Repeated evolution of iridescence and hindwing tails is associated with morphometric flight proxies in skipper butterflies

Abstract

Phenotypic evolution is shaped by phylogenetic history, ecology and biomechanical constraints. Butterfly wings offer an ideal system to explore these forces, as the relationships between wing morphology and flight characteristics have been intensively studied. Here, we focus on Eudamina skipper butterflies, which display repeated phenotypic convergences of dorsal iridescence and hindwing tails; traits linked to escape ability whose convergence may be driven by predator selection. Using a comprehensive morphometric dataset of 176 species, we assess the evolution of these convergent traits in a phylogenetic framework. We show that hindwing tails and dorsal iridescence have repeatedly evolved in tropical species. Hindwing tails are associated with intermediate body size and forewing shapes that can increase flight manoeuvrability; iridescence is more common in large species with high wing loading and aspect ratio, indicating greater flight speed and manoeuvrability. The evolution of these traits is best described by Ornstein-Uhlenbeck models, consistent with attraction towards trait optima. Further, we reveal co-evolutionary dynamics between fore- and hindwing shapes. Hindwing tails significantly affect forewing shapes in independent lineages, suggesting trade-offs between flight and defence. Together, our results suggest that convergent morphologies in Eudamina likely arose through ecological selection and biomechanical constraints, rather than neutral evolution.