Ever wonder why zebras have stripes? Scientists have too, and now they have an answer.
Researchers going as far back as Charles Darwin have offered a number
of theories about how stripes might benefit zebras. Did they develop
their unusual multi-hued coats as camouflage to help deter predators? To
keep cool beneath the harsh African sun? Do their stripes help them
identify each other? A new study topples all of those theories, leaving
just one still standing. As it turns out, stripes are an excellent bug
repellent—at least for zebras.
Researchers from the University of California at Davis knew that
certain flies avoid black and white surfaces, so they wondered: Could
zebra stripes have evolved to keep the animals free from suffering the
bites of those very same flies, which can carry fatal diseases? To
tackle that question, the researchers examined the distribution of
zebras and the locations of the best breeding grounds for the
stripe-averse flies. Sure enough, they found that they overlap. The same
was true for other animals in the horse family that had stripes on
various parts of their bodies.
“I was amazed by our results,” said lead author Tim Caro, a wildlife
biologist at UC-Davis. “Again and again, there was greater striping on
areas of the body in those parts of the world where there was more
annoyance from biting flies.”
The study, published yesterday in Nature Communications, builds on a 2012 study by
researchers at Sweden’s Lund University that used horse models painted
black and white to test whether flies would avoid stripes.
But why are stripes anathema to flies? It turns out that flies find
stretches of water to mate and lay their eggs in by looking for the
horizontally polarized light it reflects. Zebra stripes, however, are
vertical and reflect polarized light differently, which makes them
unappealing to horseflies. Unlike other African mammals, zebras have
shorter hair that flies may be able to penetrate more easily to bite
into the skin.
Researchers have yet to test their bug repellent theory in the wild,
however. Zebras have striped insect armor, but they also emit odors that
may attract flies, potentially canceling out the benefits of their
Edited by tatee - Apr 03 2014 at 6:47am