Social insects such as ants use the direct transfer of behavioral chemicals
to regulate many aspects of colony life. When ants meet, they will regurgitate
a small amount of their gut contents and exchange it with the other ant.
This is called trophallaxis. In some ant species, a behavioral chemical
identifies the members of an ant colony as nest mates. In others, the type
of food exchanged identifies members of the colony (you are what you eat!).
When meeting a member of another nest, battle may occur; this reduces competition
for resources in the area. The pavement ant, Tetramorium caespitum
L. (Hymenoptera: Formicidae) is a common ant species. It lives in cracks
in the pavement of sidewalks and roads, and incidentally in the cracks in
basement floors (a good source of ants even in winter). It conducts fierce
battles with other colonies. We have collected ants from two colonies of
pavement ants. We have also collected from a colony of pharaoh ants, Monomorium
pharaonis (L.) (Hymenoptera: Formicidae). Any other combination of ant
species will do, but these are common household pest and relatively easy
to find, even in winter. In this lab we will examine what happens when ants
from different colonies meet.
Materials
1 stereozoom microscope.
3 petri dishes with 10 ants each.
1 data sheet per group.
1 stopwatch per group (optional).
Procedures
Each lab group will be given five ants each from colonies of the two
species in covered petri dishes, and ten ants from the other pavement ant
colony in another dish. This dish serves as a "control" (who knows...maybe
they just like to fight!). Observe the ants in each dish under your microscope.
Do they fight? If they do, how would you describe the action? Learn to recognize
each species; it helps to give them a name of your own design! Begin recording
data on the behavior of the ants by having each member of the group observe
the control dish (i.e. the one with ten pavement ants) for 30 seconds. Members
of the group should time the other members by using the stopwatch provided
(or by counting slowly to 30). Record the number of ants observed fighting
on the group data sheet provided under the CONTROL column. [Note: Record
the number of ants fighting, not the number of fights, since some fights
may involve more than two ants.]
Next, take five of the pavement ants from the control dish and place
them in the pharaoh ant dish (this in an interspecific meeting, i.e. between
different species). Place the remaining five pavement ants from the control
dish into the other pavement ant dish (an intraspecific meeting, i.e. within
the same species). Observe the activity of the ants in each dish. Do they
fight? Again, how would you describe the action? Take turns observing the
ants in each dish for a 30 second period. Record the number of ants engaged
in fights during your 30 second observation on the group data sheet provided.
Be careful to record your observation under the appropriate column, either
INTERSPECIFIC or INTRASPECIFIC.
Report your results to your instructor who will prepare a "scattergram"
of your data on the computer. While waiting to report, you may continue
to observe the ants, but don't change your data! Once we have all the data
recorded, the groups should put away the microscope and ants. The next problem
is to devise a way to consolidate the data within each group and compare
the behavior of the ants when confronted with members of their own colony
(CONTROL), another colony of the same species (INTRASPECIFIC), and ants
of another species (INTERSPECIFIC).
If a different number of ants were used by some of the groups, could
your group's measure be used to compare results between groups?
One of the things that students will probably note as they record the
data is that some individuals and groups see very few fights, even in the
interspecies meetings, while others seem to see fights everywhere they look.
This is normal since this type of data tends to fit a normal distribution.
If you have enough students (about 20 minimum), and the students seem
ready for it, try plotting the data from the interspecific meetings as a
frequency distribution. To do this, plot the number of students observing
0, 1, 2...8, 9, and 10 ants fighting during their interspecific observation
on the graph provided. This can be easily done with a show of hands...i.e.
ask,"How many observed zero ants fighting?" Plot the number of
students responding above zero on the x-axis; repeat for two fighting, three
fighting, etc. [Note: the number of students observing one ant fighting
will be zero, since an ant can not fight with itself.]
With enough data points, you should end up with a bell shaped histogram,
with most students clustered around the mean number of ants fighting, and
relatively few at either extreme. You can use this exercise to explain the
importance of repeated observations and the use of averages to describe
data. With advanced classes, you might introduce the concept of variance
and standard deviation as a measure of variability around the mean.
Variance
The variance is the most basic measure of variability. It is the average
of the squared deviations from the mean. To compute it, you first compute
the mean number of fights (from the table above), then subtract the mean
from each of the student observations, square each result, add them up,
and divide by the number of observations.
Standard Deviation
The standard deviation is the most frequently used measure of variability.
To compute the standard
deviation, simply take the square root of the variance. One of the questions
you will undoubtedly get is, "why do we have to square the deviations?"
Have the students try computing the average of the deviations without squaring
them first. It will invariably sum to zero since the mean is by definition
the mid point of all the observations. Deviations above and below the means
cancel each other out.
The most valuable variation on this lab will probably be the elimination
of the interspecific comparison. This make the collection of the ants much
easier, and still provides the basic comparison between colonies (in this
case colonies of the same species). This will work for most ant species,
but not all species. for example, the pharaoh ant is notoriously nonagressive
toward other colonies of pharaoh ants. This variation also allows the lab
to be performed in less time.
