Why do zebras have stripes? To keep the bugs off,say researchers.

Why zebras have black and white stripe is a question that has intrigued scientists and spectators for centuries. According to a new study biting flies, including horseflies and tsetse flies, are the evolutionary driver for zebra stripes.

zebra 1

Such flies tend to avoid black-and-white striped surfaces, but why? Scientists had various hypotheses for the stripes of zebra stripes and even Alfred Russel Wallace and Charles Darwin discussed the problem 120 years ago.

Now a research team led by the University of California Davis has examined this riddle systematically. They set about to test the five major explanations for this infamous colouration:
- A form of camouflage
- Disrupting predatory attack by visually confusing carnivores
- A mechanism of heat management
- Having a social function
- Avoiding ectoparasite attack, such as from biting flies

After analysing the five hypotheses, they ruled out all but one: avoiding blood-sucking flies. There was no consistent support for camouflage, predator avoidance, heat management or the social interaction hypotheses.

zebra 2

According to lead author Tim Caro, a UC Davis professor of wildlife biology, the results took them by surprise. “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.”

Why would zebras evolve to have stripes whereas other hooved mammals did not? Unlike other African hooved mammals living in the same areas as zebras, zebra hair is shorter than the mouthpart length of biting flies, so zebras may be particularly susceptible to annoyance by biting flies.
Yet in science, one solved riddle begets another: Why do biting flies avoid striped surfaces?

According to the team, the study has provided ecological validity to the biting fly hypothesis. The evolutionary debate can move from why zebras have stripes to what prevents biting flies from seeing striped surfaces as potential prey, and why zebras are so susceptible to biting fly annoyance.

zebra 3

“No one knew why zebras have such striking coloration,” Caro said. “But solving evolutionary conundrums increases our knowledge of the natural world and may spark a greater commitment to conserving it.”

A solution to the riddle of zebra stripes, debated by Wallace and Darwin seems to be at hand.

Sources:
UC Davis
Nature Communications

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