]

Oct 21, 2022 1:45:40 GMT -5 OldGreenGrolar said:

Reply 2: In this case the polar bear merging with the grizzly bear might actually be a process of saving it. Perhaps they should remove the polar bear and call it Ursus Artos Maritimus/ Brown sea bear.

I am certainly in full agreement with your suggestion. Ursus arctos maritimus is a fitting scientific name for the polar bear.   
 
*Edit and add: Not all biologists agree. Also, changing a scientific name is a huge undertaking as a large number of biologists from all over the globe must be in agreement. 

[brobear]

Mar 26, 2017 12:38:47 GMT -5 brobear said:

phenomena.nationalgeographic.com/2012/04/19/polar-bear-origins-revised-theyre-older-and-more-distinct-than-we-thought/

We have two separate origin stories for polar bears because, like all animals, they have two genomes. There’s the nuclear genome that hoards most of their DNA in the centre of their cells, and the smaller mitochondrial one, housed in small battery-like structures. The nuclear genome is inherited both parents, but the mitochondrial one is only inherited from mothers. That’s important, for reasons we’ll come to.

Until now, scientists had studied polar bear evolution by looking at their mitochondrial DNA. These studies produced a model in which the polar lineage is nested within a wider brown dynasty, meaning that some brown bears are more closely related to polar bears than to other brown bears. This called the polar bear’s status as a separate species into question.

Hailer changed that by sequencing the nuclear DNA of 45 brown, polar and black bears, at 14 different sites. His results showed that polar and brown bears are actually sister groups, that branched off from each other around 603 thousand years ago. Polar and brown bears are both distinct species, and they’re as genetically different from each other as they are from black bears.

It is understandable why the fossils told a different story. Polar bears live in a world of shifting ice and freezing water, so many of their bones have been lost. But why did the mitochondrial DNA results differ so radically?

Hailer thinks that the two bears would often meet and mate with one another, long after they diverged. Indeed, they can still create hybrids today. If female brown bears mated with male polar bears, the hybrid (a pizzly bear) would carry a brown bear’s mitochondrial genome. This hitchhiking DNA could have invaded the wider polar population if the hybrids mated with other polar bears.

If you looked at the mitochondrial DNA, you’d see the footprint of these recent polar-brown liaisons, and mistake them for a split between the two groups. If you looked at the nuclear DNA, you’d see when the split actually happened. That’s exactly what Ceiridwen Edwards from Oxford University suggested when she analysed the bear’s mitochondrial DNA last year.

A biologist named Hailer disagrees. According to her findings, the polar bear diverged from the brown bear 603,000 years ago.