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Comportamiento de adaptacin del sonido en una especie de grillo (Orthoptera: Anastostomatidae) basado en un incremento de la interferencia de un coro natural hetero-especfico en San Luis, Costa Rica
Behavioral adaptability of calling in a species of cricket (Orthoptera:Anastostomatidae) based on an increase in interference from a heterospecific natural chorus in San Luis, Costa Rica
Orthoptera are among the first musicians on earth, and the deep evolutionary history of crickets involving acoustics has allowed them to greatly develop systems to produce and process such sensory information. This study attempts to contribute to the knowledge base of cricket behavioral biology through observation of changes in call
characteristics of a species of cricket based on an induced increase in heterospecific natural chorus complexity in
San Luis, Costa Rica. A chorus recording was used to induce such an increase in the complexity of the acoustic surroundings of the studied cricket in order to gain insight into how their call rates and song compositions are impacted. The results showed a decrease in calling activity(ANOVA: F = 3.09, df = 2, df Error = 126, P = 0.049), and a trend for the concentration of calls into fewer simple series of chirps during the period of increase in the
complexity of their acoustic surroundings. This suggests the ability and inclination for crickets to adjust their calling
behavior based on the calls of heterospecifics in order to most effectively and efficiently utilize singing activity, as
sound production is very energetically expensive.
Este estudio trata de contribuir al entendimiento de la biologa del comportamiento observando los cambios de las caractersticas de los sonidos de una especie de grillo como una respuesta al aumento de la complejidad de sus alrededores acsticos en San Luis, Costa Rica.
Text in English.
Crickets--Behavior--Costa Rica--Puntarenas--San Luis
Grillos--Comportamiento--Costa Rica--Puntarenas--San Luis
Tropical Ecology 2007
Heterospecific natural chorus
Ecologa Tropical 2007
Coros naturales heteroespecficos
t Monteverde Institute : Tropical Ecology
1 Behavioral a daptability of c alling in a species of cricket Orthoptera: Anastostomatidae based on an i ncreas e in interference from a heterospecific natural c horus in San Luis, Costa Rica Lee Kaiser Department of Zoology, University of Wisconsin Madiso n A BSTRACT Orthoptera are among the first musicians on earth, and the deep evolutionary history of crickets involving acoustics has allowed them to greatly develop systems to produce and process such sensory information . This study attempts to contribu te to t he knowledge base of cricket behavioral biology through observation of changes in call characteristics of a species of cricket based on an induced increase in hetero specific natural chorus complexity in San Luis, Costa Rica. A chorus recording was u sed to induce such an increase in the complexity of the acoustic surroundings of the studied cricket in order to gain insight into how their call rates and song compositions are imp acted. The results showed a decrease in calling activity ANOVA: F = 3.09, df = 2, df Error = 126, P = 0.049 , and a trend for the concentration of calls into fewer simple series of chirps during the period of increase in the complexity of their acoustic surroundings . This suggest s the ability and inclination for crickets to adju st their calling behavior based on the calls of heterospecifics in order to most effectively and efficiently utilize singing activity, as sound production is very energetically expensive . R ESUMEN Los organismos del orden Orthoptera fueron algunos de los primeros que produc ieron sonidos en este planeta. Esta historia larga de evoluc i Ã³ n acÃºsitca de los grillos propo rcionÃ³ una oportunidad para que se purdieron d esarollar mucho sus sistema de percibir y producir sonidos. Este estudio trata de contribuir al e ntendimiento de la biologÃa de comportam iento observa ndo los cambios de las caracterÃsticas de los soni dos de una especie de grillo como un a respuesta al aumento de la complejidad de sus alrededores acÃºsticos . Una grabaciÃ³n de un coro naturÃ¡l fue usada par a inducir un aumento en la complicaciÃ³n de los alrededores acÃºsticos del grillo , esto para aprender sobre la manera en que la tasa y las caracterÃsticas de los sonidos eran