Meeting Abstract
For many animals, color vision is essential for survival and reproduction. Butterflies in particular have good color vision and colorful wing patterns that often serve as both predator defense and sexual signals. In the genus Heliconius, an opsin gene duplication has resulted in expanded UV color vision in most species, but the melpomene/Silvaniform lineage has subsequently lost expression of the UV2 opsin. Heliconius species with both UV photoreceptors, or UV2 only, are better able to detect genus-specific wing patterns. With only the UV1 photoreceptor, melpomene/Silvaniform visual systems might be similar to non-Heliconius outgroups, which do not discriminate Heliconius wing patterns well. To further understand how these species might have adapted with only one UV photoreceptor, we investigated mRNA and protein expression in the compound eye of several species, and we measured photoreceptor spectral sensitivities in two representatives, H. melpomene and H. ismenius. Molecular genetic differences are found in the opsin sequences between the melpomene and Silvaniform clades, as well as between the larger melpomene/Silvaniform clade and other Heliconius species. Photoreceptor sensitivities are shifted when compared to another species with two UV photoreceptors. Differences are found in the numbers and types of ommatidia in the compound eye between species with only UV1 and those with both UV cell subtypes. Taken together, our results suggest loss of UV2 results in spectral tuning in order to better detect salient yellow wing signals.
