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Tester Set

by: Lexie Hassien

Tester Set PSY418

Lexie Hassien

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Statistics and Research Design
Dr. Jarrod Lewis-Peacock
Class Notes
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This 12 page Class Notes was uploaded by Lexie Hassien on Thursday August 11, 2016. The Class Notes belongs to PSY418 at University of Texas at Austin taught by Dr. Jarrod Lewis-Peacock in Fall 2016. Since its upload, it has received 5 views. For similar materials see Statistics and Research Design in Psychology at University of Texas at Austin.


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Date Created: 08/11/16
Investigating the Latency Time of Male Crickets to Initiate Aggression in the Presence of a Female Alexa Hassien BIO 206L, Spring 2016 47375, Dr. Martha Maas and Dr. Hans Hofmann May 5 , 2016 Investigating the Latency Time of Male Crickets to Initiate Aggression in the Presence of a Female Abstract House crickets (Acheta domestica) are an effective model for studying the evolution and mechanisms of aggressive behavior. In this study, we measured the latency time of two male crickets to initiate aggressive action both by themselves and in the presence of a female cricket. It was theorized that latency time to show aggression would decrease in the presence of female, thereby indicating that direct competition for a mate could be an evolutionary explanation for male aggressive displays. For the purposes of this experiment, we looked specifically at the latency time of male pairs to initiate mandible engagement, an event that occurs during the stereotypical sequence of escalating aggressive behavior. The average latency time for male crickets to initiate aggression by themselves was 197.84 ± 97.91 seconds, whereas the average latency time in the presence of a female was 223.2 ± 107.58 seconds. A paired t-test comparison ofthetwodatasetsyieldedap-valueof0.8803.Sincethep-valueof0.8803>0.05,weconcluded that there was not sufficient evidence to confirma difference between the latency time of males to initiate aggression with and without a female. Introduction Animal behavior and communication are complex and intriguing processes. Male and female house crickets(Achetadomestica)both engage inspecificbehavioral patternsthat communicate theirintentions. Acousticcommunicationutilizessoundtosignalinformationfromoneindividual to another. In crickets, males produce songs by rubbing their forewings (elytra) against each other. Three distinct songs have been identified: the courtship song, calling song, and rivalry song. Female Phonotaxis and the Calling Song Numerous male species in the animal kingdom vocalize songs or calls to attract females (Ryan & Rand, 1990). In crickets, the calling song is regularly patterned, fairly loud signal that is used to attract females. While female crickets themselves cannot sing, they are attracted to this signal and will approach it in a directed orientating response toward the source of the song. This behavior iscalledphonotaxis. Females havethe abilitydiscriminatebetween male songsvariants such as carrier frequency, sound pressure level and chirp rate (Hirtenlehner & Römer, 2014). It is theorized that females may use these parameters of the male song as a cue to food resources within the male’s territory that they may be able to access by approaching his song (Judge, Ting, & Gwynne, 2014). Male Aggression and the Rivalry Song Overall aggressiveness and display patterns vary considerably across cricket species (Jang, Gerhardt, & Choe, 2008). While some species only rarely escalate to physical combat, others almost always escalate. Although crickets can perform a number of different behaviors during agonistic interactions, the actual fighting behavior can be characterized as an escalating contest following a more or less fixed sequence of events (Fig. 1). Figure 1. Pictogram of the stereotyped escalating sequence of tactics characterizing aggressive encounters between male crickets. Level 0, mutual avoidance: no aggressive interaction. Level 1, pre-established dominance: only one adversary shows aggression, the other retreats. Level 2, antennal fencing: fighting is initiated when both crickets lash with their antennae. Level 3, mandible spreading (unilateral): one contestant displays broadly spread mandibles and raised body stature. Level 4, mandible spreading (bilateral): both crickets spread their mandibles. Level 5, mandible engagement: physical fighting starts when the adversaries interlock their mandibles with which they push against