The study that was not an April Fool — tsetse fly bites caused zebras’ stripes

2014-04-03 00:00

A TEAM of biological researchers at the University of California, Davis, believe they have by a process of painstaking elimination solved the evolutionary puzzle why a zebra has stripes.

In a study — unfortunately published in April Fool’s Day in the online journal Nature Communications — the scientists, led by a professor of wildlife biology at UC Davis, Tim Caro, postulated that the painful bite inflicted by horseflies and tsetse flies was the main evolutionary trigger behind zebra stripes.

He explained that Charles Darwin had been first to try and explain the zebra stripes and the hypotheses since include that stripes offer camouflage, scare off or confuse predators, help cool the zebra’s body temperature, play a social function, and finally, protect against flies. Caro said his team had tested the five major evolutionary explanations for “variation in striping of equid species and subspecies”.

“We found again and again and again [that] the only factor which is highly associated with striping is to ban biting flies,” Caro said.

They found for subspecies, there are significant associations between the number of stripes and tsetse fly distribution, several of which are replicated at the species level.

“Conversely, there is no consistent support for camouflage, predator avoidance, heat management or social interaction hypotheses. Susceptibility to ectoparasite attack is discussed in relation to short coat hair, disease transmission and blood loss,” the abstract of his concludes in Nature Communications.

But why do flies avoid stripes? Caro says they’ll need to do more research to figure that out.

Not everyone is convinced. Biologist Brenda Larison of the University of California, Los Angeles, agrees that Caro’s hypothesis is the best one supported by modeling data. However, “the story is likely to be much more complex, and this is unlikely to be the last word on the subject,” according to National Geographic.

“We really need to know what happens with live zebra in the field before we can be sure,” said Larison.

Caro is however convinced that tsetse flies will avoid zebras in a mixed herd of herbivores.

“We have moved the debate to the next level,” he said, adding that all the other theories were now basically excluded.

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

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