Drosophila melanogaster are useful in studying genetic or environmental manipulations that affect behaviors such as spontaneous locomotor activity. Here we describe a protocol that utilizes monitors with infrared beams and data analysis software to quantify spontaneous locomotor activity.
Drosophila melanogaster has been used as an excellent model organism to study environmental and genetic manipulations that affect behavior. One such behavior is spontaneous locomotor activity. Here we describe our protocol that utilizes Drosophila population monitors and a tracking system that allows continuous monitoring of the spontaneous locomotor activity of flies for several days at a time. This method is simple, reliable, and objective and can be used to examine the effects of aging, sex, changes in caloric content of food, addition of drugs, or genetic manipulations that mimic human diseases.
Fruit flies, Drosophila melanogaster, have been used as a valuable model organism to study mechanisms underlying complex behaviors, such as learning and memory, social interaction, aggression, drug abuse, sleep, sensory function, courtship, and mating1,2. One behavior that has been studied through multiple protocols is spontaneous locomotor activity. Negative geotaxis was one of the first methods developed for measuring Drosophila activity, and this protocol involves measuring the percentage of flies that reach a certain height of the vial after flies were shaken to the bottom of the container1,3. This method has advantages of being straightforward, inexpensive, and since it does not require any special equipment it can be performed in any laboratory. It has been used as a valuable screening tool to study effects of different genetic manipulations on fly mobility3. However, it is time and labor intensive and has the possibility of bias due to variable shaking of the vials and human recordings.
The negative geotaxis method was improved upon by development of the Rapid Iterative Negative Geotaxis (RING) method4,5, which takes photographs of the fly vials following shaking of the flies to the bottom. The advantage of this protocol is its sensitivity and the possibility of testing a large number of fly vials at the same time. However, this protocol still has the potential for human error, and only measures negative geotaxis. Other laboratories have used simple observation in culture vials to determine locomotor activity6.
Recently several video recording systems for measuring fly locomotor activity have been developed. One video monitoring protocol provides time for adjustment before recording7. The method described by Slawson et al. also uses an air pulse to stop movement until the start of recording, which could potentially be a stressor to the animals7. This method provides information on average speed, max speed, time spend in motion, etc. Another three-dimensional tracking system measures the maximal velocity of individual flies during ~0.2 seconds of free flight takeoff8. A three-dimensional video monitoring protocol uses flies expressing GFP and multiple cameras fitted with filters allowing for detection of fluorescence to determine fly mobility9. Flies in this protocol tend to exhibit cylindrical flight patterns, which is potentially due to the shape of Drosophila culture vials10. This method was improved by using a dome that allows measuring spontaneous movement of two flies11. A high-throughput method that uses a camera to automatically monitor and quantify the individual and social behavior of Drosophila has been also described12. Zou et al. developed a behavioral monitor system (BMS) that uses two computer-assisted cameras to record lifetime behavior and movements such as resting, moving, flying, eating, drinking, or deaths of individual tephritid fruit flies13. Several other video systems have been developed to monitor fly behavioral activity14,15.
Here we describe a method for quantifying Drosophila activity that utilizes population monitors. These monitors are housed in temperature- and humidity-controlled incubators at 25 °C on a 12 hour day-night light cycle. Each population monitor has infrared beams placed in rings positioned at three different heights. Every time a fly moves across the rings it interrupts the infrared beam, which is recorded by a microprocessor that independently records and counts the activity of flies within the vial. A microprocessor uploads the total activity within the vial to the computer at user-defined intervals that could vary from 1 second to 60 minutes. The method described here provides ample time for flies to adjust to the new environment and allows for simultaneous measuring of the spontaneous locomotor activity of as many as 120 populations of flies. In addition, we describe preparation of the food, fly maintenance, setting up the mobility population monitors in temperature controlled incubators, and potential factors that may affect results. This method can be used to study how different environmental or genetic modifications affect spontaneous locomotor activity of the flies.
Note: The Canton-S strain is the standard wild-type background line obtained from the Bloomington Stock Center.
