Did you know that fruit flies sleep? There are actually a lot of similarities between sleep in fruit flies and sleep in humans and other mammals. For example…

Caffeinated flyImage modified from Colwell, 2007
  • Like us, fruit flies get most of their sleep at night, and they also have an afternoon slump (although unlike us, they actually give in to their sleep desires instead of running for coffee).
  • Their sleep is affected by the same drugs: caffeine, cocaine, and modafinil (an alertness drug) keep them awake, while antihistamines (allergy medication) make them drowsy just like us.
  • They sleep more at higher temperatures (think of lazy summer days)
  • If they get a bad night’s sleep, they’ll try to sleep more the next day to make up for it. In fact, sleep deprivation even affects their memory performance (have you ever noticed that your memory isn’t so great after a bad night’s sleep?)

And the comparisons don’t stop there. Over the years, fruit flies have proven to be a great animal model for studying sleep, and researchers have used them to improve our understanding of why sleep is important. In fact, earlier this year a group of researchers found that young flies need sleep for normal brain development.

But, how do fly researchers actually study sleep in these tiny flies?

DAM system

The most common method is called the Drosophila Activity Monitoring (DAM) system. Flies are loaded into individual tubes (Figures A-C) and placed in a DAM machine (Figure D). An infrared beam (marked as a red line in Figure D) crosses each fly tube, and the machine notes when the beam is blocked by the fly. If the beam isn’t broken for five or more minutes (meaning the fly hasn’t moved), it’s counted as sleep. Using this method, researchers can analyze how long a fly sleeps, how many times it goes to sleep and wakes back up (called sleep bouts) and the duration of each sleep bout.

divider line

DAM system in incubatorClick here for a larger version of the picture

To conduct the sleep experiment, the machines are hooked up to a computer and placed in an incubator, which controls the humidity, temperature, and lights. The light cycle is usually set to lights-on for 12 hours (day) and then lights-off for 12 hours (night), and experiments often run for several days or even weeks. In this picture, a newer version of DAM machines is shown (one is circled in red).

divider line

Sleepless dataSleepless mutants sleep much less than normal (control) flies. Image modified from Koh et al, 2008

This system allows researchers to study the sleep habits of dozens of flies at once, and it’s relatively quick and easy (compared to studying sleep in mammals). So what’s an example of a real sleep experiment? In 2008, the Seghal lab used this system to find sleep-related genes. They ran a genetic screen in which they exposed a population of flies to toxic chemicals that caused random mutations in their DNA. Then, they tested the flies to see if any had sleep abnormalities. They found that flies with a mutation in one gene (which they aptly named sleepless) slept about 80% less! Isn’t it crazy that a single gene can affect such a complex behavior so dramatically?

Sleepless dataA common way to display fly sleep habits over the day and night period for one day. The amount of sleep within 30 minute intervals (y axis) is plotted for the time of day (x axis). Note that Sleepless mutants (open circles) sleep much less than control flies (filled circles). The bar at the bottom indicates time: white = day, black = night. Image modified from Koh et al, 2008

divider line
In another experiment that same year, the Guo lab was interested in finding out how sleep affects memory. They tested the sleeping habits of a fly mutant called amnesiac, which can’t form long-term memories. They found that amnesiac mutants had very fragmented sleep (meaning that they woke up a lot during the night). The fact that the same gene is involved in both sleep and memory provides a link that researchers can use for future studies about how these behaviors are connected.

Tracker setupA schematic of the Tracker setup. Image modified from Gilestro, 2012

Although studies have shown that the DAM system is relatively accurate for measuring fly sleep, more sophisticated methods have recently been developed for tracking fly movement. These systems (sometimes called the “Tracker” program) rely on cameras and sensitive tracking software to measure movement at a much higher resolution. As use of the Tracker program becomes more widespread, I have no doubt that we will gain yet more insights into how and why we sleep.

 
 

References:

  • Potdar S. (2013). Lessons From Sleeping Flies: Insights from Drosophila melanogaster on the Neuronal Circuitry and Importance of Sleep , Journal of Neurogenetics, 27 (1-2) 23-42. DOI: http://dx.doi.org/10.3109/01677063.2013.791692
  • Koh K., M. N. Wu, Z. Yue, C. J. Smith & A. Sehgal (2008). Identification of SLEEPLESS, a Sleep-Promoting Factor, Science, 321 (5887) 372-376. DOI: http://dx.doi.org/10.1126/science.1155942
  • Liu W., Beika Lu & Aike Guo (2008). amnesiac regulates sleep onset and maintenance in Drosophila melanogaster, Biochemical and Biophysical Research Communications, 372 (4) 798-803. DOI: http://dx.doi.org/10.1016/j.bbrc.2008.05.119
  • Donelson N., Kim E.Z., Slawson J.B., Vecsey C.G., Huber R. & Griffith L.C. (2012). High-resolution positional tracking for long-term analysis of Drosophila sleep and locomotion using the “tracker” program., PloS one, PMID: http://www.ncbi.nlm.nih.gov/pubmed/22615954
  • Gilestro G.F. (2012). Video tracking and analysis of sleep in Drosophila melanogaster, Nature Protocols, 7 (5) 995-1007. DOI: http://dx.doi.org/10.1038/nprot.2012.041