each other. Level 6, grappling: the contestants repeatedly disengage and re-engage mandibles, struggle for position, bite each other and grapple with their foreleg claws to flip the opponent. Establishment: fights terminate at any level when the loser retreats. The winner produces the rivalry song and body-jerking movements (Rillich, Schildberger, & Stevenson, 2007). Several factors can affect the willingness of male crickets to initiate aggressive behavior. Interestingly, when males of A. domesticus are individually housed (isolated) for a number of days, they become more aggressive. Energy expenditure is another factor and an important cost shaping strategy in A. domesticus. Male house crickets can expend energyat relatively high rates when fighting depending on tactic performed. For example, acoustic signaling, also known as stridulation, is the least costly tactic, while grappling is the most energetically costly tactic (Hack, 1997b). The winner's total energy expenditure usually exceeds the loser's. House crickets generally resolve contests by assessing asymmetries in both body size and their relative use of costly tactics (Hack, 1997a). It has been shown that antennal fencing may be used to assess the fighting readiness of the opponent, while mandible spreading may indicate fighting ability or strength (Hofmann & Schildberger, 2001). In a mutual assessment scenario, both contestants assess their opponent’sresource-holdingpotential (RHP) relativetotheir own, withthe selective advantage that the one with the lower RHP can quickly terminate the contest and thus reduce time, energy and risk of injury from engaging in a contest that it would inevitably lose. Variation in the abilities of contestants to assess resource-holding potential also influences fighting behavior (Arnott & Elwood, 2009). The experience of each cricket during aggressive contests often affects behavior during, and the outcome of, later contests (Hsu, Earley, & Wolf, 2006). Once a fight between two crickets has been decided, there is a winner and a loser. The rivalry song, also known as the aggressive or triumph song, is a very loud trill that is produced during combat or once a winner has been decided. While winners will usually show increased aggressive motivation and be more likely to win their next encounter (“winner effect”), losers will avoid interactions with other individuals for some time (“loser effect”). However, there is evidence to support several methods that effectively restore aggression in cricketsafter defeat. Aggressiveness recovers significantly when cricketsare allowedtoflyfora shortperiodoftime afterlosingacontest(Hofmann&Stevenson, 2000). Flying enhances aggressiveness by reducing disparities in motivation (Rillich et al., 2007). Ithasbeenshownthatbiogenicaminessuchasdopamineandoctopamine playinimportantrole in aggressive motivation after defeat. The activation of the octopaminergic system that accompanies flight is proven to facilitate submissive behaviors and decreased aggression (Stevenson, 2005). Octopamine can thus be considered as setting the motivational level of aggression(Stevenson&Schildberger,2013).Itfollowsthatinhibitingoctopamineanddopamine synthesis restores aggressive behavior (Rillich & Stevenson, 2014). Aggression and the Courtship and Calling Songs The courtship song is used when a male cricket attempts to mate with a female. It sounds more like a scraping noise of low intensity. The calling song, mentioned earlier, is the regularly patternedsignalusedtoattractfemales.Thesesongshavebeenshown elicitaggressivebehavior betweennormallynon-aggressivefemalecrickets(Rillich,Buhl,Schildberger,&Stevenson,2009). In other words, the presence of a courting male induced female–female fights which included thesameseriesofcharacteristicactionsknownfrommale–malefights,exceptfortheproduction of the rivalry song. The following experiments are based on the ideas that aggression may be facilitated by the presenceoftheoppositesex.Intheseexperiments,thelatencytimeofmale-malepairstoinitiate aggression was measured with and without a female present. The purpose of this study was to investigate the relationship between male aggression and female presence to ultimately further the understanding of the evolution of aggressive displays in crickets. For the purposes of this experiment, mandible engagement was chosen as the key point to observe aggressive encounters because it is the first point in the aggression sequence in which the males physically touch one another. This would ideally make it simpler for the observer to identify the time in which aggression is initiated. We