Sunday, June 22, 2014

Bear-ly Sustainable: Can Polar Bears Find Refuge in the Genome of Brown Bears?

Tobias Bidon
Ok today I want to write about a more contemporary topic - the genetic legacy of bears. And I want to direct your attention to a paper dealing with the complicated genetic history of modern bears - abstract here and the more accessible science daily article: Evolutionary history of bears: It's complicated. Of course you should go read the articles yourself but what the gist of the story is that the genetic history resulting in the "species" or better yet "species groups" of modern bears is vastly complicated with numerous inbreeding occurrences and hybridization events. It appears many, if not most, bear species are kissing cousins. Central to the story is Beringia, the now submerged land bridge joining Asia and North America. According to the research Beringia may have served as a bit of mixing grounds from which the modern trajectories of bears into Asia and the Americas have since went their respective ways. Of course the bear family is just one of several carnivorous mammal families (felids, canids) that readily hybridizes. There is even a wikipedia web page on the subject of ursid hybrids. This topic of course delves deeply into the surprisingly murky definition of what constitutes a species. The long and short of it from what I gather is that the definition of what constitutes a species depends on who you ask.

Now just thinking about bear hybridization events should get you thinking about the well documented hybridization of polar and brown bears. Two species that are closely related and overlap enough in range and habit that matings do and have occurred quite often it seems.

Polar/Brown hybrid. wiki
Rothschild Museum
Thinking out loud after reading these articles and with the prospect of polar/brown bear hybridization events occurring more frequently in an Arctic under the influence of AGW I wondered: instead of going extinct, might the genome of polar bears find refuge in northern populations of brown bears? That is if through increased meetings due to lack of sea ice, the polar bear gets absorbed by the larger brown bear population shifting it's range north - could such an admixture reverse in the future if climatic conditions shift back to a regime more ameliorative to polar bears? Granted that they are so close genetically anyways - why couldn't the polar bear reemerge in several thousand years from a stock of hybridized polar/brown bears? The lack of color, streamlined form, ice gripping claws, and carnivorous dentition being selected for  in such a scenario and the polar bear reemerging... why not? I think it is an interesting notion, interesting enough to write a blog post about anyways.



Anonymous said...

A similar thing is happening with spotted and barred owls as the spotteds' habitat declines and the more adaptable barred owls expand their range.
My first thought was that it was awesome- preserve some traits, perhaps create a more adaptable population, and allow for faster speciation in the future if old growth habitat becomes viable. But it turns out there was a large state sponsored movement to shoot barreds and hybrid 'sparreds' to protect spotteds?. ??? I don't know how it turned out, but I haven't heard anyone talking about the potential benefits of hybridization. Since spotteds continue to decline, it seems like interbreeding would be a timely and useful mechanism...
It may be a common thought in some circles that I'm not a part of, but I believe this post is the first I've heard on the subject... So thanks for posting, and for your blog in general. A fantastic read.

BrianL said...

This also raises the question to what extent polar bear/brown bear hybridisation occurred during the Pleistocene with fluctuations in climate and ice caps. In fact, might the close relationship between the two species be the result of repeated hybridization events and re-emergence and re-absorption in populations of mostly either species? If so, the initial split between the two might be older than it seems from DNA-studies (possibly accounting for the considerable physical differences between the two), but muddled by such regular and large scale intermixing. An interesting thought!

heteromeles said...

Keeping the northern brown bears alive under extreme climate change will be a bit of a challenge too, since it could take up to 400,000 years for Arctic winters to return, and at the height of the warmth, the Arctic Riviera will be a lot like modern day New York.

lyuti said...

Interesting. Nature follows strange paths. Perhaps there is a clue in this study about dog origins: Genomes of modern dogs and wolves provide new insights on domestication
In short, if dogs and wolves were different enough to be just "different" before dog domestication, and they are now, in some breeds, not so different, due to hybridation -of course-, then, hybridation is wolficating -if you let me use this term- some dogs. Good point.

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