Zebra stripes, tabanid biting flies and the aperture effect.
Abstract: Of all hypotheses advanced for why zebras have stripes, avoidance of biting fly attack receives by far the most support, yet the mechanisms by which stripes thwart landings are not yet understood. A logical and popular hypothesis is that stripes interfere with optic flow patterns needed by flying insects to execute controlled landings. This could occur through disrupting the radial symmetry of optic flow via the aperture effect (i.e. generation of false motion cues by straight edges), or through spatio-temporal aliasing (i.e. misregistration of repeated features) of evenly spaced stripes. By recording and reconstructing tabanid fly behaviour around horses wearing differently patterned rugs, we could tease out these hypotheses using realistic target stimuli. We found that flies avoided landing on, flew faster near, and did not approach as close to striped and checked rugs compared to grey. Our observations that flies avoided checked patterns in a similar way to stripes refutes the hypothesis that stripes disrupt optic flow via the aperture effect, which critically demands parallel striped patterns. Our data narrow the menu of fly-equid visual interactions that form the basis for the extraordinary colouration of zebras.
Publication Date: 2020-08-19 PubMed ID: 32811316PubMed Central: PMC7482270DOI: 10.1098/rspb.2020.1521Google Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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The research article explores why zebras have stripes by examining the hypothesis that the stripes serve to prevent attacks from biting flies. The researchers suggest that the stripes might interfere with the insects’ flight patterns and affect their visibility. The study focused on having horses wear different patterns to observe the behavior of the flies around these setups, providing a more realistic scenario. The data indicated that flies avoid the striped and checked areas more so than the grey areas.
Research Problem and Objective
- The article’s primary focus is to understand the zebra’s particular colouration. For many years, it has been believed that their stripes help deter attacks from biting flies. Still, there was a lack of clarity regarding how these stripes help in achieving this.
- This research aimed to bring more evidence concerning this hypothesis. The researchers investigated whether the stripes interfere with the biting flies’ visual perception and rendered them unable to make a successful landing on the zebra’s body.
The conducted experiments
- The experiment involved observing tabanid fly behaviour around horses wearing differently patterned rugs.
- The patterns included were checked, striped and grey. The choice of patterns encompassed the spectrum – from the more complex to the simple. Stripes and checks represent mixed patterns, engaging lines, and squares, while the grey pattern represents a homogenous, unbroken and plain design.
- Such an experiment provided a realistic assessment, mimicking the natural interaction between the flies and zebras in the wild.
Results and Conclusions
- The study found that flies avoided landing on, flew faster near, and did not approach as close to striped and checked rugs compared to grey ones.
- The then-current belief was that stripes could create an ‘aperture effect’, disrupting the optic flow of the flies, and was refuted in this study as even the checked patterns had similar repelling results as the stripes, removing the exclusivity of parallel pattern’s effect on tabanid flies.
- This eased the path in understanding fly-zebra visual interactions, providing clearer insight into how the zebra’s colouration mechanistically deters flies. The study, therefore, helped unpack some of the mysteries associated with the zebra’s pattern.
Cite This Article
APA
How MJ, Gonzales D, Irwin A, Caro T.
(2020).
Zebra stripes, tabanid biting flies and the aperture effect.
Proc Biol Sci, 287(1933), 20201521.
https://doi.org/10.1098/rspb.2020.1521 Publication
Researcher Affiliations
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK.
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK.
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK.
- School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK.
- Center for Population Biology, University of California, Davis, CA 95616, USA.
MeSH Terms
- Animals
- Color
- Cues
- Diptera
- Flight, Animal
- Insect Bites and Stings
- Pigmentation
Conflict of Interest Statement
We declare we have no competing interests.
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Citations
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