theorize that latency time to initiate aggression will decrease in the presence of a virgin female. Methods and Materials Control Twenty-twomalecrickets(Achetadomestica)wereisolatedseveraldayspriortotheexperiment. Behavioral trials took place between the evening hours of 6 pm and 10 pm. Each male cricket was assigned a number, and two crickets were chosen, using a random number generator, to participate in each trial. Each pair was placed in a medium-sized, clear plastic observation arena under ambient light and temperature conditions (~22°C). From there, the latency time to exhibit the mandible engagement stage of aggression was measured using a stopwatch. Mandible engagement was chosen as the key point to observe aggressive encounters because it is the first point in the aggression sequence in which the males physically touch one another. This would ideally make it simpler for the observer to identify the initiation of aggression. Each pair was observed for a maximum of 300 seconds. If the male crickets did not participate in mandible engagement, a latency time of 300 seconds was recorded. Addition of Female Crickets Afterrecordingthetimeit tookforthepairofmale cricketsto initiateaggression (or300 seconds for non-aggression), the plastic arena was shaken vigorously for several seconds to “recalibrate” thecrickets.Then,asinglefemalecricket(Achetadomestica)wasaddedtotheobservationarena (Fig. 2). Prior to the behavioral trials, the female crickets were stored in a group-housed container. The latency time for the two males to exhibit the mandible engagement stage of aggression was again measured using a stopwatch. After each trial, the female was returned to hergroup-housingcontainer,andthemaleswerereturnedtothenumbered,isolatedcontainers. Recalibration Maximum time of 300 seconds Maximum time of 300 seconds Figure 2. Set-up for each behavioral trial. Two male crickets were placed in an observational arena (left), and the latency time to initiate aggression was measured. After a brief period of “recalibration,” a single female was added to the same container (right), and latency time was measured again. Data Analysis A paired two-sample t-test was performed to determine the significance of the correlation between data sets. The 0.05 significance level was used to either reject or fail to reject the null hypothesis. Results Prior to behavioral trials, the body size (length in mm) was measured for each of the 22 male crickets. The average body size was 19.7 ± 1.1 mm. A total of 25 sets of behavioral trials were recorded for this experiment. It is important to note that during nearly half of all the trials, a latency time of 300 seconds was documented. This means that an aggressive encounter (mandible engagement) did not occur between the male crickets before the maximum observation time of 300 seconds (Fig. 3). The average latency time for male crickets to initiate aggression by themselves was 197.84 ± 97.91 seconds, whereas the average latency time in the presence of a female was 223.2 ± 107.58 seconds (Fig. 4). Frequency histograms of the latency times with and without the female show that both data sets are skewed left (Fig. 5). While the skewness of latency time to initiate mandible engagement without the female was -0.208, the skewness of latency time with the female was -0.850. A paired two-sample t-test was performed to determine the significance of the correlation between the two conditions. This test yielded a p-value of 0.8803. 350 Latency Time without Female (s) Latency Time with Female (s) 300 250 200 150 100 50 Latency Time to Initiate Mandible Engagement (seconds) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Trial Number Figure 3. The latency time to initiate mandible engagement was measured without the presence of a female and with the presence of a female cricket. Trials in which the latency time is 300 seconds signify that mandible engagement did not occur within the 300 second observation period. 