Endogenous Rhythms in the Amounts of 11-cis Retinal in the Compound Eye of Ligia Exotica (Crustacea, Isopoda)

Abstract

The volume of the rhabdom of Ligia exotica changes diurnally, with the rhythm persisting autogenically in continuous darkness. The morphological changes are accompanied by variations in the amounts of the different chromophores making up the visual pigment. The amount of 11-cis retinal was found to be high at night (26.2±3.5pmol per eye) and low during the day (10.9±2.6pmol per eye) and to display an endogenous rhythm. At dawn and dusk, the amount was 19.1±1.2pmol. This rhythmicity persisted in continuous darkness, although the average amount of 11-cis retinal present gradually increased. In the case of all-trans retinal, changes in the amount were rhythmic in light-dark conditions. The amount of all-trans retinal present in the eye increased shortly after the onset of light and decreased soon after the end of illumination. There was about twice as much 11-cis retinyl ester as 11-cis retinal in the compound eye of Ligia exotica. Rhythmicity in the amount of 11-cis retinyl ester present during the light-dark cycle was observed, but it was opposite in phase to that of 11-cis retinal. Under conditions of continuous darkness a clear rhythm was not apparent: the amount of 11-cis retinyl ester increased not only during the subjective day but also during the following subjective night. Thus, a clear correlation exists between changes in structural organization of the rhabdom and the amounts of 11-cis retinal present. Both show features of a circadian rhythm.