Information from an article in the Journal of Experiemental Biology, as reported at Science Daily:
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...That's one kind of zebra. The other kind are the referees at various sporting events; their evolution was explained eight years ago in a column at Slate:
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.
The article provides additional details on the history of referee uniforms in football, hockey, and basketball.According to an article from the archives of the conceptually brilliant Referee magazine, the striped design was the brainchild of one Lloyd Olds, a longtime high-school and college sports official from Michigan. The impetus for the idea came in 1920, when he was working a college football game while wearing a white shirt, which was customary at the time for officials in most sports. The visiting team wore white as well. At one point, the quarterback mistakenly handed off the ball to Olds. "Of course I dropped it," he later recalled, "and, thank goodness, he recovered same."..
The zebra look has infiltrated many other sports, including lacrosse, wrestling, and on at least one notable if atypical occasion, boxing. The big exception, of course, is baseball, where umpiring attire has generally been rooted in prevailing menswear fashions.
p.s. - Is a zebra black with white stripes, or white with black stripes?
Top photo: © davy liger / Fotolia
Very cool study!
ReplyDeleteCool study which raises further interesting questions.
ReplyDeleteWhy, of all the hundreds of modern species of large mammals which have warm blood available as a food source for parasitic insects and other microfauna, do only zebras have vertical stripes? Shouldn't what is true of African horseflies also have been generally true of horseflies in other parts of the world? Shouldn't evolution have led to horseflies in Africa that ignore the stripes? Equus - that family of all horse species, both living and extinct - has been around since at least five million years ago. That is biologically lots of time for the evolution of horseflies which ignore striping, and also lots of time for other animals to develop stripes. But that didn't happen.
I'm no creationist - far from it - but wait for the next chapter in this story. There must be more to come. Maybe a mutated gene led to some prehistoric horse having stripes, or something like them, and its striped offspring bred more often. That's how it works, isn't it?
Anon:
ReplyDelete"Shouldn't evolution have led to horseflies in Africa that ignore the stripes?"
Actually no, as long as other there was other food available for said horseflies, and other animals may have adopted different coloring based on other environmental considerations.
A zebra is black with white stripes, according to Wikipedia: http://en.wikipedia.org/wiki/Zebra#Stripes
ReplyDeleteStephen Jay Gould talks about this problem and more in his article "How the zebra gets its stripes", found in Hen's Teeth and Horses Toes: Further Reflections on Natural History (New York and London: W. W. Norton, 1983), pp 366-75; reprinted in The Richness of Life: The Essential Stephen Jay Gould (London: Vintage Books, 2007), pp 324-32.
ReplyDeleteThe article concludes: "Biologists often look to teratologies, or abnormalities of development, to solve such issues. [Embryologist, J. B. L.] Bard has uncovered an abnormal zebra whose 'stripes' are rows of dots and discontinuous blotches, rather than coherent lines of color. The dots and blotches are white on a black background. Bard writes: 'It is only possible to understand this pattern if the white stripes had failed to form properly and that therefore the 'default' color is black. The role of the striping mechanism is thus to inhibit natural pigment formation rather than to stimulate it.' The zebra, in other words, is a black animal with white stripes."
As I have pointed out elsewhere, my horses spend all their waking hours grazing with their heads down near the ground. Zebras likely do too. Thus, their heads, with horizontal stripes, would present with apparent vertical stripes to the flies. Their legs have horizontal stripes. My horses all get fly-bitten around their legs and faces and not around their main body areas where zebras have their vertical stripes. My guess is that vertical stripes work better for camouflage in tall grass than they do for flies.
ReplyDelete