Evolutionary aspects of the diversity of visual pigment chromophores in the class Insecta

In the class Insecta, three retinal congeners are used as the chromophore of visual pigments: retinal, (3R)-3-hydroxyretinal and (3S)-3-hydroxyretinal. The distribution of retinal and 3-hydroxyretinal superimposed on the phyletic tree of insects indicates that the original chromophore of visual pigments was retinal, and that some insects arose around the end of the Carboniferous period acquired the ability to use 3-hydroxyretinal. Xanthophylls possessing 3-hydroxy-beta-ring have been considered to be precursors of 3-hydroxyretinal, and the "oxygen pulse" in the late Palaeozoic era is discussed as a possible contributory factor in obtaining the ability to use 3-hydroxyretinal as the visual pigment chromophore. Xanthophylls possessing 3-hydroxy-beta-ring produced by plants and bacteria have only the (3R)-beta-ring, so the 3-hydroxyretinal produced directly from such xanthophylls is expected to be (3R)-3-hydroxyretinal. On investigating the absolute structure of 3-hydroxyretinal in insect compound eyes, using a chiral column, the orders Odonata, Hemiptera, Neuroptera, Coleoptera, and Lepidoptera, and suborders Nematocera and Brachycera of the Diptera were found to have only (3R)-3-hydroxyretinal. The members of the dipteran suborder Cyclorrhapha, however, were found to contain a mixture of both the (3R) and (3S)-enantiomers of all-trans 3-hydroxyretinal and (3S)-11-cis 3-hydroxyretinal. The Cyclorrhapha, which arose in the Jurassic period, have obtained the ability to produce (3S)-3-hydroxyretinal, but the metabolic pathway by which these "higher flies" form (3S)-3-hydroxyretinal has yet to be clarified. (C) 1998 Elsevier Science Inc.