| The diversity of visual appearances among animals largely stems from the various signals used in communication, e.g. for mating, avoiding predators or foraging. Sexual selection by female choice has promoted the evolution of exaggerated male phenotypes, particularly among clades of lekking birds, suggesting that choices may be arbitrary with respect to ecological characteristics of their habitats. Sensory drive, conversely, predicts that natural selection on female preferences will lead to the evolution of conspicuous male signals, and that changes in signals over evolutionary time will be associated with changes in the habitat, in order to favor detection by females. Therefore, the level of ecological differentiation observed among taxa could influence signal evolution, if sensory systems are conserved. In order to address the role of ecological differentiation in the evolution of conspicuous visual signals and in taxonomic diversification among manakins, we tested the sensory drive hypothesis of sexual selection by female choice within manakins from the Ilicura-Corapipo clade (tribe Ilicurinii). We also estimated the level of niche conservativism over evolutionary time in the family. We used spectrometers to measure the ambient light in the habitat of five species, and modeled ecological niches based on climatic and topographic data sets and known occurrences for each manakin species. The results support a role of sensory drive in the evolution of conspicuous male phenotypes within each population studied, based on chromatic contrast during male displays in all species, and on achromatic contrasts in C. gutturalis, suggesting that changes in behavior enhanced signal conspicuity. However, chromatic contrasts and female preferences within Corapipo indicate that, although changes in plumage were associated with ecological differentiation, selection of conspicuous phenotypes was unimportant in the evolution of plumage colors in the clade. Sensory drive based on brightness contrast observed in Corapipo, on the other hand, may explain the main change in plumage within the clade. The data indicate that sexual selection has promoted plumage differentiation among species occupying relatively conserved niches, and that evolution of plumage colors was associated with microhabitat variation in sensory environments. The role of conspicuous cues in mate choice in the clade is however controversial. |
