Thursday, 17 April 2014

How Did the Zebra Get Its Stripes?

by Louisa Dassow




Zoologist John Kerr applied the “dazzle” principle to WW1 ships
 in an attempt to confuse any enemy following the ships.

There have been many legends surrounding the seemingly bizarre patterning of the zebra and an equal number of scientific theories to match. Their inverse camouflage left Darwin and Wallace puzzled as it seemed at first to contradict their belief in natural selection because it made them so obvious to other predators on the African plains. However, it seems the mystery may have finally been solved.
 
A recent study published by Tim Caro and colleagues stated that, “...the only factor which is highly associated with striping is to ban biting flies”. The stripes serve as a bug repellent. Other studies have reached this conclusion before, but they have been criticised for only considering one particular factor which could lead to the striping. This study was recently published in the journal Nature Communications. The research conducted by this team of biologists considered five of the most popular hypotheses: camouflage, the “Motion Dazzle” effect (visually confusing predators when they're being attacked), heat contol, social interaction and deterring blood-sucking flies.

They started by looking at the geographical distribution of living and extinct “equid” species such as zebras, horses and donkeys. They investigated a combination of boldly striped, subtly striped and non-striped equids and then considered environmental factors in the habitats of the equids, including predators, temperature and the flies' breeding conditions.

The results showed a strong link between the striping and the possible presence of blood-sucking flies, particularly the tsetse fly and horseflies. All equids in the fly-ridden areas were striped, but in places where the flies were not a problem there were no striped equids.

One fault in the study is that they did not use maps designed to show “fly concentration”, rather they relied on areas with suitable breeding conditions for the flies because high quality “fly concentration” maps are not available. Unfortunately, there is also no explanation as to why the flies dislike the striped surfaces; scientists are now working to design a laboratory experiment which could accurately simulate the zebra's skin. In the words of Caro, “That’s what happens in science; you answer one question and it leads to six more.”

There are still more romantic interpretations of the zebra's stripes from less scientific sources, an innumerable quantity of myths surround their odd patterning. It is a subject that Rudyard Kipling resisted writing about but other African tales are equally as sweet as any Just So story.

In a Kalahari desert tribe they told of a white zebra who approaches a pool of water guarded by a selfish baboon who sits by his fire and refuses to share. The two animals exchange insults and end up fighting until the zebra gives the baboon a tremendous kick with its hindlegs and sends the baboon flying through the air to the top of a nearby cliff. The baboon lands on his behind and still has the bare patch to this day whilst the tired zebra stumbles into the baboon's fire and scorches his fur, leaving the distinctive stripes we see today.

A Ugandan folktale teaches the importance of patience as well as the origin of zebras. In the beginning there were only donkeys, but they were constantly forced to work and carry heavy loads without a break. One day two donkeys decided they didn't want to work any more and went to visit a wise old man to see if he could help them. The wise old man agreed that the donkeys should be allowed to rest and came up with an ingenious solution, painting the donkeys so that they wouldn't be recognisable. He only had two pots of paint (white and black) but, as he painted, the donkeys were transformed into zebras, never to carry a load again. When the lucky pair ambled across their original herd, they shared their secret and led them to the wise old man, who began to paint them one by one. The donkeys became impatient with the wise man and started to stomp their feet, accidentally knocking over the paint pots. No more paint, no more new zebras. The grey donkeys were forced to return to their monotonous life of non-stop work while the painted zebras galloped away to play on the plains.

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