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Friday, September 10, 2021

Young female black bears in Asheville, North Carolina, are big, have cubs early

NORTH CAROLINA STATE UNIVERSITY

Black bears (Ursus americanus) reproduced at a younger age in urban areas and were nearly twice the size of bears in national forests shortly after their first birthday, researchers from North Carolina State University and the N.C. Wildlife Resources Commission found in a new study.

Published in the Journal of Mammalogy, the study of the reproduction and size of wild black bears living in and around the city of Asheville, North Carolina, has important implications for managing urban bear populations. Also, the results raise questions about the foraging activities and diet of urban bears, and whether food from people or an abundance of natural food could be providing the bears with a reproductive advantage.

“Some of the bears in Asheville are reproducing at a young age, and they are big,” said the study’s lead author Nick Gould, postdoctoral research scholar at NC State. “It definitely leads us, as researchers, to ask additional questions: What’s driving this kind of weight gain in young bears this early in life? Are they eating natural foods, bird seed and ornamental fruit, or feeding on residential garbage?”

For this study, researchers collaborated with the residents of Asheville to capture black bears on private property between April 2014 and September 2018. The bears were temporarily sedated and then released on-site where they were captured. Researchers collected data on the bears’ weight, age, general condition, sex, and other information. The research team used GPS-equipped radio collars, which were designed to fall off naturally or to be released remotely, to track the female bears to their den sites to monitor reproductive activity.

They collected data on a total of 36 female bears around 1 year of age in Asheville. As a point of comparison, the researchers used data from three previous studies of bears living in rural areas in national forests in North Carolina and Virginia. They compared the data for urban female yearling bears to data for 95 female yearlings in rural forested areas.

Researchers determined that the 36 female bears in Asheville weighed an average of nearly 100 pounds at 1 to 1 and a half years of age. In contrast, the sample of 95 female bears living in the three national forests weighed an average of 50 pounds at a similar age.

Of the 12 female bears they were able to track back to their dens by their second birthdays in Asheville, seven produced a total of 11 cubs. In comparison, none of the three studies of bears in rural forested areas found that bears produced cubs by their second birthday.

“We didn’t expect 2-year-old females to be giving birth,” Gould said. “Based on what we know about black bears, we thought we’d see litters from bears 3 years of age and older. These results open up new areas of research to learn more about wildlife living among people in developed areas.”

The researchers analyzed and compared the availability of an important natural food source for bears – acorns and other nuts – and didn’t find differences that could help explain the larger size of these young female bears in the city.

However, researchers didn’t examine the availability of other important natural food sources like berries and didn’t investigate whether bears were eating bird seed or food and garbage left out by people. That is the current focus of ongoing research in the Asheville area led by study co-author Chris DePerno, professor of fisheries, wildlife and conservation biology at NC State, with Gould and graduate student Jennifer Strules.

“Interestingly, natural food production, in the form of nuts and other ‘hard mast’ food sources, did not influence cub production for urban bears,” Gould said. “We are left to conclude that either natural foods, in the form of soft mast like berries, or anthropogenic food sources in the form of garbage, bird seed, ornamental fruit trees or intentional feeding by people, is influencing the weight gain and early reproduction.”

Reproduction is one piece of the equation needed to better understand black bears inhabiting urban areas. Researchers said that while they appear to be reproducing earlier in some cities, urban bears’ mortality may also be high, as they are more likely to be involved in collisions with vehicles.

“If mortality is high enough to exceed reproduction, then that population is likely going to be a sink,” Gould said. “If bears are attracted to Asheville, and they establish residency because of the supplemental food sources it offers, they’re also going to be exposed to collisions with vehicles, legal harvest, and other anthropogenic threats, and therefore mortality may outpace reproduction, suggesting the population might be functioning as a sink.”

This study is part the North Carolina Urban/Suburban Bear Study, initiated by NC State and the N.C. Wildlife Resources Commission to understand urban black bears’ survival and causes of mortality, movements, reproduction and other factors when they live around cities. The goal is to help wildlife managers develop better policies for bears and other wildlife near cities.

“The entire objective is to help the Wildlife Commission better manage bears,” DePerno said. “The urban-rural interface is larger with population growth and development, and that puts greater pressure on wildlife populations.

