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Why Zebras Have Stripes

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By Mary Daily

Published Apr 1, 2015 8:00 AM


The patterns on these descendants of the horse really do serve a purpose.

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We’ve always known that zebras’ stripes are cool, but now we also know that the black-and white patterns may keep them from overheating.

Led by UCLA’s Brenda Larison Ph.D. ’07, a researcher in ecology and evolutionary biology, a team of scientists recently found they could predict the amount and intensity of zebras’ striping by the temperature of the animals’ environment. They say the striping also likely protects zebras from diseases carried by biting flies.

In the study, Larison and her colleagues examined the plains zebra, which has a wide variety of stripe patterns. On zebras in warmer climes, the stripes are bold and cover the entire body. On others — particularly those in regions with colder winters — the stripes are fewer, lighter and narrower. On some, the legs or other body parts have virtually no striping.

Scientists have hypothesized that zebras’ stripes evolved for one, or a combination of four, main reasons: confusing predators, protecting against disease-carrying insects, controlling body temperature and social cohesion. But the Larison-led study was the first to fully test a large set of hypotheses against one another.

Analyzing zebras at 16 locations in Africa and considering more than two dozen environmental factors, the researchers found that temperature was the strongest predictor of zebras’ striping. The finding provides the first evidence that controlling body temperature, or thermoregulation, is the main reason for the stripes and their patterns. Separate research has suggested that boldly striped zebras have external body temperatures about five degrees Fahrenheit cooler than other animals of the same size that do not have stripes, but live in the same areas.

Larison has studied many zebras during her fieldwork throughout Africa — including in Kenya, South Africa, Tanzania, Uganda and Zimbabwe. Since their stripes are unique, like fingerprints, she is able to distinguish one zebra from another. The team also has collected zebra tissue samples and used cutting-edge technology to sequence zebra DNA to try to identify which genes code for striping. The group is continuing to study the benefits stripes provide.

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