Guest blog post by Ed Brown: How The Zebra Got Its Stripes

The latest guest blog post comes from Ed Brown, host of the Australian podcast Science On Top. Ed describes SoT:
"Each week, we take a look at the science news that often doesn’t make it into the mainstream media. Science On Top is our attempt to shed light on the extraordinary work being done in the name of science, and discuss the world of science in general."

Have you ever wondered why zebras have black and white stripes? As camouflage goes it seems less than ideal on the grassy African plains. Surely they’d stick out, a tasty meal advertising itself to any interested predator? Well, we don’t actually know for sure why zebras have such distinctive and unusual patterns, but we have some good hypotheses.

http://commons.wikimedia.org/wiki/File:L15zebras.jpg

One hypothesis is that the stripes are for identification purposes. Every zebra has a unique pattern, and just as we recognise each other by our faces it could be that zebras recognise each other by their stripes. Zebras are pack animals, and for a variety of social and sexual reasons it’s important to know who you are and where you stand. It’s unknown, however, if zebras pay any attention at all to each other’s patterns - and it’s very hard to test that.

Another hypothesis is that the pattern helps regulate body heat. A common statistic that crops up on the internet is that the stripes deflect 70% of the heat that hits a zebra’s body. However, I’ve not been able to find a reputable source for that figure. Nevertheless it’s an interesting idea and such an ability would be useful in the hot African sun.

One of the leading hypotheses is, perhaps surprisingly, camouflage. As I said earlier, a black and white zebra on an open plain would stand out glaringly. But a pack of zebras, huddled close together, could appear as one large animal, giving a predator second thoughts. Also, it should be noted that the zebra’s main predator is the lion, which is colour blind. Therefore to a lion, the zebra’s vertical stripes could serve as camouflage against a backdrop of long grass.

But a recent experiment conducted in Hungary gives credibility to another hypothesis: the zebras stripes deter dangerous tabanids. Tabanids are a family of insects that includes tsetse flies and horseflies, which can carry diseases like sleeping sickness. To test this idea, Susanne Åkesson, an evolutionary biologist at the Lund University in Sweden, carried out an experiment on a horse farm in Hungary. Her paper was published in the Journal of Experimental Biology in March this year.

Åkesson obtained a number of life-sized plastic horses, and painted them various colours and patterns. Some were solid colours - black, brown, white - some had square patterns, and some had stripes of various widths. Then the fake horses were coated in a clear, odourless glue to trap any flies that landed on them.

At the end of the day, she and her colleagues counted how many flies were stuck and to which coloured horse, and analysed the results. Her experiment showed a clear correlation between black and white stripes and fewer flies. She believes the flies prefer the uniform light patterns of solid colours over the multiple light patterns from the high-contrast patterns. It’s a good idea and now thanks to Åkesson’s study it is supported by a little bit more evidence.

Scientists tested insects’ attraction to various black and white patterns.
http://www.nytimes.com/2012/02/14/science/zebras-stripes
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It’s not solid proof, however. The experiment was conducted on a horse farm in Hungary, and environmental conditions could be significantly different to Africa. The smells, body heat and behaviour of live horses could also affect the results. But even so, this is one of the most thorough investigations of the reasons for zebra stripes ever conducted. And as with all science, the truth is usually a combination of factors. Identification, temperature control, camouflage and flies may all have played a part in how the zebra got its stripes.

This was just one story we covered on my weekly podcast, Science on Top. Each week I talk with my panel of guests about five or six of the latest and coolest science news. If you’re interested, head over to the Science on Top website and subscribe or download it from iTunes!

Ed Brown is a science-lover, a geek and an amateur astronomer. He’s an active member of several skeptical organisations, such as Australian Skeptics and James Randi Educational Foundation.