How does an animal’s metabolism shape how much it moves and sleeps across the day?
Metabolism and behaviour are tightly linked: starved flies sleep less, and diet and gut microbes change activity and food choice. Alongside my work on chromatin in the embryo, I measure the activity and sleep of adult fruit flies with Drosophila Activity Monitor (DAM) assays, to ask how metabolism shapes daily behaviour.
Flies sleep: still periods of five minutes or more come with a higher arousal threshold and are regulated much like sleep in mammals (Shaw et al. 2000; Hendricks et al. 2000). ●Established: Replicated many times; textbook knowledge. Sleep and activity also respond to metabolism; starved flies, for example, sleep much less (Keene et al. 2010). ◕Strong evidence: Several independent studies agree. This makes behaviour a sensitive, whole-animal read-out of metabolic state, and a link to my work on metabolism and chromatin.
How a DAM assay works
How a DAM assay is set up. Each fly lives in its own small glass tube, with food at one end. An infrared beam crosses the middle of the tube; every time the fly walks through it, the monitor adds one count, and the counts are saved every minute, for days, in an incubator with controlled light and temperature (Pfeiffenberger et al. 2010). Schematic, drawn for this site.
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Day and night. Over several days in 12 hours of light and 12 of dark, flies are most active around lights-on and lights-off, take a midday siesta and sleep at night. Comparing these patterns between groups of flies shows how a change, such as in metabolism, alters behaviour. Schematic pattern, not data.
From the minute-by-minute counts I calculate total activity, total sleep, the number and length of sleep bouts, activity during waking minutes, and how these change between day and night. Kept in constant darkness, the same recordings show the fly’s internal circadian rhythm (Pfeiffenberger et al. 2010).
A single beam only sees the fly when it crosses the middle of the tube, so small movements elsewhere can be scored as sleep. Monitors with several beams, or video tracking, give finer detail (Garbe et al. 2015). ◕Strong evidence: Several independent studies agree.
Pfeiffenberger C, Lear BC, Keegan KP, Allada R (2010) Locomotor activity level monitoring using the Drosophila Activity Monitoring (DAM) system. Cold Spring Harbor Protocols 2010:pdb.prot5518. doi:10.1101/pdb.prot5518
Shaw PJ, Cirelli C, Greenspan RJ, Tononi G (2000) Correlates of sleep and waking in Drosophila melanogaster. Science 287:1834–1837. doi:10.1126/science.287.5459.1834