via Wikimedia Commons |
Despite significant differences between polar bears and brown bears (size, coloring, fur type, tooth shape, swimming ability vs. climbing ability, etc.) scientists have suspected for some time that the species have closely connected histories. The polar bear is known to have mitochondrial DNA (the part of the genome contributed by the mother) that traces back to the brown bear. But how modern polar bears acquired this brown bear DNA was a bit of a mystery.
via Wikimedia Commons |
The research team led by Shapiro and Bradley found that the hybridization of polar bears occurred much earlier than would have been possible on the ABC Islands through a genetic analysis of the bears. The study analyzed 242 samples from polar bear and brown bear mitochondrial DNA spanning 120,000 years and several different geographical regions. The researchers found that the fixation of the mitochondrial genome in polar bears likely occurred closer to 50,000 years ago in the area of present-day Ireland.
According to Shapiro, in addition to genetic evidence, the interconnected history of the polar bear and brown bear is also supported by climate events. One example of this is the British-Irish ice sheet, which reached its maximum range around 20,000 years ago. At this time parts of Ireland would have been difficult to inhabit, pushing bears from the warmer areas toward ice shelves and land exposed by lower sea levels. This would have brought the bears into close contact with their northern neighbors, showing how the animals that became two different bear species could have started out in the similar location, sharing their genes.
The polar bear is currently considered a threatened species, and future conservation efforts may be aided by this new understanding of its genetic history and its ability to hybridize with the brown bear. The research is described in the paper, "Ancient Hybridization and an Irish Origin for the Modern Polar Bear Matriline" in the journal Current Biology.
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