Behavior Lab Exercise
Bi253
PSU
(a)
(b)
Figure 1: A generalized isopod (left, a) and The Common Pillbug (right, b)
May 2013
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Introduction
Gas exchange in terrestrial isopods is via modified
gills associated with abdominal appendages. These
gas exchange organs are transitional between gills and
There are two parts to this lab exercise. In the first lungs, and different experts use either term. As the
part we will observe the behavior of pillbugs relative gills or lungs are kept moist by a water transport systo habitat selection. In the second part we will look at tem, these organisms have managed, essentially, to
food searching behavior in crickets.
maintain an aquatic gas exchanger in a terrestrial environment. Pillbugs also never invented the waxy cuticle of insects, so they dehydrate quickly. Not surprisingly, terrestrial isopods are very picky about the
2 Background Information
dryness of their habitat, and we might expect them to
be very good at finding humid spots and rejecting dry
2.1 Pillbugs
spots.
Pillbugs are isopods, in the same class of crustaceans
(Malacostraca) as crabs, lobster and shrimp. While
Crabs and their relatives are decapods, pillbugs are in
the order isopoda. Although many isopods have invaded terrestrial habitats they are still closely tied to
water and found largely in very moist environments
such as the underside of rocks, rotting logs and so
forth. Many isopods have a defensive behavior of
rolling up when disturbed, which protects the more
vulnerable parts of the animal. Cylisticus convexus can
roll up completely into a ball while other species such
as Trachelipus rathkei can only manage a “C” shape.
2.2
crickets
Crickets are extremely successful orthopteran insects
that have been around since the Carboniferous (400
Ma). They do well in almost all habitats including
dry ones. The common house cricket, Acheta domesticus will be used for our exercise which involves food
choice or preference and motivational factors.
Crickets have multiple sensory systems to find food
and avoid predators. One of the most well studied
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cricket sensory system involves hair-like appendages
on the rear cercal segments that move in response to
air acceleration. A predator strike causes rapid acceleration, different from air movement due to wind or
air movement in response to the cricket’s own locomotion. Interestingly, air movement due to a door opening
is similar to a predator strike and cockroaches, which
have the same system, are very good at disappearing
between the time you open the door and switch on
the lights! Crickets also have good vision and very
good hearing, which they take advantage of relative
to mating calls. Male crickets chirp and so attract female crickets. How do crickets find food? Antennae
are modified appendages that are covered with sensory
hairs. Many of these are chemoreceptors that capture
airborne molecules. Such sensilla are “multiporous” in
that there are many microscopic holes to allow odorant
molecules to enter. In addition the maxillary and labial
palps near the mouth are also full of sensory bristles,
used for contact chemoreception. Contact sensilla are
typically “uniporous” with one hole at the end. The
palp bristles are touched to the surface so molecules
can flow into the hole permitting the cricket to taste
the substrate.
on the question you are addressing, but also depends
on what is practical in a given observational setting. It
is always important to consider the best method and
then stick with it. Even if the technique is not perfect,
you should get some usable data. By changing techniques, though, it is possible to end up with data that
cannot be interpreted. Below are some of the standard
methods.
• Ad Libitum Sampling. This method is good for
reconnaissance, in which you are not sure what
to expect. In this case you record notes on everything you see. The problem with this method is
that you don’t control for time of day, hours of
observation, any particular animals and so forth.
So the results can be quite scattered. There is bias
in this sampling method because you are also not
controlling yourself! The other methods impose
some discipline to the sampling procedure, so you
get more consistent data.
• Focal Sampling. In this case you pick on one animal and typically pre-define a set of behaviors
that you will score. Every time the animal performs a behavior on the list you note that and the
time. When you prepare your list of behavior categories it is common to have a category of “other”
as you may not predict all the possible behaviors. For animals in the field, you would record
the time the animal enters your field of view, and
the time it leaves. Focal sampling would take
place for a pre-defined period of time, and then
repeated perhaps over multiple days.
Figure 2: A house cricket
2.3
• Instantaneous Sampling. With this technique you
record an animal’s behavior at a precise or set
time. You would set a timer and at each trigger time write down what the animal is doing.
