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Post by brobear on Mar 26, 2017 11:47:26 GMT -5
BEARS of the last frontier... Climate change in particular does not bode well for the polar bear - or any animal adapted to the cold. They spend most of their lives on the ice - a concept so incredibly alien to us that it is hard to imagine an animal being so completely comfortable on a frozen sea amid the harshest conditions on earth. They hunt, sleep, mate, and wander thousands of miles in this habitat, thriving in a world that was new to them until very recently in the evolution timeline.
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Post by brobear on Mar 26, 2017 11:54:40 GMT -5
BEARS of the last frontier... The polar bear's overnight success as a highly specialized bear came about through "quantum-speciation," a process that involves the rapid evolution of numerous physiological changes. For the polar bear these include an adaptation in fur color for camouflage, webbed toes to improve swimming ability, an elongated neck that facilitates hunting and life in and around water, hollow hairs to improve flotation and insulation, sandpaper-like foot pads to aid traction, and a thick layer of fat to keep the intense cold at bay. I've seen every one of these adaptations put to use, and combined they make for an incredibly well-designed animal. -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. It is ironic given the highly adaptable nature of their close cousin, the grizzly, that this specialization may have sealed their fate. Their dependence on ice makes polar bears the climate change "canary in the coal mine."
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Post by brobear on Mar 26, 2017 12:06:37 GMT -5
www.earthtimes.org/nature/brown-bears-versus-polar-bears/93/ The bleak future for polar bears as global warming encourages brown bears to range further north. Something that is not widely realised is that polar bears only evolved as a distinctive species as recently as 200,000 years ago during the Pleistocene. It is believed that today's polar bears are descended from a group of brown bears that became isolated by glaciers in an area near Siberia and underwent a rapid series of evolutionary changes in order to survive and adapt to Arctic life. These involved a change in the colour of their fur, the shape of their body, sharper teeth and large feet with thick, curved, non-retractable claws that are used for grasping prey as well as providing vital traction when running or climbing on ice. Polar Bears are the world's largest land carnivore and the only member of the bear family that is entirely carnivorous. They live on a diet entirely composed of seal flesh and blubber. As a result of this relatively rapid evolution into a semi-aquatic Arctic life with a very specialised diet, the polar bear has developed a cranial morphology that is weaker than that of brown bears and less suited to processing tough omnivorous or herbivorous diets. Polar bears live almost exclusively on the flesh of young ringed or bearded seals. They have 42 teeth and have developed blade-like incisors to shear off pieces of flesh, with strong canine teeth to grasp prey and tear tough hides. Since they swallow most of their food in large chunks rather than chewing it first, strong molars are not necessary and these are much smaller than those of their brown cousins. While their teeth are super-efficient for processing seal flesh and blubber, polar bears' teeth are less suited for processing bones and hard-to-chew diets with lots of vegetation. The polar bear's low, flat skull with its high-sitting eyes is ideal for a semi-aquatic life and it gives them the advantage of being able to thrust their heads into breathing holes or puppy dens. A recent study by the on-line research journal PLoS One (Public Library of Science) says that although the heads and muscle power of polar bears and brown bears are similar, tests reveal that the polar bear's skull is a 'weaker, less work-efficient structure' and does not appear to be well-suited to large amounts of chewing. Although brown bears will eat animals when they are available, they will also eat a large amount of plant material in the summer, which all requires a considerable amount of chewing before it can be swallowed. It is estimated that the world population of polar bears is between 20,000 and 25,000, of which about 60 per cent live in Canada, but the study concludes that as the earth warms and the brown bears continue to range northwards, this is likely to present polar bears with a significant challenge. Where Arctic foxes overlap with red foxes, it is always the red foxes that end up controlling the prime feeding and breeding areas and the fear is that polar bears will share a similar fate.
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Post by brobear on Mar 26, 2017 12:18:12 GMT -5
DNA study clarifies relationship between polar bears and brown bears Unusual population of brown bears on Alaskan islands turns out to have a remarkable and revealing history March 14, 2013 By Tim Stephens
At the end of the last ice age, a population of polar bears was stranded by the receding ice on a few islands in southeastern Alaska. Male brown bears swam across to the islands from the Alaskan mainland and mated with female polar bears, eventually transforming the polar bear population into brown bears.