“We have a situation in western North Carolina where we have people in a wonderful area with a lot of bears,” he added. “We want to understand: Is this a source or sink population? Are the bears moving into huntable areas? Are they considered more as residential or transitory? We are trying to understand what these bears are doing and their entire life history, including what is killing them, and what are they eating.”

Researchers also want to help educate the public.

“We want to provide good information about black bears based on the science, so we can help guide people in urban areas with bears, in Asheville or otherwise, to live responsibly with them,” Gould said.

The study, “Growth and reproduction by young urban and black rural bears,” was published online July 10, 2021, in the Journal of Mammalogy. In addition to Gould and DePerno, the other co-authors were Roger Powell and Colleen Olfenbuttel. The project was funded by the Pittman-Robertson Federal Aid to Wildlife Restoration Grant and is a joint research project between the N.C. Wildlife Resources Commission and the Fisheries, Wildlife, and Conservation Biology Program at North Carolina State University

-oleniacz-

Note to editors: The abstract follows.

“Growth and reproduction by young urban and rural black bears”

Authors: Nicholas P. Gould, Roger Powell, Colleen Olfenbuttel and Christopher S. DePerno

DOI: 10.1093/jmammal/gyab066

Published online in the Journal of Mammalogy on July 10, 2021

Abstract: Human-dominated landscapes contain fragmented natural land cover interspersed throughout an urban matrix. Animals that occupy human-dominated landscapes often grow and reproduce differently than conspecifics. Female American black bears (Ursus americanus) produce litters for the first time usually at age 4 years; 2-yearolds rarely give birth. We visited winter bear dens and trapped bears in spring and summer to compare the reproductive output and weight of female black bears within the city limits of Asheville, North Carolina, and three forested rural sites in North Carolina and Virginia representative of the undeveloped habitat of Asheville. Urban yearling females weighed nearly double (45.0 kg ± 8.1 [± SD]; n = 36) that of yearling females from the three rural study sites (23.2 ± 8.5 [Pisgah], 23.6 ± 8.3 [Virginia SW], and 23.9 ± 9.7 [Virginia NW]; n = 95). Across all sites, hard mast production during the autumn, when females were cubs, did not affect their weights as yearlings. Seven of 12 (58%) 2-year-old urban bears produced 11 cubs (mean litter size = 1.6 ± 0.8), but no 2-year-old rural females produced cubs. Production of hard mast in the autumn, when females were yearlings, did not influence cub production by 2-year-old female bears at the urban site. We hypothesize that reproduction by 2-year-old bears is linked to the availability of anthropogenic food sources associated with urban environments. To inform population level management decisions, managers and researchers should quantify urban food sources and the effects on black bear life history. If high fecundity allows urban populations to sustain relatively high mortality rates, then urban bear populations may be source populations for surrounding, rural areas. Alternately, if reproduction in urban populations cannot match high time-specific or age-specific urban mortality rates, then urban populations may be sinks for the surrounding areas.

JOURNAL

Journal of Mammalogy

DOI

10.1093/jmammal/gyab066

SUBJECT OF RESEARCH

Animals

ARTICLE TITLE

Growth and reproduction by young urban and rural black bears

ARTICLE PUBLICATION DATE

10-Jul-2021

Thursday, October 26, 2023

Opinion: Don't worry — the Hudson Bay polar bears are still doing all right

Opinion

by Special to Financial Post •

Polar bears along the shoreline of the Hudson Bay near Churchill, Man., 2022.

© Provided by Financial Post

By Susan J. Crockford

The polar bears of southern Hudson Bay are snubbed cousins of the superstars from western Hudson Bay. That’s because the west features the rail-accessible port town of Churchill, self-proclaimed “Polar Bear Capital of the World.”

Over the summer, when the sea ice melts, hundreds of polar bears come ashore near Churchill. As they wait for the ice to reform in the fall, they are viewed by tens of thousands of tourists and studied by a few dedicated polar bear scientists. Even though Southern Hudson polar bears (hereafter “southern bears”) live further south than any other in the Arctic and should logically garner the most attention from those seeking signals of human-caused climate change, it is Western Hudson polar bears (we’ll call them “western bears”) that get all the notice.

