The evolution of courtship displays in Galliformes

Species in Galliformes have elaborate ritual courtship displays, often including strutting, fluffing of tail or head feathers, and vocal sounds that serve as excellent examples of sexual selection. According to the male orientation to the female while either posturing or moving, these courtship displays of gallinaceous species can be classified into three categories: 1) ‘frontal displays’, 2) ‘lateral displays’, and 3) ‘both frontal and lateral displays’. Questions regarding which category of displays is the ancestral state and the evolutionary history of courtship displays in Galliformes remain unanswered. We collected and classified 131 species in terms of their courtship displays into the three categories listed above and carried out a large-scale comparative analysis to reveal the evolutionary trajectory of this trait. We found that the ancestral state of courtship displays of Galliformes involves both relatively short and straightforward frontal and lateral elements (i.e., the category of ‘both frontal and lateral displays’). Furthermore, ancestral trait reconstructions suggest that transitions from ‘lateral displays’ to ‘frontal displays’ occurred more frequently than the other way around (i.e., from ‘frontal displays’ to ‘lateral displays’). In addition, some transitions occurred from ‘both frontal and lateral displays’ to ‘lateral displays’ but not from ‘both frontal and lateral displays’ to ‘frontal displays’. Ancestral state reconstruction of courtship displays at the root of the Galliformes phylogeny supports the ‘both frontal and lateral displays’ first scenario. This original state then evolved towards two extremes, either ‘frontal displays’ or ‘lateral displays’, with more complicated and elaborate display components. Moreover, subsequent transitions occurred from ‘lateral displays’ to ‘frontal displays’ much more frequently than the other way around during the evolutionary history, indicating positive selection of ‘frontal displays’.