Evidence for this surprising scenario emerged from a new genetic study of polar bears and brown bears led by researchers at the University of California, Santa Cruz. The findings, published March 14 in PLOS Genetics, upend prevailing ideas about the evolutionary history of the two species, which are closely related and known to produce fertile hybrids.
Previous studies suggested that past hybridization had resulted in all polar bears having genes that came from brown bears. But the new study indicates that episodes of gene flow between the two species occurred only in isolated populations and did not affect the larger polar bear population, which remains free of brown bear genes.
At the center of the confusion is a population of brown bears that live on Alaska's Admiralty, Baranof, and Chicagof Islands, known as the ABC Islands. These bears--clearly brown bears in appearance and behavior--have striking genetic similarities to polar bears.
"This population of brown bears stood out as being really weird genetically, and there's been a long controversy about their relationship to polar bears. We can now explain it, and instead of the convoluted history some have proposed, it's a very simple story," said coauthor Beth Shapiro, associate professor of ecology and evolutionary biology at UC Santa Cruz.
Shapiro and her colleagues analyzed genome-wide DNA sequence data from seven polar bears, an ABC Islands brown bear, a mainland Alaskan brown bear, and a black bear. The study also included genetic data from other bears that was recently published by other researchers. Shapiro's team found that polar bears are a remarkably homogeneous species with no evidence of brown bear ancestry, whereas the ABC Islands brown bears show clear evidence of polar bear ancestry.
A key finding is that the polar bear ancestry of ABC Islands brown bears is conspicuously enriched in the maternally inherited X chromosome. About 6.5 percent of the X chromosomes of the ABC Islands bears came recently from polar bears, compared to about 1 percent of the rest of their genome. This means that the ABC Islands brown bears share more DNA with polar bear females than they do with polar bear males, Shapiro said.
To understand how hybridization could lead to this unexpected result, the team ran simulations of various demographic scenarios. "Of all the models we tested, the best supported was the scenario in which male brown bears wandered onto the islands and gradually transformed the population from polar bears into brown bears," said first author James Cahill, a graduate student in ecology and evolutionary biology at UC Santa Cruz. This scenario is consistent with the known behavior of brown bears and polar bears, according to coauthor Ian Stirling, a biologist at the University of Alberta in Edmonton, Canada. Mixing of polar bears and brown bears is seen today in the Canadian Beaufort Sea, where adult male brown bears wander onto the remaining sea ice in late spring and sometimes mate with female polar bears, he said. In areas such as western Hudson Bay and the Russian coast, polar bears are spending more time on land in response to climate warming and loss of sea ice, a behavior that could have left polar bears stranded on the ABC Islands at the end of the last ice age.
Young male brown bears tend to leave the area where they were born in search of new territory. They may well have dispersed across the water from the Alaskan mainland to the ABC Islands and hybridized with polar bears stranded there when the sea ice disappeared.
"The combination of genetics and the known behavior of brown and polar bears hybridizing in the wild today tells us how the ABC Islands bears came to be: they are the descendants of many male brown bear immigrants and some female polar bears from long ago," Stirling said.
The findings suggest that continued climate warming and loss of arctic sea ice may lead to the same thing happening more broadly, said coauthor Richard E. (Ed) Green, an assistant professor of biomolecular engineering in UCSC's Baskin School of Engineering. "As the ice melts in the Arctic, what is going to happen to the polar bears? In the ABC Islands, the polar bears are gone. They're brown bears now, but with polar bear genes still present in their genomes," he said.
The first genetic studies of ABC Islands brown bears looked at their mitochondrial DNA, which is separate from the chromosomes and is inherited only through the female lineage. The mitochondrial DNA of ABC Islands brown bears matches that of polar bears more closely than that of other brown bears, which led some scientists to think that the ABC Islands brown bears gave rise to modern polar bears.
The new study looks at the "nuclear DNA" carried on the chromosomes in the cell nucleus. It is the latest in a series of genetic studies of polar bears published in recent years, each of which has prompted new ideas about the relationship between polar bears and brown bears. A 2010 study of fossils and mitochondrial DNA supported the idea that polar bears evolved from the ABC Islands brown bears. But a 2011 study of mitochondrial DNA from extinct Irish brown bears showed an even closer match to polar bears and suggested that polar bears got their mitochondrial DNA from hybridization with Irish bears. Shapiro, a coauthor of that study, said she now thinks the Irish brown bears may be another example of what happened in the ABC Islands, but she can't say for sure until she studies their nuclear DNA.
