Origin of color in butterflies

January 3 – Febuary 28, 2021

Meeting Abstract

S7-2  Wed Jan 6 10:30 – 11:00  Origin of color in butterflies Reed, RD*; Brack, BJ; Cornell University; Cornell University robertreed@cornell.edu http://reedlab.org

Butterfly wings are graced by hues drawn from a palette both broad and deep. Our understanding of the pigments that generate many of these colors is surprisingly cursory, however. We have been working to understand the origin and diversification of ommochrome pigments in Nymphalidae – the largest and most diverse butterfly family. Ommochromes have an ancient origin within arthropods as red-hued visual filtering pigments, yet they appear to have a single origin as wing pigments in nymphalids. After they appeared as wing pigments, ommochromes rapidly diversified into many different pigments of different hues. Using a combination of comparative transcriptomics, HPLC, MS-imaging, genetic mapping, and CRISPR/Cas9 genome editing, we have made significant progress in identifying ommochrome genes and pigments in nymphalids. Interestingly we found that many novel major facilitator superfamily (MFS) transporter genes are involved in generating ommochromes of different hues. These genes are unrelated to well-known ommochrome ABC transporters in Drosophila (i.e., white and scarlet), and appear to have originated during several major Lepidoptera- and butterfly-specific gene family expansions. We also found that a single transcription factor called optix appears to act a master regulator of all ommochrome pigmentation in nympahlids – a function with no known precedent in other arthropods. Ultimately, the ommochrome gene network in butterfly wings is quite different from what has been described in other arthropods, and therefore a simple co-option-from-eyes origin scenario is difficult to support. Further, the large number of novel ommochrome genes we found in butterflies suggests that the diversification of butterfly wing coloration was facilitated by the expansion of pigment-related gene families.

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