An interesting variation of the experiment would involve repeated collections
of pavement ants over several days from two competing colonies. Set up petri
dishes pairing the two colonies by day. Since colony recognition relies
on exchange of behavioral chemicals provided by the queen or differences
in food being exchanged, ants removed from the influence of the queen for
several days and fed on the same food material should not display aggression
toward the other colonies. You could even design experiment that tested
whether nestmate recognition was behavioral chemical based or food based
by replicating the experiment described above, but providing each colony
with different food supplies. If aggression was retained in combinations
fed on different foods, but lost when fed on the same foods, chances are
it is food based nestmate recognition.
Some of these variations on the basic experiment may be too complex for
use in a class situation, but might make excellent science fair projects
for some students.
One of the most controversial areas of study in biology today is sociobiology,
the objective study of social interactions from a biological basis. Sociobiology
is an extension of the "Nature vs. Nurture" debate, reinvigorated
by the work of E. O. Wilson in the mid-1970's. It attempts to answer questions
about the nature of social interactions (including human social interaction)
by applying basic biological principals. Since Wilson is an entomologist
who specializes in ants, it would be very appropriate to extend this exercise
into the social studies class. As background, Fisher (1991) gives an excellent
overview of sociobiology, its origins, and the nature of the comnflict it
has engendered. It should provide enough information on sociobiology to
suggest an appropriate curriculum.
With regard to art, ants are frequently used in works of art. For example,
M. C. Escher's famous wood block print, Mobius Strip II (Red Ants), provides
an opportunity to explore math concepts (e.g. topology) in an artistic format.
Another possibility would be to have students construct anatomically correct
works of art focusing on the ant, or other appropriate insects. Scientific
illustration is an exacting and fascinating field of art that is often overlooked
in our art curriculum.
If you have the computer available, the program SimAnt provides
an excellent simulation of ant battles for territory. It integrates some
neat graphs and a excellent database of ant facts. It was inspired by Bert
Holldobler and Ed Wilson's (1990) Pulitzer Prize winning book, The Ants.
The attached exercise might be an good adjunct to this lab.
Mission Impossible?
Good Morning, Jim. We have recently learned that a colony of red ants
has invaded the territory of a black ant queen friendly to our government.
With the assistance of an excellent simulation of ant life, SimAnt,
you can become a "leader ant" in the colony of black ants. Your
mission, should you choose to accept it, is to lead the colony in an all
out effort to eliminate the red menace that shares your habitat. To do this
successfully, you will have to think like an ant and utilize all of your
instinctive abilities. You have at your disposal legions of sister ants
(assuming you can convince your queen to produce them, and you keep her
well fed), alarm and trail marking pheromones, and an unlimited number of
lives in which to accomplish your goal. As always, should you or any of
your IM force be caught or killed, the Secretary will disavow any knowledge
of your actions. . .this lab handout will self-destruct in five seconds.
Procedure
Sign up for a block of time on the computer. About one hour should be
plenty of time.
We would anticipate that the pavement ants will fight with the ants of
a different species (interspecific), and will probably fight with members
of another pavement ant colony (intraspecific), but will not fight with
members of their own colony (control). If you reverse the experimental design
and test pharaoh ants with members of another pharaoh ant colony, they probably
will not fight. This is related to the way in which they produce new colonies.
. .by budding. That is, a group of worker ants will pick up some of the
brood and move to a new location, raising a new queen from the brood. In
a sense, pharaoh ant colonies in the same general area are kind of a super
colony. On the other hand, pavement ants are notoriously aggressive, waging
massive battles with any competing colony regardless of species. Again,
you may use any combination of species within the experimental design, but
(as noted for pharaoh ants above) the results depend on the species involved.
There are at least three valid measures describing group results: the
average number of ants fighting, the total number of ants fighting, and
the percentage of ants fighting. There are likely to be others that are
not so obvious! You will have to judge their validity on a case-by-case
basis. Try to have the students determine if their measure can be used to
compare groups of data based on unequal numbers of ants, and why.
Generally speaking, the total can be used to compare observations between
groups with the same number of observers and the same number of ants. If
the number of observers is different between groups, the total will not
work, and the average becomes the proper statistic for comparisons. Finally,
if the number of ants in the experiment varies between groups (e.g.,
some petri dishes have only eight or nine ants. . .some do escape occasionally),
then the percentage of ants fighting is more appropriate.
Fisher, A. 1991. A new syntehsis comes of age. Mosaic 22 (Spring):2-17.
Holldobler, B; Wilson, E. O. 1990. The Ants. Harvard Univ. Press:
Cambridge, MA. 732 pp.
Group Member |
Control |
Intercolony |
Interspecific |
|---|---|---|---|
| 1 | |||
| 2 | |||
| 3 | |||
| 4 | |||
| 5 | |||
| 6 | |||
| 7 | |||
| Group Result |