"In retrospect, I think we were wrong about the directionality of the gene flow between polar bears and Irish brown bears," she said.
Two studies published in 2012 sought to determine when the polar bear lineage diverged from the brown bear lineage using nuclear DNA data. The first, published in April in Science, put the split at 600,000 years ago and concluded that polar bears carry brown bear mitochondrial DNA due to past hybridizations. The second, published in July in Proceedings of the National Academy of Sciences, suggested that brown bears, black bears, and polar bears diverged around 4 to 5 million years ago, followed by repeated episodes of hybridization between polar bears and brown bears. The new study does not address the question of how long ago polar bears diverged from brown bears, but it may help sort out the conflicting results of recent studies. "It's a good step in the right direction of understanding what really happened," Shapiro said.
The study does indicate that the divergence of polar bears from brown bears was only half as long ago as the split between the brown bear and black bear lineages, said Cahill. "We can tell how long brown bears and polar bears have been separate species as a proportion of how long ago they separated from more distantly related species, but putting a year on it is very difficult," he said.
Green noted that efforts to understand the relationship between polar bears and brown bears has been complicated by the unusual case of the ABC Islands brown bears. "It's as if you were studying the relationship between humans and chimpanzees and your analysis included DNA from some weird population of humans that had hybridized with chimps. You would get very strange results until you figured that out," he said.
In addition to Cahill, Green, Shapiro, and Stirling, the coauthors of the new paper include postdoctoral researchers Tara Fulton and Mathias Stiller, undergraduate Rauf Salamzade, and graduate student John St. John at UC Santa Cruz; Flora Jay and Montgomery Slatkin at UC Berkeley; and Nikita Ovsyanikov at the Wrangel Island State Nature Reserve in Russia. Green and Shapiro direct the UCSC Paleogenomics Lab. This research was funded by the Searle Scholars Program.
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Post by brobear on Mar 26, 2017 12:19:27 GMT -5
www.nbcnews.com/id/40422298/ns/technology_and_science-science/t/polar-bear-skulls-cant-take-stress-biting/#.WDSVx9UrLC0 "Question: What kind of bear is best?" Jim once asked Dwight on the television show "The Office." Answer: The brown bear, at least in comparison to the polar bear, according to research published this month in the journal PLoS One. Polar bear (Ursus maritimus) skulls may put them at a disadvantage when competing with their close relative, the brown bear (Ursus arctos), concluded a team of researchers led by Graham Slater of UCLA. The researchers created computer simulations of polar and brown bear skulls to estimate their bite strength and the stresses put on the skull by biting. They found that polar bears skulls were less capable of withstanding the strain from chewing hard foods. Polar bears are the only completely carnivorous bears. Their skulls have adapted to a diet of mostly seal meat and blubber. This diet of soft food resulted in a weaker skull. They also lost the grinding molars that brown bears use to chew up plant matter. These changes make polar bears less capable of surviving in a rapidly warming arctic, according to the study. Brown bears eat everything from caribou to berries. Their skulls are built to withstand greater stress from chewing tougher food like grasses. Since 1996, grizzly bears, a subspecies of brown bear, have been observed moving further north, encroaching on the polar bear's habitat. Arctic sea ice is also disappearing, reducing the territory of the polar bear's seal prey. With increased competition and less food, the polar bear has become the poster child for extinction threats caused by climate change. Polar bears evolved rapidly from brown bears within the last million years. They may disappear even more quickly.
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Post by brobear on Mar 26, 2017 12:35:10 GMT -5
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.
