Abstract
BackgroundFood intake of the adult fruit fly Drosophila melanogaster, an intermittent feeder, is attributed to several behavioral elements including foraging, feeding initiation and termination, and food ingestion. Despite the development of various feeding assays in fruit flies, how each of these behavioral elements, particularly food ingestion, is regulated remains largely uncharacterized.ResultsTo this end, we have developed a manual feeding (MAFE) assay that specifically measures food ingestion of an individual fly completely independent of the other behavioral elements. This assay reliably recapitulates the effects of known feeding modulators, and offers temporal resolution in the scale of seconds. Using this assay, we find that fruit flies can rapidly assess the nutritional value of sugars within 20–30 s, and increase the ingestion of nutritive sugars after prolonged periods of starvation. Two candidate nutrient sensors, SLC5A11 and Gr43a, are required for discriminating the nutritive sugars, D-glucose and D-fructose, from their non-nutritive enantiomers, respectively. This suggests that differential sensing mechanisms play a key role in determining food nutritional value.ConclusionsTaken together, our MAFE assay offers a platform to specifically examine the regulation of food ingestion with excellent temporal resolution, and identifies a fast-acting neural mechanism that assesses food nutritional value and modulates food intake.Electronic supplementary materialThe online version of this article (doi:10.1186/s13041-015-0179-x) contains supplementary material, which is available to authorized users.
Highlights
Food intake of the adult fruit fly Drosophila melanogaster, an intermittent feeder, is attributed to several behavioral elements including foraging, feeding initiation and termination, and food ingestion
As PER and food consumption can be separately assayed in the manual feeding (MAFE) assay, it can separate the effects on food ingestion from those on feeding initiation
The starved flies ingested 0.32 ± 0.01 μL liquid food on average, and the first three feeding bouts together comprised up to ~85 % of the total feeding volume (Fig. 1e). These flies ingested significantly smaller volumes of food when presented with sucrose again in the 10 min after the MAFE assay (Fig. 1f ), suggesting that they remained satiated and uninterested in food for the following short period. These results indicate that the total volume of food ingestion during the course of our MAFE assay likely defines the size of a “meal” (Fig. 1c, right), and can be used as a measurement to investigate the regulation of food ingestion
Summary
Food intake of the adult fruit fly Drosophila melanogaster, an intermittent feeder, is attributed to several behavioral elements including foraging, feeding initiation and termination, and food ingestion. Two recently developed automated assays, named FLIC (Fly Liquid-Food Interaction Counter) and flyPAD (fly Proboscis and Activity Detector), quantify the physical contact of flies’ proboscis and food surface through monitoring the changes in conductance and capacitance, respectively [6, 7].
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