BUFFALO, N.Y. -- A rare, ancient polar bear fossil discovered in
Norway in 2004 is yielding a treasure trove of essential
information about the age and evolutionary origins of the species
whose future is now seen as synonymous with the devastation wrought
by climate change.
A paper published in the current issue of the Proceedings of the
National Academy of Sciences U.S.A. by researchers at the
University at Buffalo, Penn State University, the University of
Oslo and other institutions is filling in key pieces of the
evolutionary history of polar bears and brown bears, including
their response to past climate changes.
"Our results confirm that the polar bear is an evolutionarily
young species that split off from brown bears some 150,000 years
ago and evolved extremely rapidly during the late Pleistocene,
perhaps adapting to the opening of new habitats and food sources in
response to climate changes just before the last interglacial
period," says Charlotte Lindqvist, PhD, research assistant
professor in the UB Department of Biological Sciences and lead
author on the paper with Stephan C. Schuster at Penn State's Center
for Comparative Genomics and Bioinformatics.
"Very few polar bear fossils have been found, leading to widely
varying estimates of exactly when and how polar bears evolved,"
explains Øystein Wiig, polar bear expert and co-author at
the University of Oslo's Natural History Museum. "Because polar
bears live on the ice, their dead remains fall to the bottom of the
ocean or get scavenged. They don't get deposited in the sediments
like other mammals."
But in 2004, an Icelandic geologist found a rare,
well-preserved, 110,000- to 130,000-year-old jawbone and canine
tooth fossil in the Svalbard archipelago of Norway. This specimen
was subsequently sent to Wiig for analysis.
UB's Lindqvist, who was working at Oslo's Natural History Museum
as a postdoctoral researcher, extracted DNA from the sample after
drilling into the bone and tooth to obtain the powder to
When she arrived at UB in 2008, she obtained tissue samples from
modern polar bears and brown bears and began analyzing them at UB's
New York State Center of Excellence in Bioinformatics and Life
Sciences after starting the collaboration with Schuster at Penn
This work resulted in the sequencing of the complete
mitochondrial genome of the fossil; they then used that information
to develop mitochondrial sequencing of the other bears and to
construct phylogenies showing that the ancient polar bear evolved
within the lineage of brown bears.
"Since the brown bears from Alaska's Admiralty, Baranof and
Chichagof Islands are the polar bears' closest relatives, it was
crucial to include them in our study in order to more precisely
date when polar bears appeared as a distinct species," Lindqvist
explains. "The fact that our ancient polar bear lies almost
directly at the splitting point between this unique group of brown
bears and polar bears, that is, close to their most recent common
ancestor of the two species, was very intriguing. It provided an
ideal opportunity to ultimately settle the time of polar bear
"This is, by far, the oldest mammal mitochondrial genome to be
sequenced," says Schuster. "It's about twice the age of the oldest
mammoth genome that has, to date, been sequenced."
The mitochondrial genome refers to all the DNA in the
mitochondrion, the energy-producing component of most eukaryotic
(complex) cells. Lindqvist explains that ancient DNA studies have
tended to focus on the mitochondrial genome because it generally
reveals characteristics useful for evolutionary analyses and allows
for DNA to be retrieved from ancient samples most easily.
To conduct their analyses, the researchers used a variety of
techniques, including isotope analyses, high-throughput genomic
sequencing, bioinformatics and phylogenetic analysis, which traces
evolutionary relationships among species.
While their data demonstrate how adaptive polar bears have been
historically, Lindqvist cautions against assuming that they will,
therefore, also be able to adapt to current and future changes in
"We have found that polar bears actually survived the
interglacial warming period, which was generally warmer than the
current one," she says, "but it's possible that Svalbard might have
served as a refugium for bears, providing them with a habitat where
they could survive. However, climate change may now be occurring at
such an accelerated pace that we do not know if polar bears will be
able to keep up."
Ultimately, she notes, the polar bear species may prove less
"The polar bear may be more evolutionarily constrained because
it is today very specialized; morphologically, physiologically and
behaviorally well-adapted to living on the edge of the Arctic ice,
subsisting on a few species of seals," she says.
Lindqvist and Schuster are considering working on sequencing the
nuclear genome of the ancient polar bear, work that they expect
will reveal even more about polar bear evolution.
In addition to Lindqvist, Schuster and Wiig, additional
co-authors on the paper are Yazhou Sun, Ji Qi, Aakrosh Ratan, Lynn
P. Tomsho, Lindsay Kasson and Webb Miller at Penn State; Sandra L.
Talbot of the U.S. Geological Survey's Alaska Science Center;
"lafur Ingólfsson at the University of Iceland; Jon Aars of
the Norwegian Polar Institute; and Eve Zeyl and Lutz Bachmann of
the Natural History Museum, University of Oslo.
The work was funded by the Gordon and Betty Moore Foundation,
the University at Buffalo College of Arts and Sciences, the Natural
History Museum at the University of Oslo and the U.S. Geological
Survey Alaska Science Center.
The University at Buffalo is a premier research-intensive public
university, a flagship institution in the State University of New
York system and its largest and most comprehensive campus. UB's
more than 28,000 students pursue their academic interests through
more than 300 undergraduate, graduate and professional degree
programs. Founded in 1846, the University at Buffalo is a member of
the Association of American Universities.