- 2016年05月04日10:15 来源：小站整理
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Are zebra stripes just an elaborateinsect repellent?
Imagine what it looks like to a fly
HOW the zebra got his stripes sounds like the title of one of RudyardKipling's Just So stories.
Sadly, it isn't, so the question has, instead,been left to zoologists.
But they, too, have let their imaginations rip. Somehave suggested camouflage.
Others suggest they are a way to display anindividual's fitness.
Irregular stripes would let potential mates know thatsomeone was not up to snuff.
One researcher proposed that stripes are to zebrawhat faces are to people,
allowing them to recognise each other, since everyanimal has a unique stripe-print.
Another even speculated that predators mightget dizzy watching a herd of stripes gallop by.
There is,however, one other idea: that stripes are a sophisticated form of flyrepellent.
It was originally dreamed up in the 1980s, but never proved.
Now, ateam of investigators led by Gabor Horvath of Eotvos University in Budapestreport in the Journal of experimental Biology thatthey think they have done so.
The original suggestion was that stripes repel tsetse flies.
These insectscarry sleeping sickness, which is as much a bane of ungulates as it is of people.
But tsetses are not the only dipteran foes of zebra and,
since they arerarely found in the meadows of Hungary,
Dr Horvath plumped for studying analmost equally obnoxious alternative: the horsefly.
Horseflies, too, transmit disease.
They also bite incessantly, thuskeeping grazing beasts from their dinner.
Indeed, previous research has shownthat fly attacks on horses and cattle reduce their body fat and milkproduction.
Such research has also shown something odd:
horseflies attack blackhorses in preference to white ones.
That fact got Dr Horvath wondering how theywould react to a striped horse—in other words, a zebra.
Actual zebra are hard to experiment on.
They insist on moving around andswishing their tails.
The team therefore conducted their study using inanimateobjects.
Some were painted uniformly dark or uniformly light,
and some hadstripes of various widths.
Some were plastic trays filled with salad oil.
Some were glue-covered boards. And some wereactual models of zebra.
They put these objects in a field infested withhorseflies and counted the number of insects they trapped.
Their first discovery was that stripes attracted fewer flies than solid,uniform colours.
As intriguingly, though, they also found that the leastattractive pattern of stripes was precisely those of the sort of width found onzebra hides.
Zebra stripes do, therefore, seem to repel horseflies.
Exactly why is unclear.
But Dr Horvath thinks it might be related to a horsefly'sability to see polarised light,
which imposes a sense of horizontal andvertical on an image.
Horseflies are known to prefer horizontal polarisedlight.
Possibly, the mostly vertical stripes on a zebra confuse the fly's tinybrain and thus stop it seeing the animal.
Another obvious question, though, is why other species have not evolvedthis elegant form of fly repellent,
and what the consequences would have beenif they had.
If humans, for example, were black-and-white striped,
then thehistory of intercommunal violence the species has suffered when different raceshave met might not have been quite as bad.
One for Kipling to have pondered,perhaps?