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Post by brobear on Mar 26, 2017 12:37:30 GMT -5
www.irishcentral.com/news/archaeological-evidence-links-polar-bears-to-irish-brown-bears-125180369-237397981 By studying 17 sets of brown bear teeth and skeletons, found in eight caves across Ireland, in 2011 scientists found conclusive evidence of the connection. The findings from these scientists located in Ireland, Britain, and the US were published in the journal Current Biology. Up to this discovery, it was thought that polar bears were most closely related to the brown bears living in the islands of Admiralty, Baranof and Chichagof in Alaska's Alexander Archipelago. However, the analysis of the DNA passed from mother to child (mitochondrial DNA) shows that the Irish brown bear is unmistakably linked. This proves that the two species mated opportunistically during the past 100,000 years. This means that the bears split from a common ancestor to become a new species somewhere between two million and 400,000 years ago. This means before or during the last Ice Age the two species came together and polar bears mated with the Irish brown bear. The study was the work of Prof Daniel Bradley, of Trinity College Dublin (TCD) and Dr. Ceiridwen Edwards, formerly of TCD and now at Oxford University who collaborated with Prof Beth Shapiro, of Pennsylvania State University. Dr. Edwards said "It's amazing to think that Irish brown bears are the ancestors of the modern maternal polar bear lineage. "As the hybridization between the two species occurred at a time when their home ranges overlapped, most likely during environmental stress, this has implications for polar bears in today's climate." According to the BBC reports, Prof Shapiro said "While brown bears and polar bears are hybridizing today, our results suggest that a recent hybridization led to the capture of a mitochondrial DNA sequence that was present in the population of brown bears that were living in Ireland before the peak of the last ice age. "That mitochondrial sequence replaced the previous sequence across the entire polar bear population." Evidence of the Irish brown bear has been found across the island of Ireland. The best examples can be found in the Poll na mBear (Cave of the Bears) in County Leitrim. They were discovered by Eoghan Lynch and Barry Keenan in May 1997. * Originally published in 2011.
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Post by brobear on Mar 26, 2017 12:38:47 GMT -5
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.
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Post by brobear on Mar 26, 2017 12:39:35 GMT -5
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!
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Post by brobear on Mar 26, 2017 12:42:05 GMT -5
evolution.berkeley.edu/evolibrary/news/100401_polarbearsOne small fossil, one giant step for polar bear evolution April 2010 As the fuzzy and ferocious poster child for climate change issues, polar bears get plenty of press, whether it's coverage of something as simple as the birth of a cub at a zoo or as political as a rejected ban on trading polar bear parts. Last month, however, saw a polar bear story of a different ilk — a story about the bears' evolutionary past that has implications for their evolutionary future. Polar bears, it turns out, may have evolved surprisingly quickly in response to past climactic changes. Here, we'll examine the different lines of evidence that led scientists to this conclusion. Where's the evolution? In 2004, researchers discovered a polar bear fossil preserved in Norwegian coastal cliffs. It was the lower left portion of the jaw, still containing a tooth. And though this might not sound like much information to go on, the single fossil would turn out to have a lot to say about polar bear evolution. Based on the jawbone's shape, scientists were confident that it belonged to an adult male polar bear. The rock layers in which it was embedded, along with other dating techniques, suggest that it is 110,000 to 130,000 years old — older than any other known polar bear fossils. This date alone is interesting because previous estimates for the origin of polar bears have ranged from 70,000 to more than a million years ago. But, based on the new fossil's age, we can infer that the polar bear lineage must be more than 110,000 years old. The anatomy and rocks in which the jawbone was preserved provided useful information — but the fossil had an even more powerful line of evidence: DNA. DNA breaks down over time, but new techniques allow scientists to pull these fragmented bits of DNA out of some well-preserved fossils, copy the pieces, and reassemble them into a very good estimate of the original genetic sequence. An international group of scientists used these techniques on DNA from the polar bear jawbone and announced their findings last month. They had reconstructed the sequence of the bear's mitochondrial DNA — a short loop of DNA that is housed in the cell's "powerhouse" organelles, mitochondria. The ancient mitochondrial DNA was easier for the scientists to work with than the bear's main genome (housed in the nucleus), because each cell contains many copies of its mitochondrial DNA and only one copy of its nuclear genome. The researchers compared the fossil's DNA sequence to those from different species of modern bears and from extinct cave bears. They used these sequences to reconstruct the animals' family tree. As expected, the modern and ancient polar bear DNA formed a tight group, a clade — and that clade was most closely related to the brown bears of Southeast Alaska. The surprise came when the researchers used two different lines of reasoning to learn more about the relationship between the ancestral polar bear and the fossil. First, they used the DNA sequences to extrapolate back to the sequence that the ancestor of polar bears and brown bears would likely have carried. The fossil specimen's DNA was extremely similar to the likely