LIGHT AT NIGHT ALTERS THE PARAMETERS OF THE ECLOSIONRHYTHM IN A TROPICAL FRUIT FLY, DROSOPHILA JAMBULINA

摘要

We investigated the effects of natural light at night (LAN) in the field and artificialLAN in the laboratory on the circadian rhythm of pupal eclosion in a tropical wildtype strain of Drosophila jambulina captured at Galle, Sri Lanka (6.1°N, 80.2°E). Theinfluence of natural LAN, varying in intensity from 0.004 lux (starlight intensity) to0.45 lux (moonlight intensity), on the entrainment pattern of the circadian rhythm ofeclosion at 25° ± 0.5°C was examined by subjecting the mixed-aged pupae to naturalcycles of light and darkness at the breeding site of this strain in the field. The eclosionpeak was ~2 h prior to sunrise, and the 24 h rhythmicity was the most robust. Effectsof artificial LAN at 25° ± 0.5°C were determined in the laboratory by subjectingpupae to LD 12:12 cycles in which the light intensity of the photophase was 500 luxin all LD cycles, while that of the scotophase was either 0 lux (complete darkness,DD), 0.5, 5, or 50 lux. In the 0 lux LAN condition (i.e., the control experiment), theeclosion peak was ~2 h after lights-on, and the 24 h eclosion rhythm was not asstrong as in the 0.5 lux LAN condition. The entrainment pattern in 0.5 lux LAN wasstrikingly similar to that in the field, as the 0.5 lux LAN condition is comparable tothe full moonlight intensity in the tropics. LAN at 0.5 lux dramatically altered bothparameters of entrainment, as the eclosion peak was advanced by —4 h and the 24 heclosion rhythm was better than that of the control experiment. LAN at 5 lux,however, resulted in a weak eclosion rhythm that peaked in the subjective forenoon.Interestingly, the 50 lux LAN condition rendered the eclosion events unambiguouslyarrhythmic. After-effects of LAN on the period (τ) of the free-running rhythm andthe nature of eclosion rhythm were also determined in DD by a single LD 12:12 toDD transfer. After-effects of the LAN intensity were observed on both the T andnature of the eclosion rhythm in all four experiments. Pupae raised in 0.5 lux LANexhibited the shortest T (20.6 ± 0.2 h, N = 11 for this and subsequent values) and themost robust rhythm, while pupae raised in 50 lux LAN had the longest r (29.5 ±0.2 h) and weakest rhythm in DD. Thus, these results demonstrate the intensity ofLAN, varying from 0 to 50 lux, profoundly influences the parameters of entrainmentas well as free-running rhythmicity of D. jambulina. Moreover, the observed arrhythmicity in LD 12:12 cycles caused by the 50 lux LAN condition appeared to bethe masking effect of relatively bright light at night, as the LD 12:12 to DD transferrestored the rhythmicity, although it was rather weak.