afectada s. Los result ad os mo stra ro n un a disminu ciÃ³n en la actividÃ¡d de l canto ANOV A: F = 3.09, df = 2, df Error = 126, P = 0.049 , y sus sonidos fueron concentrados mÃ¡s durante del intervalo de un aumento de la actividÃ¡d acÃºstica del coro . Estas observaciÃ³nes sugieren que existe la capacidad y la felxibilidad para que los grillos modifi que n el comportamiento de canto con refere ncia a los sonidos de los diferentes organismos para usar la energÃa mÃ¡s eficient e mente y eficazmente . I NTRODUCTION The distribution and evolution of Orthop tera reflects their ability to adapt to a variety of ec osystems and establish themselves in a suitable niche. Of the over 2000 extant species of stridulating crickets , all possess an extremely acute aptitude in perceiving and processing air currents Alexander 1962 . O f particular interest to a given cricket a re those produced by conspecifics for communication or by movements of interacting organisms such as the extension of a frogÂ€s tongue or the beating wings of a parasitic wasp. The precision involved in processing such sensory information and reacting in an appropriate manner allows crickets to accomplish a
2 wide range of necessary activities such as courtship, reproduction, predator avoidance, and territorial ity Alexander 1962, Greenfield et al . 1997, Jacobs 1995 , Mhatre and Balakrishnan 2006, Walker 1969 . With specialization and advancement of sensory systems among any organism come greater capabilities to perceive and react to stimuli suitably. Due to the high level of complexity in many natural choruses in various environments , crickets across global and even microhabitat scales are exposed to different levels of acoustic stimulants . Not only are they confronted with and therefore inclined to react to the calls of competing or cooperating conspecifics, but also those of heterospecifics Greenfield 1994 , Walker 1969 . Many crickets call in locations in close proximity to conspecifics, ref lect ing the benefi cial nature of this strategy in attracting females through synchronized calling , exhibiting superiority over conspecifics, or decreasing the ease with which an acoustic ally orie nting predator is able to locate a given individual Greenfield 1994 , Greenfield et al . 1997, Walker 1969 . Bailey and his colleagues calculated the energy efficiency of calling among several cricket species, with efficiency bein g the percentage of energy that is converted to sound by an individual during the calling process. The values they found for various cricket species ranged from 0.1 to 0.3 percent Bailey et al . 1993. As a result of this general inefficiency in energy use among crickets, they must be effective and wise in their calling habits Bailey 1995, Forrest 1982. By examining the changes in call characteristics of the studied cricket species based on an induced increase in allospecific natural chorus complexity, th is study attempts to contribute to the advancement in understanding the manner in which crickets respond to their environment. Due to the increased acoustic in ter ference , it would make it more d ifficult for a prospective female to distinguish and evaluate a maleÂ€s cal l in a more complex environment. The studied cricket doesnÂ€t move their calling locations much, and thus are relatively unable or unwilling to find a more appropriate site, demonstrating that they are subject to varying acoustic stimuli as the activity level of other organismÂ€s changes within and among any given evening. It would seem to be more efficient in terms of energy use for a male to call less often with simple acoustic surroundings, as a female would not need to hear as many calls to eff ectively evalua te and locate the calling male. As a result, I expect that a male cricket will call more frequently when they are located in a more complex chorus than they would when they have less acoustic competition. M ATERIALS AND M ETHODS This study was completed in Premontane Wet Forest on property that is part of Finca La Bella, located in San Luis, Costa Rica at an approximate elevation of 1100 meters BolaÃ±os and Watson 1993. This species of cricket is sparsely locate d along the two roads that r un through the development, and b ased on observation over a four week period, i ndividuals are always located in ag gregations of various sizes, therefore often call ing simultaneously. Their songs are composed