The earliest rough estimate of southern bear numbers (254 bears) was completed in 1973 and published in a 1976 Canadian Wildlife Service report , while the first western bear count (308 bears) was done in 1975 and published in 1977. These remarkably low estimates, although crude, reflected decades of wanton polar bear slaughter in Hudson Bay that had decimated bear populations. Evidence of similar declines across the Arctic prompted an international treaty to protect polar bears in 1973.

It is now known that both western and southern bears, as well as bears from Foxe Basin to the north, hunt on the ice over the winter, with the potential for inter-breeding during the spring mating season. A genetic study published in 2016 suggested moving the long-established boundaries for western bears, since it was apparent that they may come ashore over a much larger range of coastline than previously thought. Southern bears, on the other hand, rarely move out of James Bay, not even to hunt during the winter.

This brings us to the 2021 population surveys that revealed an apparent 27 per cent decline in the western bear population but a 30 per cent increase for southern bears. Unfortunately, the survey for southern bears was not available when news of the western bear decline was made public — and generated considerable alarm — in December 2022.

According to the report released first, which was by Stephen Atkinson and colleagues, the three most recent population estimates for western bears were 949 (range 618-1280) in 2011, 842 (range 562-1,121) in 2016 and 618 (range 385-852) in 2021. As mentioned, the apparent change from 2016 to 2021 was a 27 per cent decline — although, as the authors noted, that’s not statistically significant.

The overall drop apparently was driven by a decline of more than 200 adult females and sub-adult bears, especially in the area around Churchill. The authors considered but rejected the possibility that these bears had simply relocated into southern Hudson Bay. Oddly, in light of the 2016 study about changing habitat boundaries, they did not consider the possibility that the “missing” animals had relocated northward into Foxe Basin territory.

Sea ice in Foxe Basin almost always lingers well into August, so it might now be preferred as a summering and denning area by some western bear females and young bears looking for more predictable ice conditions. Foxe Basin bears haven’t been surveyed since 2010 but they were then doing very well, with an estimated population size of 2,580.

As for southern bears, their numbers went from 943 in 2012 (range 658-1350) to 780 in 2016 (range 590-1029), and then to a whopping 1,119 in 2021 (range 860-1,454) — which gives, as noted, an increase of 30 per cent over five years. The study’s authors don’t actually say if that’s statistically significant but it seems likely it is, since they concluded a natural increase in numbers had indeed occurred and they couldn’t verify immigration of bears from another subpopulation.

Overall, the authors of both reports seemed hard-pressed to explain their results. A loss of hundreds of western bears from 2016-2021 is not consistent with the prevailing hypothesis that lack of sea ice drives long-term declines in polar bear numbers: sea ice conditions in western Hudson Bay were better for the first four of those years than they had been in decades — only 2021 was not as good — and southern bear numbers increased markedly with similar ice conditions in their part of Hudson Bay over the same period.

Were polar bears dying in one region during 2017-2021 — for reasons not having to do with sea ice — but reproducing like crazy just next door? Or were hundreds of western bears moving undetected between subpopulation boundaries? If movement into Foxe Basin does explain the recent survey results for western bears, it means they haven’t been counted properly for decades. That’s a big problem for polar bear scientists and conservation organizations because it suggests western bears — and therefore all polar bears — may not be threatened with extinction due to loss of sea ice, as previously thought.

Susan J. Crockford, a zoologist, is author of Polar Bear Evolution: A Model for How New Species Arise (2023).

Saturday, February 15, 2020

Understanding different brown bear personalities may help reduce clashes with people

by Anthony King, From Horizon Magazine,
Horizon: The EU Research & Innovation Magazine

Understanding different brown bear personalities may help reduce clashes with people

Brown bears show individuality in the distance they travel each day, their preference for daytime or night-time movement and other behaviours, according to research. Credit: Rufus46, licensed under CC BY-SA 3.The brown bear is one of Europe's five large carnivores and can sometimes cross paths with people, with potentially fatal consequences. But bears have different personalities and behaviours, say researchers, and understanding this is the key to reducing conflict and protecting both them and humans.

