New Study Disproves Previous Hypothesis on the Role of Zebra Stripes

For over 50 years, the unique and striking coloration pattern of the zebras has intrigued scientists who generated many intriguing hypotheses to explain its importance and role.

Professor Tim Caro from the School of Biological Sciences at the University of Bristol examined and discredited many popular theories on why zebras have their stripes.

Some of these theories said that zebra stripes are used as camouflage from predators, as a cooling mechanism through convection currents formation, and something that the animal can use for social interactions.

The Role of Zebra Stripes

A widely known explanation for zebra stripes is that they serve as a camouflage to confuse its predators. However, scientific data suggests that it is too flawed. So, evidence suggests that these stripes can dazzle parasitic flies.

The Bristol scientists said that their new study, published in the journal Proceedings of the Royal Society B, provides a significant depth to that claim by deducing the possible mechanism that these stripes are made for.

In their previous, the researchers found out that parasitic horseflies would approach horses covered with striped rugs just as how they approach horses wearing plain rugs. However, the same insects failed to land or slow down upon reaching the horse with striped rugs.

In essence, flies are confounded by stripes which makes them collide with the animal's skin, or they fly away altogether. The study explored the possibility of the aperture effect as a potential mechanism explaining how the stripes could lead to this outcome.

Aperture Effect on Flies

The aperture effect is an optical illusion, also known as the barber-pole effect, named after the moving stripes of the barber pole outside the barbershops. These stripes appear to move upwards rather than their actual direction because the moving stripes appear to move at right angles rather than around the pole, says lead author Dr Martin How.

Their study is all about finding if this mechanism also holds true to the blood-sucking parasites as they approach the zebras. He added that any fly that approaches a landing surface would adjust its speed based on how quickly this surface expands according to its vision to make a slow and control landing.

However, the stripes of the zebra disrupt this 'optic flow' through the aperture effect, which leads the parasitic fly to believe that the landing surface is still far away than reality. Hence, the fly fails to slow down while landing and does land successfully.

But visual ecologists said that the confusion of flies on striped landings are not exclusive and that aperture effect does not explain it. They found that checked rugs also provide visual input without the aperture effect. Flies also had difficulties with checked rugs and found themselves hardly landing on checked or striped rugs.

The results of their study would not only bring scientists closer to understanding the mysteries of zebra stripes, but it would also help farmers and horse-wear companies in their effort in reducing the damage caused by parasitic flies, says Professor Caro.