of single chirps or those in series consisting o f anywhere up to 50 or more successive chirps, with their typical calling activity comprised of between 50 and 125 chirps per minute. Several recordings of heterospecific natural choruses that did not include the studied cricket species were taken w ith a Micromemo ipod microphone between seven and ten oÂ€clock in the evening in the forest, at varying distanc es from the forest farm boundaries , all of at least 30 meters . Recordings were in the form of .mp3 files and were transferred from the ipod to a PC lapt op for review. They were analyzed based on clarity of the recording , and ability to distinguish the differing types of calls produced by allospecifics comprising it . A best recording
3 was chosen from the set, and was of a chorus containing four distinguisha ble heterospecific call types that all differed in pulse and pitch . A given call type was produced by either a single individual or any number of neighboring conspecifics ; however no species identifications were completed for the organisms comprising the c horus. The optimal recording described above was transferred ont o a blank compact disc using a PC laptop, and was used in a Vivo Stereo CD Radio Cassette Recorder for playback . The studied crickets were detected by their call , and observations were complet ed between seven and eleven oÂ€clock in the evening . Wind conditions varied on a nightly basis, but no individuals were observed while it was raining or in a location where there was any other abiotic factor that could potentially interfere acoustically, su ch as moving bodies of water or a loud television from a nearby house. The calling rate of an individual before playback of the chorus reco rding was counted at the site during a two minute time interval determined using a handheld stopwatch. The calling r ate was defined as the number of individual chirps that were produced in the time period. After the calling rate was recorded on the data sheet , the Vivo Stereo CD Radio Cassette Recorder was used to play the two minute chorus recording at full volume on t he dial. The playback device was held at a distance between one and two meters from the individual being observed, and t he call rate was counted during playback without use of the stopwatch due to the recording being exactly two minutes long. After the CD player was turned off and the rate during playback was written on the data sheet, the call rate after playback was recorded . The time intervals in between observing calling rates before, during, and after playback were of vary ing lengths that were usually around fifteen seconds , but were always less than one minute. Data on the variability in the series of chirps produced by this species of cricket were also recorded for two minute time intervals before, during, and after playback of the chorus recording , i ndependent ly of the call rate observations . For the purposes of this study, ea ch time an individual produced a single chirp or a series of consecutive chirps that totaled five or less, it was considered a simple series. Any series composed of more than fiv e consecutive chirps was considered complex. The same procedure as above was used to collect this information, substituting the observation of calling rate with the number of simple and complex series. Each individual was utilized only once per evening , h owever, a given individual was revisited a few times over the course of the study. The total number of times an y given individual was observed is unknown. E ach aggregation of crickets was located in a given area along the road that was consistent on a nigh tly basis. However, the ir close proximity to one another and the fact that an individualÂ€s exact calling s ite within the given area was inc onsistent on a fine spatial scale created an inability to differentiate them without physically marking them, which w as not done. Data were grouped into sets, one of call rates, another for simple chirp series, and a third for complex series. A one way ANOVA statistical test was completed for each data set, utilizing the three time intervals before, during and after play back as the treatments. R ESULTS The calling rate of the studied cricket species during playback recording was si gnificantly lower than the rates obse rved before and after playback F ig. 1 . ANOVA: F = 3.09, df = 2, df Error = 126, P = 0.049.