1. Food Preparation and Recipe for 1,000 ml of Food
Note: This section describes the protocol for food preparation. Large metal pots are used to prepare about 18 L of food at a time. The protocol described here is downsized and uses 1,000 ml H2O. Food is autoclaved twice.
2. Preparation of Glass Vials
3. Maintenance of the Parental Flies
4. Collection of Experimental Flies
5. Setting Up the Mobility Monitors
6. Setting Up the Experiment
7. Running the Activity Monitors and Calculating the Total Spontaneous Activity
8. Data Analysis
The spontaneous locomotor activity in Drosophila depends on fly gender (Figure 3A), calorie content of the food (Figure 3B) and the light/dark cycle. Once the light is switched off fly activity dramatically decreases. Figure 3A illustrates 24 hours of locomotor activity recordings of male and female flies. An asterisk on the x-axis marks the time when the light was switched off and the transition to dark cycle. Figure 3B illustrates the standard deviation between the average spontaneous locomotor activity collected in three population monitors for Male flies age 3 days on corn food. The data collected for the spontaneous physical activity during the 24 hours can be also expressed as the total activity per fly during a 24 hour period, Figure 3C.
Figure 1: Population monitor setup for monitoring of spontaneous locomotor activity of flies. A) Several population monitors are connected with a 4-wire telephone cable to 5-way splitters and placed in a temperature-controlled incubator. B) Higher magnification of two population monitors, which show placement of the vials within the population monitors and three rings with infrared beams positioned at three different heights. Click here to view larger image.
Figure 2: Screen shot of the raw data generated by the software showing Date, Time and data collected in Rings 1, 2, and 3. R stands for Ring. Click here to view larger image.
Figure 3: A) Average spontaneous locomotor activity of male (Black) and female (Magenta) flies during 24 hours on standard laboratory diet. The data are collected in 10 minute bins and represent average activity per fly calculated as average activity between three vials each containing 10 flies. B) Average spontaneous locomotor activity of male flies during 24 hours on standard laboratory diet. The data are collected in 10 minute bins and represent average activity per fly calculated as average activity between three vials. Standard deviations are marked in green. C) Total activity of 20 days old male flies on low-calorie (0.5X) (Green) and high-calorie (1.5X) (Brown) food over 24 hours. Click here to view larger image.
Spontaneous locomotor activity of flies is influenced by many factors such as age, genetic background, and gender2,13,18,19. In addition, environmental factors such as caloric content of the food, temperature of the environment, addition of different drugs, and day/night light cycle can affect fly activity. For instance, male flies of the same age have a higher spontaneous physical activity compared to females (Figure 1). Therefore, flies of the same age and gender should be compared to each other. When examining the effect of genetic manipulations on fly activity, such as overexpression or loss of function of a particular gene, the experimental and control flies must be in the same genetic background to remove any potential effects of different genetic background or second site modifiers. This can be achieved by backcrossing experimental female flies to w1118 or yw males for 10 generations. After 10 generations of backcrossing, w1118 or yw flies could be used as a genetic control. Another way to control for the genetic background is to use the inducible GAL4 GeneSwitch (GAL4-GS)-UAS binary system, which allows overexpression or down-regulation (RNAi) of the gene of interest in a time and tissue-specific manner in flies fed food with the addition of mifepristone (RU486) 20,21. RU486 is necessary for GAL4 to dimerize and bind to the UAS sequence. Genetic controls are sibling flies kept on food with the addition of EtOH (Ru486 diluent).
Various methods have been used to record Drosophila mobility. The method described here is simple, reliable, more informative, and has less potential of bias compared to other methods used to determine Drosophila mobility, such as negative geotaxis. It has the advantage of objective simultaneous recording of multiple populations of flies for a long period of time in standard culture conditions. Measuring locomotor activity by using population monitors can be useful for studying how different caloric contents of the food affect fly activity or to study genetic mechanisms underlying increased activity of flies on CR16. Similarly, this system has been used to study the effects of different genetic mutations, aging, or the addition of different drugs on fly spontaneous physical activity. Use of individual tubes instead of population monitors allows measuring H2O2 resistance in different genotypes of flies, studying circadian rhythms in vivo, analyzing sleep behavior, and others17,22-24.
