limited Does food resource affect level of aggression in crickets, Acheta domesticus?
Phuong Lam
BIO 206, Spring, 2011
Unique # 48840, Mary-Kay Johnson
April 26th, 2011
Does limited food resource affect level of aggression in crickets, Acheta domesticus?
Abstract:
Animals compete against one another for numerous reasons in order to survive.
Many agonistic displays in animals have been observed and studied for decades. One
good model to study the aggressive behaviors of animals is field cricket. In this
experiment, we observed 78 crickets, Acheta domesticus, on their aggressive behaviors
by manipulating the limited resource, a food pellet. We had a control group, which was
given no food pellet, and variable group, given one food pellet. The purpose of this study
was to see if the limited resource, food, would affect the level aggression in crickets. The
crickets were starved for one week prior to the experimentation in order to test if hunger
drove their motivation and willingness to compete for limited food pellet. The
observations during the encounters between two crickets were recorded based on
agonistic behaviors: antenna fencing, mandible spreading, mandible biting, wing
movement, and chirping. Throughout the experiment, we noticed that the one who had
the longest possession of food tended to show more agnostic behaviors; thus, he was
most likely to win. Although the means and standard deviations show that aggressive
behaviors tend to be higher in the encounters with food pellet, the T-test showed that
there is not enough evidence (statistically insignificant) in the experiment to prove that
the level of aggressive behavior in crickets was linked to limited food resource.
Introduction:
Crickets aggressive behaviors have been observed for thousands of years and can
even be dated all the way back to the ancient Chinese (Alexander, 1961; Rillich, et al.,
2007). In the last few decades, much research and many studies have been carried out to
observe the different aspects of the behaviors of different species of crickets and to
explain what drives those agnostic behaviors. Aggressive behaviors in animals can be
varied, complex and caused by numerous reasons. Crickets are convenient models to
study animal behaviors because they are small, easy to maintain, and can also be
manipulated in different ways. Aggressive behaviors in conspecific crickets tend to show
more frequently in males than in females (Alexander 1961; Tachon, 1999). Female
crickets compete against each other for mating when the males produce the calling songs
(Brown al et, 2007). Male crickets often compete against each other for multiple reasons
such as mating, limited food resources, and shelter (Hsu, 2006; Nosil, 2002). Although
aggressive encounters of crickets might benefit them in obtaining food or mates, they can
be very energetically costly. The agonistic behaviors could also harm crickets in many
other ways such as physical injuries and become easy targets for predation (Buena &
Walker, 2008; Arnott &Elwood, 2009). The motivation for crickets to enter a fight
depends on the scarcity of the resources and the opportunity costs of energy as well as the
benefits.
During encounters between the crickets, they assess their opponents motivational
state and fighting ability in order to decide if they should fight or take flight (Hofmann &
Schildberger, 2001). Several noteworthy communication methods are displayed during
the encounters including antennal fencing, unilateral mandible spreading, bilateral
mandible spreading, mandible biting, and mounting. (Brown, 2006; Hofmann &
Stevenson, 2001; Briffa, 2008). These agnostic displays escalate from one to another till
the crickets determine the winner and the loser. The winner shows more aggressive
displays such as jerking his body and rubbing his forewings against each other to creating
a rivalry song. He is most likely to dominate again in the future fight. The loser retreats to
avoid any more contacts with other crickets (Hofmann, et al. 2011). This feeling to retreat
and avoid other crickets, called the loser effect, can be reversed by the biogenic amine
octopamine (Stevenson et al., 2005).
Since the most important resources to crickets are territory, food, and mating
partners when these resources in the population become limited, their willingness to fight
or defend their possession is more likely to increase (Hofmann & Schildberger, 2001;
Nosil, 2002). Resource value has a key role in influencing an individual's aggressive
behaviour (Buena & Walker, 2008). Thus, we designed and performed an experiment to
test if the level of aggression would be higher if there was limited resource, food pellet.
The cricket models we used in this experiment were field crickets, Acheta domesticus.
Methods and Materials:
In the experiment, we tested a total of 78 male crickets, Acheta domesticus. We
had two different groups: the control group, which was not given a food pellet, and the
variable group, which was given one food pellet. . We hypothesized that with the limited
food resource, the crickets in the variable group would show more aggressive behaviors.
