SWEENEY, A*; JIGGINS, C; JOHNSEN, S; Duke University; Smithsonian Tropical Research Institute; Duke University: Bio-optics and Visual Ecology of Heliconius Color Patterns

An astonishing diversity of wing color patterns exists in the genus Heliconius. These buttterflies are also a classic example of Mullerian mimicry. Although some genetic models invoke drift, fixation and reinforcement, questions about the maintenance of diversity of these patterns remain largely unanswered. Because much of Heliconius ecology is driven by coloration, these wing patterns must be considered. This study addresses the adaptive value of Heliconius color pattern elements in different forest habitats through optical measurements, modeling, and behavioral experiments. Factors considered are the spectral constancy of pattern elements in forest microhabitats, color vision in different taxa, and the role of iridescence. Our results indicate that the variability of wing radiance in spectrally dynamic forest light environments may confound the problem of interspecific recognition. Different taxa of Heliconius may have evolved different solutions involving both color perception and red wing pigmentation in response to this problem of changing radiance. Reflections from iridescent wing regions are approximately 90% linearly polarized. Changing this linearly polarized reflection to circularly polarized reflection results in a significant decrease in mate recognition by male butterflies, indicating that polarization vision is important in interspecific recognition. We hypothesize that red pigment and polarized iridescence may be adaptations for intraspecific recognition in variable light environments, and that highly reflective white and yellow wing regions may be adaptations for visibility in dim forest light. These results may be relevant in other areas of tropical forest visual ecology, as well as in other complex light environments such as coral reefs.