Acoustic communication and sexual selection in Orthoptera (Insecta)

Comparison of calling and courtship songs and mating strategies in different groups of Orthoptera shows that acoustic signals in bush crickets (Tettigonioidea) are used for searching conspecific mates at a distance, and song evolution is primarily driven by the acoustic surroundings and simultaneously singing other species. The role of sexual selection in the evolution of acoustic signals in bush crickets is much less important than in the evolution of other nonacoustic signals employed during direct contact. Acoustic signals of crickets (Grylloidea) are involved in both distant and short-range communication. Acoustic courtship signals, along with other courtship components, may offer the material for sexual selection, although, essentially, evolution of acoustic signals in crickets is determined by the acoustic surroundings. Acoustic communication in the grasshoppers of the subfamily Gomphocerinae is mainly a short-distance communication. Acoustic signals of Gomphocerinae are highly variable and elaborate in temporal parameters, and therefore can serve for evaluation of the mate "quality". Song evolution in this group is to a greater extent driven by sexual selection than by the acoustic surroundings and, therefore, could proceed faster than in other groups of Orthoptera and play a major role in speciation.     

昆虫求偶鸣曲的行为特征与功能及其生态学意义

以直翅目昆虫为重点,从鸣曲器官的结构特征与鸣曲机理,求偶鸣曲的定位及其精度,求偶鸣曲的适度调节,求偶鸣曲的结构参数及其生物学意义,受体对求偶鸣曲的反应与识别五个方面对昆虫求偶鸣曲的行为特征与功能作了综述。在此基础上,从求偶鸣曲的遗传与进化,求偶鸣曲与自然选择和性选择,求偶鸣曲与物种的分化和进化三个角度探讨了求偶鸣曲的生态学意义,并展望了该领域未来的发展趋势和研究方向。     

Acoustic signals in insects: A reproductive barrier and a taxonomic character

In singing insects, the song is an important component of the specific mate recognition system (SMRS). In communities of sympatric singing species, there is a partitioning of communication channels, the so-called “acoustic niches.” Within one community, the songs of different species always differ in temporal or frequency characters, i.e. occupy different acoustic niches. However, conspecific songs do not always act as an interspecific reproductive barrier, despite always being a SMRS component. The species that do not communicate acoustically due to allopatry, different timing of vocalization, inhabiting different biotopes, or unmatched food specializations can produce similar songs while forming reproductively isolated communities. Individuals of different sexes need not only to recognize a conspecific mate but also to evaluate its “quality.” The close-range signal (courtship song) provides more opportunities for choosing the “best” male than does the distant signal (calling song). In many species of Orthoptera, courtship includes not only acoustic but also vibrational, visual, chemical, and mechanical signals. An analysis of cricket songs showed the courtship songs to be on average more elaborate and variable than the calling songs. At the same time, due to the difference in mating behavior between the two groups, the acoustic component of courtship is used for mate quality evaluation to a greater extent in grasshoppers than in crickets. The courtship songs of grasshoppers are generally more elaborate in temporal structure than cricket songs; moreover, they may be accompanied by visual displays such as movements of various body parts. Thus, song evolution in grasshoppers is more strongly driven by sexual selection than that in crickets. According to the reinforcement hypothesis, the premating barrier between hybridizing species becomes stronger in response to reduced hybrid fitness. However, our behavioral experiments with two groups of hybridizing grasshopper species did not confirm the reinforcement hypothesis. We explain this, firstly, by a low level of genetic incompatibility between the hybridizing species and secondly, by high hybrid fitness when attracting a mate. A high competitive capability of hybrids may be accounted for by attractiveness of new elements in hybrid courtship songs. When we divide similar forms based on their songs, we in fact distinguish biological species using the criterion of their reproductive isolation. Acoustic differences between species are usually greater than morphological ones. Therefore, song analysis allows one to determine the real status of doubtful species-rank taxa, to distinguish species in a medley of sibling forms, and to reveal cryptic species in the cases when morphological studies fail to provide a univocal result. At the same time, songs are subject to intraspecific variation the range of which is different in different groups. Therefore, it is necessary to study which degree of difference corresponds to the species level before interpreting the status of some forms based on song comparisons. Besides, song similarities cannot indicate conspecificity of acoustically isolated forms; on the other hand, song differences between these forms prove that they are full-rank species.     