sequence of the polar bear ancestor! Second, they used molecular clocks to estimate the date of the split between polar bears and brown bears. Molecular clocks are stretches of DNA that evolve at a fairly regular pace can be used as evolutionary tape measures to estimate how long ago different events happened. The more differences a clock-like stretch of DNA has accumulated since a divergence, the more time has probably passed since that divergence. The differences among the bears' sequences pointed to a split between polar bears and brown bears just 150,000 years ago. All this means that the fossil (which may be as many as 130,000 years old) likely represents one of the very earliest members of the polar bear lineage! Having already investigated the fossil's anatomy, stratigraphy, and mitochondrial DNA (as well as the molecular clock in that DNA), the team of researchers studied one more line of evidence unearthed with the fossil: the atoms that compose the tooth embedded in the jawbone. An organisms' diet strongly influences the sort of atoms that are deposited in its body — specifically the ratios of atoms with different numbers of neutrons. By studying the carbon and nitrogen in the bear's tooth, the researchers discovered ratios that were exactly what we'd expect to observe of a bear that gets its nutrition from seafood! Just 20,000 years or so after they diverged from forest-dwelling brown bears, polar bears had already evolved their distinctive marine lifestyle. For a large mammal, that's evolution at breakneck speed! This rapid pace of polar bear evolution may have been related to changes in the climate going on at the time. The polar bear and brown bear lineage split during a glacial age. This may have provided the ecological setting for the evolution of the seafood eating, sea ice-loving polar bear lifestyle. The newly formed polar bear lineage survived one warm interglacial period before being plunged back into another glacial age. Now of course, the planet is warming again — this time due to human actions. Will polar bears survive? The answer is not clear, but the new research does shed some light on the issue. We now know that polar bears have evolved surprisingly quickly in the past. However, today, the Earth is heating up much faster than it ever has before — and the unprecedented pace of that change makes it difficult for slow reproducing organisms like polar bears to evolve to keep up. One thing is for certain: knowing more about how polar bears have responded to climate change in their evolutionary past can help us figure out how to help them survive into the future.
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Post by brobear on Mar 28, 2017 3:25:47 GMT -5
www.adn.com/arctic/2017/02/19/could-a-giant-polar-bear-skull-found-at-an-eroding-alaska-archaeological-site-be-the-legendary-weasel-bear/ Alaska News Could this giant polar bear skull be the legendary 'weasel bear'? Aboriginal hunters from Arctic Canada have a couple of names for what they say is an extremely rare polar bear that is huge, narrow-bodied, fast-moving and lithe: "tiriarnaq" or "tigiaqpak," meaning "weasel bear." Now the thawing and rapidly eroding Chukchi Sea coastal permafrost has produced evidence that one of these legendary weasel bears — or some other strange kind of bear — roamed Arctic Alaska centuries ago. A huge, fully intact and unusually shaped polar bear skull emerged in 2014 from an eroding archaeological site about 13 miles southwest of Utqiaġvik (Barrow). It is one of the biggest polar bear skulls ever found — and quite different from most modern polar bear skulls. It is slender, elongated in the back and has unusual structural features around the nasal area and other areas. "It looks different from your average polar bear," said Anne Jensen, an Utqiaġvik-based archaeologist who has been leading excavation and research programs in the region. Through radiocarbon dating and subsequent analysis, Jensen and her colleagues estimate that the big bear skull — which appears to be the fourth largest ever found — is from a period between the years 670 and 800. It is possibly the oldest complete polar bear skull found in Alaska, inspiring a name for the departed creature that owned it: The Old One. Exactly what accounts for its differences is yet to be determined; genetic testing is needed for that, Jensen said. It could have been a member of a subspecies or a member of a different "race" in genetic terms — similar to the varying breeds that are found among dogs — or possibly something else entirely, said Jensen, who works for the science department of the Native village corporation, Ukpeaġvik Iñupiat Corp., or UIC. The Old One's skull was only one of several treasures newly found at the now-eroding site, which is called Walakpa and has been known to archaeologists for at least half a century.
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Post by brobear on Apr 12, 2017 18:15:58 GMT -5
Very often fossil remains of an ancient animal are discovered and the scientists are too quick to give it a name. They are sometimes way off base. A good example is Basilosaurus. First thought to be a sea serpent but later found to be an ancient whale. When this happens - IMO - the animal should be renamed. Another creature misnamed - IMO - is ourselves. Homo sapien means "wise man" but are we? More appropriately we should be renamed "inventive man." If we were wise, the world would not be covered in concrete and asphalt and wild animals would still be plentiful. IMO - the polar bear should be renamed Ursus arctos maritimus. We now know that, although the polar has scant amounts of other bear dna, he is primarily a grizzly fully adapted to his arctic environment. No brown bear family tree is complete without the polar bear. As for Ursus maritimus tyrannus, this bear should have been awarded a temporary name, perhaps Ursus tyrannus, until more evidence is discovered. As of now, his relationship with grizzlies and polars is completely unknown.
