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Scientists Solve the Mystery of Why Zebras Have Stripes
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.'"
'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.'"
So, this is why very few referees suffer from fly bites? I always wondered.
You know, if you're going to just copy and paste part of the article as your summary, you might as well post the last paragraph, and get to the actual explanation:
Zebras have stripes because biting flies have an aversion to landing on striped surfaces.
Relevant quotes missing from summary:
"researchers built horse mannequins, painted them in a variety of patterns, coated them with sticky stuff, and found that horseflies seemed to avoid landing on the fake horses that were painted with black and white stripes."
"The proposed explanation was that the flies preferred to land on dark surfaces. Such surfaces reflect the kind of polarized light that reminds the flies of the water or mud where they breed. Light surfaces aren't as attractive, but dark-and-light patterns are even worse — perhaps because such patterns confuse the flies' navigational sense."
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.