Like any method, there are limitations to this monitoring system. When monitoring flies for a long period of time, there is a potential for fly death, especially if using aged flies. Using only healthy flies will help prevent this. We also try to use more than 3 biological replicates per group if the flies are old or prone to dying. One solution is to keep flies only for 2 days in the mobility monitors and use data collected during day 2, after flies have adjusted to the environment. If death occurs we do not use the data collected for the vial in calculations. Although we have been using vials positioned only vertically in the Trikinetics activity monitors, there is a possibility to place the vials horizontally. We choose to place vials vertically because the food is at the bottom of the vial, which is similar to standard incubator culture conditions. This allows flies to have more space to walk up and down the vials, and it is more similar to negative geotaxis experiments. The humidity of the incubator should also be monitored if food desiccation becomes a problem24. This system provides data in terms of average activity, and does not provide specific details about the nature of the activity. In addition, if two flies cross the beam at the same time, it will only be recorded as one interruption. The protocol described here is useful for quantifying total activity, but other protocols could provide useful data if more precise information such as flight trajectory or velocity are desired12,14,25.
Following this experiment, differences in spontaneous locomotor activity due to genetic or environmental manipulations will be known. A future modification of this protocol could be to analyze the different levels of activity of flies at the top, middle, and bottom rings of the population monitors. This would determine whether the fly populations spend most of their time at the bottom of the vial near the food or at the top. The protocol in its current form allows for accurate, simultaneous quantification of spontaneous locomotor activity of Drosophila experimental and control populations.
The authors have nothing to disclose.
This work was supported by a grant from the National Institutes of Health (AG023088 to B.R.).
Sucrose FCC Food Grade 100 LB, | Fisher Scientific MP Biomedicals | ICN90471380 | |
Brewer’s Yeast | Fisher Scientific MP Biomedicals | ICN90331280 | |
Drosophila Agar Fine | SciMart | DR-820-25F | |
Cornmeal | Fisher Scientific MP Biomedicals | ICN90141125 | |
Methyl4-hydroxybenzoate, tegosept | Sigma | H5501-5KG | |
EtOH | Pharmco-AAPER | 111000200 | |
Active Dry Yeast | Fisher Scientific | ICN10140001 | |
Fly CO2 pad | LabScientific | BGSU-7 | |
Stereo Microscope | Olympus | SZ40 | |
Drosophila carbon dioxide (CO2) tank | Airgas | UN1013 | |
Small paint brush for pushing the flies | |||
Shell vial wide | Fischer Scientific | AS519 | |
Buzzplugs for wide plastic vials | Fischer Scientific | AS275 | |
Glass vials (25x95mm) | Fischer Scientific Kimble 60931-8 | AS-574 | |
Sponge plugs for glass vials | SciMart | DR-750 | |
Drosophila Food Dispenser | Applied Scientific (Fischer Scientific) | AS780Q | |
DPM Drosophila Population Monitor | Trikinetics Inc. | ||
DC Power Supply with line cord | Trikinetics Inc. | ||
PSIU9 The Power Supply Interface Unit | Trikinetics Inc. | ||
Telephone cables and 5 way splitters | Trikinetics Inc. | ||
Universal Serial Bus (USB) hardware | Trikinetics Inc. | ||
Macintosh or Windows PC with UCB port | |||
DAMSystem308X Data Acquisition Software for Macintoch OSX (Intel) | www.trikinetics.com | ||
DAMSystem308 Data Acquisition Software for Windows PC (XP/Vista/7) | www.trikinetics.com | ||
DAMFileScan108X software for Macintosh | www.trikinetics.com | ||
DAMFileScan108X software for Windows PC (XP/Vista/7) | www.trikinetics.com | ||
USB software (PSIUdrivers.zip) | www.trikinetics.com | ||
DAMSystem Notes 308 | (http://www.trikinetics.com/Downloads/DAMSystem%20Notes%20308.pdf |