Gene expression underlying adaptive variation inHeliconiuswing patterns: non-modular regulation of overlappingcinnabarandvermilionprepatterns

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Abstract
Geographical variation in the mimetic wing patterns of the butterflyHeliconius eratois a textbook example of adaptive polymorphism; however, little is known about how this variation is controlled developmentally. Using microarrays and qPCR, we identified and compared expression of candidate genes potentially involved with a red/yellow forewing band polymorphism inH. erato. We found that transcripts encoding the pigment synthesis enzymescinnabarandvermilionshowed pattern- and polymorphism-related expression patterns, respectively.cinnabarexpression was associated with the forewing band regardless of pigment colour, providing the first gene expression pattern known to be correlated with a majorHeliconiuscolour pattern. In contrast,vermilionexpression changed spatially over time in red-banded butterflies, but was not expressed at detectable levels in yellow-banded butterflies, suggesting that regulation of this gene may be involved with the red/yellow polymorphism. Furthermore, we found that the yellow pigment, 3-hydroxykynurenine, is incorporated into wing scales from the haemolymph rather than being synthesizedin situ.We propose that some aspects ofHeliconiuscolour patterns are determined by spatio-temporal overlap of pigment gene transcription prepatterns and speculate that evolutionary changes invermilionregulation may in part underlie an adaptive colour pattern polymorphism.

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