Brown bears once thrived in woodlands throughout Europe, but human persecution decimated their numbers. Today, populations are highest in mountainous rural regions close to the Balkans and Carpathian Mountains, which are home to around 12,000 of Europe's 17,000 brown bears.

With greater legal protections, bears are recovering and recolonising landscapes, such as the Alps and Pyrenees. The challenge now is in managing co-existence of people and carnivores, as brown bears prey on livestock, raid beehives and sometimes pose a threat to people.

In Romania, home to an estimated 6,000 bears, they may enter villages, towns, even cities. They can maim or kill people, with brown bears being responsible for multiple deaths in 2019.

People are also a problem for the bears. "We have this return of large carnivores often returning to landscapes that are human dominated and that is a challenge for many of the carnivores themselves," said Professor Thomas Mueller, an expert in animal movements at the Senckenberg Biodiversity and Climate Research Centre in Frankfurt, Germany.

Adolescent bears typically can suffer high death rates, for example due to road collisions.

Understanding carnivore behaviour is one way to help manage conflict between people and animals, said Prof. Mueller.

Movements

According to Dr. Anne Hertel, who studies bear behaviour as part of Prof Mueller's group, this needs to be done at an individual level. As part of her Ph.D. studies at the Norwegian University of Life Sciences, she tracked bear movements in Swedish forests, examining how they foraged, avoided humans and selected areas to live.

Bears hibernate in dens from November to April, when females give birth to cubs. Females stay with their mothers for around two years and set up home nearby, whereas males disperse much further. Dr. Hertel never once chanced upon a wild bear in Sweden.

"They avoid humans at all cost, which makes studying their personality hard," she explained. She relied on movement data from radio-collared bears, generally captured as cubs with their mother in their second year. Before release, a sample of hair was taken.

By tracking 46 adult brown bears, she identified six ways in which bears' behaviour can vary: the distance they travel per day, the distance between where they began and where they ended up each day, their preference for night-time or day-time movement, and whether they liked or avoided open areas including roads, bogs and forest clearings.

"We find that bear behaviour is consistent over time, with some more active in daytime, and some selecting habitat closer to roads, or more open habitat such as bogs and clear-cut forest," Dr. Hertel said. "Bears are quite different from each other. Nocturnal bears tend to be quite sedentary, while others more active during daytime move a lot."

Carnivory

Swedish bears eat mostly forest berries, but some have a higher meat intake, preying on young moose. Dr. Hertel is determining which bears eat more meat by examining a chemical signature in the hair collected. "Our next step is to see whether carnivory is a trait which can be learnt from their mother," she said.

Europe, according to the IUCN's Large Carnivore Initiative for Europe, 44% of which live in the Carpathian mountains, which span Romania, Poland, Slovakia and Serbia. Credit: Horizon

She is also trying to work out how individuality in behaviour can change over time through learning, or remain stable, and whether it can be predicted, as part of a project called PERSONALMOVE. Her findings could feed into predictions of bear movements, especially of young males which disperse to establish new territories, and help understand which ones are most likely to move through areas where people live.

Whether findings from Sweden can be translated to other parts of Europe, such as Romania, is unclear as conditions are different and there is very little data to test the hypothesis, says Dr. Hertel.

"Romania is one country in Europe which has the most bears by far, and they have more conflict in terms of them entering human settlements and causing problems," she said. She believes that this conflict stems from a combination of bear behavioural traits, opportunities for them to feed on foods like human trash and management techniques.

Hunting

Romania traditionally allowed bear hunting, but when it entered the EU in 2007, bears became a protected species. Hunting was banned altogether in 2016, but it is difficult to know the effect this has had on bear populations as there is no data available.

"Previously, populations were managed in order to maximise hunting bags," said Dr. Valeria Salvatori at the Istituto di Ecologia Applicata in Italy. "The population of bears in Romania has been maintained at artificially high levels through artificial feeding for decades."

Forestry activity has risen since the country joined the EU, and some suggest that disturbance is driving bears out to search villages for food. But Dr. Salvatori had first seen bears eating from city garbage dumps almost two decades ago, when she did Ph.D. research in the Carpathians.

