Convergence in sympatric swallowtail butterflies reveals ecological interactions as a key driver of worldwide trait diversification

Abstract

Ecological interactions may fuel phenotypic diversification in sympatric species. While competition can enhance trait divergence, other ecological interactions may promote convergence in sympatric species. Within butterflies, evolutionary convergences in wing color patterns have been reported between distantly-related species, especially in females from palatable species, where mimetic color patterns are promoted by predator communities shared with defended species living in sympatry. Wing color patterns are also often involved in species recognition in butterflies, and divergence in this trait has been reported in closely-related species living in sympatry as a result of reproductive character displacement. Here we investigate the effect of sympatry between species on the convergence vs. divergence of their wing color patterns in relation to phylogenetic distance, focusing on the iconic swallowtail butterflies (family Papilionidae). We developed a new unsupervised machine-learning-based method to estimate phenotypic distances among wing color patterns from 337 species allowing to finely quantify morphological diversity at global scale within and among species, allowing to compute pairwise phenotypic distances between sympatric and allopatric species pairs. We found that sympatry promoted strong convergence, while divergence in sympatry was less frequent and weaker. The effect of sympatry on convergence was stronger on females than males, suggesting that differential selective pressures acting on the two sexes drove sexual dimorphism. Our results highlight the significant effect of ecological interactions driven by predation pressures on trait diversification in Papilionidae and evidence the interaction between phylogenetic proximity and ecological interactions in sympatry acting on macroevolutionary patterns of phenotypic diversification.