Evolution: Zebra stripes deter biting flies

The stripes seen on many equids, such as zebras, have evolved mainly as a method to avoid biting flies and not as a camouflage against predators according to research published in Nature Communications.

Zebra, among many other species, present a characteristic stripped pattern, whose function has been suggested to relate to camouflage, disrupting predatory attack, reducing thermal load, avoiding biting flies or even a social function; however, to date no studies have tested all these hypotheses together. Tim Caro and colleagues examine the regional distribution of current and extinct equid species, which includes both those with and without stripes, and test these hypotheses against each other. Predator avoidance has been recently suggested to be the main evolutionary driver for zebra stripes; however, certain flies are known to avoid black and white surfaces, providing an alternative evolutionary scenario. The authors find that the distribution of striped species overlaps with the ranges where these flies are active. They note that this is consistent across different types of striping (facial, neck, flank, rump or leg stripes and shadow striping), and different species of equids. In contrast, they do not find a consistent support across species for the camouflage, predator avoidance, heat management or social interaction hypotheses.