July 24, 2012
DNA Shows Polar Bears Are Ancient, Related To Brown Bears
Michael Harper for redOrbit.com — Your Universe Online
New research suggests polar bears and brown bears come from the same DNA as ancient bears. In an international study, led by Penn State University and the University at Buffalo, researchers have found that polar bear populations changed with climatic events over the past million years, with fewer polar bears roaming the Earth in times of warmer weather.
This new research also suggests the relationship between brown bears and polar bears is tied to climate change, noting that the two species interbred with one another until recently. This interbreeding between the two species may have also been tied to changes in the Earth´s climate when a glacial disappearance brought the two bears closer together.
“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 co-lead author Stephan Schuster, a professor of biochemistry and molecular biology at Penn State.
The team´s findings are published in the Proceedings of the National Academy of Sciences.
This new study goes beyond what other studies have documented, taking DNA samples from existing polar bears, black bears and brown bears and comparing the results to DNA from an ancient polar bear skull. The team performed a “deep genome” analysis to compare the DNA between the species and found that the split between the brown and the polar bears occurred anywhere from 4 to 5 million years ago; around the same time ice began to cover the Arctic Sea. This evidence also shows that polar bears could have roamed the earth as early as 5 million years ago.
Schuster explained the survey in a statement, saying: “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 thousand year old individual; very few vertebrate species have such comprehensive genomic resources available.”
“We showed, based on a consideration of the entire DNA sequence, that earlier inferences were entirely misleading,” said another co-author, Webb Miller, a Penn State professor of biology and computer science.
“This means polar bears definitely persisted through warming periods during Earth´s history,” said Charlotte Lindqvist, the study's senior author.
Though polar bears are much older than originally thought, Lindqvist says their endurance doesn´t mean they´ll be around forever. The team came up with computer simulations to analyze the bear´s deeply sequenced genomes.
“This is the first time we can see, from their genes, how the population history of polar bears tracked Earth´s climate history,” said Lindqvist.
“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.”
“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.”
If previous history is any indication, polar bears and brown bears may start warming up to one another once more as our earth´s temperatures are on the rise.