Physiological and photochemical studies reveal that some butterflies possess unusually broad sensitivity to light, ranging from the ultraviolet to the red. In the retina of Papilio butterflies four (P. aegeus) or five (P. xuthus) spectral classes of receptors have been previously identified, with peak sensitivities at 360 nm (UV), 390 nm (violet), 460 nm (blue), 530 nm (green), and 600 nm (red). Variation in spectral sensitivity between photoreceptors is primarily conferred by variation in the amino acid sequence of the visual pigments (op-sins) expressed within those cells, as only a single retinal chromophore, 3-hydroxyretinal, has been found in Papilio butterflies. Until now the molecular variation of the opsins underlying the broad spectral sensitivity in butterflies has been unknown. I re- port the cloning of six opsin gene fragments from the tiger swallowtail butterfly, Papilio glaucus. Their placement within a phylogeny of insect opsins suggests that these butterflies possess at a minimum four long-wavelength opsins and one blue- and one ultraviolet-sensitive opsin.
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