the Does limited food resources affect the level of aggression in male crickets?
Phuong Lam
BIO 206, Spring, 2011
Unique # 48840, Mary-Kay Johnson
April 26th, 2011
Does the limited food resources affect the level of aggression in male crickets?
Abstract:
Limited of resources such as shelter, food, air, etc. could lead to many aggressive
behavior in animals, including crickets. Crickets have been used as great model
organisms for the aggressive behaviors. In this experiment, we have observed roughly
about 80 crickets on their aggressive behaviors based on food (variable group) and no
food (control group). Crickets were starved for a week before the experiment to see if
they were willing to compete for only one food pellet. Hunger can drives the crickets to
fight for their survival. The observations were recorded based on 6 behaviors such as
latency, antenna fencing, mandible spreading, mandible bite, wing movement, and
chirping during the contest between two male crickets. We hypothesized that limited
resource lead to more aggressive behavior in order to earn the food. Through out the
experiment, we observed that the one who did not get the control of food first tend to start
latency to fight for the food. However, the one with the control of food for the longest
time seemed to be more aggressive in order to protect his resource. They are what we call
the winner. Although we saw more aggressive behaviors on the graphs if limited
resource (food pellet) was involved between the two male crickets, the T-test of the data
has shown that there is not enough evidence (statistically insignificant) in the experiment
to prove that level of aggressive behaviors in crickets due to limited resources.
Introduction:
Crickets aggressive behaviors have been observed for many years
(Alexander, 1961), (Rillich, et al., 2007). Crickets are very convenient models for
observing aggressive behavior because not only do many species compete for limited
territory, food, and shelter (Hsu, 2006), but they can also display highly aggressive
agonistic interactions. Several noteworthy communication methods are displayed during
fighting including antennal fencing, mounting, spreading of the mandibles, and
mandibles biting (Alexander, 1961), (Briffa, 2008), (Brown, 2006), (Hofmann,
Stevenson, 2001), (Stevenson, et al., 1999), (Tachon, et al., 1999), which carry both
motivational signals as well as signifying their strength. Other displays observed during
combat include body jerking and a rivalry song. Different species differ in the sequence
of agonistic behavior, some displaying these behaviors only for competition for survival
resources or mating, and others escalating in an encounter with other males or while
being isolated for a period of time (lab manuel). Interestingly, frequent competition
between male crickets is an essential factor that has led to these types of agonistic
behaviors over time (Hack, 1997).
Since the most important resources to crickets are territories, food, and mating
partners and when the number of resources in the population decreases, the value of their
territory and willingness to defend it is more likely to increase (Hofmann and
Schildberger, 2001). We carried out an experiment to see the level of aggression if there
was limited food resource. In our experiment, we hypothesized that in the cricket species,
Acheta domesticus, aggression level increases if they must compete for limited resources.
Methods and Materials:
In our cricket experiment, we had total of 84 male crickets. These crickets were
isolated and starved for about one week before the experiment. The crickets with colorcoded on the top of their heads to help us distinguish different crickets when we recorded
data. The observation sand-covered arena (which was a big clear box with compartment
dividers) was provided as a location for the contests between these crickets. We had a
control group, which was no food, and a variable group with food pellet. Half of the
experiment, which totaled of 42 crickets, was for contests without food and the other half
was for fights with limited food. We prepared an Excel with different sections for
observed behaviors for data recording. These observed behaviors included latency,
antenna fencing, mounting, mandible spreading, mandible bite, chirping, and wing
movement. We did not weight and measured the length of the crickets before the crickets
encounter to ensure that no external factors affect the experiment results. Due to some
unexpected circumstances, few crickets died during the experiment. Therefore, we ended
up with less crickets for the experiment then we were given. We got data from 20 sets
with-food contests and 19 with-no-food contests.
For limited food resource contests, we placed two male crickets in separate
compartments and allowed them to acclimatize the surrounding for about 1 minute. After
a minute has passed, we removed the divider and immediately dropped in the food pellet.
The observation for the contest between each set of crickets was about 5 minutes long.
