Taste Preference Assay for Adult Drosophila

Summary

Taste is an important sensory process which facilitates attraction to beneficial substances and avoidance of toxic substances. This protocol describes a simple ingestion assay for determining Drosophila gustatory preference for a given chemical compound.

Abstract

Olfactory and gustatory perception of the environment is vital for animal survival. The most obvious application of these chemosenses is to be able to distinguish good food sources from potentially dangerous food sources. Gustation requires physical contact with a chemical compound which is able to signal through taste receptors that are expressed on the surface of neurons. In insects, these gustatory neurons can be located across the animal's body allowing taste to play an important role in many different behaviors. Insects typically prefer compounds containing sugars, while compounds that are considered bitter tasting are avoided. Given the basic biological importance of taste, there is intense interest in understanding the molecular mechanisms underlying this sensory modality. We describe an adult Drosophila taste assay which reflects the preference of the animals for a given tastant compound. This assay may be applied to animals of any genetic background to examine the taste preference for a desired soluble compound.

Introduction

Animals use chemosensation to distinguish advantageous conditions apart from disadvantageous conditions. This perception can be critical for such things as determining the best food source, avoiding toxic substances or determining the best mating partner¹. Chemosensation is often divided into two sensory components: olfactory senses and gustatory senses. A main distinguishing characteristic of these senses is that olfaction (smell) is used to sample the surrounding gaseous chemical environment while gustation (taste) requires physical contact with a nonvolatile substrate. Both sensory modalities stimulate neurological responses which are processed and decod....

Protocol

1. Starvation

1. Prepare fly starvation vials by saturating a cotton ball with 18.2 MΩ water at the bottom of a standard fly vial. Alternatively, similarly saturate a small strip of filter paper with 18.2 MΩ water and place at an angle within the vial.
2. Collect flies into sets of ~100 animals on a CO₂ pad and then add the flies to a prepared vial.
   Note: Best results are obtained with animals that are less than 5 days old. However, the exact age of the animals can be controlled as an experimental variable to determine changes in taste preference over time.
3. Use a cotton ball or foam stopper to secure the vials clos....

Results

Some typical results from taste preference assays are shown below. In most experiments some variation in intensity of abdominal coloring will be seen (Figure 1). Any coloring in the abdomen whether intense or weak is considered a positive ingestion. It is therefore advisable for researchers to score animals while blind to the experimental condition so as to limit any potential biases.

It is also important to cho.......

Discussion

We have described a simple but effective protocol for determining taste preference in Drosophila. Versions of this assay are routinely used in experiments to determine the contributions of gustatory receptors (GRs) to perceiving the different qualities (bitter, sweet, sour, salty, and umami) of taste compounds. The Drosophila genome contains approximately 60 genes which encode 68 identified gustatory receptors by alternative splicing^8,9. However, other proteins such as ionotropic glutamate re.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Blue Food Coloring (Water, Propylene Glycol, FD&C Blue 1 and Red 40, Propylparaben)	McCormick	N/A
Cryo/Freezer Boxes w/o Dividers	Fisher	03-395-455
Dumont #5 Forceps	Fine Science Tools	11251-20
Glacial Acetic Acid	Fisher	BP2401-500
Leica S6 E Stereozoom 0.63X-4.0X microscope	W. Nuhsbaum, Inc.	10446294
Petri dish (100 mm x 15 mm)	BD Falcon	351029	Reuseable if thoroughly washed and dried
Quick-Snap Microtubes	Alkali Scientific Inc.	C3017
Red Food Coloring (Water, Propylene Glycol, FD&C Reds 40 and 3, Propylparaben)	McCormick	N/A
Sucrose	IBI Scientific	IB37160