Circadian phase-response curves for light in nymphal and adult crickets, Gryllus bimaculatus

The circadian locomotor rhythm of the cricket, Gryllus bimaculatus, is regulated by two pacemakers, one located in each optic lamina-medulla complex of the protocerebrum, and is readily entrained to light-dark cycles. We investigated effects of light pulses on nymphal (diurnal) and adult (nocturnal) free-running locomotor rhythms. When a 3 h light pulse was given, adult crickets free-running under constant darkness showed a clear phase shift in a manner dependent on time of day. The phase-response curves for the light pulses showed phase delays in the early subjective night, phase advances in the late subjective night, and little response in the mid-subjective day. Unilateral removal of the lamina-medulla-compound eye complex had no effects on phase-responsiveness to 3 h light pulses, suggesting that the shape of the phase-response curve reflects the property of a single circadian pacemaker. The average free-running period for the operated animal [23.73±0.25 (SD) h, N = 58] was significantly shorter than that of the intact animal [23.86±0.24 (SD) h, N = 99] (t-test, P <0.01), suggesting the existence of mutual interaction between the optic lobe pacemakers. Eighth-instar nymphal crickets were revealed to have a phase-response curve similar to that of adults, although their circadian rhythm is quite different from that of adults not only in phasing but also in free-running period and waveform. The fact strongly suggests that the adult nocturnal and the nymphal diurnal rhythms share common pacemakers.