Now We Know Why Zebra Stripes Are So Effective : ScienceAlert

two zebras

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In what once seemed like a nice case of black and white camouflage, the explanation for the zebra’s striking pattern now seems to have more to do with keeping blood-sucking flies at bay.

As scientists grow increasingly confident about why zebras have stripes, they are now paying attention to how it works. A new study thinks it has found at least part of the answer, once again with the help of some flashy black-and-white patterned blankets and some patient accomplices.

Several years ago, a study led by researchers at the University of Bristol in the UK found that zebra stripes were reasonably good protection against biting flies.

By placing blankets of different designs on the horses’ backs and then filming the behavior of the horseflies as they approached and interacted with the horses, the scientists were able to see the effects of various stripe and checkerboard designs.

Now members of the same team are using a similar method to better understand exactly what the stingray pest hate is all about.

“We knew that horseflies are reluctant to land on scratched objects,” says evolutionary ecologist Tim Caro of the University of Bristol in the UK. “Several studies have now shown this, but it’s not clear what aspects of rays they find aversive.”

“Is it the thinness of the stripes? The contrast of black and white? The polarized signal that objects can emit? So we set out to explore these issues using different horse-printed fabrics and filming incoming horseflies.”

While horseflies were most attracted to large, dark objects in their environment, with all-gray blankets resulting in most landings, once the dark color is broken up with some white, the flies become less anxious. for interacting.

Coats with large black triangles placed in different positions were shown to be the next most popular design among flies, followed by coats with small checkerboard patterns. The stripes were the most unpleasant for flies, with the highest contrast stripes attracting the fewest fly landings during testing.

The researchers believe the key is to remove the strong outline of a large dark spot in the horseflies’ field of view, something the bold black and white stripes do quite well. In other words, it means that the zebras seem like less of a target.

Photos of the horse cloth designs, with polarized images to the right. (Caro et al., Journal of Experimental Biology2023)

“This suggests that any hoofed animal that reduces its overall dark outline against the sky will benefit in terms of reduced ectoparasite attack,” says Caro.

According to the findings of this study, the flies are not deterred by any kind of optical illusion effect or by the polarization of light (certain parts of the zebra appear brighter). The fine striped pattern that acts as a kind of camouflage after all; not against large predators, but small ones.

Scientists have been trying to figure out the purpose of the zebra’s stripes for years; it was previously suggested that they are some kind of temperature control mechanism or a way to confuse approaching horseflies.

The next question up for debate is why zebras are the only hoofed mammals we know of that have developed this special design on their bodies. That is something that can be looked at in the future.

“We know that the fur of zebras is short, which allows the mouthparts of horseflies to reach the skin and blood capillaries below, which can make them particularly susceptible to annoyance by flies,” says Caro.

“Perhaps most importantly, the diseases they carry are fatal for the horse family, but less so for ungulates. This needs research.”

The research has been published in the Journal of Experimental Biology.


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