The research team from the University of California, Davis tested five popular theories regarding zebras and their stripes and was able to reject all but one hypothesis.
Writing in Nature Communications, the researchers assert the zebra’s striped coating is the result of an evolutionary response to annoying and possibly harmful biting flies, such as horse flies and tsetse flies.
“I was amazed by our results,” said lead author Tim Caro, a University of California, 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.“
Studies, including those conducted previously by the team, revealed that these fly species seemed to be most attracted to animals with dark solid coloring, while avoiding black-and-white striped surfaces. The researchers found these blood sucking flies were more attracted to solid dark surfaces that reflected light waves which were constant and oriented in the same direction. Scientists surmised the light waves reflected from dark surfaces were similar to those reflected from pools of water where the flies are known to lay their eggs. By contrast, striped surfaces might be less inviting to flies because they emit multiple light patterns.
The research team said evolution provided zebras with their stripes, while other hooved animals in the same vicinity remained stripe free, because the zebra’s hair is much shorter than the mouth part length of biting flies. This led the research team to think that zebras might especially vulnerable to the 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.”
While the team solved one mystery others remain to be explained, such as what prevents these blood sucking flies from seeing striped surfaces as potential prey, and why are zebras, in particular, so vulnerable to these annoying insects.
Other theories as to why zebras have stripes include that the stripes protect them from attack by hiding them in the grass or by visually confusing their predators; that they serve as a form of heat management; or provide the animals with a social function.