Experimental evidence suggests that specular reflectance and glossy appearance help amplify warning signals
Waldron, S., Endler, J. A., Valkonen, J., Honma, A., Dobler, S., & Mappes, J. (2017). Experimental evidence suggests that specular reflectance and glossy appearance help amplify warning signals. Scientific Reports, 7, 257. doi:10.1038/s41598-017-00217-5
Published in
Scientific ReportsAuthors
Date
2017Discipline
Ekologia ja evoluutiobiologiaCopyright
© the Authors, 2017. This is an open access article distributed under the terms of a Creative Commons License.
Specular reflection appears as a bright spot or highlight on any smooth glossy convex surface and
is caused by a near mirror-like reflectance off the surface. Convex shapes always provide the ideal
geometry for highlights, areas of very strong reflectance, regardless of the orientation of the surface
or position of the receiver. Despite highlights and glossy appearance being common in chemically
defended insects, their potential signalling function is unknown. We tested the role of highlights in
warning colouration of a chemically defended, alpine leaf beetle, Oreina cacaliae. We reduced the
beetles’ glossiness, hence their highlights, by applying a clear matt finish varnish on their elytra. We
used blue tits as predators to examine whether the manipulation affected their initial latency to attack,
avoidance learning and generalization of warning colouration. The birds learned to avoid both dull
and glossy beetles but they initially avoided glossy prey more than dull prey. Interestingly, avoidance
learning was generalized asymmetrically: birds that initially learned to avoid dull beetles avoided glossy
beetles equally strongly, but not vice versa. We conclude that specular reflectance and glossiness can
amplify the warning signal of O. cacaliae, augmenting avoidance learning, even if it is not critical for it.
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