While pro-hunting groups highlight conflicts between bears and people, Dr. Salvatori says that in rural areas, attitudes towards bears are not negative.

In places such as Hargita, a hotspot for bears in Transylvania, people believe that the current situation and the damage being caused by bears is not sustainable, but they are used to bears and often seek to explain and even excuse bear behaviour when conflict arises, says Dr. Salvatori.

She ran EU-funded workshops to try to improve co-existence with bears in Romania, with livestock owners, beekeepers, game managers, hunters, and small environmental organisations included in monthly meetings.

Normal

"The general attitude is that it is normal to have bears, but that encounters with bears should be better managed," Dr. Salvatori said. "There is no strong opposition to using hunting as a management tool, provided that it is not detrimental to their population." Also, people felt that bear tourism needed to be better regulated.

Her workshops generated various recommendations to avoid conflicts with bears and stop them raiding beehives and crops and killing livestock, such as securing bins in bear areas, and putting up electric fences in touristic spots.

Another, more individual, option highlighted by Dr. Hertel is hazing, where specific problem bears are targeted with rubber bullets or dogs to deter them from people.Scientists, animal activists: Don't cull Romanian brown bear

Provided by Horizon: The EU Research & Innovation Magazine

Thursday, June 16, 2022

Shaky oasis for some polar bears found, but not for species

SETH BORENSTEIN
Thu, June 16, 2022

An adult female polar bear, left, and two 1-year-old cubs walk over snow-covered freshwater glacier ice in Southeast Greenland in March 2015. With limited sea ice, these Southeast Greenland polar bears use freshwater icebergs spawned from the shrinking Greenland ice sheet as makeshift hunting grounds, according to a study in journal Science released Thursday, June 16. (Kristin Laidre via AP)

With the polar bear species in a fight for survival because of disappearing Arctic sea ice, a new distinct group of Greenland bears seem to have stumbled on an icy oasis that might allow a small remote population to “hang on.”

But it’s far from “a life raft” for the endangered species that has long been a symbol of climate change, scientists said.

A team of scientists tracked a group of a few hundred polar bears in Southeast Greenland that they show are genetically distinct and geographically separate from others, something not considered before. But what’s really distinct is that these bears manage to survive despite only having 100 days a year when there’s sea ice to hunt seals from. Elsewhere in the world, polar bears need at least 180 days, usually more, of sea ice for them to use as their hunting base. When there’s no sea ice bears often don’t eat for months.

With limited sea ice, which is frozen ocean water, these Southeast Greenland polar bears use freshwater icebergs spawned from the shrinking Greenland ice sheet as makeshift hunting grounds, according to a study in Thursday’s journal Science. However, scientists aren't sure if they are thriving because they are smaller and have fewer cubs than other polar bear populations.

“These polar bears are adapted to living in an environment that looks like the future,” said study lead author Kristin Laidre, a polar bear biologist at the University of Washington, who over nine years tracked, collared and tested the all-white bears usually from a helicopter hovering the white snow and ice backdrop. “But most bears in the Arctic don’t have glacial ice. They don’t have access to this. So it can’t be taken out of context like somehow this is like a life raft for polar bears around the Arctic. It’s not. Greenland is unique.”

“We project large declines of polar bears across the Arctic and this study does not change that very important message," Laidre said. "What this study does is show that we find this isolated group living in this unique place... We’re looking at where in the Arctic polar bears can as a species hang on, where they might persist.”

The freshwater ice will keep coming off the ice sheet for centuries giving limited hope that this is “a place that polar bears might continue to survive’’ but it’s separate from an overall trend of sea ice loss in the summer because of emissions of heat-trapping gases from the burning of coal, oil and natural gas, said National Snow and Ice Data Center deputy lead scientist Twila Moon, a study co-author.

These bears hunt on the fresh glacial ice that has more peaks and valleys than the flatter sea ice, often in house- or car-sized bergs, called bergy bits, Moon said.

This population of polar bears are on the southeast tip of the giant island, where there are no towns. For years scientists figured these bears were part of the same population in Northeast Greenland, just roaming up and down the massive coast. But they don’t, Laidre said. An unusual set up of winds, currents and geographical features around 64 degrees North make it next to impossible for bears to move north of that point, the current sends them south fast, she said.

