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Scientists Solve the Mystery of Why Zebras Have Stripes 190

Hugh Pickens DOT Com (2995471) writes "There have been many explanations for the zebra's impressive stripes including Darwin who thought that the stripes help males and females make sensible choices about whom they mate with. Now Henry Nicholls reports at The Guardian that Tim Caro at the University of California, Davis, has taken a completely original approach, stepping back from one species of zebra and attempting to account for the differences in patterning across different species and subspecies of zebras, horses and asses to see if there is anything about the habitat or ecology of these different equids that hints at the function of stripes. To answer that question, Caro and his colleagues created a detailed map charting the ranges of striped vs. non-striped species and subspecies. Then they worked on a map for the bloodsuckers that targeted those species — specifically, abanid biting flies (horse flies) and tsetse flies.

'I was amazed by our results,' says Caro. 'Again and again, there was greater striping on areas of the body in those parts of the world where there was more annoyance from biting flies.' Where there are tsetse flies, for instance, the equids tend to come in stripes. Where there aren't, they don't. Biologists who buy into the bug-repellent hypothesis say that, all other things being equal, striped animals would have an evolutionary advantage because they wouldn't suffer from the loss of blood, reduced weight gain and lowered milk production that's associated with bug bites. Tsetse flies are also associated with the transmission of diseases. 'There are a lot of them, such as sleeping sickness, equine anemia and equine influenza,' Caro says. Why would zebras evolve to have stripes whereas other hooved mammals did not? The study found that, unlike other African hooved mammals living in the same areas as zebras, zebra hair is shorter than the mouthpart length of biting flies, so zebras may be particularly susceptible to annoyance by biting flies. 'It's clear that the flies can get through that hair and get to the skin.'"
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Scientists Solve the Mystery of Why Zebras Have Stripes

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  • by YalithKBK ( 2886373 ) on Thursday April 03, 2014 @08:22AM (#46647841)

    I thought the stripes broke up the outlines of individuals and made it harder for predators to single one out of a crowd? Or did no actual research go into that claim?

  • Re:Terrible summary (Score:5, Interesting)

    by Thanshin ( 1188877 ) on Thursday April 03, 2014 @08:42AM (#46647973)

    biting flies have an aversion to landing on striped surfaces.

    Biting flies can't evolve?

    I found the whole thing very unconvincing.

    If it's proven that biting flies have aversion to landing on striped surfaces, it makes no sense to say it can't be true because flies would evolve. One should rather ask "Why didn't flies evolve past this limitation?"

    One could start with various hypotheses like:
    - It's a behavior that protects them from something. Maybe the advantage of biting zebras has a lesser weight than the disadvantage of losing that protection.
    - It's a behavior that's consequence of something they can't evolve past without not being flies anymore. Maybe their eyes are not able to know the distance of a striped surface with the required precision, for whatever physical reasons, and better eyes would be too expensive.

  • Hypothesized in 1982 (Score:5, Interesting)

    by DarwinSurvivor ( 1752106 ) on Thursday April 03, 2014 @08:54AM (#46648069)

    Zebra stripes have traditionally been thought of as an adaptation against detection by vertebrate predators such as lions and hyaenas. A different hypothesis is suggested: that the stripes are an adaptation against visually orienting biting flies and act by obliterating the stimulus presented by a large dark form, which is important in host-finding by many Diptera. This hypothesis is supported by some indirect evidence, and by a field experiment in Zimbabwe in which biting fly catches were compared on moving and stationary black, white and striped models. Striped models caught significantly fewer tsetse (Glossina morsitans) Westwood and other flies (including tabanids) than solid black or white models, but this difference was much reduced in the presence of olfactory attractants.

    ~Waage, J. K. (1981) []

    Maybe people studying zebras should start by reading the zebra wikipedia page [].

  • by wonkey_monkey ( 2592601 ) on Thursday April 03, 2014 @09:40AM (#46648539) Homepage

    Nope, it seems that predators are not a threat to zebras, and it's all about flies.

    There's no such implication in the article.

    The question is not "Why are zebras camoflauged?" but "Why do zebras have stripes?"

    As an AC below [] has suggsted:

    as stripless equine species also had predators to deal with but not the flies the flies are the more plausible answer. the effects against predators are therefor likely to be a secondary benefit, and could have caused zebra's to have evolved into forming larger groups then most other animals their size to take advantage of that.


    I cant wait for the next "science" article here on slashdot.

    And I can't wait for the next hastily ill-informed, condescendingly dismissive post in reply to that article.

"What the scientists have in their briefcases is terrifying." -- Nikita Khrushchev