Name: high-resolution quantification of odor-guided behavior in drosophila melanogaster using the flywalk paradigm
Uploaded: 2015-12-11T15:00:00
Description: Watch this Scientific Journal Video about High-resolution Quantification of Odor-guided Behavior in Drosophila melanogaster Using the Flywalk Paradigm at JoVE.com

We thank Daniel Veit for technical assistance and Pedro Gouveia at Electricidade Em P&#242; (electricidadeempo.net) for customizing the tracking software for our demands. We&#160;also thank Tom Retzke for support during the filming process. This study was supported by the Max Planck Society.

The construction and technical details of Flywalk have been described elsewhere26 (in case of any problems of establishing this set up, further information can be obtained from MK). Here we focus on detailed instructions on the handling of the paradigm that will help to obtain reliable results.
1. Fly Handling
<ol>
	<li>Rear flies in low to medium density cultures on food medium27 under a 12 hr:12 hr light:dark regime at 23-25 &#176;C and 70% relative humidity. ...

<ol>
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I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Asymmetric+neurotransmitter+release+enables+rapid+odour+lateralization+in+Drosophila.">Asymmetric neurotransmitter release enables rapid odour lateralization in Drosophila.</a> Nature. 493 (7432), 42442-42448 (2013).</li><li>Quinn, W. G., Harris, W. A., Benzer, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Conditioned+behavior+in+Drosophila+melanogaster.">Conditioned behavior in Drosophila melanogaster.</a> Proc. Natl. Acad. Sci. USA. 71 (3), 708-712 (1974).</li><li>Ramdya, P., Lichocki, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanosensory+interactions+drive+collective+behaviour+in+Drosophila.">Mechanosensory interactions drive collective behaviour in Drosophila.</a> Nature. 519 (7542), 233-236 (2014).</li><li>Bhandawat, V., Maimon, G., Dickinson, M. H., Wilson, R. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Olfactory+modulation+of+flight+in+Drosophila+is+sensitive,+selective+and+rapid.">Olfactory modulation of flight in Drosophila is sensitive, selective and rapid.</a> J. Exp. Biol. 213 (21), 3625-3635 (2010).</li><li>Duistermars, B. J., Chow, D. M., Frye, M. 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Although the Flywalk system appears rather sophisticated at first glance, once set up and running it is easy to use and produces very robust results. To stress the consistency of the results produced with the bioassay it may be said that the representative results shown here were obtained almost 2 years after some of the results shown in a previous study29 with a modified setup using a new tracking software and light source. Nevertheless, the attractant responses are - despite slightly higher response amplitud...

