Entrainment of eclosion and preliminary ontogeny of circadian clock gene expression in the flesh fly, Sarcophaga crassipalpis

Timing of circadian activities is controlled by rhythmic expression of clock genes in pacemaker neurons in the insect brain. Circadian behavior and clock gene expression can entrain to both thermoperiod and photoperiod but the availability of such cues, the organization of the brain, and the need for circadian behavior change dramatically during the course of insect metamorphosis. We asked whether photoperiod or thermoperiod entrains the clock during pupal and pharate adult stages by exposing flies to different combinations of thermoperiod and photoperiod and observing the effect on the timing of adult eclosion. This study used qRT-PCR to examine how entrainment and expression of circadian clock genes change during the course of development in the flesh fly, Sarcophaga crassipalpis. Thermoperiod entrains expression of period and controls the timing of adult eclosion, suggesting that the clock gene period may be upstream of the eclosion pathway. Rhythmic clock gene expression is evident in larvae, appears to cease during the early pharate adult stage, and resumes again by the time of adult eclosion. Our results indicate that both patterns of clock gene expression and the cues to which the clock entrains are dynamic and respond to different environmental signals at different developmental stages in S. crassipalpis.