Divergence between the Courtship Songs of the Field Crickets Gryllus texensis and Gryllus rubens (Orthoptera, Gryllidae)

Acoustic mating signals are often important as both interspecific prezygotic isolating mechanisms and as sexually selected traits in intraspecific mate choice. Here, we investigate the potential for cricket courtship song to act as an isolating mechanism by assessing divergence between the courtship songs of Gryllus texensis and Gryllus rubens , two broadly sympatric cryptic sister species of field crickets with strong prezygotic isolation via the calling song and little or no postzygotic isolation. We found significant species-level differences in the courtship song, but the song has not diverged to the same extent as the calling song, and considerable overlap remains between these two species. Only two related courtship song characters are sufficiently distinct to play a possible role in prezygotic species isolation.     

Multimodal signalling in estrildid finches: song,dance and colour are associated with different ecological and life‐history traits

Sexual traits (e.g. visual ornaments, acoustic signals, courtship behaviour) are often displayed together as multimodal signals. Some hypotheses predict joint evolution of different sexual signals (e.g. to increase the efficiency of communication) or that different signals trade off with each other (e.g. due to limited resources). Alternatively, multiple signals may evolve independently for different functions, or to communicate different information (multiple message hypothesis). We evaluated these hypotheses with a comparative study in the family Estrildidae, one of the largest songbird radiations, and one that includes many model species for research in sexual selection and communication. We found little evidence for either joint evolution or trade‐offs between song and colour ornamentation. Some negative correlations between dance repertoire and song traits may suggest a functional compromise, but generally courtship dance also evolved independently from other signals. Instead of correlated evolution, we found that song, dance and colour are each related to different socio‐ecological traits. Song complexity evolved together with ecological generalism, song performance with investment in reproduction, dance with commonness and habitat type, whereas colour ornamentation was shown previously to correlate mostly with gregariousness. We conclude that multimodal signals evolve in response to various socio‐ecological traits, suggesting the accumulation of distinct signalling functions.     

Reproductive Isolation in the Wood Cricket Gryllus vernalis (Orthoptera: Gryllidae)

Two species of closely related wood crickets, Gryllus vernalis (Orthoptera: Gryllidae) and G. fultoni, occur together in the eastern USA and have a similar calling‐song structure, consisting of three‐pulse chirps. Previous studies revealed that male calling song and female selectivity were divergent between sympatric and far allopatric populations of G. fultoni, consistent with the pattern expected of reproductive character displacement. We studied the reproductive isolation of G. vernalis in relation to G. fultoni by investigating the geographic variation in calling songs of G. vernalis and by examining close‐range mating behaviors. Neither field nor laboratory studies revealed differences in any of the calling‐song characters between sympatric and allopatric populations, but this could reflect the limited sampling within the relatively small region of allopatry for G. vernalis. Although close‐range mating trials revealed that females of both species discriminated against heterospecific mating partners, the strength of discrimination was especially strong in females of sympatric G. vernalis populations. Our studies of long‐range and close‐range mating behaviors suggest that selection pressures for reproductive isolation are exerted primarily on close‐range mating behaviors in G. vernalis but on long‐range mating behaviors in G. fultoni.     

Behavioural mechanisms of sexual isolation involving multiple modalities and their inheritance

Speciation research dissects the genetics and evolution of reproductive barriers between parental species. Hybrids are the “gatekeepers” of gene flow, so it is also important to understand the behavioural mechanisms and genetics of any potential isolation from their parental species. We tested the role of multiple behavioural barriers in reproductive isolation among closely related field crickets and their hybrids (Teleogryllus oceanicus and Teleogryllus commodus). These species hybridize in the laboratory, but the behaviour of hybrids is unusual and there is little evidence for gene flow in the wild. We found that heterospecific pairs exhibited reduced rates of courtship behaviour due to discrimination by both sexes, and that this behavioural isolation was symmetrical. However, hybrids were not sexually selected against and exhibited high rates of courtship behaviour even though hybrid females are sterile. Using reciprocal hybrid crosses, we characterized patterns of interspecific divergence and inheritance in key sexual traits that might underlie the mating patterns we found: calling song, courtship song and cuticular hydrocarbons (CHCs). Song traits exhibited both sex linkage and transgressive segregation, whereas CHCs exhibited only the latter. Calculations of the strength of isolation exerted by these sexual traits suggest that close‐range signals are as important as long‐distance signals in contributing to interspecific sexual isolation. The surprisingly weak mating barriers observed between hybrids and parental species highlight the need to examine reproductive isolating mechanisms and their genetic bases across different potential stages of introgressive hybridization.     

