The Coevolution of Colour Patterns and Hindwing Shapes on a Large Phylogenetic Scale Reveals Predation-Driven Adaptive Syndromes in Swallowtail Butterflies.

Traits that reduce predation success may evolve together, leading to repeated evolution of similar anti-predator syndromes. In butterflies, predation likely shapes wing shape and colour patterns, promoting either aposematic or deflective features. Here, we studied the evolution of hindwing tail shape and colour pattern across swallowtail butterflies. Using standardised museum specimen photographs, we quantified colour variation via computer vision and tail shape with geometric morphometrics. We found significant evolutionary correlations between colour patterns and hindwing tail shapes across the phylogeny. Long tails were linked to high-contrast stripes and marginal spots, while short tails were associated with simple, spotted patterns. While accounting for developmental constraints, we show that stripes, spots, and long tails evolved in correlation and likely form a visual syndrome promoted by natural selection to deflect predator attacks. These results provide evidence that selection can drive the coordinated evolution of complex anti-predator traits over large evolutionary timescales.