Temperature Entrainment of Circadian Locomotor and Transcriptional Rhythms in the Cricket, Gryllus bimaculatus

Most animals exhibit circadian rhythms in various physiological and behavioral functions regulated by circadian clock that resides in brain and in many peripheral tissues. Temperature cycle is an important time cue for entrainment, even in mammals, since the daily change in body temperature is thought to be used for phase regulation of clocks in peripheral tissues. However, little is known about the mechanisms by which temperature resets the clock. In the present study, we investigated the effect of temperature on circadian activity rhythm and clock gene transcription by using the cricket, Gryllus bimaculatus. We show that temperature cycle can entrain both behavioral and transcriptional rhythms of clock genes, such as period, timeless, cryptochrome2 and cycle in the circadian pacemaker tissue, optic lobe. Under temperature cycle, phase of evening peak of locomotor activity occurred 1 h before the warm-to-cold phase transition, which is associated with earlier peaks of mRNA expression rhythm of the clock genes than that under light/dark cycles. When the temperature cycle was advanced by 6 h, behavioral rhythms re-entrained to newly phased temperature cycle after ∼16 transient cycles. The mRNA oscillation of period and timeless gained stable rhythm under phase advanced temperature cycles with a lesser number of transient cycles than cryptochrome2 and cycle. These results suggest that temperature cycle can entrain behavioral and molecular rhythms in cricket and clock genes vary in sensitivity to temperature. It is thus likely that clock genes play differential roles in resetting the clock with environmental temperature changes.