Female Ancestor of All Living Polar Bears Was
THURSDAY, July 7 (HealthDay News) -- The female ancestor of all
living polar bears was a brown bear that lived in the vicinity of
present-day Britain and Ireland 20,000 to 50,000 years ago,
according to an international team of scientists.
It's likely that climate changes that affected the North
Atlantic ice sheet led to periodic overlaps in bear habitats and
interbreeding between brown bears and polar bears. This resulted in
maternal DNA from brown bears being introduced into polar bears,
explained team co-leader Beth Shapiro, an associate professor of
biology at Penn State University.
Previous research suggested that the ancient female ancestor of
modern polar bears lived on three Alaskan islands (Admiralty,
Baranof, and Chichagof) only 14,000 years ago.
Polar bears and brown bears such as Grizzlies and Kodiaks are
markedly different species in terms of behavior and physical
features such as body size, skin and coat color, fur type, tooth
"Despite these differences, we know that the two species have interbred opportunistically and probably on many occasions during the last 100,000 years," Shapiro said in a Penn State news release. "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."
For this study, Shapiro and her colleagues analyzed 242 brown
bear and polar bear mitochondrial lineages from a number of
regions. The specific population of brown bears that contributed
maternal DNA to modern polar bears has been extinct for about 9,000
years, but there's clear genetic evidence that these brown bears
and polar bears were in contact long before brown bears vanished
from the British Isles.
Learning more about the polar bear's genetic history and its
response to previous environmental changes may help guide efforts
to conserve the dwindling population of polar bears, Shapiro
The study was published July 7 in the journal
Polar Bears International has more about
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