The Compound Eye Possesses a Self-Sustaining Circadian Oscillator in the Cricket Gryllus bimaculatus

Many insects show daily and circadian changes in morphology and physiology in their compound eye. In this study, we investigated whether the compound eye had an intrinsic circadian rhythm in the cricket Gryllus bimaculatus. We found that clock genes period (per), timeless (tim), cryptochrome 2 (cry2), and cycle (cyc) were rhythmically expressed in the compound eye under 12-h light/12-h dark cycles (LD 12:12) and constant darkness (DD) at a constant temperature. After the optic nerves were severed (ONX), a weak but significant rhythmic expression persisted for per and tim under LD 12:12, while under DD, tim and cyc showed rhythmic expression. We also found that more than half of the ONX compound eyes exhibited weak but significant circadian electroretinographic rhythms. These results clearly demonstrate that the cricket compound eye possesses an intrinsic circadian oscillator which can drive the circadian light sensitivity rhythm in the eye, and that the circadian clock in the optic lobe exerts its influence on the oscillator in the eye.