The overarching goal of any neuroethological research is to establish a causal link between the activity states of single neurons or neuronal circuits and the behavior of an organism. To achieve this goal neuronal activity and behavior should be monitored under identical stimulus conditions and these stimulus conditions should ideally be similar to those the nervous system under scrutiny evolved to make sense of. Particularly when it comes to behavioral bioassays, these requirements have historically proven quite demanding in Drosophila melanogaster olfactory neuroethology.
Once released from the source, odor plumes rapidly break up into thin filaments with turbulent diffusion caused by air movement being the main determinant of odor distribution1. As a result, an insect navigating towards an odor source experiences intermittent stimulation with odor packages interspersed with variable intervals of clean air. Both walking and flying insects - including Drosophila- have been demonstrated to exploit this intermittent stimulation regime for navigation by surging upwind upon plume encounter and predominantly moving cross-wind in the absence of odors2-5. Whereas stimulation procedures in physiological experiments largely mimic those an insect may experience in its natural environment by either providing single puffs of odors interspersed with extended periods of clean air or dynamic stimulation sequences6-11, many behavioral bioassays used in Drosophila neuroethology such as trap assay, open-field arenas or T-maze rely on odor-gradients12-15. However, because odor gradients by definition are variable in concentration depending on the distance from the odor source, a particular behavior cannot be attributed to a precise odor concentration using these paradigms. In addition, the slope of an odor gradient critically depends on the physicochemical properties of the odorant. A gradient of a highly volatile compound will be shallower than that created by a less volatile compound and therefore also harder to track for an organism relying on measuring concentration differences in space as the only means of navigation16-20, which may lead to a misinterpretation of olfactory preferences particularly in choice assays. This effect is also highly detrimental when investigating behavior towards odor mixtures because it leads to different blend component ratios at every point in space and therefore again precludes a clear correlation between physiology and behavior.
While vinegar flies tend to aggregate on fermenting fruit, they are solitary in their navigation towards food sources and oviposition sites. Nevertheless, rather than testing individual animals many behavioral paradigms used in Drosophila neuroethology examine the odor-guided behavior of cohorts of flies and attraction is scored as the fraction of flies choosing the odor over a control stimulus. These cohort experiments have contributed greatly to the understanding of fly neuroethology and many of the observations made by using them could be confirmed in single-fly experiments. However, it has been observed that flies can influence each other&#180;s decision21 and in extreme cases the evaluation of an odor can switch from indifference to avoidance depending on population density22. Additionally, results from these kinds of experiments often provide only the endpoint of a sequence of behavioral decisions rather than observing what the fly is doing while it is doing it, which would be desirable when attempting to correlate behavior with neuronal activity. These rather low-resolution cohort experiments are contrasted by high-resolution single-fly methods such as tethered flight arenas and treadmills which allow for a direct observation of behavioral responses at the time the stimulus is presented20,23,24. Nevertheless, cohort experiments are still popular, because they are very efficient and provide robust results even at comparably low sample sizes because inter-individual and inter-trial variability are partially averaged out due to the observation of populations over extended periods of time. While tethered flight and treadmill probably provide the gold standard concerning stimulus presentation and temporal resolution, the arenas used are designed for single animals and it is therefore time-consuming to obtain sample sizes necessary for a statistical analysis. Several other approaches have recently been developed that allow an efficient acquisition of high-resolution behavioral data in combination with a well-defined stimulus regime. These include unsupervised 3D-tracking of multiple vinegar flies in a windtunnel in combination with an accurate 3D-model of the odor plume5, tracking of multiple individual flies in choice chambers supplied with airstreams from both sides25 and the Flywalk paradigm26.
In Flywalk, 15 individual flies are situated in small glass tubes and continuously monitored by an overhead camera under red-light conditions. Odors are added to a continuous airstream of 20 cm/sec and travel through the glass tubes at a constant speed. The airstream is humidified by passing it through 250 ml bottles containing distilled water (humidifiers) before entering the odor delivery system. The flies&#180; positions are recorded within a square region of interest (ROI) encompassing most of the length of the odor tubes (but excluding the outer edges of the tubes (approximately 5 mm at each side) where the flies cannot move further up- or downwind) around the time of odor presentation (Figure 1A, B). Fly identities are kept constant by the tracking system throughout the experiment on the basis of their Y-positions (i.e. their glass tube limits). Odor stimulation is achieved using a multi-component stimulus device which allows the presentation of up to 8 single odors and all possible mixtures thereof26,29 (Figure 1B). The course of an experiment is controlled by a computer regulating the odor delivery system and collecting temperature and humidity information (computer 1, Figure 1C). This computer also controls a datalogger (start/stop recording) on a second computer which continuously tracks fly positions at 20 frames per sec (computer 2). Fly positions, odor valve status (i.e. time-point of valve opening), odor ID, temperature and humidity around odor stimulation cycles are logged on computer 2. This way information on odor and fly positions are synchronized and exported as .csv-files which can be further processed and analyzed using custom-written analysis routines. Because the whole system is computer-controlled, no human intervention is necessary during an experimental session.

