AP Biology Lab 11
Animal Behavior
The Effect of Different Stimuli on Isopod Behavior
April Clark
09/11/08
AP Biology
Mrs. Clark’s awesome class
Abstract:
There were three main purposes for this investigation. First, isopods were
observed so behavior and structures could be recorded. Then the isopods were exposed
to two different scenarios, wet vs. dry and acidic vs. neutral, to determine which
environment they preferred. In the different scenarios, a total of 10 pillbugs were placed
in choice chambers with different environments and observed for 10 minutes. It was
observed that the pillbugs preferred wet conditions over dry and acidic conditions over
neutral. The pillbugs displayed taxis behavior in both scenarios.
Theory:
Ethology is the study of animal behavior. An animal’s behavior is its response to
sensory input. There are three types of behaviors: orientation, agonistic, and mating.
Orientation behaviors take the animal to its most favorable environment. Taxis is then an
animal moves toward or away from a stimulus. Taxis is often observed in response to
changes in light, heat, moisture, sound, or chemicals. Kinesis is random movement and
doesn’t involve stimuli. Agnostic behavior is when animals respond to each other in
aggressive or submissive movements. An example would be when the hair on a dog’s
back stands up when it is being aggressive. Mating behaviors are activities that involve
finding, courting, and mating with a member of the same species. An example would be
a peacock fluffing up its feathers to attract females. (AP Lab Manual)
To observe animal behavior in this lab, isopods will be isolated in a controlled
experiment. Terrestrial isopods are more commonly known as pill bugs, rolly pollies,
potato bugs, or sow bugs. They are crustaceans with a hard exoskeleton, seven pairs of
legs, and antenna. Isopods are related to lobsters, crabs, and crayfish. Some roll up into
a ball when disturbed, while others crawl away quickly. They generally eat decaying
wood, leaves, and other vegetation. Isopods breathe with gills, so they are restricted to
areas with high humidity, under rocks or logs, in leaf litter or in crevices. They prefer
darkness as well. (Pillbugs)
Figure 1 (Pillbugs)
Hypothesis:
When isopods are exposed to wet and dry conditions, they will prefer to stay in
the wet environment because they are used to living in dark, moist conditions. When
isopods are exposed to acidic and neutral conditions, they will prefer the acidic
conditions because they are usually found in soil and the soil in this area is slightly
acidic.
Materials:
The following materials were used in this experiment: pill bugs (isopods), Petri
dish, connected chamber, water, pipette, filter paper, timer, magnifier, paint brush, dilute
hydrochloric acid.
Procedure:
1. Place isopods in a Petri dish and observe them for 10 minutes. Handle the
isopods with only a paint brush. Record any observations that are
characteristic to the bugs. Sketch a drawing of one isopod.
2. Place filter paper on both sides of connected chamber. Add water to one side
of the chamber until the filter paper is damp. Add the isopods to the
chambers. Observe how many isopods are in each chamber. Record the
number of isopods that are in each chamber every 30 seconds for 10 minutes.
3. Place filter paper on both side of the connected chamber. Add 1%
hydrochloric acid to one side of the chamber until the filter paper is damp.
Add the isopods to the chambers. Observe how many isopods are in each
chamber. Record the number of isopods that are in each chamber every 30
seconds for 10 minutes.
Data/Observations:
1. General observations:
a. Larger isopods climb over smaller ones
b. Move fast
c. Tend to move as a group
d. Movement around edges
e. Use antenna to sense edge and other isopods
f. When flipped over will either play dead, roll up, or kick off from
ground to turn over
g. See attached drawing of isopod
Table 1 - Isopod taxis in wet vs. dry
Time
(minutes)
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
10.0
Number of isopods
in wet chamber
5
9
8
8
9
10
9
7
9
9
8
7
9
7
7
7
8
9
7
8
9
Number of isopods
in dry chamber
5
1
2
2
1
0
1
3
1
1
2
3
1
3
3
3
2
1
3
2
1
Average isopod number in wet chamber = 8
Average isopod number in dry chamber = 2
See attached graph.
Observations
Climbing on top of each other
4 in one pile along edge
Movement slowed down
Large sitting groups
Little movement
Table 2 - Isopod taxis in acid vs. neutral
Time
(minutes)
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
10.0
Number of isopods
in neutral chamber
5
7
6
4
5
3
3
2
3
4
4
1
3
2
1
0
1
0
0
0
0
Number of isopods
in acidic chamber
5
3
4
6
5
7
7
8
7
6
6
9
7
8
9
10
9
10
10
10
10
Observations
Backing away from acid
More movement on acid
Clustering into group
Less active
Little movement
Average number of isopods in neutral conditions = 4.1
Average number of isopods in acidic conditions = 5.9
See attached graph.
Analysis/Discussion:
In this investigation there were several variables. The independent variables were
the different conditions in the chambers. For the first experiment, the independent
variables were the wet and dry conditions. In the second experiment, the independent
variables were the acidic and neutral conditions. For both experiments, the dependent
variable was the isopod behavior. The main control for this experiment was the initial
observation. The kinesis observed at this time was used to determine if the isopod
behavior in the two experiments was truly taxis behavior in response to the different
conditions. Other controls include using the same amount of bugs, using a timer, using
the same chamber, and using similar textures in the chambers.
In the first experiment, the isopods preferred the wet conditions. This is probably
because this is closer to their natural habitat. Isopods use gills, so they need moist
conditions to survive. In the second experiment, the isopods preferred the acidic
conditions over the neutral conditions. This is probably due to the fact that they live in
soil and under logs, which are acidic conditions. They must need this type of
environment to maintain homeostasis.
In the first experiment, other groups in the class got various results. This could
have been due to different wet conditions. The isopods may avoid an area if it is too wet
and this would skew the results. The class didn’t compare data from the second
experiment.
Isopods locate appropriate environments by using their antennae. They used their
antennae at all times while mobilizing around the chambers. They must rely on antennae
over eye-sight.
If you suddenly overturned a rock and found isopods, the expected behavior
would be for them to move around quickly. Eventually, the movement may slow down.
It is likely that they would continue to move until they found another moist, dark
environment.
I would classify the isopods movement in response to a wet environment as taxis.
They eventually slowed down their movement, with most settling on the wet side.
Conclusion:
In this investigation the behaviors of isopods were observed and investigated.
The isopods preferred the wet environment because their normal habitat is moist. My
hypothesis was proven correct.
In the acid vs. neutral experiment, it was observed that the isopods preferred the
acid conditions. Most soils in forested areas are acidic. Again the isopods chose the
environment that was closest to their natural habitat. The hypothesis stated was correct.
Since the classroom data wasn’t consistent during the wet and dry experiment, a
larger sample size is probably needed. The larger the sample size, the more likely the
data will represent true isopod behavior. In addition to sample size, the isopods could be
observed for longer periods of time to get more accurate data.
References: