How Much Pigment Should Flowers Have? Flowers With Moderate Pigmentation Have Highest Color Contrast

Casper J Van Der Kooi

doi:10.3389/fevo.2021.731626

Abstract

Floral pigments are a core component of flower colors, but how much pigment a flower should have to yield a strong visual signal to pollinators is unknown. Using an optical model and taking white, blue, yellow and red flowers as case studies, I investigate how the amount of pigment determines a flower’s color contrast. Modeled reflectance spectra are interpreted using established insect color vision models. Contrast as a function of the amount of pigment shows a pattern of diminishing return. Low pigment amounts yield pale colors, intermediate amounts yield high contrast, and extreme amounts of pigment do not further increase, and sometimes even decrease, a flower’s color contrast. An intermediate amount of floral pigment thus yields the highest visibility, a finding that is corroborated by previous behavioral experiments on bees. The implications for studies on plant-pollinator signaling, intraspecific flower color variation and the costs of flower color are discussed.

Highlights

IntroductionFlower coloration is due to two optical principles: reflection and scattering of light by the flower’s surface and interior structures, and wavelength-selective absorption of scattered light by floral pigments (Kay et al, 1981; Kevan and Backhaus, 1998; van der Kooi et al, 2016, 2019)
The coloration of flowers is a major component of plant-pollinator signaling
Color Contrast Follows a Pattern of Diminishing Return

Summary

Introduction

Flower coloration is due to two optical principles: reflection and scattering of light by the flower’s surface and interior structures, and wavelength-selective absorption of scattered light by floral pigments (Kay et al, 1981; Kevan and Backhaus, 1998; van der Kooi et al, 2016, 2019). Whether and how scattering structures and floral pigments are tuned so to yield visually contrasting floral displays to pollinators remains an open question. Pigmentation is probably more evolutionarily and developmentally labile than are the structural properties of flowers. This difference in variation of pigmentation vs scattering structures can be understood from both a mechanistic and functional point of view. Intraspecific flower color variation can be discrete (Schemske and Bierzychudek, 2007; Streinzer et al, 2019; von Witt et al, 2020; Buide et al, 2021) or continuous, e.g., covering

Objectives

Methods

Results

Conclusion