Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Polar Bear Evolution Tracked Climate Change, Study Suggests

25.07.2012
An analysis of newly sequenced polar bear genomes is providing important clues about the species' evolution, suggesting that climate change and genetic exchange with brown bears helped create the polar bear as we know it today.

The international study, led by the Pennsylvania State University and the University at Buffalo, found evidence that the size of the polar bear population fluctuated with key climatic events over the past million years, growing during periods of cooling and shrinking in warmer times.

The research also suggests that while polar bears evolved into a distinct species as many as 4-5 million years ago, the animals may have interbred with brown bears until much more recently.

These intimate relations may be tied to changes in the Earth's climate, with the retreat of glaciers bringing the two species into greater contact as their ranges overlapped, said Charlotte Lindqvist, the study's senior author and an assistant professor of biological sciences at UB.

"Maybe we're seeing a hint that in really warm times, polar bears changed their life style and came into contact, and indeed interbred, with brown bears," said Stephan Schuster, co-lead author, a professor of biochemistry and molecular biology at Penn State, and a research scientist at Nanyang Technological University in Singapore.

The findings will be published online in the early edition of the Proceedings of the National Academy of Sciences on July 23. The study is the most extensive analysis to date of polar bear DNA, scientists say. The research team, representing 13 institutions in the U.S., Canada, Europe and Asia, as well as Mexico's Laboratorio Nacional de Genomica para la Biodiversidad (Langebio), sequenced and analyzed the nuclear genomes of 28 different bears, with many DNA samples provided by the U.S. Geological Survey and the Norwegian Polar Institute.

"We generated a first-rate set of data, including deep sequence coverage for the entire genomes of a polar bear, three brown bears and a black bear, plus lower coverage of 23 additional polar bears, including a 120,000-year-old individual; very few vertebrate species have such comprehensive genomic resources available," Schuster said. Using this vast amount of data, the scientists discovered that polar bears are actually an older species than previously thought -- indeed, far more ancient than suggested by a recent study that placed the species' age at 600,000 years old. That analysis looked only at small segments of DNA.

"We showed, based on a consideration of the entire DNA sequence, that earlier inferences were entirely misleading," said study co-lead author Webb Miller, a Penn State professor of biology and computer science and engineering. "Rather than polar bears splitting from brown bears a few hundred thousand years ago, we estimate that the split occurred 4-5 million years ago."

"This means polar bears definitely persisted through warming periods during Earth's history," UB’s Lindqvist said. She cautions, however, that the species' endurance over several million years doesn't guarantee its future survival.

To model historical populations of the polar bear, the scientists used computer simulations to analyze a deeply sequenced polar bear genome.

"This is the first time we can see, from their genes, how the population history of polar bears tracked Earth's climate history," Lindqvist said. "We see an increase in polar bears at the end of the Early Pleistocene as the Earth became much colder, and a continuous decline in the size of the population during warmer times.

“We also found, perhaps unsurprisingly, that polar bears occur in much smaller numbers today than during prehistory," Lindqvist continued. "They have indeed lost a lot of their past genetic diversity, and because of this, they are very likely more sensitive to climate change threats today."

Discrepancies between the estimated age of polar bears in the new study and past studies could be explained by interbreeding between polar bears and brown bears since the species split from each other.

The new analysis uncovered more genetic similarities than previously known between polar bears and ABC brown bears, an isolated group from southeastern Alaska -- suggesting that these animals have exchanged genes since becoming separate species.

"The ABC brown bears' mitochondrial sequences are much more like polar bears' than like other brown bears'," Miller said. "This made us wonder what other parts of their genomes are 'polar-bear-like.' We mapped such regions, which constitute 5 to 10 percent of their total DNA, onto the genomes of two ABC brown bears. As such, brown/polar bear hybridization, which has been observed recently in Arctic Canada, has undoubtedly contributed to shaping the modern polar bear's evolutionary story."

This intermingling between species is just one interesting finding emerging from the enormous trove of data that the PNAS study produced. Another question that the research is beginning to address: What makes a polar bear a polar bear?

Polar bears have genetic differences from brown bears that let them survive in an Arctic climate with very different diets, and the new study identified genes that may be responsible for traits such as polar bears' pigmentation and the high fat content of their milk.

This study received financial support from Penn State University, the College of Arts and Sciences at the University at Buffalo, U.S. Geological Survey's Changing Arctic Ecosystem Initiative, U.S. Fish and Wildlife Service, Ontario Ministry of Natural Resources in Canada, Alaska Department of Fish and Game, the National Institutes of Health and the National Science Foundation.

CONTACTS
Charlotte Lindqvist: cl243@buffalo.edu, (+1) 510-388-1831 or (+1) 716-645-4986
Webb Miller: webb@bx.psu.edu, office (+1) 814-865-4551 mobile (+1) 814-234-6289
Stephan Schuster: scs@bx.psu.edu, mobile after 23 July (+1) 814-441-3513
Charlotte Hsu (PIO at UB): chsu22@buffalo.edu, (+1) 716-645-4655 or (+1) 510-388-1831

Barbara Kennedy (PIO at Penn State): science@psu.edu, (+1) 814-863-4682

Charlotte Lindqvist | Newswise Science News
Further information:
http://www.buffalo.edu

More articles from Studies and Analyses:

nachricht Real-time feedback helps save energy and water
08.02.2017 | Otto-Friedrich-Universität Bamberg

nachricht The Great Unknown: Risk-Taking Behavior in Adolescents
19.01.2017 | Max-Planck-Institut für Bildungsforschung

All articles from Studies and Analyses >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Safe glide at total engine failure with ELA-inside

On January 15, 2009, Chesley B. Sullenberger was celebrated world-wide: after the two engines had failed due to bird strike, he and his flight crew succeeded after a glide flight with an Airbus A320 in ditching on the Hudson River. All 155 people on board were saved.

On January 15, 2009, Chesley B. Sullenberger was celebrated world-wide: after the two engines had failed due to bird strike, he and his flight crew succeeded...

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

New pop-up strategy inspired by cuts, not folds

27.02.2017 | Materials Sciences

Sandia uses confined nanoparticles to improve hydrogen storage materials performance

27.02.2017 | Interdisciplinary Research

Decoding the genome's cryptic language

27.02.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>