Phyletic aspects of the distribution of 3-hydroxyretinal in the class Insecta.

The distribution of 3-hydroxyretinal (R3), a recently discovered retinoid used as the visual pigment chromophore in some insects, was investigated in the class Insecta using HPLC technology. We studied 138 species in 24 orders, sampling from a wide range of taxonomic groups as well as varied habitats. In addition to groups already known to have R3, we find this retinoid in Hemiptera (suborder Heteroptera), Plecoptera, Megaloptera, and Hymenoptera. We also find retinal (R1) in Hemiptera (suborder Homoptera), Mecoptera, and Trichoptera, groups previously thought to have only R3. The pattern of R3 occurrence indicates that this retinoid cannot be considered a phylogenetic marker, having a scattered distribution in the class Insecta as well as within some orders of insects. Several environmental factors that might influence the selection of chromophore have been considered, but none correlates with its distribution. The evolutionary reasons for the pattern of occurrence of R3 therefore remain unknown.