Why zebras have black and white stripes is a question that has intrigued scientists and spectators for centuries. Evolutionary theories include a form of camouflage, a mechanism of heat management, and disrupting predatory attack by confusing carnivores.
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In order to better understand the black and white stripe evolution, a research team led by the University of California, Davis, has now examined this riddle systematically, and what they found is that biting flies, including horseflies and tsetse flies, play a major role as the evolutionary driver for zebra stripes.
The team mapped the geographic distributions of the seven different species of zebras, horses and asses, and of their subspecies, noting the thickness, locations, and intensity of their stripes on several parts of their bodies. Their next step was to compare these animals’ geographic ranges with different variables, including woodland areas, ranges of large predators, temperature, and the geographic distribution of glossinid (tsetse flies) and tabanid (horseflies) biting flies. They then examined where the striped animals and these variables overlapped.
After analyzing other hypotheses, the scientists ruled out all but one: avoiding blood-sucking flies.
“I was amazed by our results,” said lead author Tim Caro, a UC Davis professor of wildlife biology. “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? The study found that, 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.
“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 greater commitment to conserving it.”
The study was published April 1, in the online journal Nature Communications.
See more at UC Davis.
Zebra image via Shutterstock.