4 F IGURE 1. Number of chirps produced during the singing activity of the observed cricket species before, during, and after playback of a recording of a natural chorus of heterospecifics in San Luis, Costa Rica . Data on the number of simple series of chirps for the three time intervals in relation to playback revealed a trend of fewer simple series during chorus playback, though the results wer e not statistically significant Fig. 2 . ANOVA: F = 0.93, df = 2, df Error = 42, P = 0.40 . T here was no trend apparent through ANOVA testing for the number of complex series produced during singing activity in relation to the three time intervals . However, nine of the fifteen observed individuals exhibited their highest percent of complex series during singing activity in the time period during chorus playback. Â€Std. Dev. Â€Std. Err. Mean # chirps 80 100 120 140 160 180 200 220 240 260 Before During After
5 Â€Std. Dev. Â€Std. Err. Mean TREATMENT # SIMPLE 0 10 20 30 40 50 60 Before During After F IGURE 2. Number of series of simple chirps produced throughout the singing activity of the observed cricket species based on two minute time intervals bef ore, during, and after playback of a recording of a natural chorus of heterospecifics in San Luis, Costa Rica . A simple series was defined as one that was composed of five or less consecutive chirps. D ISCUSSION Through observing the calling habits of t he studi ed cricket species in 58 total trials in San Luis, Costa Rica , a tendency towards behavioral adjustment to an induced increase in complexity of the surrounding heterospecific chorus became apparent. Specifically, individuals appear to concentrate t heir chirps in a more complex environment, such that overall calling activity is reduced, but the chance of any one chirp in a given series being sufficiently a pparent to a potential mate is maximize d. Some of this reduction in the calling rate may have be en accounted for by a reaction of the cricket to an abrupt and possibly startling change in acoustic stimuli. A decreased rate of calling after the recording period would then be expected as a result of an equal but opposite abrupt change in acoustic stimu li upon termination of the chorus playback. However, t his decrease was not seen after playback, and in fact the rates in this period were strikingly similar to those before playback the difference in mean calling rates be tween the two intervals was 0.37 c alls per minute , suggesting that startling effects of an abrupt change in acoustic stimuli had li ttle effect on the observed calling rates . Due to all calling organisms in the recording being those that naturally occur near this species of cricket, their calls w ere f amiliar to the crickets, most likely negating a disruptive impact on their calling rate because of a need for an individual to process and evaluate the stimuli extensively because of unfamiliarity .
6 The trend of decreased calling activity whil e located in a more complex acous tic environment is most likely principally a consequence of the implications of the extremely energetically costly nature of sound production in crickets. An individual has a finite amount of energy stores, and only a certa in portion of this stored energy is spent on calling activity. Due to the fact that the acoustic stimuli around an individual vary both in and among any given evening, it seems beneficial for a cricket to expend most of their energy dedicated to calling ac tivity in times when their signaling would be most likely to be received by a potential mate Sakaluk and Snedden 1990 . Therefore, calling would logically be con centrated in times when there i s less possible interference from other acoustically active org anisms . T hese times of reduced interference are all relative and are subject to the acuity of each given individual Â€s perception of their surroundings and what they are accustomed to . Through the induced increase in acoustic surroundings, an interval of re latively higher auditory interference was generated, and responded to behaviorally by this species of cricket with a decrease in calling activity in order to maximize the effectiveness of energy use. An additional response to the increased chorus intricac y was a reduction in the number of simple series of chirps produced. This would logically be expected to be coupled with an increase in the number of complex series; however this was not apparent through statistical analysis. This lack of a trend of an inc rease in complex series is most likely resulting from a relatively small sample size, based on the fact that analysis of the proportion of complex series for each time interval on an individual basis showed a slight trend towards a relative increase in com plex series during chorus playback . Due to variability in general acoustic activity in the study site on a nightly basis, each individual was not subject to the exact same basal acoustic complexity throughout the study . This could have potentially impacted the perceived relative increase in auditory complex ity through chorus playback and thus combined with a small sample size in order to contribute to the lack of a trend seen for complex series. The tendency f or a reduction in the number of simple series pr oduced during playback is likely another result of the constrictions