Characterization of Circadian Feeding Rhythms in Drosophila Using the Fly Liquid-Food Interaction Counter (FLIC) Assay.

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 (FLIC), 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 wild-type and commonly used Drosophila strains display anticipatory morning and evening peaks of feeding under a 12-hour-light/12-hour-dark cycle (LD) that resembles locomotor rhythms. Analysis of the feeding behavior of mutants lacking the central circadian rhythm gene clock revealed that morning and evening anticipation of feeding are dependent on the canonical molecular circadian clock. Moreover, flies lacking gene function in the positive limb of the molecular clock but not negative limb were characterized by increased food consumption, suggesting that feeding consumption is under the regulation of certain clock genes. We also found that the abundance of hemolymph (blood) trehalose (the predominant circulating sugar in flies) displayed circadian clock dependent regulation in a restricted feeding paradigm. All of these findings lay a foundation for an understanding of circadian feeding behavior in flies and set the stage for further dissection of the neuronal circuitry underlying rhythmic feeding behavior.