While most bears travel 25 miles (40 kilometers) over four days, the Southeast Greenland bears go about 6 miles (10 kilometers) in the same time, the study said.

“They just stay in the same place for years and years," Laidre said.

Genetic testing Laidre and colleagues did showed they are more different from the neighboring populations than any other pair of polar bear populations on Earth, said study co-author Beth Shapiro, a University of California Santa Cruz evolutionary geneticist.

Occasionally, a bear from elsewhere breeds with the southeast bear, but Shapiro said it’s infrequent and only one-way with no bear heading north and breeding with that population.

In general these bears are thinner than other Arctic bears, with females weighing about 400 pounds (185 kilograms), compared to 440 to 560 pounds (199 to 255 kilograms) elsewhere in the North American Arctic, Laidre said. And they also tend to have fewer cubs, which could be because they are so isolated and don’t get as many mating opportunities, she said.

Because this group hadn’t been studied before, Laidre said it is impossible to tell if the Southeast Greenland polar bear population has just adapted to be smaller and have fewer cubs or whether these are indicators of a stressed population and not a good sign for survival. Shapiro and others don't think it looks good.

“They’re not reproducing as much as other individuals,” Shapiro said. “They’re not as healthy as other individuals who are in a better habitat. So it’s kind of an oasis maybe, but it’s not a happy oasis. It’s a I’m-struggling-to-get-by-but-just-making-it kind of oasis.”

Long-time polar bear scientist Steve Amstrup of Polar Bear International, who wasn’t part of the study, said he worries that people will wrongly take this research to mean polar bears can adapt to climate change, when it’s about one small group that is prolonging their ability to persist, adding that this “does not offer salvation.” While this group is distinct he said he fears that calling attention to it “may in fact diminish the natural isolation they currently enjoy.”

This shows “that we can still really have surprises,” Moon said. “And I’m constantly reminded that there’s not ever a point where we throw in the towel.”

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Follow AP’s climate coverage at https://apnews.com/hub/climate

___

Follow Seth Borenstein on Twitter at @borenbears

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Associated Press climate and environmental coverage receives support from several private foundations. See more about AP’s climate initiative here. The AP is solely responsible for all content.

Isolated Greenland polar bear population adapts to climate change

Thu, June 16, 2022
By Will Dunham

WASHINGTON (Reuters) - An isolated population of polar bears in Greenland has made a clever adaptation to the decline in the sea ice they depend upon as a platform for hunting seals, offering a ray of hope for this species in at least some locales in the warming Arctic.

This population of several hundred bears, inhabiting part of Greenland's southeast coast on the Denmark Strait, has survived with only abbreviated access to ice formed from frozen seawater by hunting instead from chunks of freshwater ice breaking off from the huge Greenland Ice Sheet, researchers said on Thursday.

"They survive in fjords that are sea-ice free more than eight months of the year because they have access to glacier - freshwater - ice on which they can hunt. This habitat, meaning glacier ice, is uncommon in most of the Arctic," said University of Washington polar scientist Kristin Laidre, lead author of the study published in the journal Science.

They were found to be the world's most genetically isolated polar bears, distinct from the species' 19 other known populations. They have been almost entirely cut off from other polar bears for at least several hundred years, with no evidence of any leaving, though some evidence of an occasional arrival from elsewhere.

These bears are "living at the edge of what we believe to be physiologically possible," said evolutionary molecular biologist and study co-author Beth Shapiro of the University of California, Santa Cruz and the Howard Hughes Medical Institute.

"These bears are not thriving. They reproduce more slowly, they're smaller in size. But, importantly, they are surviving. It's hard to know yet whether these differences are driven by genetic adaptations or simply by a different response of polar bears to a very different climate and habitat," Shapiro added.

Polar bears, numbering roughly 26,000 in all, are particularly imperiled by climate change as rising temperatures reshape the Arctic landscape and deprive them of their customary sea-ice platform for hunting their main prey, ringed seals and bearded seals.

"Loss of Arctic sea ice is still the primary threat to all polar bears. This study does not change that," Laidre said.

