Tinamou egg color displacement at ecoregion co-partitioning

The divergence of reproductive traits frequently underpins the evolution of reproductive isolation. One of the most enduring puzzles on this subject concerns the variability in egg coloration among species of tinamou (Tinamidae), endemic to neotropics. Here we investigated the hypothesis that tinamou egg coloration is a mating signal and its diversification was driven by reinforcement. For most tinamou species, the male guards the nest that is sequentially visited and laid eggs in by multiple females. The colorations of the existing eggs in the nest could signal mate quality and species identities to the upcoming females, preventing costly hybridization, thus were selected to diverge among species (Mating Signal Character Displacement Hypothesis). If so, two predictions should follow: (1) egg colors should coevolve with known mating signals as the tinamou lineages diverged; (2) species that partition similar ecoregions should display different egg colors. The tinamou songs are important mating signals and are highly divergent among species. We found that the egg luminance was significantly associated with the first principal component of the song variables, which supports prediction (1). In addition, we found support for (2): tinamou species that co-partition ecoregions tend to display different egg colors, controlling for song variation. Egg color and songs could be multimodal mating signals that are divergently selected as different tinamou species diverged. Mating signal evolution could be opportunistic and even exploit post-mating trait as premating signals that undergo character displacement at sympatry.