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Post by brobear on Jan 11, 2018 6:53:20 GMT -5
www.crystalinks.com/fossilbear.html What may be the oldest known remains of a polar bear have been uncovered on the Svalbard archipelago in the Arctic. The jawbone was pulled from sediments that suggest the specimen is perhaps 110,000 or 130,000 years old. Tests show it was an adult, possibly a female. The find is a surprise because polar bears are a relatively new species, with one study claiming they evolved less than 100,000 years ago. If the Svalbard jawbone's status is confirmed, and further discoveries can show the iconic Arctic beasts have a deeper evolutionary heritage, then the outlook for the animals may be more positive than some believe.
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Post by brobear on Jan 11, 2018 6:56:50 GMT -5
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Post by brobear on Oct 2, 2018 4:29:27 GMT -5
polarbearscience.com/tag/pleistocene/ Polar bears barely survived the sea ice habitat changes of the last Ice Age, evidence suggests. While the polar bear is an Ice Age species, genetic and fossil evidence suggests it barely survived the profound sea ice changes associated with the Last Glacial Maximum, one of the most severe glacial periods of the Pleistocene. A map of sea ice extent at the climax of the Last Glacial Maximum (both perennial and seasonal ice), prepared with the help of a colleague, makes it possible to discuss what genetic and fossil evidence can tell us about the probable effects of glacial conditions on polar bears and ringed seals. Ancient Polar Bear Remains of the World Posted on November 26, 2012 | Comments Off on Ancient Polar Bear Remains of the World How does the ancient distribution of polar bears – based on finds of natural-death remains (“fossils”) and bones found in archaeological sites – compare to the modern distribution of polar bears? I have pulled together information from all of the reports I could find that listed ancient polar bear remains and summarized them into one table and one map. A low resolution copy of the map and a simplified version of the map notes are embedded in this post but a higher resolution version of the map and map notes (with pertinent details, including references) is available as a pdf. This document has been assigned an ISBN number (which means it is copyrighted and filed at Library and Archives Canada). The pdf can be downloaded below and will also be available on the PolarBearScience “references” page. Is it plausible that polar bears are 4-5 million years old? Part 3, sea ice Posted on August 23, 2012 | Comments Off on Is it plausible that polar bears are 4-5 million years old? Part 3, sea ice Last in a three-part series of my critique of Miller et al.’s (2012) paper on the newest genetic evidence for the origin of polar bears. Part 1 here, Part 2 here. Here is my final (I hope) comments on the claims made in that paper, suggesting why we might want to take them with a grain of salt. These are the points regarding this paper that I think deserve a critical look. In this post, I’ll elaborate on Claims #3 and #4. I’ve added one more to the original three listed. Claim #1 Polar bears and brown bears (aka grizzlies) arose 4-5 million years old.
Claim #2 Hybridization in both directions occurred repeatedly throughout the evolutionary history of polar bears and brown bears.
Claim #3 Svalbard may have been an important refugium for polar bears during warm interglacial periods – and related sea ice issues related to the origin of polar bears as a species.
Claim #4 Polar bear population numbers (population size estimates) over the last one million years track changes in climate (warmer/colder periods).
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Post by brobear on Jan 7, 2019 12:52:06 GMT -5
www.pbs.org/wnet/nature/arctic-bears-how-grizzlies-evolved-into-polar-bears/777/ Arctic Bears How Grizzlies Evolved into Polar Bears June 10, 2008 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.
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Post by Deleted on Jan 9, 2019 23:14:58 GMT -5
Great article. It confirms most of my opinions.