The southeast Greenland population is geographically hemmed in, with jagged mountain peaks and the Greenland Ice Sheet on one side and the open ocean on the other. In springtime, the bears roam sea ice and glaciers, with icebergs frozen solid into the sea ice. In summertime, there is open water with floating pieces of glacial ice at the fronts of glaciers, from which the bears hunt. This type of habitat is found only in parts of Greenland and Svalbard, an Arctic Ocean archipelago.

"This use of glacier ice has not been documented before and represents a unique behavior," said John Whiteman, chief research scientist for the conservation group Polar Bears International and a biology professor at Old Dominion University in Virginia, who was not involved in the study.

"This study should also prompt a search for similar habitats across the current polar bear range. However, glacial ice is a minor component of the marine ice cap in the Arctic, in comparison to ice formed from freezing seawater," Whiteman said.

The researchers gathered genetic, movement and population data including satellite tracking of some bears and observing them from a helicopter.

"They simply look like a small yellow dot on the white ice, or you follow their tracks in the snow to find them," Laidre said.

Shapiro said the findings may provide a glimpse of how polar bears survived previous warm periods over the roughly 500,000 years since they split evolutionarily from brown bears.

"Polar bears are in trouble," Shapiro added. "It is clear that if we can't slow the rate of global warming that polar bears are on a trajectory to become extinct. The more we can learn about this remarkable species, the better able we will be to help them to survive the next 50 to 100 years."

(Reporting by Will Dunham, Editing by Rosalba O'Brien)

Tuesday, June 07, 2022

How species form: What the tangled history of polar bear and brown bear relations tells us

It’s complicated. Rather than simple splitting events, the species histories of polar and brown bears, like those of humans, hide convoluted stories of divergence and interbreeding, study finds

Peer-Reviewed Publication

UNIVERSITY AT BUFFALO

BUFFALO, N.Y. — A new study is providing an enhanced look at the intertwined evolutionary histories of polar bears and brown bears.

Becoming separate species did not completely stop these animals from mating with each other. Scientists have known this for some time, but the new research draws on an expanded dataset — including DNA from an ancient polar bear tooth — to tease out more detail.

The story that emerges reveals complexities similar to those that complicate human evolutionary history.

“The formation and maintenance of species can be a messy process,” says Charlotte Lindqvist, PhD, associate professor of biological sciences in the University at Buffalo College of Arts and Sciences, and an expert on bear genetics. “What’s happened with polar bears and brown bears is a neat analog to what we’re learning about human evolution: that the splitting of species can be incomplete. As more and more ancient genomes have been recovered from ancient human populations, including Neanderthals and Denisovans, we’re seeing that there was multidirectional genetic mixing going on as different groups of archaic humans mated with ancestors of modern humans. Polar bears and brown bears are another system where you see this happening.”

“We find evidence for interbreeding between polar bears and brown bears that predates an ancient polar bear we studied,” she says. “And, moreover, our results demonstrate a complicated, intertwined evolutionary history among brown and polar bears, with the main direction of gene flow going into polar bears from brown bears. This inverts a hypothesis suggested by other researchers that gene flow has been unidirectional and going into brown bears around the peak of the last ice age.”

The study will be published the week of June 6 in the Proceedings of the National Academy of Sciences. It was led by Lindqvist at UB in the U.S.; Luis Herrera-Estrella at the National Laboratory of Genomics for Biodiversity (LANGEBIO) in Mexico and Texas Tech University in the U.S.; and Kalle Leppälä at the University of Oulu in Finland. Tianying Lan, PhD, a former UB postdoctoral researcher now at Daicel Arbor Biosciences, was co-first author with Leppälä.

The concept of Arctic-adapted polar bears capturing genetic material from brown bears, which are adapted to life in lower latitudes, is one of several findings of possible interest for scientists concerned with climate change impacts on threatened species.

As the world warms and Arctic sea ice declines, polar bears and brown bears may run into each other more frequently in places where their ranges overlap. This makes their shared evolutionary history a particularly intriguing subject of study, Lindqvist says.

CAPTION

An adult male polar bear in northwestern Greenland.

