Abstract
The circadian clock offers an internal estimate of the external time of day and is used to precisely time behavior and physiology to promote survival and fitness. In mammals, mounting evidence has established a correlation between a disrupted circadian clock and metabolic dysfunction, presumably due to the desynchronization of feeding with the optimal phase of endogenous metabolic rhythms. Although much is known about how feeding is positively and negatively regulated through endocrine and neuronal control, relatively little is known about how the central circadian clock regulates feeding. Thanks to its genetic tractability and relative simplicity of its central nervous system, Drosophila melanogaster is a powerful model organism for understanding the genetic and neural basis of circadian rhythms. Here we have used a sensitive and high through-put feeding assay, the fly liquid-food interaction counter, to systematically characterize the circadian feeding behavior of flies in a manner that allows for the extended observation of feeding behavior in the absence of experimental perturbation, an approach that makes possible the recording of diurnal and circadian rhythms in feeding over many cycles. We found that commonly used genetic backgrounds display anticipatory morning and evening peaks of feeding under a 12-hour-light/12-hour-dark cycle (LD) that are highly reminiscent of locomotor rhythms. Analysis of the feeding behavior of loss of function clock gene mutants reveal that morning and evening anticipation are dependent on the canonical molecular circadian clock. Moreover, using a highly sensitive assay for circulating sugars, we establish that trehalose levels are tightly regulated by circadian clock genes, per, in a restricted feeding regimen.