Polar bears descended from extinct Irish female ancestors

 

IRELAND CAN claim part ownership of a new and unexpected export – the polar bear. All polar bears alive today are descended from a common female ancestor, a now extinct Irish brown bear.

This is no extravagant claim from a Government seeking to talk up attractive export statistics. The discovery comes from an international team of scientists who compared the genetic profiles of bears from around the world.

The study looked at genetic material from more than 240 bears, both living and long dead, said research leader Prof Dan Bradley, of the Smurfit Institute of Genetics at Trinity College Dublin.

Samples from living animals were easy to collect for analysis but the researchers from eight countries, including Ireland, also studied ancient DNA retrieved from bones of extinct bears, he said.

The National Museum of Ireland held bones recovered in 1997 from the Poll na mBéar cave, which overlooks Ben Bulben in Co Sligo, Prof Bradley said.

These and other local samples yielded up bear DNA showing the extinct Irish bears were the female ancestors of all living polar bears that prowl the Arctic today.

“We found they were the closest species yet to polar bears,” Prof Bradley said. Details of the research were published yesterday by Current Biology.

Modern brown bears disappeared from Ireland about 3,000 years ago, but their descendants continue to live today in western Europe, he said.

The extinct bears, however, lived much earlier – 11,000- 38,000 years ago during the height of the last ice age, said Prof Pete Coxon of the department of geography at Trinity, an expert in Ireland’s glacial history.

The western seaboard near the Poll na mBéar cave would have been covered by 500 metres (547 yards) of ice and an ice shelf would have extended 30-40km out into the Atlantic then, he said.

Lead author Dr Ceiridwen Edwards of Trinity and later Oxford University produced mitochondrial DNA sequences using Irish bear bones from animals that lived as far back as 43,000 years ago. Mitochondrial DNA is genetic material only passed on from mother to offspring.

These sequences were compared with those from modern polar bears. The researchers discovered that bears living during the Ice Age between 11,000 and 38,000 years ago had mitochondrial DNA very similar to today’s polar bears, proving the genetic connection, Prof Bradley said.

Before this, the closest match was with brown bears living on Alaskan islands. “Our bears are much, much closer,” he said.

At some point during the last major Ice Age, more than 11,000 years ago, the paths of Arctic bears and the Irish bears would have crossed, allowing them to “hybridise” or cross-breed, the mating of related but distinct species. “This can happen at times of environmental stress,” he said.

It is happening now with polar bears increasingly encountering brown bears as the Arctic ice cover retreats, according to co-author Prof Beth Shapiro of Pennsylvania State University. Her DNA comparisons across all genetic samples showed polar and brown bears are cross-breeding in the wild today.