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Post by King Kodiak on Mar 7, 2019 6:50:53 GMT -5
EVOLUTION Lessons from Polar Bear Studies This is the first in a series of posts responding to the extended critique of Darwin Devolves by Richard Lenski at his blog, Telliamed Revisited. Professor Lenski is perhaps the most qualified scientist in the world to analyze the arguments of the book. He is the Hannah Distinguished Professor of Microbial Ecology at Michigan State University, a MacArthur (“Genius Award”) Fellow, and a member of the National Academy of Sciences with hundreds of publications, who also has a strong interest in the history and philosophy of science. His own laboratory evolution work is a central focus of the book. I am very grateful to Professor Lenski for taking time to assess Darwin Devolves. His comments will allow interested readers to quickly gauge the relative strength of arguments against the book’s thesis. Although it was not the topic of his first post, I will begin with Lenski’s discussion of the example with which I open my book — the polar bear genome — because it illustrates some principles that will be useful going forward. For readers who don’t have time to read to the end, here are a couple of take-home lessons: Experimental evidence strongly supports my conclusion (disputed without good reason by Lenski and others) that highly selected mutations in the polar bear genome work by breaking or blunting pre-existing functions. A “function” of a protein is a lower-level molecular feature or activity, such as being a gear or a tether; it should not be confounded with higher-level phenotypic effects, such as “lowers cholesterol” or “makes the organism happy.” Ignoring the distinction leads to much confusion. Where We Agree At the beginning of Darwin Devolves I discuss work by researchers who compared the genome of the brown bear (Ursus arctos) with that of the polar bear (Ursus maritimus). Those species separated from a common ancestor hundreds of thousands of years ago. By analyzing the DNA sequence data, the researchers were able to determine the genes whose selection most strongly adjusted the polar bear lineage to a frigid environment. One of those genes, called APOB, is involved in fat metabolism. As I wrote: The scientists who studied the polar bear’s genome detected multiple mutations in APOB. Since few experiments can be done with grumpy polar bears, they analyzed the changes by computer. They determined that the mutations were very likely to be damaging — that is, likely to degrade or destroy the function of the protein that the gene codes for. In fact, about half of the mutations in the 17 most highly selected polar bear genes were predicted to be damaging. What’s more, since many genes had multiple mutations, I noted that about two-thirds to four-fifths of selected genes had suffered at least one damaging mutation. I used this example to set the stage for the main theme of the book, that Darwin’s mechanism works chiefly by degrading pre-existing genetic information, which sometimes helps a species survive. Echoing blogged arguments by his lesser-known co-authors of the appalling review of my book in Science, Professor Lenski points out (as I repeatedly do in the book) that the computer analysis is a prediction that a particular mutation will or won’t be damaging; it is not an experimental demonstration. In other words, the prediction could be wrong. Further, the program categorizes mutations into just three categories: probably damaging, possibly damaging, and benign. (Benign means simply that, as far as the program can tell, no damage has been done to the protein by that change; it does not mean the change is constructive.) Thus, as he stresses, the program is not set up to detect if in fact some new function had been gained by the protein. He goes on to emphasize that the polar bear is superbly adapted to its high-fat diet — much better in that regard than the brown bear. All of which, I happily agree, is true. Where We Disagree But then, without benefit of supporting data, Lenski waxes strongly optimistic. He quotes an author of the study and then stresses his own view in bold face: In a news piece about this research, one of the paper’s authors, Rasmus Nielsen, said: “The APOB variant in polar bears must be to do with the transport and storage of cholesterol … Perhaps it makes the process more efficient.” In other words, these mutations may not have damaged the protein at all, but quite possibly improved one of its activities, namely the clearance of cholesterol from the blood of a species that subsists on an extremely high-fat diet. Lenski is almost certainly wrong about the bolded text. Here’s why. In 1995 researchers knocked out (destroyed) one of the two copies of the APOB gene in a mouse model — the same gene as has been selected in polar bears. Although APOB is itself involved in the larger process of the transport of cholesterol, mice missing one copy of the APOB gene actually had lower plasma cholesterol levels than mice with two copies. (Mice missing both copies died before birth.) What’s more, the researchers noted that “When fed a diet rich in fat and cholesterol, heterozygous mice were protected from diet-induced hypercholesterolemia.” researchers admitted they did not know how it all came together — how that effect on the complex cholesterol-transport system resulted from breaking the gene. Nonetheless, there is no ambiguity about the mouse results. Simply by lowering the amount/activity of APOB, mice were