Two scientific papers in June on polar bear evolution got a bit of media attention but not what the topic deserves. I’ve not written about them because I am currently working on a larger piece putting this conflicting genetic information into full context. Have patience, it’s coming.
Comments Off on Polar bear evolution and recent genetic papers
Posted in Evolution, Hybridization, Sea ice habitat
Tagged brown bear, divergence, evolution, genetics, polar bear, speciation
Researchers have discovered that the 300 or so polar bears living in SE Greenland (below 64 degrees N) are so genetically distinct and geographically isolated that they qualify as a unique subpopulation, adding one more to the 19 subpopulations currently described by the IUCN Polar Bear Specialist Group.
Previously, polar bear researchers simply assumed all of the bears in East Greenland were part of the same subpopulation but no field work had been conducted in the extreme southern area until 2015-2017. When they included this region, they got a big surprise: now they are spinning it as significant for polar bear conservation (Laidre et al. 2022).
Continue readingComments Off on Newly-discovered SE Greenland polar bear subpopulation: another assumption proven false
Posted in Life History, Population, Sea ice habitat
Tagged genetically distinct, genetics, glaciers, Greenland, IUCN, movements, new subpopulation
A story that broke in Alaska newspapers a month ago made the UK press this weekend about the archaeological discovery of 1,300 year old polar bear skull that may be associated with an unusual body type known to Inuit hunters. See the Mail Online cropped headline below, full story here – and some quotes and critical background below.
Comments Off on Prehistoric polar bear find has elongated body type Inuit know as a ‘weasel bear’
Posted in History, Life History
Tagged ancient, archaeological remains, body type, genetics, history, king bear, polar bear, race, subspecies, weasel bear
A new genetics paper suggests that global warming will “fragment” polar bear habitat to such an extent that it will further reduce the already-low genetic variability documented in the bears, with disastrous effects on survival.
However, that argument only works if you disregard a rather large body of literature on other mammals as well as the history of polar bears themselves. I’ve addressed this issue before (“Low genetic diversity will not make polar bears more vulnerable to extinction”) and what I said then needs to be repeated now:
“…there is lots of evidence to support my contention that polar bears are not more vulnerable to extinction just because they have low genetic diversity.”
I continued:
“Many populations that were reduced to very low numbers (i.e., gone through a ‘bottleneck’ ), ending up with low genetic variation, have subsequently recovered dramatically without adverse affects.
In other words, they not only recouped their population size after a population bottleneck but did so while dealing with subsequent environmental fluctuations and other natural threats to their survival (Lehman 1998:R723-724).
In some cases, genetic diversity increased after a population bottleneck, via mechanisms biologists are only just beginning to understand.”
In fact, there is good evidence to suggest that ice age cooling is what previously fragmented polar bear populations: past warm interglacial periods brought bears closer together, confined more or less to the area within the Arctic Circle – even in winter.
Go back and read the entire genetic diversity post. I concluded it by recounting several examples of abundant and successful mammal populations with low genetic diversity (with references), including Northern elephant seals, Guadalupe fur seal, Sand Nicolas Island fox, Mouflon sheep, and North Atlantic right whale. The details are worth reviewing. If you can’t access a paper you want to read, contact me via the contact page above and I’ll send it along.
Regarding this new paper (Kutschera et al. 2016), what I said before needs repeating:
“To suggest that polar bears cannot endure a bit of Arctic warming in the future (whether natural or due to human influences on climate, or a bit of both) is absurd: climatic extremes have defined the evolutionary history of polar bears, which means that climatic extremes have fine-tuned their biological adaptability.”
In fact, the paleoclimate/genetics paper by Cronin and Cronin (2015) which I summarized a few days ago, documents those climatic extremes. See below for details on the polar bear genetic diversity paper.
