Horseflies spark evolutionary chain reaction

Why do zebras have stripes?

A University of California, Davis research team has solved the enigma that is the origins of a zebra’s stripes. This evolutionary problem has been debated for 120 years and some hypotheses include the stripes being a form of camouflage, a heat management system or a countermeasure to attack from biting flies. According to the University of California, Davis website, a zebra’s stripes are there to ward off biting flies.


Until recently, the origins of the iconic black and white stripes of zebras have mystified scientists and has been a subject of continuous debate. (photo by Emilee Hafler)

“I was amazed by our results,” says lead author Tim Caro, a University of California, Davis professor of wildlife biology on the website. “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.”

Yes, it seems as though the constant pestering of horseflies and tsetse flies is enough to start an evolutionary chain reaction and foster a wholly unique species. Prior to this finding, research has shown that such biting flies avoid surfaces that are striped black-and-white. As opposed to other hoofed mammals living alongside zebras, the latter has shorter hair than the mouthpart of biting flies, thus increasing their vulnerability to the flies’ annoyances.

“It’s fascinating how one gene could flip and create a whole new species just because of something as small as a fly,” says Erica Brooks ‘16.

According to the site, the research team mapped the geographic distributions of the different species of zebra and noted the thickness, intensity and locations of the zebras’ stripes on their bodies. They then compared this data with variables, like the ranges of large predators, the geographic distribution of the biting flies and temperature, and analyzed where the zebras and the variables overlapped. Their analysis revealed that striping in zebras is highly correspondent with several consecutive months of ideal biting fly reproductive conditions. The more the flies reproduce, the more stripes there are on a zebra.

As this century-old question is laid to rest, more questions are raised and the debate continues, only this time over the biting flies and not their victims.

“It’s like a new outlook on the world. Now that we have this answer, where do we go from there,” says Parker Malkoc ‘16.

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