Flower iridescence increases object detection in the insect visual system without compromising object identity
Whitney, Heather M
Rands, Sean A
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Whitney, H. M., Reed, A., Rands, S. A., Chittka, L., & Glover, B. (2016). Flower iridescence increases object detection in the insect visual system without compromising object identity. Current Biology
Iridescence is a form of structural colouration, produced by a range of structures, in which hue is dependent on viewing angle [1-4]. One of these structures, the diffraction grating, is found both in animals (for example beetles ) and in plants (on the petals of some animal pollinated flowers ). The behavioural impacts of floral iridescence and its potential ecological significance are unknown [6-9]. Animal-pollinated flowers are described as ‘sensory billboards’ , with many floral features contributing to a conspicuous display which filters prospective pollinators. Yet floral iridescence is more subtle to the human eye than that of many animal displays because the floral diffraction grating is not perfectly regular [5-9]. This presents a puzzle: if the function of petals is to attract pollinators, then flowers might be expected to optimise iridescence to increase showiness. On the other hand, pollinators memorise floral colours as consistent advertisements of reward quality, and iridescence might corrupt flower colour identity. Here we tested the trade-off between flower detectability and recognition, requiring bumblebees (Bombus terrestris) to identify artificial flowers that varied in pigmentation and degree of iridescence. We find that iridescence does increase target detectability but that ‘perfect’ iridescence (produced by an artificial diffraction grating) corrupts target identity and bees make many mistakes. However, ‘imperfect’ floral iridescence does not lead to mistaken target identity, while still benefitting flower detectability. We hypothesise that similar trade-offs might be found in the many naturally imperfect iridescence-producing structures found in animal-animal, as well as other plant-animal, interactions.
We thank Divykriti Chopra, Matthew Dorling, Lucy Sandbach and James Philpott for assistance with experiments, and Edwige Moyroud for helpful discussions. We thank James Foster for assistance with measurement of flight arena light level measurements. HW is supported by ERC Starting Grant 260920. AR was supported by a BBSRC doctoral training grant studentship. LC is supported by a Royal Society Wolfson Research Merit Award and ERC Advanced Grant 339347.
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