Does Environmental Temperature Affect the Chirp Loudness (dB) of Gryllus assimilis?
Acoustic
signals are imperative to natural selection among crickets. In a study done by
Ulagaraj & Walker (1973), in which they studied the orientation of mole
crickets (Scapteriscus acletus and Scaperiscus vicinus) movement towards a
source of sound. They compared natural
and synthetic male calling sounds being played on speakers placed in a field of
mole crickets with speakers that produced no sound (controls). The results showed mole crickets from as far
as 100 meters away flying on or near the speakers where the calling songs were
broadcast being from. The controls
“caught” next to no crickets, further emphasizing the acoustic importance in
cricket communication.
The
chirping sound produced by a variety of common crickets is created when the
cricket elevates and rubs his wings together (Walker, 1969) creating many small
vibrations that occur with each beat of the wings (Bennet-Clark & Ewing,
1968). These chirps are often
synchronized among the species for mate selection as well as to ward off
predators (Velez & Brockmann, 2006).
The
vibrational movement of a cricket’s wings is a result of muscle contractions
(Ritchie, et al. 2001). These muscle
contractions in the wings are what determine the rate and loudness of a
cricket’s calling sounds. Since the
temperature can affect muscle movement, it could, in turn, have an impact on a
cricket’s ability to vary their acoustic signals (Ritchie, et al. 2001).
Ritchie,
et al., (2001) studied the female preference for male calling signals in the Drosophila montana. Their study showed the mean carrier
frequencies having a direct correlation with the temperature. They found that the carrier frequency of
chirps was more commonly associated with temperature variations in the males
but not in females. Since the quality of the male calling signal is what
determines the reliability of sexual selection (Andersson, 1994), crickets with
higher frequencies of chirp sounds would be more likely to be favored for mate
selection.
These
findings have led us to conduct an experiment that tests the impact of
temperature in relation to chirp loudness in G. assimilis. We hypothesized that G. assimilis will
chirp louder within a warmer environment than within an ambient temperature
environment.
Methods
Participants
The twenty-four crickets that were
used consisted of a mixture of adult male and female Gryllus assimilis. They were randomly selected from a
pre-existing environment within Pet World Warehouse Outlet pet store. Twelve
crickets were placed in each of two separate containers. The subjects were
tested between the hours of 12:00pm and 12:30pm Monday through Friday for one week. The crickets were already habituated to human
vocalization and activity.
Materials
Two 21.59cm
x 12.7cm x 13.97cm critter cages were used to house the crickets. Cardboard egg cartons were collected and
placed into each cage for shelter purposes and to prevent the crickets from
killing one another. Fluker’s Calcium
Fortified Cricket Quencher was the food source used daily to nourish the
crickets during experimentation. A
Traceable to Nist Calibrator Decibel Meter (part number: 981001448) was used to
read the decibels in which the crickets were chirping at a given time. Two Biotronette Mark III environmental
chambers were used to house the cricket cages in order to maintain stable, predetermined
temperatures for each cricket population.
Two Taylor digital thermometers (part number: 1455) were used, one in
each environmental chamber, to determine and maintain correct temperatures in
each chamber.
Procedure
The
decibel meter was obtained and calibrated according to the instructions within
its original box. It was calibrated to
94.0dB. Before any recordings were
taken, the decibel meter was set to the following settings: Range = low
(35-100dB); Response = slow; and C- Function.
After the
crickets were purchased, cardboard egg cartons were placed into each cage.
Twelve crickets were housed in the cage placed into the heated environmental
chamber. The temperature was set to 6 on
the temperature dial. Twelve were housed
in the cage placed into the ambient temperature environmental chamber. No lights were turned on within either
chamber and no timers were set. The
digital thermometers were each set to the “out” setting and placed near the
cage within each chamber. The crickets
were given 4 cubes per cage of Fluker’s Calcium Fortified Cricket Quench and a
few sprinkles of water. They were then
given 24 hours to habituate to their new environments and to allow the
temperature to rise within the heated environment. The temperature at test time within the
heated environment was 25 degrees Celsius and the temperature at test time
within the ambient temperature environment was 23 degrees Celsius.
The
recordings began the afternoon of Monday, March 23, 2009 and ended Friday,
March 27, 2009. The decibel readings
were recorded between the times of 12:00pm and 12:30pm each day. Prior to any recordings the decibel meter was
placed 5cm away from the cage within the heated chamber first (set to the
appropriate settings) for three minutes.
This three minute time period allowed the crickets to regain their
normal behavior after being disrupted by the noise from opening and closing the
chamber door and placing the meter next to the cage. After this three minute process, the
recordings were taken for one minute only when crickets chirped. The same process was repeated for the ambient
temperature cage in the other environmental chamber. After the recordings were finished each
cricket cage was given 4 cubes of Fluker’s cricket quench and a few sprinkles
of water to prevent dehydration and starvation of the animals. After data was gathered an independent T-test
was used to calculate the p-value to determine significance. This experiment was one tailed because past
research has lead to believe that crickets chirp more in warmer temperatures
than colder temperatures.
Results
Our
findings concluded that our hypothesis was not supported. However, there was significance in the
chirping loudness of crickets between heated and ambient temperature
environments (Fig. 1, p = 0.0008). The
heated environment ranked lower for cricket loudness (dB) (M= 73.7, SD
= 1.48) than the loudness within the ambient temperature environment (M=78.7,
SD = 1.84). The independent
T-test and the variance suggest that there was a significant difference between
the loudness of cricket chirping between the heated environment and the ambient
temperature environment. There was louder chirping from crickets within the
ambient temperature environment than within the heated environment.
Figure 1. Loudness of chirping by Gryllus
assimilis in relation to the type
of environment (room temperature M=78.7dB, SD= 1.84; heated M=73.7dB,
SD=1.48); Error bars reflect standard deviation.
Discussion
The hypothesis was not supported in
that the loudness of cricket chirps was not affected by warmer temperatures but
rather by ambient temperatures. Several
challenges arose during the limited duration of this experiment. Such challenges included maintaining
consistent environmental temperatures, maintaining a consistent quantity of
crickets, and maintaining a constant balance between male and female crickets
within each environment. Each of these factors may have influenced the results
of the experiment. It would have been
beneficial to have a prior working knowledge of the intended environmental
chambers as well as familiarity with cricket behavior if we were to repeat this
experiment.
Because the
loudness of chirps has been found to be more characteristic of male crickets
than female crickets (Ritchie, et al., 2001), an option for similar research in
the future may be to use only male crickets for a more accurate measure of
chirp loudness. Since our results indicated a significant difference in the
level of loudness in ambient (cooler) temperatures as opposed to in the warmer
environment, this might be an option for future research, as well.
It is possible that temperature may
not have an impact at all on how loud the crickets chirp, but rather the noise
of the outside environment may cause cricket chirping to be more noticeable, especially
at night.
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