Tag Archives: hybridization

New genetics paper is not about whether climate change causes polar bear hybrids

A new paper on the evolutionary history of bears (Bears breed across species borders: Kumar et al. 2017) has concluded that hybridization is common and natural among all species of ursids. And while some media outlets (e.g. DailyMail) have framed this as surprisingly convincing proof that experts were wrong to claim that climate change is the cause of recent polar bear X grizzly hybrids, definitive evidence against that interpretation has been available for years to anyone who bothered to look: see my recent “Five facts that challenge hybridization nonsense.”

This genetic evidence is just a cherry on top of the rest but will help get the paper the media attention the authors crave.

Polar bear X grizzly hybrids were known long before climate change and sea ice decline became an issue. See also previous posts here, here, and here. In fact, as I’ve pointed out, “most polar bear hybrids said to exist have not been confirmed by DNA testing” (including virtually all of the bears specialist Andrew Derocher claimed were hybrids, including the latest one from 2016 that prompted such gems as “Love in the time of climate change”).

pizzly_andrewderocher_300dpi_2017 paper

A polar bear X grizzly hybrid, see Kumar et al. 2017. Photo by A. Derocher.

In my opinion, the most important conclusion of this paper is that occasional but widespread hybridization among bears is why it has been so hard to say with confidence when polar bears arose (which I addressed years ago, in my Polar bear evolution series: Part 1, Part 2, and Part 3). You cannot use traditional methods of pinpointing the timing of speciation events from genetic data if one or more of the species have hybridized (traded genes). See the long, fuzzy “divergence times” for bears in the image below from the Kumar paper.

Kumar et al 2017 hybridization in bear evolution_fig 5

From Kumar et al. 2017, Fig. 5: “The scale bar shows divergence times in million years and 95% confidence intervals for divergence times [speciation events] are shown as shadings.”

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Polar bear hybrid update: samples sent for DNA testing to rule out blonde grizzly

That putative polar bear hybrid shot in Arviat last week has been sent for DNA testing.

hybrid-bear_didji-ishalook-15 May2016_facebook

Just out from NunatsiaqOnline (24 May 2016): Nunavut biologist sends possible “grolar” bear DNA for analysis: Unusual bear killed in Arviat could just be a blonde grizzly bear

Additional details confirm the animal shot was a female, which could account for the fact it was described as “small”. The Nunavut biologist who sent in the sample for testing warned it could also be a blonde grizzly, as I pointed out last week.

UPDATE 24 May 2016: Comments added below from a Toronto Star news report below on the hybrid identity of this animal.

UPDATE 28 May 2016: See this 27 May 2016 follow-up post (Most polar bear hybrids said to exist have not been confirmed by DNA testing) for details on unconfirmed sightings or reports of hybrids.
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Challenging NOAA’s “Arctic Report Card 2014” on polar bears

NOAA’s list of purported evidence for harm being caused to polar bears by Arctic warming is short and weak. It puts the gloomiest spin possible on the current well-being of an animal with all the earmarks of a healthy, well-distributed species.

Arctic report card 2014 screencap_Dec 18 2014

This year, polar bears are virtually the only species that NOAA mentions in their Arctic Report Card – they’ve put all their icon-eggs in one leaky basket [what happened to walrus??]. But polar bears are doing so well that to make an alarming case for polar bears as victims of Arctic warming, many important caveats had to be left out or misrepresented. Some details given are simply wrong.

This year’s polar bear chapter was penned by IUCN Polar Bear Specialist Group chairman Dag Vongraven (you might recall his email to me earlier this year) and a polar bear conservation activist from Polar Bears International (whose battle cry for donations is Save Our Sea Ice!”), Geoff York.

I challenge their four weak talking points one by one below.

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Ancestor of the polar bear by any name: grizzly vs. brown bear monikers explained

Apparently, all media outlets (except Fox News) so confused the distinction between the two common names used for the ancestor of polar bears, Ursus arctos, that they got the point of a recent news story totally wrong. An Alaskan journalist explains.

Coastal brown bears from Admiralty Island, southeast Alaska. See previous post here.

