Washington: An international team of scientists has discovered that the female ancestor of all living polar bears was a brown bear that lived in the vicinity of Britain and Ireland around 20,000 to 50,000-years-ago.
Beth Shapiro, the Shaffer Associate Professor of Biology at Penn State University and one of the team’s leaders, explained that climate changes affecting the North Atlantic ice sheet probably gave rise to periodic overlaps in bear habitats.
The overlaps then led to hybridisation, or interbreeding, which is an event that caused maternal DNA from brown bears to be introduced into polar bears.
“Despite the differences, we know that the two species have interbred opportunistically and probably on many occasions during the last 100,000 years,” Shapiro said.
“Most importantly, previous research has indicated that the brown bear contributed genetic material to the polar bear``s mitochondrial lineage -- the maternal part of the genome, or the DNA that is passed exclusively from mothers to offspring.
“But, until now, it was unclear just when modern polar bears acquired their mitochondrial genome in its present form,” she added.
The research, led by Shapiro and Daniel Bradley of Trinity College Dublin, is expected to help guide future conservation efforts for polar bears, which are listed as threatened under the Endangered Species Act.
The results of the study will be published on 7 July 2011 in the journal Current Biology.