You get data on the number of times a particular
behavior is happening and because the sampling
How Behavior is Measured
There are different standard techniques for animal behavior observation. Which technique you use depends
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intervals are constant it is easy to get good sta- 3 Pillbug Experiments
tistical data. This gets around the problem that
a given observer cannot be totally focused at all
times, for hours and hours. It is better to have 3.1 Pillbug objectives
50 accurate measures in a day, than a continuous
record which is biased by observer fatigue. As
with focal sampling you need a pre-defined set of The objectives of this section of the lab are as follows:
behaviors. The sample interval must be set before you start, and is appropriate for the animal.
• Observe and record the general behavioral charReconnaissance sampling may be needed to esacteristics of pillbugs. How much time do the
tablish this.
pillbugs spend stationary, hiding, or moving? Do
they tend to aggregate/associate or prefer to be
• Scan Sampling. This is a variation on Instantasolitary. Are there differences in behavior based
neous sampling where you scan over multiple inon size? If you elicit defensive behavior, how
dividuals in a field of view. This illustrates one
long does it take the Pillbug to resume its normal
additional advantage of Instantaneous Sampling
activity?
in that it allows scanning. At each time point
you can record what animal A, B, C, etc is do• Formulate a hypothesis about pillbug habitat seing which would not be possible for one observer
lection. Would you predict that pillbugs have
using Focal Sampling.
adapted to perceive and react to certain environ• All Occurrences Sampling. Here you concentrate
mental changes?
on a particular behavior and can ask how often
• Design and execute an experiment to determine
that behavior takes place. This is useful when you
how pillbugs respond to environmental changes.
are observing a group of animals and cannot identify individuals. For example, you might be interested in “dewlapping”, a behavior in which male
lizards produce a visual display to threaten in- 3.2 Pillbug procedure
truders and attract females. There might be a tree
with 20 lizards on it all moving about. With All
Occurrences sampling you could score the num- 3.2.1 General Observations
ber of dewlap behaviors in an hour, and divide by
1. Place several pillbugs in the behavior tray and
the number of individuals to get a measure of the
carefully observe them for at least 10 minutes. In
average time spent performing this behavior.
Table 1 in the Analysis section, document any behaviors you see. Remember to document even the
You should spend some time with your lab partners
seemingly unimportant behaviors. Try to docutalking about the best way to observe different behavment the behaviors observed in chronological oriors with pillbugs and crickets. There may not be just
der. Note: Do not disturb the pillbugs; shaking or
one “correct” way to get your data. Which method you
tipping the tray will cause unnatural behavior in
use should be documented, however, and you should
the pillbugs.
be consistent.
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• Hydrotaxis: The orientation of an organism in relation to the presence of water.
2. Taxis Experiments
(a) Place one piece of masking tape on either
side of the behavior tray and label one side
A, the other B.
First, formulate a hypothesis regarding environmental
preferences and how the pillbugs may react to dif(b) Place five pillbugs in each chamber of the
ferent conditions. Write this on the form provided in
tray.
the last section of this exercise. After this design an ex(c) Every minute for 10 minutes, count the
periment to test the environmental factor you were asnumber of pillbugs in each chamber.
signed. Explain your experimental setup in the Analy(d) Record your observations in Table 3 in the sis section.
Analysis section.
(e) Calculate the average number of pillbugs in
each chamber in the 10 minute time period.
Enter the results in Table 3.
• Phototaxis: To test phototaxis, vary the amount of
light the pillbugs are exposed to and record their
responses.
(f) Using the data from every group in the class,
calculate the class average for number of
pillbugs in each chamber in a 10 minute
time period. Enter the results in Table 3.
3.2.2
• Chemotaxis: To test chemotaxis, simulate an alkaline or acidic environment-place several drops
of either a weak acid or weak base on a filter paper on one side of the behavior tray. Think about
an appropriate contol for this experiment!
Experiment Formulation & Experiment Design
• Hydrotaxis: To test hydrotaxis, simulate a moist
environment-place several drops of water on a filter paper on one side of the behavior tray.
Your instructor will assign you one of three environmental factors that affect pillbug behavior. These environmental conditions elicit different types of pillbug
taxis.
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Cricket Experiments
The idea of the cricket experiment is to introduce different food objects and record the number of crickets
that begin eating the food at successive time intervals.
The food objects vary in the following ways:
• Phototaxis: The orientation of an organism in relation to the presence of light. Movement toward
a light source is positive phototaxis; movement
away from light is negative phototaxis.
• Chemotaxis: The orientation of an organism in
relation to the presence of a particular chemical.