Coastal brown bears from Admiralty Island, southeast Alaska (courtesy Jim Baichtal, US Forest Service, Alaska). See previous post here.

Tundra grizzly from the Yukon (courtesy Government of Yukon Territory). These bears also occur across the north slope of Alaska and are the bears that occasionally hybridize with polar bears, as explained here.

Tundra grizzly bear from the Yukon (courtesy Government of Yukon Territory). These bears also occur across the north slope of Alaska and are the bears that occasionally hybridize with polar bears this time of year, as explained here.

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Polar bears have not been harmed by sea ice declines in summer – the evidence

PB  logo colouredThe polar bear biologists and professional activists of the IUCN Polar Bear Specialist Group (PBSG) continue to insist that since 1979 increasingly smaller amounts of Arctic sea ice left at the end of summer (the September ice minimum) have already caused harm to polar bears. They contend that global warming due to CO2 from fossil fuels (“climate warming” in their lexicon) is the cause of this decline in summer ice.

In a recent (2012) paper published in the journal Global Change Biology (“Effects of climate warming on polar bears: a review of the evidence”), long-time Canadian PBSG  members Ian Stirling and Andrew Derocher (both of University of Alberta) summarized their position this way:

“Climate warming is causing unidirectional changes to annual patterns of sea ice distribution, structure, and freeze-up. We summarize evidence that documents how loss of sea ice, the primary habitat of polar bears (Ursus maritimus), negatively affects their long-term survival”

I’ve spent the last year examining their evidence of on-going harm, but in addition, I’ve looked at the evidence (much of it not mentioned in the Stirling and Derocher paper1) that polar bears have either not been harmed by less sea ice in summer or have thrived in spite of it.

This is a summary of my findings. I’ve provided links to my original essays on individual topics, which are fully referenced and illustrated. You are encouraged to consult them for complete details. This synopsis (pdf with links preserved, updated; pdf with links as footnotes, updated) complements and updates a previous summary, “Ten good reasons not to worry about polar bears” (pdf with links preserved; pdf with a foreword by Dr. Matt Ridley, with links as footnotes).

Update 8 September 2013: to include links to my post on the recently published Chukchi population report; updated pdfs have been added above.

Update 22 January 2014: added figure comparing March vs. September sea ice extent using the same scale, from NOAA’s “2014 Arctic Report Card,” discussed here.
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Biologists spreading misinformation: hybridization with grizzlies not due to polar bears moving inland

A paper published last week in the journal Science, written by a team of biologists and atmospheric scientists, expounds on a possible dire future for a range of Arctic animals. It’s called, “Ecological consequences of sea-ice decline” and surprisingly, polar bears are discussed only briefly.

However, with the inclusion of one short sentence, the paper manages to perpetuate misinformation on grizzly/polar bear hybridization that first appeared in a commentary essay three years ago in Nature  (Kelly et al. 2010)1. The Post et al. 2013 missive contains this astonishing statement (repeated by a Canadian Press news report):

Hybridization between polar bears and grizzly bears may be the result of increasing inland presence of polar bears as a result of a prolonged ice-free season.

Lead author of the paper, Professor of Biology Eric Post, is quoted extensively in the press release issued by his employer (Penn State University, pdf here). In it, Post re-states the above sentence in simpler terms, removing any doubt of its intended interpretation:

“… polar and grizzly bears already have been observed to have hybridized because polar bears now are spending more time on land, where they have contact with grizzlies.

Both statements are patently false. All recent hybridization events documented (2006-2013) occurred because a few male grizzlies traveled over the sea ice into polar bear territory and found themselves a polar bear female to impregnate (see news items here and here, Fig. 1 below). These events did not occur on land during the ice-free season (which is late summer/early fall), but on the sea ice in spring (March-May).

Grizzlies have been documented wandering over the sea ice of the western Arctic since at least 1885 (Doupe et al. 2007; Fig. 2, below) and the presence in this region of hybrid grizzly/polar bear offspring is not an indicator of declining summer sea ice, whether due to global warming or natural causes, or some combination thereof.

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Polar bears cavorting with ABC brown bears not supported by geological and fossil evidence

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.

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