Scientist’s said that they have Finally solved the question why zebras have stripes.
Why do zebras have striking black and white stripes?
The mystery has fascinating people for centuries, and scientists have speculated endlessly about it.
Finally, it appears that a research team led by the University of California, Davis has found half an answer after examining this riddle systematically. Their answer is published in the online journal Nature Communications.
Caro and colleagues found that biting flies, including horseflies and tsetse flies, are the revolutionary driver for zebras stripes. Experiments had previously shown that such flies tend to avoid black-and-white striped surfaces, but many other hypotheses for zebra stripes have been proposed since Alfred Russel Wallace and Charles Darwin debated the problem of 120 years ago.
- A form of camouflage
- Disrupting predatory attack by visually confusing carnivores
- A mechanism of heat management
- Having a social function
- Avoiding “ectoparasite” attack, such as from biting flies.
The scientists found that biting flies, including horseflies and tsetse flies, are the evolutionary driver for zebra’s stripes.
“I was amazed by our results,” said lead author Tim Caro, a UC 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.”
Experimental work had previously shown that such flies tend to avoid black-and-white striped surfaces, but many other hypotheses for zebra stripes have been proposed since Alfred Russel Wallace and Charles Darwin debated the problem 120 years ago. These include: camouflage, disrupting predatory attack by visually confusing carnivores, heat management, having a social function and avoiding ectoparasite attack, such as from biting flies.
The team mapped the geographic distributions of the seven different species of zebras, horses and asses, and of their subspecies, noting the thickness, locations, and intensity of their stripes on several parts of their bodies. Their next step was to compare these animals’ geographic ranges with different variables, including woodland areas, ranges of large predators, temperature, and the geographic distribution of glossinid (tsetse flies) and tabanid (horseflies) biting flies. They then examined where the striped animals and these variables overlapped.
After analyzing the five hypotheses, the scientists ruled out all but one: avoiding blood-sucking flies.
Why would zebras evolve to have stripes whereas other hooved mammals did not? The study found that, unlike other African hooved mammals living in the same areas as zebras, zebra hair is shorter than the mouth part length of biting flies, so zebras may be particularly susceptible to annoyance by biting flies.
But the riddle is not fully resolved. Scientists now have to answer the question: Why do biting flies avoid striped surfaces? Caro said that now that his study has provided ecological validity to the biting fly hypothesis, the evolutionary debate can move from why zebras have stripes to what prevents biting flies from seeing striped surfaces as potential prey, and why zebras are so susceptible to biting fly annoyance.
“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.”
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