Zebras' Stripes Help Ward Off Tiny Predators
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A zebra's stripes act as a camouflage, hiding their owner from hungry lions and cheetahs. But the stripes also fend off a much smaller pest, researchers say.
Bloodsucking horseflies are less attracted to the black and white stripes of a zebra than they are to the solid white or black coats of horses.
"It's a very powerful reduction in attractiveness," said Susanne Akesson, an evolutionary ecologist at Lund University in Sweden and one of the researchers involved with the work. She and her co-authors report their findings in The Journal of Experimental Biology.
For their research, they traveled to a horsefly-infested horse farm in Hungary, where they tested the insects' attraction to panels with different types of black and white patterns.
The panels with the narrowest stripes attracted the fewest horseflies, and the new research suggests this may be why zebras evolved their familiar pattern.
In a previous study, Dr. Akesson and her team found that horseflies were attracted to horizontally polarized light; since white does not reflect it, white horses are luckier than black ones.
But zebras seem to be the luckiest of all. When the researchers measured the polarized light reflected from real zebra hides, they found that it matched light patterns that were the least attractive to horseflies.
Because bloodsucking insects can spread diseases, Dr. Akesson said, having an attractive hide could impose a "severe fitness cost" in the course of evolution.
She said her team would like to study how the flies may be combining their senses to find blood sources.
"The odors from a zebra host, for example," she said, "we don't know whether that could be overriding the effect of the visual pattern."
First Published February 15, 2012 12:00 am
