The Evolution of Pattern Formation in Butterfly Wings

I employed a comparative gene expression approach to address the evolution of butterfly wing pattern formation at several levels, including early pattern determination and pigment gene regulation during late development. Expression analysis of the receptor molecule Notch suggested several previously unknown roles for Notch signaling in butterfly wing patterning. Notch upregulation was found to precede the activation of the transcription factor Distal-less during early eyespot color pattern determination. A phylogenetic comparison of expression time series from multiple moth and butterfly species suggested that changes in a Notch / Distal-less temporal pattern formation process were associated with the gain and loss of both eyespot and midline color patterns during wing pattern evolution. Notch expression was found to occur in a grid pattern in the butterfly wing epithelium shortly after pupation. This observation, together with previous expression and simulation studies, support a Notch-mediated lateral inhibition model of wing scale organization. Tryptophan-derived pigments, including the ommochromes, are a derived feature of nymphalid butterfly wings. These pigments appear in wing scales shortly before adult emergence. I found that multiple genes in the ommochrome biosynthetic pathway were expressed in the wings of some nymphalid butterflies. Additionally, transcriptional regulation of genes encoding the ommochrome synthesis enzymes vermilion and cinnabar was found to be associated with the polymorphism and development of forewing band patterns in the mimetic butterfly Heliconius erato.