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Article:
Wynne Parry, LiveScience Senior Writer
Date: 23 July 2012 Time: 03:01 PM ET
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Polar bears' past may echo their future, indicates a genetic study that finds the white-furred, sea
ice-dwelling bears interbred with brown bears long after the two species separated as much as 5 million
years ago.
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Climate change likely drove this mixing among bears, writes the research team, noting there is evidence this is happening
again.
"Maybe we're seeing a hint that in really warm times, polar bears changed their lifestyle and came into contact, and indeed
interbred, with brown bears," said study researcher Stephan Schuster, a professor of biochemistry and molecular biology at
24/07/2012 4:34 PM
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Pennsylvania State University, and a research scientist at
Nanyang Technological University in Singapore, in a statement.
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The study estimates polar bears split from brown bears between 4
million and 5 million years ago, after which they endured
fluctuations in climate, including ice ages and warmer times.
Polar bears are currently facing the effects of climate change, thi
time caused by humans, as the Arctic sea ice upon which they
live recedes to unprecedented levels.
A comparison of the
complete genetic
blueprints from polar,
brown and black bears
estimated they
diverged roughly 4 to 5
million years ago.
(ABC brown bears are
a genetically isolated
population in Alaska.)
CREDIT: Penn State University
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"If this trend continues, it is possible that future [polar bears] throughout most of their range may be forced to spend
increasingly more time on land, perhaps even during the breeding season, and therefore come into contact with brown bears
more frequently," the researchers write in results published today (July 23) in the journal Proceedings of the National
Academy of Sciences.
"Recently, wild hybrids and even second-generation offspring have been documented in the Northern Beaufort Sea of Arctic
Canada where the ranges of brown bears and [polar bears] appear to overlap, perhaps as a recent response to climatic
changes," they write. [Album: 8 Bizarre Hybrid Animals]
Schuster and colleagues sequenced genomes (the complete genetic blueprint) of three brown bears and a black bear and
compared them with the genomes of polar bears, one modern and the other obtained from remains from a 120,000-year-old
polar bear.
Based on differences they found in the bears' genetic codes, the team estimated polar and brown bears split apart about the
same time black bears became a distinct species After the split between polar and brown bears, the two species remained
isolated for some time, allowing genetic changes to accumulate, before interbreeding more recently, their analysis indicates.
This complicated history may explain why other research has estimated a much younger age for polar bears, the researchers
write.
A study published earlier this year estimated polar bears evolved 600,000 years ago, contradicting a previous estimate of
150,000 years ago.
24/07/2012 4:34 PM