| The diversity of butterfly wing patterns makes them a model of choice for the study of evolutionary tinkering, where novelty is achieved by the combinatorial arrangement of pre-existing elements. In this work I expand our knowledge of the developmental genetic toolkit that drives both color pattern formation and variation. Using a candidate gene approach and macro-evolutionary comparisons, I first show that a Lepidoptera-specific copy of the homeobox transcription factor aristaless is expressed as a conserved pre-pattern that may provide positional information for recruitment of the DII pattern element. I also show that the signaling gene wingless marks several elements of an archetypal lepidopteran wing groundplan, clarifying homology relationships between pattern elements of different clades. Using a forward genetics approach at the micro-evolutionary timescale, I then identify two genes that are driving phenotypic variation in wing patterns of known adaptive relevance in the genus Heliconius. Cis-regulatory variants of the homeobox transcription factor optix switch color pattern identities prior to pigmentation, resulting in red patterns that are used as warning signals to predators. Similarly, cis-regulatory variants of the signaling ligand WntA determine differences in the shape of melanic patterns involved in mimicry. Both optix and WntA qualify as genetic hotspots of adaptation on Heliconius wings since they have been independently involved in driving adaptive phenotypic variation in separate clades, including the convergent evolution of co-mimetic phenotypes. Overall, the comparative and developmental insights obtained from these data yield important implications for an empirical understanding of evolutionary tinkering. |
