Recruitment of a hedgehog regulatory circuit in butterfly eyespot evolution

The origin of new morphological characters is a long-standing problem in ev olutionary biology. Novelties arise through changes in development, but the nature of these changes is largely unknown. In butterflies, eyespots have evolved as new pattern elements that develop from special organizers called foci. Formation of these foci is associated with novel expression patterns of the Hedgehog signaling protein, its receptor Patched, the transcription factor Cubitus interruptus, and the engrailed target gene that break the c onserved compartmental restrictions on this regulatory circuit in insect wi ngs. Redeployment of preexisting regulatory circuits may be a general mecha nism underlying the evolution of novelties.