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Resolving the Riddle of Why the Zebra Has Stripes

Etosha National Park, Namibia – I’m sitting in a truck in Etosha National Park, dart rifle in hand, watching a herd of zebra when 9-year-old Olivia, already a keen observer of nature, pipes up. “Is that a melanistic zebra over there?”  A melanistic zebra is one whose stripes haven’t developed correctly. It’s not fully black like most melanistic animals you might think of. It looks more like the stripes arose mid-body and were trying to migrate out to the head and feet, but got stuck.

 

"zebra herd with melanistic foal"
Zebra herd with melanistic foal. Photo by Brenda Larison.

 

Melanistic zebra are not extremely common, and may not survive long, but each trip I find a couple more to sample. I quickly darted this one, hopped out of my vehicle (after peering around for lion, elephants and other potential dangers) and walked out to pick up the dart. The dart was fitted with a needle to take a small skin sample from the zebra, which had already returned to grazing. Melanistic zebra are one potential key to the question of how the zebra got its stripes, a question I am studying from two angles – the how and the why.

The question of how the zebra got its stripes really grabs my interest because stripes make the zebra seem so conspicuous. Zebra are one of the lion’s favorite prey so you might expect them to be less conspicuous to avoid predation.

Do Stripes Confuse Lions?

There are many ideas floating around about what the advantage of striping might be, but none are proven yet in spite of all the just-so stories you may have heard. Stripes might actually help prevent predation by confusing the lion, creating a blur of stripes in a herd running this way and that, or by making it hard to tell where one zebra stops and the other begins. They might even make the zebra less conspicuous in brush or at dawn and dusk, prime lion hunting times. Another tantalizing idea is that they help zebra avoid being bitten by tsetse flies and thus avoid sleeping sickness!

What is interesting, and what is the main focus of my research, is that even among zebra with normally developed stripes, not all are as stripy as others. In eastern Africa they are fully striped, head to toe, while in southern Africa they are less stripy, often with no stripes at all on their legs. I am using this variation to test ideas about why the zebra is striped by correlating variation in striping with climatic and habitat variation. These correlations can provide clues about why zebras are (or aren’t) striped, giving us leads that we can follow up on with more direct tests. I’m also using this variation to discover the gene or genes that cause and control striping. The genes themselves can also tell us something about whether striping is adaptive, as selection leaves its mark on the genome.

 

"variation in zebra stripe patterns"
Left: Very striped zebra in Tanzania, Right: Less striped zebra in Namibia. Photos by Brenda Larison.

 

My next trip is to Uganda to sample some very stripy zebra. Ultimately, I plan to sample from six populations for the genetic work and am collecting photos from all over Africa (mine, those of friends, from people on Flickr etc.) to do the environmental correlations.

So why are zebra striped? It’s still an open question. For every hypothesis out there you can come up with good reasons it could be the answer and good reasons why it’s not! Maybe it’s something no one has thought of yet, maybe it’s a combination of things, or maybe it’s historical. With all the new tools at our disposal these days, I think we’re getting close to the time when we’ll have an answer.

Zebra stripes are among the most striking mammalian coat patterns. How these dramatic patterns are produced remains mysterious, as does their adaptive value. Brenda Larison of the University of California at Los Angeles received a grant from the National Geographic Society’s Committee for Research and Exploration to investigate the genetic basis and adaptive significance of stripe pattern variation in plains zebra (Equus burchelli). The study represents a unique opportunity to gain new insights about the evolution of zebra stripes. You can also help Brenda fund her field work by making a donation on her site.

Comments

  1. Matt
    January 25, 7:51 am

    I like the idea of cohesive camouflauge between multiple zebra but I don’t understand how it would of been selected for? Have people investigated this at all? Off the top of my head I’m struggling to think of a way this could occur naturally but then again I’m a chemist so I leave the soft squishy things to you guys :D

  2. Johny Kundoh
    Malaysia
    October 14, 2013, 2:36 pm

    That is called disruptive correlation

  3. william carter
    ky.
    December 13, 2012, 10:37 pm

    in the 1611 kjv. bible genesis chapter 1-v.24,25 it has stripes because God made them to what he likes.

  4. simara burgins
    Steubenville,Ohio 43952
    October 22, 2012, 12:02 pm

    who did zebras get there spots really because im in school now doing a report and need to know

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  7. Brenda Larison
    June 27, 2012, 12:43 pm

    Another interesting fact that I just ran across is that some wild, pre-domestic horses were spotted much like appaloosas. Archeologists have wondered whether ~25000 year old cave paintings that depict spotted horses were accurate. A recent study published in PNAS (also reported in the July 2012 National Geographic) found that the genotype for spotting was present in predomestic horses.

