Structural colours reflect individual quality: a meta-analysis

Ornamental colouration often communicates salient information to mates, and theory predicts covariance between signal expression and individual quality. This has borne out among pigment-based signals, but the potential for honesty in structural colouration is unresolved. Here I synthesised the available evidence to test this prediction via meta-analysis and found that, overall, the expression of structurally coloured sexual signals is positively associated with individual quality. The effects varied by measure of quality, however, with body condition and immune function reliably encoded across taxa, but not age nor parasite resistance. The relationship was apparent for both the colour and brightness of signals and was slightly stronger for iridescent ornaments. These results suggest diverse pathways to the encoding and exchange of information among structural colours, while highlighting outstanding questions as to the development, visual ecology, and evolution of this striking adornment.