Abstract
Closely-related species are often partitioned into different geographic areas or micro-habitats as a result of competition and reproductive interference. Here, we investigate how the evolution of shared adaptive traits may shape ecological interactions and genetic divergence, and facilitate coexistence in sympatry. In closely-related Morpho butterfly species living in the understory of the neo-tropical rainforest, the blue iridescent coloration of the wings is likely involved in predation evasion as well as in mating recognition and courtship. These contrasted selective pressures acting on this visual trait shared between closely-related species has likely shaped their coexistence. We used spectrophotometry, behavioral experiments, visual modeling and chemical analyses applied to samples from allopatric and sympatric populations of Morpho helenor and Morpho achilles to characterize how the evolution of visual and chemical traits might favor their coexistence in sympatry: we quantified the differences in wing iridescence and tested for variations in the sexual preference for this trait between allopatric vs. sympatric populations. We found a strong similarity in iridescence among species in sympatry, suggesting convergence driven by predation. Although behavioral results suggest that iridescent signals could also be used as visual cues during mate choice, convergent iridescent signals may impair the visual recognition of sympatric Morpho species. In contrast, divergent chemical bouquets among species suggest that the visual similarity of sympatric Morpho species might have favored the divergence of alternative traits involved in species recognition such as chemical cues. This study underlines how ecological interactions and trait evolution can shape species coexistence in sympatry.</p></div> <div>Significance Statement<p>By changing the visual aspect of animals in movement, iridescence likely impacts multiple visual interactions within and among species, and might therefore shape ecological interactions and species diversification in sympatry. Here we study the relative importance of predation-driven mimicry and sexual selection on the evolution of iridescence on the wings of sister-species of Morpho butterflies. We finely quantify this conspicuous wing phenotype and used behavioral experiments to test whether the sexual preference for this trait can vary between allopatric and sympatric populations of sister-species. We find that convergent iridescence in sympatric Morpho species, putatively driven by predators and supporting the hypothesis of evasive mimicry, impairs species recognition and could promote the divergence in alternative chemical cues involved in mate discrimination.