Hybridization due to Climate Change / Arguments Fly

Climate change exists and always has: Climate change has been a major force in the evolution of life – and life has also changed climate. The most spectacular “incident” is probably the Great Oxidation Event which literally “fueled” the evolution of life as we know it today. Oxygen is a terrific supplier of energy.

Definition (Springer.com) The great oxygenation event (GOE) corresponds to the time when excess free oxygen started to accumulate in noticeable concentration in the atmosphere. This first rise of oxygen in the atmosphere took probably place at the Archean/Proterozoic boundary, around 2.45 Ga ago and was the result of photosynthetic activity of cyanobacteria. Oxygen partial pressure in the atmosphere before life was likely less than 10−13 bars. Oxygen could have been locally produced by photosynthesis well before the GOE, as early as 3.0 Ga. However, most of the produced oxygen was then consumed to oxidize the rocky surface of the Earth and the pO2 was maintained as low as 10−5 times the present atmospheric level (21% vol. of O2). (O2 concentration has fluctuated throughout earth history, with direct effect on life)

As usual, the “hype” surrounding whether or not hybridization is being driven by climate change (global warming today), exists at all, or is a “threat” or “salvation” for affected species (and what “humans” ought to do about it”) gets more internet “attention” than the scientific questions involved.

Here are two sample websites – Polar Bear / Grizzly Bear hybrids.

Environmental change drives evolution: Poor Polar Bears? We're in the same precarious position as any other animal.

Environmental change drives evolution: Poor Polar Bears? Humans are in the same precarious position as any other animal.

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Five facts that challenge polar bear hybridization nonsense May 23, 2016 http://www.polarbearscience.com A refutation of claims about “Grolars” or “Pizzlies” – their existence and connection to global warming:

“It was inevitable, I suppose, that the putative hybrid shot in Arviat, Nunavut last week (see my post here) would initiate the global warming blame game.”

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A descriptive article: ScienceNordic http://sciencenordic.com/grizzly-polar-bear-hybrids-spotted-canadian-arctic

“…These unusual looking bears, which are a mixture of polar bear and grizzly bear, have been popping up around the Canadian Arctic since the first reported shooting in 2006. Eight further sightings have followed and were confirmed as polar-grizzly hybrids by DNA testing. A ninth sighting is now awaiting the results of a DNA analysis before that too can be confirmed as a hybrid.

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“We’ve known for a long time that hybrids between polar bears and grizzly bears were possible. We’ve known from zoo studies in Europe that you can take a male and female from either species and hybridise them, and that their offspring are fully fertile,” says polar bear scientist Andrew Derocher, from the University of Alberta, Canada, who studies polar bear populations in the Canadian Arctic and Hudson Bay.

“To date, all the confirmed hybrids are in Canada. But that doesn’t mean that they couldn’t exist in Russia for example, where these species come very close to each other, or in Alaska, where they also overlap,” he says.

Grolar bears a result of climate change (this ought to be a question, rather than a statement of fact)

Climate change is in part responsible for the emergence of these grolar hybrids, as polar bears that live and hunt on the ever-shrinking Arctic sea ice are forced on land during mating season in spring and summer. At the same time, male grizzly bears are expanding their habitats, roaming into polar bear territories, and emerging from hibernation earlier in the year.

Inuit hunters have spotted grizzly bears in the Arctic for decades, but numbers are believed to have increased recently, causing males to disperse further in search of a female. The result is that where the two species meet, they mate, says Derocher.

Genetic similarities allow cross breeding

Interbreeding between two closely related species is nothing new, says evolutionary biologist Eline Lorenzen, from the University of Copenhagen, Denmark. All it takes is for two species or sub-species that were separated for a period of time to be brought back into contact. So long as they still have enough genetic similarities, they can mate and produce fertile offspring. And we only have to look at our own species for evidence of this.

“Neanderthals living in Eurasia and Homo sapiens in Africa are a good example. They diverged for a couple of hundred thousand years and then came back into contact. Now all human populations outside of Africa carry a genetic signature from Neanderthals,” says Lorenzen.

“So in our own species, hybridisation and borrowing genetic material from another lineage that allows you to adapt to your environment, has occurred before,” she says.

Read more: Oldest human genome reveals a story of sex and migration (Ust’-Ishim, Siberia)

Polar bears and grizzlies have interbred before

Studies of bear DNA shows that polar bears and brown bears have also interbred before, says Lorenzen, who has previously mapped the genome of 89 polar bears. She discovered that polar bears and brown bears first diverged as a species between 479,000 and 343,000 years ago. Since then, the two species have met and interbred several times, and today, brown bears (also referred to as grizzly bears) still retain some of this ancient polar bear DNA, and vice-versa.

“So the fact that species are mixing is not unique in any way. But what is unique now, is that there is a very real chance that a large portion of Arctic sea ice is going to disappear relatively rapidly, and so we will see many more examples of the two species meeting than has been the case before,” says Lorenzen.

Read more: Arctic sea ice is at a record low

The polar bear’s unique set of genetic adaptations could be lost

Some of the recent pizzly sightings in Canada are now second generation hybrids, dominated by grizzly DNA.

“When I say hybrids I’m referring to half polar bear and half grizzly bear. But I know of four individuals that are three quarters grizzly and one quarter polar bear. So we have a hybrid mating with a grizzly bear and we get a second generation that is three quarters grizzly,” says Derocher.

The dominance of grizzly DNA is a concern to both Derocher and Lorenzen, who suggest that polar bears’ unique genetic traits that allow them to live on sea ice and survive on a high fat diet of seals, might ultimately lose out to the dominant population of grizzlies. (But if the Polar bear’s environment of sea ice is disappearing, then isn’t this a necessary change, and not a “good-or-bad” thing”?) 

“Ultimately, one species will be integrated into the other, and it’s likely that it will be polar bears that integrate into brown bears,” say Lorenzen.

“As polar bears are forced to go on land and interbreed with brown bears then the selective pressures for being able to metabolise fatty acids–that polar bears need–won’t be important any more. So these will likely be lost. Now if that’s your definition of a polar bear then that will be lost as well,” she says. (That human rush-to-judgment impulse again: our “interpretation and interference” in nature has a long and disastrous history. Is it really up to us to “save” our “preserve” our (highly skewed) version of evolution?)

No new species of bear expected any time soon

So could these hybrids and their offspring become a new species? Until now, they have been considered more of a scientific curiosity, but they are receiving more attention as their numbers continue to rise.

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“The first hybrid lived a more terrestrial lifestyle. But I’ve seen from as early as 1986 and most recently in 2013 and 2014, male grizzlies on the sea ice, much further away from where we’d expect to see them and well into polar bear territory. It looked like it was hunting seals, which it wouldn’t normally do,” he says.

But asked whether they expect a new species of bear to arise any time soon, both Derocher and Lorenzen say, no. It would take somewhere in the order of hundreds of thousands of years for a new species to arise, and it certainly could not occur within our life times, says Lorenzen. (Is this true?)

Country Denmark

Related; Also from ScienceNordic: New evidence that early chimps and bonobos interbred

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