Combinatorial Wnt Signaling induces Margin Color Elements in Swallowtail Butterfly Ground Plan.

The intricate wing patterns of butterflies are thought to derive from a morphological ground plan that anchors homology relationships between individual color pattern elements and serves as an archetype for comparative analysis. These patterns undergo modifications that drive the diverse morphologies observed in nature. While brush-footed butterflies (Nymphalidae) have been well studied, assigning homologies with other lepidopteran families remains challenging due to substantial divergence. Here, we focus on swallowtails (Papilionidae), an early-diverging butterfly lineage known for its outstanding diversity in wing shapes and patterns but lacking a developmental framework. Through qualitative and phylogenetic analyses, CRISPR perturbation assays, and in situ expression experiments, we investigate homologies between papilionid butterflies, offering phylogenetic and molecular characterization of the Papilionidae wing ground plan. Our results highlight the roles of WntA and Wnt6 in patterning papilionid signature wing elements, such as the glauca and the Submarginal spots. Notably, the nymphalids distinct Central Symmetry System is either reduced or absent in the family, with marginal systems expanding proximally. Our data illuminate a highly adaptable patterning system driven by Wnt signaling pathways in developing butterfly wings.