<table border="0" cellpadding="0" cellspacing="0" width="866">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Flywalk setup</td>
			<td style="width:325px;">Custom</td>
			<td style="width:119px;"></td>
			<td style="width:207px;">details available upon request</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">stimulus device</td>
			<td style="width:325px;">Custom</td>
			<td style="width:119px;"></td>
			<td>details available upon request</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">LED cluster</td>
			<td style="width:325px;">Custom</td>
			<td style="width:119px;"></td>
			<td>details available upon request</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">HD Pro Webcam C920</td>
			<td style="width:325px;">Logitech, Lausanne, Switzerland</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">2 Computers</td>
			<td style="width:325px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="18">
			<td height="18" style="height:18px;width:216px;">Flywalk Reloaded v1.0 software</td>
			<td style="width:325px;">Electricidade Em P&#243; (electricidadeempo.net)</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Labview 11.0 software</td>
			<td style="width:325px;">National Instruments, Austin, TX</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Standard fly food</td>
			<td style="width:325px;">Custom</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="18">
			<td height="18" style="height:18px;width:216px;">Standard fly vials</td>
			<td style="width:325px;">Greiner bio-one GmbH, Frickenhausen, Germany</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Standard fly vials</td>
			<td style="width:325px;">Greiner bio-one GmbH, Frickenhausen, Germany</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">aspirator</td>
			<td style="width:325px;">Custom</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">mineral oil</td>
			<td style="width:325px;">Sigma-Aldrich (www.sigmaaldrich.com)</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">odors</td>
			<td style="width:325px;">Sigma-Aldrich (www.sigmaaldrich.com)</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="18">
			<td height="18" style="height:18px;width:216px;">200 &#181;l PCR reaction tubes</td>
			<td style="width:325px;">Biozym Scientific GmbH, Oldendorf, Germany</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

high-resolution quantification of odor-guided behavior in drosophila melanogaster using the flywalk paradigm

In their natural environment, insects such as the vinegar fly Drosophila melanogaster are bombarded with a huge amount of chemically distinct odorants. To complicate matters even further, the odors detected by the insect nervous system usually are not single compounds but mixtures whose composition and concentration ratios vary. This leads to an almost infinite amount of different olfactory stimuli which have to be evaluated by the nervous system.
To understand which aspects of an odor stimulus determine its evaluation by the fly, it is therefore desirable to efficiently examine odor-guided behavior towards many odorants and odor mixtures. To directly correlate behavior to neuronal activity, behavior should be quantified in a comparable time frame and under identical stimulus conditions as in neurophysiological experiments. However, many currently used olfactory bioassays in Drosophila neuroethology are rather specialized either towards efficiency or towards resolution.
Flywalk, an automated odor delivery and tracking system, bridges the gap between efficiency and resolution. It allows the determination of exactly when an odor packet stimulated a freely walking fly, and to determine the animal&#180;s dynamic behavioral reaction.

Because flies are allowed to distribute freely within their glass tubes between odor pulses and the odor pulse travels through the glass tubes at a constant speed flies encounter the odor at different times depending on their x-position at the time of stimulation. As a result, the onsets of the upwind trajectories evoked by a 500 msec pulse of an attractive 10-3 dilution of ethyl acetate are delayed by about 1 sec for flies at the downwind end of their glass tubes compared to those of flies sitting closer to t...

Watch this Scientific Journal Video about High-resolution Quantification of Odor-guided Behavior in Drosophila melanogaster Using the Flywalk Paradigm at JoVE.com

High-resolution Quantification of Odor-guided Behavior in Drosophila melanogaster Using the Flywalk Paradigm

The automated tracking system Flywalk is used for high-resolution quantification of odor-guided behavior in Drosophila melanogaster.

High-resolution Quantification of Odor-guided Behavior in Drosophila melanogaster Using the Flywalk Paradigm

In their natural environment, insects such as the vinegar fly Drosophila melanogaster are bombarded with a huge amount of chemically distinct odorants. To ...

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