title: Flower Iridescence Increases Object Detection in the Insect Visual System without Compromising Object Identity.
abstract: Iridescence is a form of structural coloration, 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 [2]) and in plants (on the petals of some animal pollinated flowers [5]). The behavioral impacts of floral iridescence and its potential ecological significance are unknown [6-9]. Animal-pollinated flowers are described as "sensory billboards" [10], with many floral features contributing to a conspicuous display that 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 optimize iridescence to increase showiness. On the other hand, pollinators memorize floral colors as consistent advertisements of reward quality, and iridescence might corrupt flower color 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 hypothesize 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.
authors.affiliation: School of Biological Sciences, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol BS8 1TQ, UK. Electronic address: heather.whitney@bristol.ac.uk.
authors.forename: Heather M
authors.initials: HM
authors.lastname: Whitney
authors.affiliation: Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK.
authors.forename: Alison
authors.initials: A
authors.lastname: Reed
authors.affiliation: School of Biological Sciences, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol BS8 1TQ, UK.
authors.forename: Sean A
authors.initials: SA
authors.lastname: Rands
authors.affiliation: Department of Experimental and Biological Psychology, School of Biological and Chemical Sciences, Queen Mary University of London, London E1 4NS, UK.
authors.forename: Lars
authors.initials: L
authors.lastname: Chittka
authors.affiliation: Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK. Electronic address: bjg26@cam.ac.uk.
authors.forename: Beverley J
authors.initials: BJ
authors.lastname: Glover
mesh_terms: D000818:Animals; D001516:Bees / Q000502:physiology*; D003118:Color Perception / Q000502:physiology*; D035264:Flowers / Q000502:physiology*; D000068897:Iridescence; D010364:Pattern Recognition, Visual / Q000502:physiology*; D013997:Time Factors