Sexual dimorphism in Optix-positive male vein structures among basal Heliconiini. (a) Examples of dorsal forewing Cu1 veins among Heliconiinae. Veins of the Dryas, Agraulis and Dione genera show striated pheromone-spreading structures in males only, as previously described in Agraulis[50, 51]. (b) Sexual dimorphism in Optix expression associated with the male-specific striated vein structures of Dryas iulia (see also panel a). Scale bars: 100 μm. (c) Character mapping and ancestral reconstruction of vein sexual dimorphism in Heliconiinae with probability of loss ≥10x probability of gain (black: presence; white: absence; grey ancestral nodes: equivocal). (d, upper panels) Expression of Optix and Doublesex in Agraulis vanillae forewings. optix mRNA (purple staining) and protein products (green arrows) marks male-specific scale cell precursors during pupal wing development. Vein epithelia of dimorphic veins express Doublesex (red brackets). Male forewing 1A veins are devoid of adult striated organs and lack Optix and Doublesex expression. (d, lower panels) Sexual dimorphism in Optix and Doublesex in male forewing veins.