CREDIT

Credit: Øystein Wiig

Splitting of species can be a messy process

As Lindqvist explains, scientists once thought modern humans and Neanderthals simply split into separate species after evolving from a common ancestor. Then, researchers found Neanderthal DNA in modern Eurasian people, implying that modern human populations received an influx of genes from Neanderthals at some point in their shared evolutionary history, she says.

Only later did scientists realize that this genetic intermingling also supplemented Neanderthal populations with modern human genes, Lindqvist adds. In other words, interbreeding can be complex, not necessarily a one-way street, she says.

The new study on bears reveals a remarkably similar story: The analysis finds evidence of hybridization in both polar bear and brown bear genomes, with polar bears in particular carrying a strong signature of an influx of DNA from brown bears, researchers say. Earlier research proposed the inverse pattern only, Lindqvist says.

“It’s exciting how DNA can help reveal ancient life history. Gene flow direction is harder to determine than merely its presence, but these patterns are vital to understanding how past adaptations have transferred among species to give modern animals their current features,” says Leppälä, PhD, postdoctoral researcher in the research unit of mathematical sciences at the University of Oulu.

“Population genomics is an increasingly powerful toolbox to study plant and animal evolution and the effects of human activity and climate change on endangered species,” says Herrera-Estrella, PhD, President’s Distinguished Professor of Plant Genomics and director of the Institute of Genomics for Crop Abiotic Stress Tolerance in the Texas Tech Department of Plant and Soil Science. He is also a professor emeritus at LANGEBIO. “Bears don’t provide simple speciation stories any more than human evolution has. This new genomic research suggests that mammalian species groups can hide complicated evolutionary histories.”

CAPTION

The subfossil jawbone of a polar bear that lived 115,000 to 130,000 years ago in Norway’s Svalbard archipelago. A genomic study includes an analysis of DNA extracted from a tooth attached to this jawbone, which is now housed at the Natural History Museum at the University of Oslo.

CREDIT

Credit: Photo by Karsten Sund, Natural History Museum (NHM), University of Oslo

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CREDIT

Credit: Photo by Karsten Sund, Natural History Museum (NHM), University of Oslo

Evidence from modern bear genomes — and DNA from an ancient tooth

The study analyzed the genomes of 64 modern polar and brown bears, including several new genomes from Alaska, a state where both species are found.

The team also produced a new, more complete genome for a polar bear that lived 115,000 to 130,000 years ago in Norway’s Svalbard archipelago. DNA for the ancient polar bear was extracted from a tooth attached to a subfossil jawbone, which is now housed at the Natural History Museum at the University of Oslo.

Using this dataset, researchers estimate that polar bears and brown bears started to become distinct species about 1.3 to 1.6 million years ago, updating prior assessments made by some of the same scientists. The age of the split has been and remains a topic of scientific debate, with past interbreeding and limited fossil evidence for ancient polar bears among factors that make the timing hard to pinpoint, Lindqvist says.

In any case: After becoming their own species, polar bears endured dramatic population decline and a prolonged genetic bottleneck, leaving these bears with much less genetic diversity than brown bears, the new study concludes. The findings confirm past research pointing to the same trends, and add evidence in support of this hypothesis.

Together with the analysis of gene flow, these findings are providing new insights into the messy, intertwined evolutionary history of polar bears and brown bears.

The international research team included scientists from UB, LANGEBIO, Texas Tech, the University of Oulu, the Far Northwestern Institute of Art and Science, the Alaska Department of Fish and Game, the Natural History Museum at the University of Oslo, Nanyang Technological University, University of Helsinki, and Aarhus University.

The research was funded by the National Fish and Wildlife Foundation, U.S. National Science Foundation, Alaska Department of Fish and Game, and U.S. Geological Survey.

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Genomes analyzed in a new study on bears include that of this bear, pictured here in 1995 on Alaska's North Slope. Scientists had wondered if this bear might be a brown bear-polar bear hybrid, but the new research finds that, “This bear is not a hybrid, but simply a light-colored brown bear,” says University at Buffalo biologist Charlotte Lindqvist.

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Credit: Richard Shideler, Division of Wildlife Conservation, Alaska Department of Fish and Game