Format: ORAL

Miranda Sinnott-Armstrong1,2, Silvia Vignolini2,3, Stacey D. Smith1

1 Department of Ecology and Evolutionary Biology, University of Colorado Boulder, Boulder, CO, USA 2 Department of Chemistry, University of Cambridge, Cambridge, UK 3 Sustainable Biomaterials, Max Planck Institute of Colloids and Interfaces, Golm, Potsdam, Germany

Most plants use pigments to color their flowers, fruits, and leaves, but structural colors are increasingly being described. In contrast to pigments, structural colors are nanostructures that interfere with light to create color. Due to the limited study of structural colors in plants, especially compared to their study in animals, our understanding of how and why structural colors evolve in plants is lacking. Here, we examine the evolution of structural color in Elaeocarpus, a tropical lineage with the first described structurally colored fruit. We confirm that E. angustifolius has a multilayered structure, but we find that the structure is made of lipids rather than of polysaccharides (as was previously described). The use of lipids to build a multilayer reflector is similar to that of recently described species (Viburnum tinus and Lantana strigocamara), although the type of lipid is different. Furthermore, anatomically, the structure in Elaeocarpus differs in that it occurs in the extracellular space, rather than embedded in the cell wall as in Viburnum and Lantana. These anatomical and chemical differences indicate that the structure in Elaeocarpus has very different evolutionary origins to similar structures described previously. Additionally, we observe that all blue-fruited species in Elaeocarpus exhibit the same type of structure, and that the structure was lost multiple times in black-, brown-, yellow-, and red-fruited species. This is the first time that losses of structural color have been documented in plants, and suggests that the energetic investment in building large structures out of lipids may not always be advantageous in fruits.