Auditory pattern recognition and steering in the cricket Teleogryllus oceanicus

Male crickets Teleogryllus oceanicus (Le Guillou) produce a complex species‐specific calling song with phrases combining groups of single pulses (chirps) and groups of double‐pulses (trills) to attract females, which fly or walk towards singing males. In open‐loop trackball experiments, phonotactic steering responses to normal calling song phrases consisting of chirps and trills are strongest, suggesting that both components are necessary for maximal attractiveness. Sequences of just chirps or trills are less effective in eliciting phonotactic walking and steering. Split‐song paradigms are used to analyze the steering behaviour underlying orientation in more detail. The females' phonotactic steering reflects the alternating acoustic pattern of the split‐song paradigm. Analysis with high temporal resolution demonstrate, that even when the calling song is presented only from one side, the steering velocity and lateral deviation towards the song is modulated by steering events to single‐sound pulses. Therefore, pattern recognition, which integrates the structure of the song, appears not to be directly involved in the rapid steering response. This organization of phonotactic behaviour with a parallel processing of pattern recognition and steering is similar to other cricket species and may allow T. oceanicus females to steer transiently towards distorted song patterns as they occur in natural habitats.     

雄性稻绿蝽对雌性鸣唱反应的物种特异性

雌性稻绿蝽的鸣唱开始了在基质中产生的通讯并引起雄性不同的特定反应。在两种自然情况下 ,我们检验了雄性稻绿蝽对N viridula ,Thyantapallidovirens和Thyantacustatoraccerra个体鸣唱刺激反应的物种特异性水平 ,并对反应强度和同种及异种刺激性鸣唱的时间特性进行了相关分析 ,证明雄性求偶鸣唱的发送和震动源的定位是最具物种特异性的反应。然而 ,即便是在这个水平上 ,雄性稻绿蝽不能将同种雌性个体的鸣唱与T .custatoraccera的第二个雄性个体的鸣唱区分开来 ,后者与前者有相似的脉冲持续时间和重复时间值。本文也讨论了涉及交配行为鸣唱期的有关信号的物种特定性的概念     

Ambient temperature and sound power of cicada calling songs (Hemiptera: Cicadidae: Tibicina)

Abstract.  Male cicadas produce a loud calling song that attracts females at long range. In some cases, ambient temperature has been shown to have an effect on the temporal structure of this acoustic signal. Here, a positive correlation is reported for the first time between the ambient temperature and the sound power of the calling song. This relationship is illustrated in three species of the Palaearctic genus Tibicina : Tibicina corsica fairmairei Boulard, Tibicina garricola Boulard and Tibicina tomentosa Olivier. It is suggested that the males thermoregulate behaviourally. The minimal ambient temperature range that the Tibicina species need to call is 22–24 °C. The effect of ambient temperature on calling song power is assumed to be the result of thermal effects in the response of the acoustic system (i.e. muscle activity of the acoustic system being temperature-dependent). Inter-individual and interspecific differences in calling song power are interpreted in the general context of the Tibicina sound behaviour.     

Spatio-Temporal Dynamics of Field Cricket Calling Behaviour: Implications for Female Mate Search and Mate Choice

Amount of calling activity (calling effort) is a strong determinant of male mating success in species such as orthopterans and anurans that use acoustic communication in the context of mating behaviour. While many studies in crickets have investigated the determinants of calling effort, patterns of variability in male calling effort in natural choruses remain largely unexplored. Within-individual variability in calling activity across multiple nights of calling can influence female mate search and mate choice strategies. Moreover, calling site fidelity across multiple nights of calling can also affect the female mate sampling strategy. We therefore investigated the spatio-temporal dynamics of acoustic signaling behaviour in a wild population of the field cricket species Plebeiogryllus guttiventris. We first studied the consistency of calling activity by quantifying variation in male calling effort across multiple nights of calling using repeatability analysis. Callers were inconsistent in their calling effort across nights and did not optimize nightly calling effort to increase their total number of nights spent calling. We also estimated calling site fidelity of males across multiple nights by quantifying movement of callers. Callers frequently changed their calling sites across calling nights with substantial displacement but without any significant directionality. Finally, we investigated trade-offs between within-night calling effort and energetically expensive calling song features such as call intensity and chirp rate. Calling effort was not correlated with any of the calling song features, suggesting that energetically expensive song features do not constrain male calling effort. The two key features of signaling behaviour, calling effort and call intensity, which determine the duration and spatial coverage of the sexual signal, are therefore uncorrelated and function independently.     

