Polar bear
New DNA research on modern day polar bears show that they originate from an now extinct brown bear hybridization with a polar bear. That original hybrid individual lived in a region now known as Britain and Ireland. It is estimated that modern polar bears originated between 20,000 and 50,000 years ago.
The research just published in current biology was undertaken by scientists at Trinity College Dublin and The Pennsylvania State University. They looked at the evolutionary history of the polar bear using the mitochondrial DNA. This is a piece of DNA that gets pasted down through the maternal line. The study of this produces what is known as the matriline of a species.
Finding polar bears mitochondrial Eve.
The method used produced a genealogical map back to the mitochondrial eve of polar bears in much the same way that genetic researchers traced back human evolution to mitochondrial Eve to East Africa 200,000 years ago.
The study showed that polar bears have been regularly interbreeding with brown bears over the last 100,000 usually driven by climate change. As climate changes the range of polar bears and brown bears can overlap and this gives the two species an opportunity to produce hybrids.
“We found that brown bears and polar bears, which are hybridizing today in the wild, have been hybridizing opportunistically throughout the last 100,000 years and probably longer,” said Beth Shapiro of The Pennsylvania State University. “Generally, this seems to happen when climate changes force the bears to move into each others’ habitat. When they come into contact, there seems to be little barrier to them mating.”
Modern polar bears originate from Europe during the last Ice Age.
The evidence from this latest study seems to suggest that the modern polar bear originated from a hybrid that was produced either shortly before or during the last ice age. This was when the now extinct polar bear species could mate with European brown bears. The results of the DNA study changes the view that polar bears originated from bears from Alaska in particular the islands of Admiralty, Baranof and Chichagof on the Alexander archipelago.
“This approach provides a means to go back in time and directly measure the movement of species in response to past climate change,” said study author Daniel Bradley of Trinity College Dublin.
As the temperatures rise due to climate change there is now more opportunities for brown bears and polar bears to mate. There are increasing reports of hybrid bears being seen across Canada.
Climate change producing a new era of hybridisation.
The researchers were keen to point out that the new finding should not impact on the conservation measures and the protection of both polar bears and brown bears. ”There is no reason that past hybridization and genetic introgression with brown bears should affect at all the conservation status of polar bears,” Shapiro said. “The two species are very different, each adapted to a particular lifestyle, and each playing a crucial role in their ecosystem.“
The researcher concluded, “The reconstructed matrilineal history of brown and polar bears has two striking features. First, it is punctuated by dramatic and discrete climate-driven dispersal events. Second, opportunistic mating between these two species as their ranges overlapped has left a strong genetic imprint. In particular, a likely genetic exchange with extinct Irish brown bears forms the origin of the modern polar bear matriline. This suggests that interspecific hybridization not only may be more common than previously considered but may be a mechanism by which species deal with marginal habitats during periods of environmental deterioration.“
External sites:
Current biology
The Pennsylvania State University
