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Black bears have black fur, right? It’s there in the name. “In the eastern
part of North America, where I grew up, we have American black bears,
and they’re only black,” said Emily Puckett, an evolutionary biologist at
the University of Memphis in Tennessee. People are even warned with a
colour-coded aphorism about how to behave during a bear encounter: “If
it’s black, ght back; if it’s brown, lie down; if it’s white, say good night.”
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The American black bear, Ursus americanus, did not get the memo when
that saying was circulated: It comes in a variety of shades, including blond
and cinnamon. The cinnamon bear is a U. americanus that wears a reddishbrown coat and can look strikingly similar to grizzlies and other brown
bears of the species Ursus arctos.
Recently, Puckett and colleagues uncovered the mutation that gave rise to
this cinnamon situation millenniums ago, which potentially gave some
bears an evolutionary edge. The scientists also discovered a mutation
responsible for the amber coat of the grizzly. Their ndings were
published in the journal Current Biology on Friday.
To nd out what genetic change or changes could have led to the
cinnamon coat, the researchers sequenced the genomes of nearly 200 U.
americanus bears and identi ed a mutation in the gene for the protein
TYRP1, known to be involved in melanin pigment production. The same
mutation causes a form of albinism in people. The researchers uncovered a
different mutation, also in TYRP1, in U. arctos. The researchers suspected
that a mutant version of TYRP1 would be enough to produce a lightercolored coat. To test this, they introduced the U. americanus and U. arctos
mutations — separately — into pigment-producing cells, and they did
indeed nd that those cells produced little to no pigment. They then
calculated that the TYRP1 mutation rst cropped up in U. americanus
more than 9,000 years ago in western North America, where it is still most
common.
Scientists have proposed that a lighter coat mimicking that of grizzlies
would be advantageous in the west, where American black bears and
grizzlies share territory and resources. A lighter coat also absorbs less heat,
potentially bene ting a bear in the warm southwest. Puckett and
colleagues proposed that this could be a case of crypsis — matching the
environment to avoid predation. While black bears grow to be strong
predators in their own right, especially as cubs, they can become meals for
mountain lions, wolves, bobcats, even other bear species. In the case of U.
americanus, a cinnamon coat would match the more open southwest
landscape, while a darker coat would blend into the forests back east.
American black bears aren’t the rst bears thought to use cryptic
coloration; the giant panda is believed to use its opposing colors to blend
into a mix of dark and light surroundings. But the researchers aren’t ruling
out the possibility that mimicry, thermoregulation and crypsis could be
working together to bene t U. americanus, “providing little tness
advantages on multiple physiological and behavioral fronts,” Puckett said.
More people will likely encounter U. americanus, as the bears continue to
expand their range, said Sue Fairbanks, an ecologist at Oklahoma State
University who was not involved in the work.
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Over the last few decades, increased protections for U. americanus —
including stricter hunting laws — as well as restoration of their deforested
habitats and, in some places, bear reintroduction programs, have meant
humans and bears are coming face to face more often. In Fairbanks’ state,
for instance, people will report seeing grizzlies. But grizzlies don’t live in
Oklahoma. “We have to keep reminding people that black bears can be
brown,” she said.
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