Acoustic communication in Okanagana rimosa (Say) (Homoptera: Cicadidae)

The cicada Okanagana rimosa (Say) has an acoustic communication system with three types of loud timbal sounds: (i) A calling song lasting several seconds to about 1 min which consists of a sequence of chirps at a repetition rate of 83 chirps per second. Each chirp of about 6 ms duration contains 4-5 pulses. The sound level of the calling song is 87-90 dB SPL at a distance of 15 cm. (ii) An amplitude modulated courtship song with increasing amplitude and repetition rate of chirps and pulses. (iii) A protest squawk with irregular chirp and pulse structure. The spectra of all three types are similar and show main energy peaks at 8-10 kHz. Only males sing, and calling song production is influenced by the songs of other males, resulting in an almost continuous sound in dense populations. In such populations, the calling songs overlap and the temporal structure of individual songs is obscured within the habitat. The calling song of the broadly sympatric, closely related species O. canadensis (Provander) is similar in frequency content, but distinct in the temporal pattern (24 chirps per second, 24 ms chirp duration, eight pulses per chirp) which is likely important for species separation in sympatric populations. The hearing threshold of the auditory nerve is similar for females and males of O. rimosa and most sensitive at 4-5 kHz. Experiments in the field show that female phonotaxis of O. rimosa depends on parameters of the calling song. Most females are attracted to calling song models with a 9 kHz carrier frequency (peak frequency of the calling song), but not to models with a 5 kHz carrier frequency (minimum hearing threshold). Phonotaxis depends on temporal parameters of the conspecific song, especially chirp repetition rate. Calling song production is influenced by environmental factors, and likelihood to sing increases with temperature and brightness of the sky. Correspondingly, females perform phonotaxis most often during sunny conditions with temperatures above 22 degrees C. Non-mated and mated females are attracted by the acoustic signals, and the percentage of mated females performing phonotaxis increases during the season.     

The structure and function of songs emitted by southern green stink bugs from Brazil, Florida, Italy and Slovenia

Nezara viridula (L.) (Pentatomidae: Heteroptera) from Brazil, Florida, Italy and Slovenia, communicate by vibratory songs associated with long‐range calling and close‐range courting, rivalry and repelling. Each song is composed of spectrally and temporally different units. Spectrally different pulses of duration less than 300 ms are present in the male calling song. The female calling song is characterized by pulse trains composed of pulses shorter than 150 ms and pulse trains composed of a longer (> 700 ms) and shorter (< 250 ms) pulse. Shorter and longer pulses have different spectral characteristics. The male and female courtship songs are characterized by fusion of shorter (< 150 ms) pulses into a pulse train usually followed by a shorter (< 200 ms) postpulse in the case of the male courtship song. The female repelling song is a several seconds long vibration of irregular temporal structure. The short (< 400 ms) male rival song pulses are frequency modulated. The dominant frequency peaks of the songs investigated lie between 70 and 130 Hz. The dominant frequency and the microstructure of song spectra show no population specificity. The average duration varies more in calling than in courtship songs. The repetition time varies extensively in songs of different populations. Normal communication followed by copulation was observed between mates from Slovenia and Brazil and between mates from Florida and Italy. The potential role of different temporal and spectral parameters for species recognition and mate location is discussed in view of the expected distortion of the characteristic signal structure during transmission through plants.     

Relative Amplitude of Courtship Song Chirp and Trill Components Does Not Alter Female Teleogryllus oceanicus Mating Behavior

Low‐amplitude acoustic signals intended for short‐range communication, often called soft songs, remain poorly studied, especially among acoustically communicating invertebrates. Some insects do employ low‐amplitude acoustic signals, but it remains unclear what the specific function, if any, is of quietness per se. Male Teleogryllus oceanicus, or Pacific field crickets, produce a two component, short‐distance courtship song consisting of a high‐amplitude series of chirps followed by a lower‐amplitude trill. We investigated whether female T. oceanicus prefer to mate with males that sing courtship songs containing trill components that are equally as loud as (?0 dB) or quieter than (?3 dB and ?10 dB) the loudest chirp (90 dB). We found no evidence that modifying trill amplitude affects female mate preference. We did, however, find that previously unmated females were faster to mount males than were females that had mated once before. Previous mating status showed no significant interaction with trill amplitude. What, if any, function of low‐amplitude components of field cricket courtship song remains to be determined.     

