New idea on how the zebra got its stripes

January 14, 2015 by Bob Yirka report
A photo showing two Zebras in Mikumi National Park. Credit: Sajjad Sherally Fazel / Wikipedia. (Creative Commons Attribution-Share Alike 3.0 Unported)

(Phys.org) —A small team of researchers affiliated with the University of California has found little evidence to support prior theoretical explanations of why zebras have evolved to have stripes and instead suggest that temperature appears to be a factor. In their paper published in Royal Society Open Science, the team describes how they tested other theories and found them wanting and instead found temperature variation to be a predictive factor in striping.

People throughout history have wondered about the black and white stripes displayed by zebras, many asking themselves what caused the evolutionary changes that led to the unique design. Many ideas have been put forth, from suggestions that the stripes ward off flies, to ideas that they somehow confuse lions when they are in a herd. In this new effort, the researchers looked at many of the most prominent ideas and tested them for soundness. They also noted that there is considerable stripe variation among the zebras depending on where they live.

In studying prior theories, the researchers found no evidence that any of them were sound—lions appeared to be unfazed by the stripes, for example, and only some types of biting flies appeared to be put off by the stripes. That led them to wonder if some other factor might be at play that might be revealed by stripe pattern variations between groups. To find out, they noted stripe characteristics on zebras at 16 different locations and compared them with 29 environmental factors such as heat, biting flies, predation, etc. In analyzing the data, the only correlation they could make was stripe pattern and heat—lower temperatures meant fewer or fainter stripes—higher temperatures meant more or darker stripes.

The researchers do not know why temperature might have caused stripes to come about, but suggest it might have something to do with body heat regulation (the difference between the heat absorbing black and reflective white might create air movement) or that stripes evolved in for a variety of reasons related to both heat and as a means of warding parasites or some other unknown problem. They believe more research needs to be done before the riddle can be truly solved.

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Explore further: How the zebra got its stripes

More information: How the zebra got its stripes: a problem with too many solutions, Royal Society Open Science, Published 14 January 2015. DOI: 10.1098/rsos.140452

Abstract
The adaptive significance of zebra stripes has thus far eluded understanding. Many explanations have been suggested, including social cohesion, thermoregulation, predation evasion and avoidance of biting flies. Identifying the associations between phenotypic and environmental factors is essential for testing these hypotheses and substantiating existing experimental evidence. Plains zebra striping pattern varies regionally, from heavy black and white striping over the entire body in some areas to reduced stripe coverage with thinner and lighter stripes in others. We examined how well 29 environmental variables predict the variation in stripe characteristics of plains zebra across their range in Africa. In contrast to recent findings, we found no evidence that striping may have evolved to escape predators or avoid biting flies. Instead, we found that temperature successfully predicts a substantial amount of the stripe pattern variation observed in plains zebra. As this association between striping and temperature may be indicative of multiple biological processes, we suggest that the selective agents driving zebra striping are probably multifarious and complex.

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12 comments

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Maggnus
5 / 5 (6) Jan 14, 2015
In other words: We don't know.
Iochroma
5 / 5 (4) Jan 14, 2015
Real reason: the ladies dig it.
rgw
3 / 5 (2) Jan 14, 2015
Yes we do. God was stoned that day.
verkle
Jan 15, 2015
This comment has been removed by a moderator.
Vietvet
3.7 / 5 (6) Jan 15, 2015
It surely wasn't evolution that did it.



You surely don't have a brain.
Rute
4.5 / 5 (2) Jan 15, 2015
Some African predators like striped hyena and aardwolf have high contrast stripes that camouflage them to the environment (they would be extinct if the stripes didn't help them to camouflage). There are also some herbivores like bongo (a species of antelope), okapi, and Barbary striped grass mouse, that have similarily high contrast stripes, probably for the same reason. I would be surprised if the origin of zebra's stripes doesn't have something to do with camouflage.

Lions and hyenas predate during the night with the help of rod cells. Rod cells do not perceive color (only differences in light) so I guess it doesn't matter if zebra's stripes are not brown if lions and hyenas are their major predators.
Rustybolts
not rated yet Jan 15, 2015
Well it's better than a optical illusion theory or biting flies. The stripes are generally the same on all of them with small amounts of randomness. The pattern is the key to finding out what there really used for. There number one predator has no problem seeing or smelling them so that's out.
Rute
2 / 5 (1) Jan 15, 2015
During night the sky is black. The grass in the savannah is almost white. So wouldn't zebra's stripes be the perfect camouflage against nocturnal predators?
I Have Questions
4 / 5 (4) Jan 15, 2015
It surely wasn't evolution that did it.

It surely wasn't God either.
Joker23
1 / 5 (4) Jan 15, 2015
We still don't know and more research is necessary. Where have I heard THAT before? As long as research like this is paid for by private foundation and not my tax money, I Don't mind. Is it interesting? Yes. Does it help anyone? I don't think so.
OZGuy
4.4 / 5 (7) Jan 15, 2015
verkle
We've missed your scintillating and thought provoking insights into the natural world.

Must be nice to be content to say "god did it" when asked the answer to any question you can't or don't want to answer, saves all that tiresome learning and thinking the rest of us do.
mreda14
not rated yet Jan 17, 2015
I agree with the Camouflage theory. It is a combination of special kind of Camouflage combined with the effect of the strips on the Mirage. At a long distance in the heat of Africa these black strips has different optical effect on the Mirage. This require a serious study on the science of optics.

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