placed upon calling activity by the inefficiency in energy conversion in the calling process. In a complex heterospecific natural chorus, periods of silence are few and far between, and o ften those organisms that are most acoustically apparent are the loud est ones. Because this species of cricket is not especially loud in reference to the majority of organisms that comprise their surrounding choruses, they must find an alternate way to be sufficiently detect ed by prospective mates . One such manner for this to be accomplished is through relative timing in relation to the other organisms in the chorus. The best way to ensure that an individualÂ€s call is produced in the irregular and infrequen t split seconds of relative acoustic inactivity in the chorus is by exhibiting more complex calls. In this manner, a crick et has a higher likelihood of at least one of the c hirp s in any series being located in any given unpredictable quiet period, while st ill being able to reduce the total number of chirps per given amount of time so as not to be careless with their energy use . In order to increase the strength of the arguments made in this study, and to emphasize and better establish trends in calling beh avior, a larger sample size could be used. To the same effect, increasing the length of observation intervals would be beneficial. Due to time constraints, only one chorus recording was used to examine behavioral changes in calling. Through using various c horus recordings of differing complexities, longer durations and an increased number of observations would allow for more insight into the trends of changes in calling activity. Car eful selection of chorus recordings would need to be utilized if this were done, as other possible factors among recordings other than an increase in complexity could emerge and thus impact the
7 observed behavior. Relocation of an i ndividual so he is not near any calling conspecifics and observation of call characteristics while s olitary could provide interesting insight in to the beneficial nature of being located near others. Behavioral adaptability in singing among crickets based on the acoustic activity of nearby conspecifics has been shown by many studies Allard 1918, Greenfie ld 1994, Greenfield and Sneeden 2002, Greenfield et al . 1997, Mhatre and Balakrishnan 2006, Walker 1969. However, little is know about the influence that the calling activity of heterospecifics has on cricket behavior. As a result of crickets being among the first musicians on the planet, it seems logical that this long acoustic evolutionary past has allowed them to be able to most efficiently and effectively utilize their calling behavior through taking into account the calls of heteros pecifics Carde and Resh 2003. A CKNOWLEDGEMENTS I graciously thank Milton Brenes Salazar for his permission regarding property access, and for his support, assistance, and hospitality . T hanks to Sea Bear and T Bone for their patience, hard work, and constant willingness t o be as helpful as possible. To my profess ors Tania ChavarrÃa Piz arro , and Ala n and Karen Masters, I thank you for the continual guidance, inspiration, and assistance throughout the semester . Thanks to Ezies, Dish Pan, and the Thirstman Thruster for being beautiful and incredible people, and allowing for the preservatio n of my sanity. L ITERATURE C ITED Alexander, R. 1962. Evolutionary change in cricket acoustical communication. Evolution 16:4. 443 467. Allard, H. A. 1918. Rhythmic synchronism in the chirpin g of certain crickets and locusts. The American Naturalist 52:622. 548 552. Bailey, W. J. 1995. Costs of calling in Tettigoniid Orthoptera: a case study of Requena verticalis Tettigoniidae: Listroscelidinae. Journal of Orthoptera Research 4: 65 73. Baile y, W . J., P.C. Withers, M. Endersby and K. Gaull. 1993. The energetic costs of calling in the bushcricket Requena verticalis Orthoptera: Tettigoniidae: Listroscelidinae. Journal of Experimental Biology 178: 21 37. BolaÃ±os, R. A. and V. Watson. 1993. Mapa ecolÃ³gico de Costa Rica. Centro CientÃfico Tropical, San JosÃ©, Costa Rica. Carde, R . T. and V. H. Resh. 2003. Encyclopedia of Insects. Academic Press, London, England. Forrest, T. G. 1982. Acoustic communication and baffling behaviors of crickets. The Flo rida Entomologist 65:1. 33 44. Greenfield, M. D. 1994. Cooperation and conflict in the evolution of signal interactions. Annual Review of Ecology and Systematics 25: 97 126. Greenfield , M. D. and W. A. Sneeden. 2002. Selective attention and the spatio temp oral structure of Orthopteran choruses. Behaviour 140: 1 26. Greenfield, M. D., W. A. Sneeden and M. K. Tourtellot . 1997. Precedence effects and the evolution of chorusing. Proceedings: Biological Sciences 264:1386. 1355 1361. Jacobs , G. A. 1995. Detection and analysis of air currents by crickets. BioScience 45:11. 776 785.
8 Mhatre, N. and R. Balakrishnan. 2006. Male spacing behaviour and acoustic interactions in a field cricket: implications for female mate choice. Animal Behaviour 72: 1045 1058. Sakaluk, S . K. and W. A. Snedden. 1990. Nightly calling durations of male sagebrush crickets, Cyphoderris strepitans : size, mating and seasonal effects. Oikos 57:2. 153 160. Walker , T. J. 1969. Acoustic synchrony: two mechanisms in the snowy tree cricket. Science 16 6:3907. 891 894.