Chemotaxis is universal in protozoa and most organisms; they avoid most chemicals and exhibit a
positive taxis to some weak acids.
• color
• smell
• familiarity
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• green colored food
• value (nutrient content)
• water substitute (gel). This is similar to the normal food but is only a hydration gel and has no
nutritive value
In addition, we will be interested in the parameter
of cricket hunger, that is, how motivated the crickets
are to seek out food. You will be able to select crickets
that have been deprived of food for different numbers
of days. Of course your hypothesis would be that the
longer the cricket is deprived, the greater is its motivation.
• food that has been plastic-coated such that it cannot be eaten and does not smell like food.
Finally, we will do an experiment in which one blob 4.2 Initial Equipment Configuration
of food is illuminated with a spotlight while a second,
equivalent blob of food is in the shade. Would you
1. Make sure your apparatus is connected as per the
expect well lit food to be preferred over dimly lit food?
figure, and that you can see the entire arena bottom from a comfortable seating position at the
mirror.
4.1
Equipment Needed
2. Switch on the spotlight and note the position of
the spot. It should be centered in the arena’s short
axis and about 1/3 of the way along the long axis.
Here is the gear you should find at your station:
3. Have your TA inspect your set-up to doublecheck that everything is configured properly.
1. A box that serves as a behavior arena. The box
has dark sides which makes the crickets more
comfortable and prevents them from being distracted by movements outside the box.
4.3
2. A mirror on a ring stand. You will observe the
crickets via the mirror. This minimizes the observer’s influence on the cricket’s behavior.
Procedure
1. Food Preference Experiment: When you are
ready with your first design plan, and have verified it with the TA, put two food choices in the
arena. Then transfer six crickets from their home
cage into your arena. As soon as you do this, start
the timer.... A good method is to have two students record the data. One student will be able
to see one blob of food and the other student the
second blob. This also minimizes errors because
the two observers can check each other. If there
is a third student in your group, that person can
record data as the other two call it out.
3. A light source on a ring stand. This is for illuminating one of the food sources. See procedure,
below.
4. A timer.
In addition, there are different batches of food:
• orange colored food
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3. What do crickets like to eat, and what is in cricket
chow gel cubes?
2. Hunger Days Experiment: Take one cricket from
the 1-day cage and place in your arena. Record
the position of the cricket every 10 seconds for
five minutes. At the end of the experimental trial
you should return it to the “retired” cricket cage.
Next take a cricket from the 3-day cage and repeat
the experiment. Although in this example you
were told to start with the 1-day crickets and then
move to the 3-day crickets, in fact you should randomize your selection. After you have tested one
cricket from each of the food-deprived days, repeat the series of experiments with a different set
of crickets. Overall you should repeat the experiment five times, so that you can have an average
of five data points for each food-deprived day.
4. Make a list of the different factors, environmental
and physiological, that would affect your behavior experiments. For example, what would you
expect if you made the environment colder. What
would happen if you were a female cricket with
eggs?
5. What sort of observer biases can you think of, for
example in terms of categorizing behaviors, and
are there strategies to obviate them?
Bibliography
3. Illumination Experiment: Here we will try to devalue one of the food choices by shining a light
on it. At the moment you add the set of six crickets to the arena, switch on the LED illuminator. It
should make a spot of bright light on one of the
food blobs.
4.4
1. Klein, Ulla (1981) Sensilla of the Cricket Palp. J.
exp. biol. 72: 217-227.
2. For a nice web reference on pillbugs see:
http://www.northern.edu/natsource/INVERT1/Pillbu1.htm
3. Everything you want to know about crickets can
be found on this web page:
Statistical Analysis
http://webs.lander.edu/rsfox/invertebrates/acheta.html
This part is not yet written. Maybe this year, maybe
not...
Forms and Tables Follow
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Study Questions
1. How do the sensory appendages of isopods and
crickets differ?
2. If you are interested in finding a place with high
humidity, you need a humidity sensor! Imagine
how an organism could construct such a sensor.
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Observations of Pillbug Behavior:
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Sketch of Pillbug:
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Pillbug Taxis
Time (min) number of pillbugs Side A number of pillbugs Side B
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Avg.
Class Avg.
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Experiment Formulation
Hypothesis:
Design:
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Pillbug Taxis with Altered Environmental Conditions
Condition Tested:
Time (min) number of pillbugs Side A number of pillbugs Side B
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Avg.
Class Avg.
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