350 300 250 223.2 197.84 200 150 100 50 0 Average Latency Time without Female Average Latency Time with Female Figure 4. Average latency time for male crickets to initiate aggression by themselves was 197.84 seconds, whereas average latency time for male crickets to initiate aggression in the presence of a female was 223.2 seconds. Error bars indicate one standard deviation above and below each mean. A B Figure 5. Frequency of latency time to initiate mandible engagement between two males without the presence of a female (A) and with the presence of female (B). Latency times with the female are more clearly skewed left. Discussion One of the first major observationsto be noted was the average latency time varied greatly from trial totrial. Both data sets showed abnormallylarge standard deviations that were nearlyhalf of their respective means (Fig. 4). It is also important to recognize that the skewness of both data setsreflectsthehighfrequencyoflatencytime300 seconds,the maximumtimeallottedfor each behavioral trial. Both of these outcomes indicate that not enough trials were performed to accurately reflect the tendencies of each condition or the maximum observation time of 300 seconds was not long enough to encompass longer latency times. Ultimately, more trials and a longer maximum observation time would be needed to yield more accurate results. There are several reasons why the crickets in these trials may have been unwilling to initiate aggression. A. domesticus is a gregarious species; the animals live in groups of usually five to 20 individuals in a relatively small space. Even though the male crickets were isolated beforehand to facilitate aggressiveness, it is possible that the isolation time was not sufficient for some individuals to become aggressive. It is also possible that potential energy expenditure was a contributing factor in the assessment of males to participate in aggressive behavior. Because crickets are ectotherms, they rely heavily on the heat of the environmental to fuel physiological processes. Both crickets could have theoretically assessed the costliness of energy expenditure and found it best to avoid aggressive encounters. It would be sensible to carry out a similar experiment in the future under different environmental conditions, such as under a heat lamp. A paired t-test of the two means yielded a p-value of 0.8803 which is vastly greater than 0.05 significance level. This means that there is weak evidence to support that the presence of a female has an effect on the latency time of males to initiate aggression, in this case mandible engagement. In other words, the current results do not definitely prove a difference between male aggression before and after a female is introduced. References Arnott, G., & Elwood, R. W. (2009). Assessment of fighting ability in animal contests. Animal Behaviour, 77(5), 991–1004. Hack, M. a. (1997a). Assessment strategies in the contests of male crickets,Acheta domesticus(L.). Animal Behaviour, 53(4), 733–747. Hack, M. a. (1997b). The energetic costs of fighting in the house cricket, Acheta domesticus L. Behavioral Ecology, 8(1), 28–36. Hirtenlehner, S., & Römer, H. (2014). Selective phonotaxis of female crickets under natural outdoor conditions. Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology, 200(3), 239–250. Hofmann, H. A., & Schildberger, K. (2001). Assessment of strength and willingness to fight during aggressive encounters in crickets*. Animal Behaviour, 62, 337–348. Hofmann, H. A., & Stevenson, P. A. (2000). Flight restores fight in crickets. Nature, 403(6770), 613. Hsu, Y., Earley, R. L., & Wolf, L. L. (2006). Modulation of aggressive behaviour by fighting experience: mechanisms and contest outcomes. Biological Reviews of the Cambridge Philosophical Society, 81(1), 33–74. Jang, Y., Gerhardt, H. C., & Choe, J. C. (2008). A comparative study of aggressiveness in eastern North American field cricket species (genus Gryllus). Behavioral Ecology and Sociobiology, 62(9), 1397–1407. Judge, K. A., Ting, J. J., & Gwynne, D. T. (2014). Condition dependence of female choosiness in a field cricket. Journal of Evolutionary Biology, 27(11), 2529–2540. Rillich, J., Buhl, E., Schildberger, K., & Stevenson, P. A. (2009). Female crickets are driven to fight by the male courting and calling songs. Animal Behaviour, 77(3), 737–742. Rillich, J., Schildberger, K., & Stevenson, P. A. (2007). Assessment strategy of fighting crickets revealed by manipulating information exchange. Animal Behaviour, 74(4), 823–836. Rillich, J., & Stevenson, P. A. (2014). A fighter’s comeback: Dopamine is necessary for recovery of aggression after social defeat in crickets. Hormones and Behavior, 66(4), 696–704. Ryan, M. J., & Rand, A. S. (1990). The Sensory Basis of Sexual Selection for Complex Calls in the Tungara Frog, Physalaemus pustulosus (Sexual Selection for Sensory Exploitation). Evolution, 44(2), 305. Stevenson, P. A. (2005). Octopamine and Experience-Dependent Modulation of Aggression in Crickets. Journal of Neuroscience, 25(6), 1431–1441. Stevenson, P. A., & Schildberger, K. (2013). Mechanisms of experience dependent control of aggression in crickets. Current Opinion in Neurobiology, 23(3), 318–23.


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