Tag Archives: genetics

Prehistoric polar bear find has elongated body type Inuit know as a ‘weasel bear’

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.

Weasel bear headline with skull graphic 18 March 2017

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Genetic similarity of polar bears does not make them vulnerable to global warming

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.

Beaufort Sea male polar bear USGS_2005 Amstrup photo

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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Paleoclimate + genetic study confirms: Arctic species adapted to sea ice changes

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.

Healy Aug  24 2015 Polar-Bear V Tim Kenna

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:

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Polar bear gene flow blamed on melting ice is another model result that doesn’t make sense

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.

Svalbard as a potential warm refugium_Jan 8 2015_PolarBearScience

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.

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Evolution by geneticists again: yet another date for when polar bears arose

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.

Lui et al. 2014 figure provided in the abstract.

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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New genetic study confirms polar bears survived several warm Interglacials

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).

Figure1 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 from the Chukchi, Beaufort and Barents Sea populations.

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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New polar bear population status documents completed but have been withheld

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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