How the Zebra Got Its Stripes

Since the time of Charles Darwin and Alfred Russel Wallace, scientists and the novice have wondered about zebras and their interesting stripe pattern. Scientists have recently claimed to have found the reasoning, and it’s not what you would’ve guessed.

Some biologists suggested that the stripes on zebras help manage heat by reducing the thermal loads brought on by the intensity of life in the African savanna. While most of us have accredited the patterning to predator avoidance; we have often attributed the function of the zebras’ alternating coloration to crypsis, a type of camouflage that works when the zebra is in tall grass against predators, whom are believed to be color-blind. It was also hypothesized that the stripes were a form of disruptive color, which is when the herd is in a tight bunch and the stripes blend and contour into the neighbor’s, these optical illusions confuse predators and parasites from making a meal out of them.

            Tim Caro from the University of California, decided it was time that someone tested all these hypothesizes and went with the idea of having the theories running together through his study. He and his team examined the equid species, which include zebras, horses and asses, and the geographic distribution of current and extinct species and how they fair with large predators, ectoparasites, what are their breeding conditions and the temperature at which they normally live. The ended up with seven species and subspecies to be examined, some with and some without stripes. They found that the ranges of the most distinctively striped species, Equus burchelli, E. zebra, and E. grevyi, overlap remarkably with the areas where disease-carrying blood-suckers, such as horseflies and tsetse flies, are active. This was consistent across different types of striping areas, facial, neck, flank, buttock, belly, or the legs. The stripes were of varying intensity and thickness, as well as shadow striping, and for the different equid species and subspecies. Caro stated, "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.” It is also known through various studies, apparently, that certain flies will avoid black and white surfaces and prefer ones that are uniformly colored.

In contrast, they didn’t find consistent support across species for hypotheses about camouflage, predator avoidance, heat management, or some aspect of social interaction. And Caro also found that zebras, unlike other African hooved mammals living in the same areas, have hair that’s shorter than the biting apparatus length used by biting flies, making them particularly susceptible to annoyance, which lead the natural selection of the trait when it evolved.

 

http://news.ucdavis.edu/search/news_detail.lasso?id=10879

Nicole Peterkin (3)