Evolution of Color Vision in a Mimetic Butterfly Complex

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Monarch and viceroy butterflies are the most famous example of defensive wing color mimicry, but little is known about the visual system of either species. Like the typical adult insect, monarchs and viceroys have color vision mediated by ultraviolet (UV), blue (B) and long (L) wavelength-sensitive visual pigments. Monarch eyes also have heterogeneously-expressed filtering pigments that may extend the range of color vision in the red-green part of the visible spectrum. By contrast, viceroy eyes lack these filtering pigments and are color-blind in the same part of the spectrum, which includes their own orange wing color. In addition, there is significant variation in the absorbance spectrum maximum of the L sensitive visual pigment among this genus of butterflies, with the viceroy L pigment being significantly blue-shifted. Behavioral tests will be used to examine comparative color vision, and wing reflectance data from viceroys and monarchs will be collected and used in the context of mating preference experiments. Behavioral experiments will then be performed to test the hypothesis that the orange-blind viceroys use the UV-reflecting white spots as a cue when selecting mates. Moreover, Drosophila transgenesis and site-directed mutagenesis will functionally evaluate the native visual pigments of these butterflies and use mutant visual pigments to define residues under positive selection. Comparative color vision and mating preference data will provide important biological insights into positive selection on the eyes and color vision system of butterflies for red-green color-blindness. This project will provide an excellent training environment for a postdoctoral associate in multi-level integrated approaches. Undergraduates at UCI from the NSF-funded Minority Science Program student pool will be recruited and trained in molecular biology. Lectures on butterfly vision and behavior will be developed for an upper-division course on insect physiology and made publicly available on the web.