The role of zebra stripes in deterring biting flies
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The evidence overwhelmingly supports the hypothesis that zebra stripes serve as an adaptation against biting flies. The visual disruption and polarization effects of the stripes, combined with zebras’ behavioral responses, significantly reduce the success of fly landings. While other hypotheses exist, they lack the robust experimental support that the fly-deterrence hypothesis enjoys. Future research may continue to explore these alternative theories, but for now, it appears that the primary function of zebra stripes is to protect against biting flies.
The striking black-and-white stripes of zebras have long intrigued scientists and laypeople alike. While various hypotheses have been proposed to explain this unique coloration, recent research increasingly supports the idea that zebra stripes serve as an adaptation against biting flies. This article explores the evidence and mechanisms by which zebra stripes deter these ectoparasites.
Mechanisms of Fly Deterrence
Visual Disruption
One of the primary mechanisms by which zebra stripes deter biting flies is through visual disruption. Studies have shown that the stripes interfere with the flies’ ability to execute controlled landings. For instance, flies approach zebras faster and fail to decelerate before contact, leading to fewer successful landings compared to uniformly colored horses1. This disruption is thought to be due to the stripes creating false motion cues, known as the aperture effect, and spatio-temporal aliasing, which misleads the flies’ visual systems3.
Polarization of Light
Another significant factor is the polarization of light reflected from zebra stripes. Research indicates that the alternating black and white stripes reflect light with different polarization signatures, which confuses the flies’ visual orientation mechanisms. This polarization effect is less attractive to flies, reducing their likelihood of landing on zebras2 8. The stripes’ specific widths also play a role, with narrower stripes being more effective at deterring flies8.
Behavioral Responses
Zebras also exhibit behavioral adaptations that complement their striped coloration. When faced with fly attacks, zebras are more likely to swish their tails and move away, reducing the time flies spend on their bodies. In contrast, horses tend to rely more on skin twitching, which is less effective1.
Experimental Evidence
Comparative Studies
Comparative studies between zebras and other equids provide strong evidence for the fly-deterrence hypothesis. For example, experiments where horses wore striped coats showed significantly fewer fly landings compared to when they wore solid-colored coats1. Additionally, field studies in Africa have demonstrated that striped models attract fewer flies than solid-colored ones, further supporting the hypothesis7.
Field Observations
Field observations have also been crucial in understanding the effectiveness of zebra stripes. In natural habitats, zebras are less frequently targeted by biting flies compared to other animals. This reduced targeting is attributed to the visual and polarization effects of their stripes, which are less visible to flies from a distance2 5.
Alternative Hypotheses
While the fly-deterrence hypothesis is strongly supported, other theories have been proposed. These include camouflage, predator avoidance, social functions, and thermoregulation. However, these hypotheses lack consistent experimental support. For instance, studies have found no significant evidence that stripes provide effective camouflage or social benefits4 6. Thermoregulation has been suggested as a secondary benefit, with the temperature differences between black and white stripes potentially aiding in cooling10.
Zebras have stripes as an adaptation against biting flies.
Maj Rundlöf has answered Likely
An expert from Lunds University in Ecology
I believe that this is the currently dominating theory. Tim Caro and colleagues have published a review on the function of zebra stripes (Caro et al. 2014) and their conclusion is that there is most support for the theory that that the stripes reduce attacks by biting flies. There was no consistent support for the other four tested theories: camouflage, predator avoidance, heat management or social interaction.
Experimental evidence suggests that zebra-striped horse models are less attacked by horse flies (tabanids) than black, brown, grey or white horse models and that this most likely is caused by the striped pattern reflecting polarized light that disrupt the flies ability to find their host (Egri et al. 2012).
References
Egri, Á. et al. 2012. Polarotactic tabanids find striped patterns with brightness and/or polarization modulation least attractive: an advantage of zebra stripes. Journal of Experimental Biology 215: 736-745.
Caro, T. et al. 2014. The function of zebra stripes. Nature Communications 5: 3535.