title: How to colour a flower: on the optical principles of flower coloration.
abstract: The coloration of flowers is due to the wavelength-selective absorption by pigments of light backscattered by structures inside the petals. We investigated the optical properties of flowers using (micro)spectrophotometry and anatomical methods. To assess the contribution of different structures to the overall visual signal of flowers, we used an optical model, where a petal is considered as a stack of differently pigmented and structured layers and we interpreted the visual signals of the model petals with insect vision models. We show that the reflectance depends, in addition to the pigmentation, on the petal's thickness and the inhomogeneity of its interior. We find large between-species differences in floral pigments, pigment concentration and localization, as well as floral interior structure. The fractions of reflected and transmitted light are remarkably similar between the studied species, suggesting common selective pressures of pollinator visual systems. Our optical model highlights that pigment localization crucially determines the efficiency of pigmentary filtering and thereby the chromatic contrast and saturation of the visual signal. The strongest visual signal occurs with deposition of pigments only on the side of viewing. Our systematic approach and optical modelling open new perspectives on the virtues of flower colour.
authors.affiliation: Department of Computational Physics, University of Groningen, Groningen, The Netherlands Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland casper.vanderkooi@unil.ch.
authors.forename: Casper J
authors.identifier: 0000-0003-0613-7633
authors.initials: CJ
authors.lastname: van der Kooi
authors.affiliation: Department of Plant Ecophysiology, University of Groningen, Groningen, The Netherlands.
authors.forename: J Theo M
authors.initials: JT
authors.lastname: Elzenga
authors.affiliation: Department of Plant Ecophysiology, University of Groningen, Groningen, The Netherlands.
authors.forename: Marten
authors.initials: M
authors.lastname: Staal
authors.affiliation: Department of Computational Physics, University of Groningen, Groningen, The Netherlands.
authors.forename: Doekele G
authors.identifier: 0000-0002-2518-6177
authors.initials: DG
authors.lastname: Stavenga
mesh_terms: D000818:Animals; D001516:Bees; D035264:Flowers / Q000033:anatomy & histology / Q000737:chemistry*; D008954:Models, Biological; D017956:Photoreceptor Cells, Invertebrate / Q000737:chemistry; D010858:Pigmentation; D010860:Pigments, Biological / Q000737:chemistry; D054817:Pollination; D013053:Spectrophotometry
chemical_list: D010860:Pigments, Biological
keywords: absorbance; anatomy; pigment; pollination; reflectance; vision model