Integrating functional and evolutionary approaches to the study of color-based animal signals

Bright and/or conspicuous displays of color constitute a major, functionally diverse class of animal signals. Despite the complexities of color production, however, researchers have been largely pre-occupied with understanding how a few select pigments, such as carotenoids, contribute to the honest signaling of mate quality. As a consequence, the field has largely overlooked a large family of non-pigment-based colors-the so-called 'structural colors'-and also tended to understate the true complexities of color (which often results from the concerted effects of diverse suites of pigments and reflecting structures acting upon incident light). More recent research has explored the true complexity of color signals from both functional and evolutionary perspectives. Mechanistic studies have identified precise suites of pigments, characterized myriad structural color-producing devices, and defined the relative roles of pigments and structures in determining patterns of signal variation. Behavioral and ecological studies have discovered hitherto unprecedented levels of variation, across a mechanistically and visually diverse breadth of color signals. This variation has been linked to salient selective contexts, such as mate selection, male-male competition and predator avoidance. Evolutionary theoreticians have, in turn, drawn upon these knowledge advances to expand existing color signaling hypotheses, and to generate new hypotheses for future evaluation. In this chapter we outline these advances, drawing upon exemplar cases across fishes, insects and birds, and with a focus on the role of surface structures in determining evolutionarily relevant properties of color signals.