Our null hypothesis (H0) was there is no difference in the level of aggressive behaviors in
crickets whether there is limited food pellet or no food pellet. We wanted to test the
alternative hypothesis, which was that the presence of limited food resource had an affect
on the level of aggression. The control group was used to compare the result of the
variable group and see whether the crickets would be equally or more aggressive when
presented with the variable, food.
The male crickets were put in separate containers and isolated from each other to
prevent the experience-dependent (Rillich, schildberger, Stevenson, 2007). They were
also starved for about one week prior to experimentation. This step was necessary in
order to see if the hunger level increases the aggression of crickets and how that could
determine the success of the fight (Nosil, 2002). The crickets were color-coded on the top
of their heads to help us distinguish them when we observed and recorded the results.
The sand-covered arena, a big clear box with compartments separated by removable
dividers, was the location for the fight between two crickets (Figure 1). Half of the
crickets were used for contests with food and the other half was without food. The
behaviors that we observed were these: latency, antenna fencing, mounting, mandible
spreading, mandible bite, chirping, and wing movement.
Figure 1: Arena with separate compartments. Crickets are in the acclimation period of about 1
minute. Photo credited to Alyssa Acuna.
For the limited food resource contests, we placed two male crickets in separate
compartments allowed and them to become acclimated with the surrounding for about
one minute (Figure 1). After the acclimation period passed, we removed the divider and
immediately dropped in the food pellet. We observed the encounter between those two
crickets (which lasted about five minutes) and recorded the behaviors that were listed
earlier. These steps were repeated for the control group except no food pellet was
dropped into the arena. After the 5-minute observation of each contest, we removed the
crickets from the arena and measured their weights and lengths.
Results:
Based on the data recorded, the Kolmogorov-Smirnov Comparison test of two
data sets (food and no food) was carried out to test the normality of the data. The result of
the K-S test showed that our data was not normally distributed (K-S test, food p-value=
0.00 and no food p-value= 0.004). However, I chose parametric tests to increase power of
the analyses. The unpaired T-test was applied to examine the behaviours of crickets with
respect to the food vs. no food results. The calculations of the means and standard
deviations were also calculated to compare the result between the two groups.
Figure 2: The mean of total aggressive acts in male crickets, Acheta domesticus, is higher in
encounters with food pellet than without food pellet.
Figure 3: The mean of chirping is
Figure 4: The mean of aggressive
less in encounters without
act, antenna fencing, is higher
food than with food.
in limited food contests.
Figure 4: As the crickets had the more control of food, their total aggressive acts increased.
The mean and standard deviation of total aggressive acts are higher in contests
with food than contests with no food (With food: mean = 10.5 and stdev= 6.73; with no
food: mean = 8.13 and stdev= 6.51) (Figure 2). Few calculations for individual
aggressive acts such as chirping and antenna were also done (Figure 3, Figure 4) and
they both showed that the mean for aggressive acts increased in present of limited food
resource. Figure 4 showed that in the encounters with limited food pellet, the crickets had
the longer possession of food tend to show more aggressive behaviors.
However, the results of aggressive acts in the encounters with food were not
statistically significant when compared to the control group that had no food (student ttest, t-value= 1.666, 76 df, p-value= 0.122).
Discussion:
We performed an experiment that was similar to many that have been done before
to see if the levels of aggression in crickets would increase if they had to compete for
limited resource such as food. Based on the result of students t-test with the p-value of
0.122, which is greater than 0.05 (level of significant), we conclude that the data is not
statistically significant. Therefore, we fail to reject the null hypothesis that there is no
difference in the level of aggression in crickets whether there is a limited food resource
present or not. The result came out different from what we previously expected.
In the experiment, we observed that the crickets in possession of the food tend to
be more aggressive to protect his asset against the opponent, who wanted to get the
control of food pellet (Nosil, 2002). The aggression tends to escalate when the antennas
of the two male crickets come in contact (Ghosal, et al., 2009). Success of fighting can be
determined by the RHP, resource-holding power, as well as the value of resource (Nosil,
2002). The winner usually has spent more energy in fights than losers (Hack, 1997). Once
the winner of the fight has been determined, the winner performs a victory dance as well
as a rivalry song while the loser tries to escape the arena to avoid contact with the
dominant male cricket (Ghosal, et al. 2010).
Unlike the outcome of our experiment, other scientists have done similar studies
and concluded that when there is scarce of the resource, the level of aggression in crickets
would increase (Buena &Walker, 2008.) As the level of hunger increases, there is greater
fighting success in crickets (Brown al et, 2007.)
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