protected from the effects of a high-fat diet. Deletion of one copy of the gene may have made the process of cholesterol removal more efficient, as Rasmus Nielsen speculated above about the polar bear, but it did so by decreasing the activity of mouse APOB. Just to be extra clear about the relevance of the mouse results to the interpretation of the polar bear genome, let me state my reasoning explicitly. Given the experimental results with mice, it is most parsimonious to think APOB is broken or blunted in polar bears. For mice, having only half as much APOB activity protects them from a high fat diet. For polar bears, having mutated APOB genes protects them from a high fat diet. If those polar bear mutations decreased the activity of APOB by half or more, then we might expect a similar protective effect as was seen in the mouse. Given that computer analysis also estimated the APOB mutations in the polar bear as likely to be damaging, it is most reasonable to think the activity of the protein has been blunted by the mutations. Thus there is no good reason to speculate about possible new activities of the coded protein in the polar bear. Rather, the simplest hypothesis is that the mutations in the polar bear lineage that were judged by computer analysis as likely to be damaging did indeed blunt the activity of the APOB protein in that species — that is, made it less effective. That molecular loss gave rise to a happy, higher-level phenotypic result — an increased tolerance of polar bears for their high fat diet. The Way to Bet The caveats mentioned above by Professor Lenski — about how computer-assignment of a mutation as “damaging” is not a guarantee, and that the protein may have secretly gained some positive new function — are correct. He is also quite right to say that without detailed biochemical and other experiments we cannot know for sure how the change affected the protein and the larger system at the molecular level. Nonetheless, computer methods of analyzing mutations are widely used because they are generally accurate. And they do not suddenly lose their accuracy when I cite their results. So, in the absence of specific information otherwise, that’s the way for a disinterested scientist to bet. There is no positive reason — other than an attempt to fend off criticism of the Darwinian mechanism — to doubt the conclusion. The APOB gene is exceptional in having such detailed research done on it. Most other genes haven’t been so closely investigated. Nonetheless, in the absence of positive evidence to doubt a prediction for a specific case, the results of the computer analysis should be tentatively accepted for other genes to which it has been applied as well. Skepticism on the matter seems to stem less from the data than it does from reflexive defensiveness. (One of Lenski’s co-reviewers actually talked himself into thinking that “it is entirely possible that none of the 17 most positively selected genes in polar bears are ‘damaged.’” Now there’s a great opportunity for someone to make a few dollars with a friendly wager.) Lower-Level Functions Versus Higher-Level Purposes I’d like to highlight one final critical point. Let me set it up with a homey analogy. When I was 14 I worked weekends at McDonald’s, and sometimes I’d be assigned to operate the milkshake machine. The machine was broken down each night for cleaning. One of my tasks early in the morning before opening was to reassemble its parts. There were maybe a dozen parts to put together — sprockets, clamps, gaskets, and such. Shakes were very popular back then (mid 1960s) and made many customers happy for a while. Nonetheless, the function of the parts of a shake machine is not “to make people happy.” The function of a sprocket or a clamp isn’t even “to make a milkshake.” Rather, they have lower-level mechanical duties that are subservient to the overarching higher purposes of the systems. The same is true of APOB. Its function is not “to help polar bears survive,” nor even “to clear cholesterol.” Rather, it has one or more lower level functions that are subservient to those higher purposes. Thus the fact that cholesterol might be cleared more efficiently in polar bears does not at all mean that APOB hasn’t been degraded, any more than breaking the off-switch of a shake machine so that it works continuously throughout lunch hour means some new improved function was added. In both Darwin Devolves and my Quarterly Review of Biology paper on which it is based, I repeatedly stressed the need to look beneath higher-level, phenotypic changes to associated underlying molecular-level mutations. Did they help by constructing or by degrading what I termed Functional Coded elemenTs (FCTs)? Helpful higher level changes can often be misleading, because they might actually be based on degradative molecular changes. There is every reason to think that’s what occurred in the evolution of the examples I cite in Darwin Devolves, definitely including the magnificent Ursus maritimus. The more effective clearance of its cholesterol allows the polar bear to thrive on a diet of seal blubber, but it is the result of a mutation that breaks or blunts APOB. evolutionnews.org/2019/03/lessons-from-polar-bear-studies/
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Post by Deleted on Mar 30, 2019 6:04:18 GMT -5
Although polar bears eat a lot of blubber, they also burn fat very fast.
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Post by brobear on Oct 26, 2019 10:02:28 GMT -5
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