Then we observed the encounter between those two crickets and recorded down the
behaviors that listed above. After all the with-food-contest was completed, we then did
the same steps for no-food tests except with no food pellet. The crickets were removed
from the arena and we measured the weight of each on the top loading balance and the
length with standard metric ruler.
Results:
Before I analyzed the results of my experiment, I carried out two tests:
Kolmogorov-Smirnov and T-test. First, I used Kolmogorov-Smirnov Comparison of two
data sets to test the normality of the data. Based on the result of the K-S test, it shows that
our data is not normally distributed (K-S test p-value for food is 0.00 and p-value for nofood is 0.04). However, to increase power of our analyses, I chose parametric tests. I used
an unpaired T-test to examine cricket behaviours with respect to food vs. no food.
The calculation was determined to compare the results between the two data, food
vs. no food total aggressive acts. The variable group with-food has the total aggressive
acts with mean of 10.5 and standard deviation is 6.73. For no-food total aggressive acts,
mean = 8.13 and stdev = 6.51. Based on the T-test result, the variable group with food is
not statistically significant (T-test, t-value= 1.66, 76 p-value= df, 0.122) compared to
control group of no food.
Even though, the T-test shows that with-food total aggressive acts is not
significant, the following graph somewhat shows that there is some difference between
groups of food vs. no food. The bar graph shows the frequency of aggressive acts and the
lines above the bars represent the error or standard deviation away from the mean. Figure
2 is graph on specific aggressive acts, antenna fencing. This also shows that with limited
resource, they tend to show more aggressive behavior, specifically antenna fencing.
Figure 1: shows the mean of aggressive acts (y-axis) with food and no food (x-axis)
Figure 2: the mean of antenna fencing (y-axis) with food and no food (x-axis)
Discussion:
Crickets behaviors for different reasons such as food, shelter, mates, etc. have
been studied and observed by many scientists and researchers. In this experiment, we
performed an experiment that similar to many that have been done to show if the levels of
aggression in crickets increase if they have to compete for limited resources. Based on
the result of T-test (students t-test, t-value= 0.122), 0.122 is greater than 0.05 (level of
significant). Therefore, the data is not statistically significant and we fail to reject the null
hypothesis that the level of aggression is not due to the limited resources. This result is
the opposite of what we expected. However, there could have been possible errors that
affect the results during the experiment. First of all, two crickets unexpected died and
some group provided missing data; therefore, the numbers of sample size were actually
smaller than what was planned. Secondly, there could have been possible errors while
observing the behaviors of crickets such as miss counted the different behaviors and
misheard the chirping of the crickets due to the loudness in the room. Also, the behaviors
of crickets were observed by different students, thus, each of us could have interpreted
the behaviors slightly different.
Throughout the experiment, we have observed that cricket, whose in possessed of
food tend to be more aggressive to protect his asset against the other cricket, who wanted
to get control of the food pellet (Nosil, 2002). Another point that showed the trend for the
winner, who had the control of the food longest, was if he had the acquired the food pellet
first (Nosil, 2002). Contemporary sociobiological and behavioural concepts envisage the
complex escalating fighting strategies characteristic of intraspecific aggression as having
evolved in order to enable an individual to secure limited resources at minimal cost
(Rillich, et al. 2007). Antennal contact between the crickets usually triggers the
aggressive behavior (Kaushik, et al., 2009). The crickets recognize the opponents by
chemicals they secrete (Ghosal, et al. 2010). We observed the escalating sequence of
aggressive behaviors when the crickets encounter each other. These escalating sequence
included from antenna fencing, body rocking, chirping, flaring of the mandibles, and
wresting/mounting (Tachon, et al., 1999), (Leslie and Walker, 2007). We noticed that the
losers in the contests tend to try to escape avoiding contact with the dominant male.
(Ghosal, et al. 2010). The owners probability of winning the contest will be grater when
the value of the resource is greaterthe costs of contest would rise for both individuals
as the value of the resource increased. (Buena, Walker, 2008)
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