Courtship Sounds Advertise Species Identity and Male Quality in Sympatric Pomatoschistus spp. Gobies

Acoustic signals can encode crucial information about species identity and individual quality. We recorded and compared male courtship drum sounds of the sand goby Pomatoschistus minutus and the painted goby P. pictus and examined if they can function in species recognition within sympatric populations. We also examined which acoustic features are related to male quality and the factors that affect female courtship in the sand goby, to determine whether vocalisations potentially play a role in mate assessment. Drums produced by the painted goby showed significantly higher dominant frequencies, higher sound pulse repetition rates and longer intervals between sounds than those of the sand goby. In the sand goby, male quality was predicted by visual and acoustic courtship signals. Regression analyses showed that sound amplitude was a good predictor of male length, whereas the duration of nest behaviour and active calling rate (i.e. excluding silent periods) were good predictors of male condition factor and fat reserves respectively. In addition, the level of female courtship was predicted by male nest behaviour. The results suggest that the frequency and temporal patterns of sounds can encode species identity, whereas sound amplitude and calling activity reflects male size and fat reserves. Visual courtship duration (nest-related behaviour) also seems relevant to mate choice, since it reflects male condition and is related to female courtship. Our work suggests that acoustic communication can contribute to mate choice in the sand goby group, and invites further study.     

Low levels of chromosomal differentiation between the grasshoppers Chorthippus brunneus and Chorthippusjacobsi (Orthoptera; Acrididae) in northern Spain

The grasshopper species Chorthippus brunneus and C. jacobsi (Orthoptera: Acrididae) form a hybrid zone in northern Spain. These species probably diverged while isolated in southern refugia during one of the recent ice ages, and are clearly distinguished by morphology and male calling song. However, in contrast to other Chorthippus taxa that form hybrid zones in Europe, these two species cannot be reliably distinguished on the basis of characteristics of the karyotype such as heterochromatin banding patterns and composition, as revealed by C-banding and fluorochrome staining. Silver staining also reveals the presence of two autosomal nucleolar organiser regions (NORs) in both species. However, differentiation between C. brunneus and C. jacobsi was revealed on the X chromosome using fluorescent in situ hybridisation (FISH). C. brunneus individuals showed additional rDNA sequences on the X chromosome that were not observed in any C. jacobsi individuals. These sequences are not transcribed, indicating either mutational silencing of an ancestral NOR on the X chromosome, or the transposition of non-functional sequences from the autosomes. The implications of these results for the evolution of NOR number in Chorthippus are discussed.     

The importance of calling song and courtship song in female mate choice in the variable field cricket

Male field crickets produce calling songs, courtship songs, tactile signals and chemical signals. Although calling songs are known to play an important role in female mate choice, the importance of the other signals in mate choice is poorly understood. In the variable field cricket, Gryllus lineaticeps, females select mates, in part, based on variation in male calling song. Females prefer higher chirp rates, a trait which is partially dependent on male nutrient intake, and females prefer longer chirp durations, a trait which appears to be independent of male nutrient intake. We tested whether females also have preferences based on variation in male courtship song, and whether the structure of male courtship song varies with nutrient intake. First, we reexamined female preference for calling song chirp rate. Then, we examined: (1) female preference based on courtship song chirp rate; (2) the relative importance of calling song and courtship song chirp rate; (3) the nutrition dependence of courtship song chirp rate; and (4) the correlation between calling song and courtship song chirp rate. As reported previously, females preferred higher calling song chirp rates, and in addition, preferred higher courtship song chirp rates. Females were more likely to switch from a speaker broadcasting more attractive calling song to a speaker broadcasting less attractive calling song when the attractive calling song was associated with an unattractive courtship song than when it was associated with an attractive courtship song. Preferences based on courtship song may thus cause females to alter the choices that they made based on calling song. Males that received greater nutrients did not produce higher courtship song chirp rates. There was no correlation between calling song and courtship song chirp rate. As a result, the two traits may provide information to females about different aspects of male quality. Copyright 2000 The Association for the Study of Animal Behaviour.