The evolution of signal design in manakin plumage ornaments
Animal signals are characterized by two design components: efficacy (detectability) and content (message being conveyed). Selection for efficient signal perception should favor the evolution of traits that exhibit an optimal balance between these two design components. We examined the evolution of signal design in the colorful plumage ornaments of manakins (Aves: Pipridae). We used a model of avian color space to quantify how differences in plumage coloration would be perceived by a typical passerine bird and examined patterns of coloration across 50 species of manakin. Using phylogenetically independent contrasts, we show that plumage contrast against the background increases with sexual dichromatism in males but not females, suggesting that sexual selection has favored the evolution of male plumage ornaments that enhance signal efficacy. Plumage contrast within individuals also increased with dichromatism in males but not females. Finally, plumage colors produced by different mechanisms, which may reveal different aspects of quality, resulted in different degrees of contrast against the background. Our findings suggest that selection for signal efficacy and content may sometimes be opposing, creating a trade-off between these two components of signal design. Manakins may mediate this trade-off by combining multiple plumage ornaments that differ in efficacy and content.