The Paradox of Iridescent Signals

• Published in: Trends in ecology & evolution (Amsterdam) Vol. 36; no. 3; pp. 187 - 195
• Main Authors: Stuart-Fox, Devi, Ospina-Rozo, Laura, Ng, Leslie, Franklin, Amanda M.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-03-2021
• Subjects: animal communication; Color; color vision; Humans; Iridescence; Lighting; optical effects; Reproducibility of Results; structural color; visual ecology; visual ecology; animal communication; optical effects; structural color; color vision
• ISSN: 0169-5347; 1872-8383
• DOI: 10.1016/j.tree.2020.10.009

Signals reliably convey information to a receiver. To be reliable, differences between individuals in signal properties must be consistent and easily perceived and evaluated by receivers. Iridescent objects are often striking and vivid, but their appearance can change dramatically with viewing geometry and illumination. The changeable nature of iridescent surfaces creates a paradox: how can they be reliable signals? We contend that iridescent color patches can be reliable signals only if accompanied by specific adaptations to enhance reliability, such as structures and behaviors that limit perceived hue shift or enhance and control directionality. We highlight the challenges of studying iridescence and key considerations for the evaluation of its adaptive significance.
Iridescent color patches are often considered to be signals because they tend to be eye-catching and vivid. The appearance of iridescent color patches changes with viewing geometry and illumination, but paradoxically, signals should be consistent and reliable.To understand the evolution of iridescent signals, iridescence, or the property of angle-dependent hue shift, must be distinguished from other optical effects produced by structural coloration.Understanding how animals present and process both the spatial and temporal components of iridescent color patches is essential to understand their reliability as signals.To ensure reliability, iridescent signals require accompanying adaptations, such as structures or behaviors, to limit hue shift or control directionality.