Fruit Fly Behavior: Biology Lab

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  • 0:02 Drosophila Melanogaster
  • 2:22 Investigating Fruit…
  • 5:44 Analysis of…
  • 7:24 Lesson Summary
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Lesson Transcript
Instructor: Jennifer Szymanski

Jen has taught biology and related fields to students from Kindergarten to University. She has a Master's Degree in Physiology.

Drosophila melanogaster, the common fruit fly, is a model organism used in many types of biology experiments. In this lesson, you'll explore how to design an experiment to see how this animal responds to an environmental stimulus.

Drosophila Melanogaster

Genetics experiments. They bring to mind Frankenstein, mad scientists, and...fruit flies? Though not nearly as exciting as Godzilla or other sci-fi movie monsters, Drosophila melanogaster, the common fruit fly, is an ideal model organism with which to study science.

What characteristics make this little insect such a good model? First, they are fairly easy to care for; give them some rotting fruit or fungi, and they'll happily munch away. Moreover, they breed, grow, and develop very rapidly, going from egg to adult in a little over a week. Furthermore, and probably most importantly, they have a very simple genome. That is, their sum total of genetic material is not especially complicated, and this genetic material is fairly closely related to that of humans. Scientists know quite a bit about Drosophila's genome - it has been sequenced, manipulated to create mutations, and even used to determine how genes influence an organism's behavior.

There's a fairly standard procedure for working with fruit flies. First, it's important that you are able to sex the insects, or determine which are male and which are female. Both sexes are pictured. Take a moment to observe what makes them different.

Example of male and female fruit fly

Obviously, there's a potential problem when working with flying insects - they tend to escape! Therefore, there are a few simple steps you must complete in order to move Drosophila from culture vial to culture vial. First, gently tap the bottom of the vial to bring the flies to its bottom. Then, quickly remove the plug from the vial and place an empty vial over the top of the 'full' vial, grasping the seam between the two vials tightly, so as to not lose any flies. Invert both of the vials, and tap again, gently. When the flies have been knocked into the empty vial, quickly cover it. You're now ready to use these flies in your behavior experiments.

Investigating Fruit Fly Behavior

Before we explore Drosophila behavior, let's review just a few terms associated with studying animal behavior. First, behavior itself is defined as any action that results from a stimulus. A stimulus, in turn, is defined as a change in an organism's environment. That change might be internal, like a toxin released by a bacterium in the bloodstream, or external, like an increase in temperature or the presence or absence of light.

The Greek root, 'taxia,' which means 'movement,' is frequently used in describing responses to external stimuli. You might remember this by recalling that a taxi moves people from one place to another. The other part of the word sometimes mentions the stimulus that causes the movement. For example, 'chemotaxis' means a 'movement caused by a chemical,' while 'phototaxia' is 'movement due to light,' and a geotactic response is caused by gravity.

Every good scientific investigation begins with a question caused by an observation. You may have observed fruit flies hovering over bananas and thought, 'Are fruit flies really attracted to fruit, or is it just the fruit's location?' To test this question, we'll create a choice chamber out of two dried empty water bottles taped together. It's a simple design, but one that will do the job. If the stimulus causes a positive taxic response, the flies will move to that end of the chamber.

Because fruit flies are living organisms, they'll need some time to adjust to their surroundings. After using a funnel to tap 20-30 flies into the chamber, and using cotton balls with distilled water to close both ends of the chamber, we need to allow the flies to acclimate by letting the chamber sit, undisturbed. After about five minutes, we will count how many flies are in each half of the choice chamber, recording the values in a table. This is our control condition, since both ends have plain water.

Note the use of the distilled water - moisture itself might cause a response, so it's important to account for that in the experimental design. This, you might recall, is a standardized variable, a variable that's controlled, or kept the same in all conditions. In other words, we need to control all of the things that might affect the outcome of the experiment except for one, so that we can truly isolate the nature of the response, which is the dependent variable, or lack of response, to what we are changing between conditions, the independent variable. We'll use these terms in an example in a minute.

Now, you're ready to test a stimulus. But what stimulus? That's the question. It can be anything, as long as you control your standardized variables and make sure you test for only one thing at a time. Some things to consider:

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