Evolution of developmental control mechanismsWingless is a positive regulator of eyespot color patterns in Bicyclus anynana butterflies

- The gene wingless is expressed in eyespot centers during the early pupal stage of Bicyclus anynana.
- Transgenic wg-RNAi butterflies produced less wg mRNA and had narrower eyespot rings.
- Wingless is a likely morphogen contributing to eyespot ring differentiation.

Eyespot patterns of nymphalid butterflies are an example of a novel trait yet, the developmental origin of eyespots is still not well understood. Several genes have been associated with eyespot development but few have been tested for function. One of these genes is the signaling ligand, wingless, which is expressed in the eyespot centers during early pupation and may function in eyespot signaling and color ring differentiation. Here we tested the function of wingless in wing and eyespot development by down-regulating it in transgenic Bicyclus anynana butterflies via RNAi driven by an inducible heat-shock promoter. Heat-shocks applied during larval and early pupal development led to significant decreases in wingless mRNA levels and to decreases in eyespot size and wing size in adult butterflies. We conclude that wingless is a positive regulator of eyespot and wing development in B. anynana butterflies.