Animal Behavior
Drosophila as a Model Organism
The common fruit fly, Drosophila melanogaster, is a widely used model organism in biology, though it may be more common…
Have you ever left a fruit bowl out for a while and return to discover a fruit fly settlement? But why is the fruit fly attracted to ripe fruit in the first place? In other words, what is the stimulus that tells them where to go? This analysis is part of a wider field called ethology, which is the study of animal behavior.
A stimulus may cause two types of animal movement. Kinesis, which is non-directional or random, or taxis, which is directional. An example of kinesis would be the movement of the flies in random directions when chased away. Conversely, an example of taxis would be the directed movement of the flies back towards the ripe fruit. This specific type of taxis is referred to as chemotaxis and since it is towards the stimulant, food, it is further defined as positive chemotaxis. An example of negative chemotaxis would be the fly moving away from an insect repellent. Another common type of taxis is phototaxis, which is movement is response to a light stimulus. Moths are showing positive phototaxis when they move towards a light source. On the contrary, cockroaches that scuttle away when the light is turned on are being negatively phototactic. Geotaxis, also known as gravitaxis, is movement in response to gravity. Moving in the direction of gravity is positive geotaxis, while movement in the opposite direction is negative geotaxis. There are many other types of taxis, including aerotaxis, barotaxis, hydrotaxis, and magnetotaxis - which are movement in response to oxygen, pressure, water and magnetic fields respectively.
So why do scientists study animal behaviors like these? One of the goals may be to find the genetic basis for the behaviors exhibited by individuals or groups within a species. Sometimes, a behavior can even be traced to a specific mutation in a single gene. On a broader scale, understanding how genetics and behavioral traits are linked can also help us to gain a better understanding of behaviors across the animal kingdom, including our own.
In this lab, you will assess the geotactic, phototactic and chemotactic responses of the fruit fly Drosophila melanogaster, using choice chambers.
Have you ever left a fruit bowl out for a while and return to discover a fruit fly settlement? But why is the fruit fly attracted to ripe fruit in the first place? In other words, what is the stimulus that tells them where to go? This analysis is part of a wider field called ethology, which is the study of animal behavior.
A stimulus may cause two types of animal movement. Kinesis, which is non-directional or random, or taxis, which is directional. An example of kinesis would be the movement of the flies in random directions when chased away. Conversely, an example of taxis would be the directed movement of the flies back towards the ripe fruit. This specific type of taxis is referred to as chemotaxis and since it is towards the stimulant, food, it is further defined as positive chemotaxis. An example of negative chemotaxis would be the fly moving away from an insect repellent. Another common type of taxis is phototaxis, which is movement is response to a light stimulus. Moths are showing positive phototaxis when they move towards a light source. On the contrary, cockroaches that scuttle away when the light is turned on are being negatively phototactic. Geotaxis, also known as gravitaxis, is movement in response to gravity. Moving in the direction of gravity is positive geotaxis, while movement in the opposite direction is negative geotaxis. There are many other types of taxis, including aerotaxis, barotaxis, hydrotaxis, and magnetotaxis - which are movement in response to oxygen, pressure, water and magnetic fields respectively.
So why do scientists study animal behaviors like these? One of the goals may be to find the genetic basis for the behaviors exhibited by individuals or groups within a species. Sometimes, a behavior can even be traced to a specific mutation in a single gene. On a broader scale, understanding how genetics and behavioral traits are linked can also help us to gain a better understanding of behaviors across the animal kingdom, including our own.
In this lab, you will assess the geotactic, phototactic and chemotactic responses of the fruit fly Drosophila melanogaster, using choice chambers.
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Q1: What is the difference between kinesis and taxis in animal behavior?
Kinesis is non-directional, random movement triggered by a stimulus, such as fruit flies moving randomly when chased away. Taxis, by contrast, is directional movement toward or away from a stimulus. For example, flies moving back toward ripe fruit demonstrate taxis. Both are forms of stimulus-induced movement studied in ethology, the science of animal behavior.
Q2: What is positive chemotaxis and how does it relate to fruit fly behavior?
Positive chemotaxis is directed movement toward a chemical stimulus. Fruit flies exhibit positive chemotaxis when attracted to ripe fruit, moving toward the odor cues. This contrasts with negative chemotaxis, where an animal moves away from a chemical stimulus, such as flies avoiding insect repellent. Chemotaxis is one of many taxis types that help organisms locate resources or avoid threats.
Q3: How do phototaxis and geotaxis differ as directional behaviors?
Phototaxis is movement in response to light, while geotaxis, also called gravitaxis, is movement in response to gravity. Moths showing positive phototaxis move toward light sources, whereas cockroaches exhibit negative phototaxis by moving away from light. Positive geotaxis means moving with gravity; negative geotaxis means moving against it. Both are distinct taxis behaviors with different stimulus triggers.
Q4: Why is Drosophila melanogaster used as a model organism for studying animal behavior?
Drosophila melanogaster is ideal for behavioral research due to its short two-week generation time, allowing study of multiple generations quickly. Flies are easily maintained in small tubes and show clear sexual dimorphism, enabling researchers to distinguish males from females. Over 27,000 unique Drosophila lines are maintained at stock centers, providing diverse genetic tools for studying behavior and its genetic basis.
Q5: What is a choice chamber and how is it used to study taxis behavior?
A choice chamber is a laboratory apparatus that allows researchers to observe directional responses of flies to specific stimuli like gravity, light, or chemicals. Flies are placed in the chamber's center and allowed to move freely, with alternative stimuli presented on opposing sides. After a period of wandering, researchers count flies on each side and use statistical analysis to determine stimulus preference and taxis behavior.
Q6: What is the genetic basis for studying animal behavior in organisms like Drosophila?
Scientists study animal behaviors to identify their genetic basis, sometimes tracing specific behaviors to mutations in single genes. Understanding how genetics and behavioral traits link helps reveal how behaviors are hard-wired and have evolved. This knowledge applies across the animal kingdom, including humans. Comparing mutant and wild-type Drosophila reveals how specific genes control directional responses to stimuli.
Q7: What other types of taxis exist beyond chemotaxis, phototaxis, and geotaxis?
Beyond chemotaxis, phototaxis, and geotaxis, scientists study aerotaxis, barotaxis, hydrotaxis, and magnetotaxis. Aerotaxis is movement in response to oxygen levels, barotaxis responds to pressure changes, hydrotaxis responds to water or moisture, and magnetotaxis responds to magnetic fields. These diverse taxis behaviors demonstrate how organisms sense and respond to various environmental stimuli for survival and adaptation.