A line of defence for zebras

Scientists claim to have finally solved the mystery of why zebras evolved their distinctive black and white stripes.

London: Scientists claim to have finally solved the mystery of why zebras evolved their distinctive black and white stripes — to keep blood-sucking flies at bay.
Researchers from Hungary and Sweden, who detailed their study in the Journal of Experimental Biology, said the pattern of narrow stripes makes zebras “unattractive” to the flies.

The key to this effect was in how the stripe pattern reflected light, said Susanne Akesson from Lund University in Sweden, a member of the international team that carried out the study.

“We started off studying horses with black, brown or white coats. We found that in the black and brown horses, we get horizontally-polarised light [light waves move along a horizontal plane],” Dr. Akesson was quoted as saying by the BBC News. This effect made the dark-coloured horses very attractive to horseflies, she said.

“From a white coat, you get unpolarised light,” Dr. Akesson explained. Unpolarised light waves travel along any and every plane, and are much less attractive to flies. As a result, white-coated horses are much less troubled by horseflies than their dark-coloured relatives.

Having discovered the flies` preference for dark coats, the team then became interested in zebras. They placed a blackboard, a whiteboard and several boards with stripes of varying widths at a field in Hungary.

It was found that the striped board that was the closest match to the actual pattern of a zebra`s coat attracted by far the fewest flies, even less than the white boards that were reflecting unpolarised light. The team then put four life-size “sticky horse models” on the field — one brown, one black, one white and one striped like a zebra. The researchers collected the trapped flies every two days, and found that the zebra-striped horse model attracted the fewest.

Prof. Matthew Cobb, an evolutionary biologist from the University of Manchester pointed out that the experiment was “rigorous and fascinating” but did not exclude the other hypotheses about the origin of zebras` stripes which say stripes may help the animals regulate their temperature, and that zebras recognise other individuals by their stripes.


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