Rapid male plumage evolution drives sexual dichromatism in Ficedula flycatchers

Sexual dichromatism represents a major form of phenotypic differentiation between the sexes in birds, and its evolution is likely shaped by the interplay between sexual and natural selection. The genus Ficedula, widely distributed across Eurasia, exhibits pronounced interspecific variation in both sexual dichromatism and migratory behavior, making it an ideal study system for investigating the evolutionary patterns and drivers of avian sexual dichromatism. In this study, we conducted a phylogenetic comparative analysis of plumage complexity and sexual dichromatism across 32 Ficedula species. We further explored how life-history traits influence the evolution of sexual dichromatism. Our results reveal a strong positive correlation between male plumage complexity and the degree of sexual dichromatism, with males evolving plumage complexity at significantly faster rates than females. Migratory species exhibit significantly higher levels of dichromatism. Furthermore, compared to monochromatic species, sexually dichromatic species are characterized by higher latitudinal occurrence, broader geographic distributions, and greater flight capacity. These findings demonstrated how sexual and natural selection jointly drive evolution of sexual dichromatism in Ficedula within phylogenetic constraints, advancing our understanding of the evolutionary drivers of avian sexual dichromatism.