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How the zebra got its stripes

Date:
February 9, 2012
Source:
The Journal of Experimental Biology
Summary:
Horseflies are unpleasant insects that deliver powerful bites and now it seems that zebras evolved their stripes to avoid attracting the unpleasant pests. New research show that zebras have the least attractive hides for horseflies.

Zebra. If there was a 'Just So' story for how the zebra got its stripes, I'm sure that Rudyard Kipling would have come up with an amusing and entertaining camouflage explanation. But would he have come up with the explanation that Gábor Horváth and colleagues from Hungary and Sweden have: that zebra's stripes stave off blood-sucking insects?
Credit: © davy liger / Fotolia

If there was a 'Just So' story for how the zebra got its stripes, I'm sure that Rudyard Kipling would have come up with an amusing and entertaining camouflage explanation. But would he have come up with the explanation that Gábor Horváth and colleagues from Hungary and Sweden have: that zebra's stripes stave off blood-sucking insects?

The team publishes their discovery that zebra stripes is the least attractive hide pattern for voracious horsefiles in the Journal of Experimental Biology at http://jeb.biologists.org/.

Horseflies (tabanids) deliver nasty bites, carry disease and distract grazing animals from feeding. According to Horváth, these insects are attracted to horizontally polarized light because reflections from water are horizontally polarized and aquatic insects use this phenomenon to identify stretches of water where they can mate and lay eggs. However, blood-sucking female tabanids are also guided to victims by linearly polarized light reflected from their hides. Explaining that horseflies are more attracted to dark horses than to white horses, the team also points out that developing zebra embryos start out with a dark skin, but go on to develop white stripes before birth. The team wondered whether the zebra's stripy hide might have evolved to disrupt their attractive dark skins and make them less appealing to voracious bloodsuckers, such as tabanids.

Travelling to a horsefly-infested horse farm near Budapest, the team tested how attractive these blood-sucking insects found black and white striped patterns by varying the width, density and angle of the stripes and the direction of polarization of the light that they reflected. Trapping attracted insects with oil and glue, the team found that the patterns attracted fewer flies as the stripes became narrower, with the narrowest stripes attracting the fewest tabanids.

The team then tested the attractiveness of white, dark and striped horse models. Suspecting that the striped horse would attract an intermediate number of flies between the white and dark models, the team was surprised to find that the striped model was the least attractive of all.

Finally, when the team measured the stripe widths and polarization patterns of light reflected from real zebra hides, they found that the zebra's pattern correlated well with the patterns that were least attractive to horseflies.

"We conclude that zebras have evolved a coat pattern in which the stripes are narrow enough to ensure minimum attractiveness to tabanid flies," says the team and they add, "The selection pressure for striped coat patterns as a response to blood-sucking dipteran parasites is probably high in this region [Africa]."


Story Source:

The above story is based on materials provided by The Journal of Experimental Biology. The original article was written by Kathryn Knight. Note: Materials may be edited for content and length.


Journal Reference:

  1. Ádám Egri, Miklós Blahó, György Kriska, Róbert Farkas, Mónika Gyurkovszky, Susanne Ĺkesson And Gábor Horváth. Polarotactic tabanids find striped patterns with brightness and/or polarization modulation least attractive: an advantage of zebra stripes. Journal of Experimental Biology, 2012 DOI: 10.1242/jeb.065540

Cite This Page:

The Journal of Experimental Biology. "How the zebra got its stripes." ScienceDaily. ScienceDaily, 9 February 2012. <www.sciencedaily.com/releases/2012/02/120209101730.htm>.
The Journal of Experimental Biology. (2012, February 9). How the zebra got its stripes. ScienceDaily. Retrieved September 17, 2014 from www.sciencedaily.com/releases/2012/02/120209101730.htm
The Journal of Experimental Biology. "How the zebra got its stripes." ScienceDaily. www.sciencedaily.com/releases/2012/02/120209101730.htm (accessed September 17, 2014).

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