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Comments Off on Genetic similarity of polar bears does not make them vulnerable to global warming
Posted in Conservation Status, Evolution, Sea ice habitat
Tagged Cronin, diversity, extinction, facts, fragmentation, genetics, global warming, ice age, Iceland, Kutschera, paleoclimate, polar bear, polar bear habitat, sea ice, similarity
A new paper that combines paleoclimatology data for the last 56 million years with molecular genetic evidence concludes there were no biological extinctions [of Arctic marine animals] over the last 1.5M years despite profound Arctic sea ice changes that included ice-free summers: polar bears, seals, walrus and other species successfully adapted to habitat changes that exceeded those predicted by USGS and US Fish and Wildlife polar bear biologists over the next 100 years.
Cronin, T. M. and Cronin, M.A. 2015. Biological response to climate change in the Arctic Ocean: the view from the past. Arktos 1:1-18 [Open access] http://link.springer.com/article/10.1007/s41063-015-0019-3
Thomas Cronin is a USGS paleoclimatologist at the Eastern Geology and Paleoclimate Science Center, and Matthew Cronin is a molecular geneticist at the University of Alaska Fairbanks (see previous posts here and here about Matt’s work on the genetics of polar bear evolution).
From the Abstract:
Arctic climatic extremes include 25°C hyperthermal periods during the Paleocene-Eocene (56–46 million years ago, Ma), Quaternary glacial periods when thick ice shelves and sea ice cover rendered the Arctic Ocean nearly uninhabitable, seasonally sea-ice-free interglacials and abrupt climate reversals.
The final discussion and two summary graphics from this paper (copied below) are especially useful:
Comments Off on Paleoclimate + genetic study confirms: Arctic species adapted to sea ice changes
Posted in Evolution, Sea ice habitat, Summary
Tagged adaptation, Arctic, arctic seals, biological responses, climate change, climate extremes, Cronin, evolution, facts, genetics, glacial, he, ice-free summer, information, interglacial, LGM, marine mammals, paleoclimate, polar bear, resilience, sea ice, USGS, walrus
Polar bear researchers just published a study that suggests polar bears have moved around the Arctic in direct response to recent sea ice changes — a conclusion I suggest you take with a grain of salt and a raised eyebrow.
That’s because they have also proposed, among other things, that the Svalbard Archipelago was a sea ice refugium during warm interglacial periods, and could be again if the Arctic warms as predicted. That they would accept and promote such a model-based conclusion, which has no relationship with reality, calls their scientific judgment into question.
Based on genetic model results, the Svalbard Archipelago (circled) has been proposed as a sea ice refugium for polar bears during previous warm Interglacial periods and during predicted sea ice declines in the future. Yet most years since 1979 (2014 was one exception), this region has been ice free during the summer, making Svalbard a decidedly poor candidate for retaining sea ice when it’s much warmer than today.
Comments Off on Polar bear gene flow blamed on melting ice is another model result that doesn’t make sense
Posted in Population, Sea ice habitat
Tagged Canadian Arctic Archipelago, Cronin, DNA, extinction, gene flow, genetics, Hamilton, Miller, models, PBSG, Peacock, polar bear, Polyak, predictions, refugium, sea ice, warming Arctic
The latest addition to the never-ending story of when-and-why polar bear evolution took place according to geneticists (Liu et al. 2014 — the 8th such paper in less than 4 years, if you can believe it) is getting way, way more media attention than it deserves.
Liu et al. 2014 figure provided in the abstract.
This multi-member research team used a new data set (mostly Scandinavian brown bears and Greenland polar bears, for a change) to add not much of anything new on the evolutionary insight front except yet another estimate of when polar bears came to be.1
However, the real focus of the paper is the description of their finding of a few genetic differences between brown bears and polar bears that they identified. They found a few genes in polar bears were different than brown bears and made a boat load of assumptions about what these might mean.
Their discovery was not accompanied by any attempt to demonstrate that the changes in gene architecture they found also involved a change in the function of the genes or were associated with different effects on bear physiology. If a changed gene cannot be shown to act differently or to have a demonstrated new physiological effect on the animal in question, the changes themselves mean next to nothing – especially for evolution!
That’s my take – see what you think. It looks long but a lot of it is quotes.