  8. SKEPTIC
    TORONTO,ONTARIO
    June 25, 2012, 8:24 pm

    It may have evolved from a group of leucistic dark horses. It might have been evolved from dark horses becauses they have dark mouth just like other leucistic dark animals with dark mouth and light discoloration. The random discoloration of white stripes may have been an evolutionary advantage and eventually it turned into a trait. I think the organised patterns are the result of sexual selection.

  9. misnomer
    Pampanga, Philippines
    June 24, 2012, 7:16 pm

    How I love to know the truth behind this.

  10. Karl Hickel
    June 24, 2012, 5:51 pm

    True. Looking at something striped, a room for example, gives an optical illusion to the effect of losing spacial relation of foreground and background. It has a disorienting affect.The lion must look to the ground for balance?

  11. Mark
    June 24, 2012, 5:38 pm

    I read an experiment a few months ago that indicated the stripes help protect zebras from insects…

  12. fred
    pensacola, Fl
    June 24, 2012, 4:57 pm

    I would equate it to looking at something through a chain link fence and you change focus slightly and you end up cross eyed and confused on the depth perception

  13. Thom
    United States
    June 24, 2012, 4:40 pm

    One thing about zebras that is even more important than how or why it has stripes, is why it is the #1 animal that, if domesticated, would have changed both African and World history by giving Africans a reliable beast of burden and mode of transportation. Without a domesticated zebra, Africans remained, like those in the New World who also had to do without the horse, were unable to progress much past their stone age ancestors, even though some Central and So. American civilizations accomplished great feats without them.

  14. Myriam
    Belgium
    June 24, 2012, 4:38 pm

    Good question. From what I know Zebras are the only fully striped equids.
    You will find stripes on the legs of many “primitive/rustique” horsebreeds such as Icelandic horses, Fjord horses, Prewalzki horses, Shetland ponies. Often these breeds also have this dark line down their back
    There are some rare cases of brindle horses http://www.brindlehorses.com I’d say that they come closest to the zebra striping in a domesticated equine.

  15. Eva
    Michigan
    June 23, 2012, 3:39 pm

    I love Zebra’s, they are my favorite animal. I have a breath taking painting of a Zebra hanging in my living room. I look forward to getting updates on your work, on your website.

  16. Ronak Patel
    Australia
    June 23, 2012, 6:25 am

    Awesome question asked,
    I believe it has something to do with it’s food,weather conditions and it’s ancient relatives DNA. This all may have sync and produced something Zebs have these days, I would prefer to study the species above Zebs and I would get more idea, what do you think ?
    Very nice observations, I loved small clip,,,, 5*

    • Brenda Larison
      June 23, 2012, 8:46 am

      I do agree that multiple factors have probably been at work especially given the variation that we see in stripe pattern. I think studying other equids could be useful as some of those also have stripes and some don’t. As equids can readily hybridize a study of second generation hybrids would be great if you could find enough of them. Glad you liked the video.

  17. Rich
    Cebu, Philippines
    June 23, 2012, 4:40 am

    Your study seems so interesting. If only I could help,, hehee

  18. Suruchi Patel
    India
    June 23, 2012, 4:09 am

    This question striked my mind too.But I satisfied this question with the elementary idea of codominance like we have in other animals.

  19. sello
    Katlehong, Gauteng, Johannesburg
    June 22, 2012, 11:17 am

    i would like to know more its so facinating and i acknoledge that some nature animals were made puposely

  20. Ajij Mujawar
    June 22, 2012, 9:03 am

    Are zebras black in white or white in black?

    • Brenda Larison
      June 23, 2012, 12:56 am

      Hard to know for certain and maybe it’s neither. Since their skin is black throughout one might guess white on black. On the other hand, when zebra appear less striped, and have no stripes on the legs or over even more of the body like the extinct quagga subspecies, the unstriped areas are beige or tan, not black.

  21. João Sá
    Portugal
    June 22, 2012, 3:49 am

    From my point of view, it’s all about focusing a striped patern – when I use my camera, a stiped patern is the ultimate chalenge for the autofocus system. So, if predator’s eyes work the same way, the difficulty for them is to focus and though, to determine the distance separating them from the zebra. This would represent a major chalenge in the pre-evaluation phase when the lion is waiting lying down hidden and even more of a chalenge when running after the zebra and having to choose the right moment to jump over it. Imagine running after something and never being sure about the distance separating you and from your objective.
    Must be something like this … the autofocus problem with striped paterns

    • Brenda Larison
      June 23, 2012, 12:46 am

      Joao – this is an interesting observation. I would have thought that a pattern would be easier for the camera to focus on than something more plain. Testing this would be a useful experiment.