Zebras are known for their distinctive stripes and now researchers know why the animals have these strange markings.
Camouflage was thought to be the reason zebras developed striped bodies. There is also a blurring effect caused when the striped animals run, making the creatures slightly more difficult to target for predators. If either of these were significant factors in the evolution of stripes, then other equine species would also be expected to exhibit similar patterns, However, zebras are the only members of the family of animals which possesses such distinct markings, although other equines do have stripes.
Tim Caro, a biologist at the University of California, led an investigation into the purpose of zebra markings. His team found animals with striped patterns were most common in areas also populated by large numbers of tabanids, or horse flies. Furthermore, zebras were shown to be particularly sensitive to bites from the tiny insects.
Based on a new study, the markings actually serve to ward off biting flies. These flying bloodsuckers are not just irritating to zebras. They can also drain significant quantities of the animal's blood and can spread disease.
Caro and his team created horse mannequins and noticed the flies landed on solid-colored surfaces far more often than on striped fur. Dark fur may remind the horse flies of mud and puddles where they breed. Horse flies preferred not to land on white fur, but alternating lines were their least favorite place to set down. Zebra stripes may make it more difficult for the insects to land on the animal, study says.
"Biting flies are attracted to hosts by odor, temperature, vision and movement that may act at different stages during host seeking, but vision is thought to be important in the landing response," researchers told the press.
Caro studied striping patterns and locations of seven species and 20 subspecies of equines. They mapped the native locations of these animals and plotted them against areas populated by large numbers of horse flies. A statistical model was used to equate the population patterns.
Locations where animals with striped body patterns lived were also the same areas where tabanids were found en masse. This seems to suggest the flies may be the driving force behind the evolution of animals with striped patterns.
"Conversely, there is no consistent support for camouflage, predator avoidance, heat management or social interaction hypotheses," researchers wrote in the article announcing the results of their study.
Charles Darwin and Alfred Russel Wallace began a discussion back in 1870 over the role stripes played in the evolution of zebras.
"No one knew why zebras have such striking coloration," Caro said.
Study of the role stripes play in warding off flies was published in the online journal Nature Communications.
