Composition and distribution of retinal and 3-hydroxyretinal in the compound eye of the dragonfly.

Retinoids in the compound eyes of nymphs and adult dragonflies in 11 families of the 3 suborders were extracted by the oxime method, and analysed by high performance liquid chromatography. Almost all of the species examined contained both retinal and 3-hydroxyretinal in the compound eye. The ratio of 11-cis 3-hydroxyretinal to 11-cis retinal (3-OH ratio) was calculated as an index of the retinoid composition. The 3-OH ratios of the whole eye of nymphs in all the suborders and of adults of the suborder Zygoptera were very high, 2.2 at the minimum, but in Anisozygoptera and Anisoptera most of the ratios were distributed between 1 and 2.7. In the family Gomphidae, exceptionally low 3-OH ratios, less than 1, were observed in several species. The regional distributions of the retinals in the adult compound eyes were also examined. In the Zygopteran compound eye, both retinals were distributed evenly all over the eye, while in the compound eye of the other two suborders, the 3-OH ratios in the dorsal area of the eye were extremely low. In several species of Gomphidae and Libellulidae the ratios in the dorsal areas were zero. From the correspondence of these results and the compartment of the compound eye, it appeared that the large ommatidia in the dorsal area contained only retinal. This was confirmed when the large facet region in the dorsal part of the compound eye of an Anax was excised and examined, and only retinal was detected. However, the ventral area of the true dragonflies' compound eye which did not include the large ommatidia contained both retinals, and the 3-OH ratio was more than ten. The biological significance of using both retinals as chromophores of visual pigments in the dragonfly eye is discussed in relation to the structure of the ommatidia and to the vision of dragonflies.