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Comments Off on Evolution by geneticists again: yet another date for when polar bears arose
Posted in Evolution
Tagged adaptation, age of polar bears, APOB gene, blubber, brown bear, evolution, fat genes, genetic divergence, genetics, high-fat diet, Liu, polar bear, speciation, UC Berkeley, when polar bears arose
There is a new polar bear genetics paper out in the Journal of Heredity, by University of Alaska Fairbanks genetics professor Matt Cronin and colleagues. Matt Cronin, in case you didn’t know, was the first to pick up the close genetic relationship between polar bears and grizzlies, as a result of research he and colleagues did back in the early 1990s (Cronin et al. 1991).
Figure 1 from Cronin et al. 2014 (in press) showing the locations of bear samples used in their genetic study. MT, Montana; AK, Alaska; Polar bear samples were taken from the Chukchi, Beaufort and Barents Sea populations.
While no earth-shattering new information was revealed in this new study, reported over the weekend by the Alaska paper SitNews (March 15), it used a more detailed method to confirm the results of previous work – that polar bears have been around long enough to have survived several past Interglacial periods that were warmer than today (with less ice in the Arctic) and are genetically distinct from grizzlies.
A feature that really set this work apart was how it was promoted.
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Comments Off on New genetic study confirms polar bears survived several warm Interglacials
Posted in Evolution, Hybridization, Sea ice habitat
Tagged Beth Shapiro, Cahill, Ed Green, genetics, geological time, global warming, Matthew Cronin, polar bear, polar bear evolution, survival, University of Alaska Fairbanks, warm interglacials
I suggested in my last post of 2013 that the biologists of the IUCN Polar Bear Specialist Group (PBSG) might have learned some lessons over the last year about the folly of withholding evidence, fudging data, and trying to hide good news. However, it appears that was wishful thinking.
In the course of writing the essay on my top posts of 2013, I went to the PBSG website to check something, and blow me over with a feather, found an announcement that had been added a few weeks ago (December 16, 2013) without a whisper to the media.
The old PBSG page, “Population status” – which used to say “The total number of polar bears worldwide is estimated to be 20,000 – 25,000” – has been replace by a notice entitled “Population status reviews.”
The former estimate population estimate (“20,000 – 25,000”) can no longer be found on the website and no other figure is offered.
The sidebar menu option “Status table” says “will be published soon.”
I’ve copied the short PBSG notice in its entirety below (pdf here):
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Comments Off on New polar bear population status documents completed but have been withheld
Posted in Conservation Status, Population
Tagged advocacy, communication, genetics, IUCN, PBSG, Polar Bear Specialist Group, population status, population status review, press release, subpopulation boundaries
The authors of a new paper out in PLoS Genetics (Cahill et al. 2013, entitled “Genomic Evidence for Island Population Conversion Resolves Conflicting Theories of Polar Bear Evolution”) propose to explain how and why the brown bears (aka grizzlies) of the ABC islands of southeast Alaska (Admiralty, Baranof, and Chicagof – see previous post here), got to be so genetically distinct from brown bears on the Alaska mainland and so surprisingly similar (genetically) to polar bears. The authors determined (using a model) that this genetic pattern could be explained by an ancient hybridization event resulting from female polar bears cavorting with male brown bears in SE Alaska.
I had some issues with the way the paper was promoted by some of the co-authors, which I dealt with separately here. More importantly, I found the scenario these geneticists offered to explain how hybridization might have occurred to be patently implausible. Geological and fossil evidence from SE Alaska largely refutes their scenario, although another explanation may be more tenable. It is not impossible, in my opinion, that hybridization occurred in SE Alaska during the last Ice Age, but if it did, it almost certainly did not happen the way Cahill and colleagues suggest.
Comments Off on Polar bears cavorting with ABC brown bears not supported by geological and fossil evidence
Posted in Evolution, Hybridization
Tagged ABC bears, black bears, brown bears, Cahill, genetics, Haida Gwaii, hybridization, Jim Baichtal, last glacial maximum, polar bear evolution, Prince of Wales Island, ringed seals, SE Alaska, sea ice extent, Tim Heaton
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