Light and temperature cooperate to regulate the circadian locomotor rhythm of wild type and period mutants of Drosophila melanogaster

Abstract

In the wild type (Canton-S) and period mutant flies of Drosophila melanogaster, we examined the effects of light and temperature on the circadian locomotor rhythm. Under light dark cycles, the wild type and per S flies were diurnal at 25°C. However, at 30°C, the daytime activity commonly decreased to form a rather nocturnal pattern, and ultradian rhythms of a 2∼4 h period were observed more frequently than at 25°C. The change in activity pattern was more clearly observed in per 0 flies, suggesting that these temperature dependent changes in activity pattern are mainly attributable to the system other than the circadian clock. In a 12 h 30°C:12 h 25°C temperature cycle (HTLT12:12), per 0 flies were active during the thermophase in constant darkness (DD) but during the cryophase in constant light (LL). The results of experiments with per 0; eya flies suggest that the compound eye is the main source of the photic information for this reversal. Wild type and per 0 flies were synchronized to HTLT12:12 both under LL and DD, while per S and per L flies were synchronized only in LL. This suggests that the circadian clock is entrainable to the temperature cycle, but the entrainability is reduced in the per S and per L flies to this particular thermoperiod length, and that temperature cycle forces the clock to move in LL, where the rhythm is believed to be stopped at constant temperature.