Zebra stripes, tabanid biting flies and the aperture effect

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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 coloration of zebras.
Original languageEnglish
Number of pages8
JournalProceedings of the Royal Society of London B: Biological Sciences
Volume287
Issue number1933
Early online date19 Aug 2020
DOIs
Publication statusPublished - 26 Aug 2020

Keywords

  • zebra stripes
  • optic flow
  • tabanid
  • vision
  • insect flight

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