The Effect of Timing of Female Vibrational Reply on Male Signalling and Searching Behaviour in the Leafhopper Aphrodes makarovi

Sexual communication in animals often involves duetting characterized by a coordinated reciprocal exchange of acoustic signals. We used playback experiments to study the role of timing of a female reply in the species-specific duet structure in the leafhopper Aphrodes makarovi (Hemiptera: Cicadellidae). In leafhoppers, mate recognition and location is mediated exclusively by species- and sex-specific substrate-borne vibrational signals and a female signal emitted in reply to male advertisement calls is essential for recognition and successful location of the female. In A. makarovi, males have to initiate each exchange of vibrational signals between partners, and in a duet the beginning of a female reply overlaps the end of the male advertisement call. Results of playback treatments in which female replies were delayed and did not overlap with the male call revealed that in order to trigger an appropriate behavioural response of the male, female reply has to appear in a period less than 400 ms after the end of the initiating male call. Results also suggest that males are not able to detect a female reply while calling, since female reply that did not continue after the end of male call triggered male behaviour similar to behaviour observed in the absence of female reply. Together, our results show that vibrational duets are tightly coordinated and that the species-specific duet structure plays an important role in mate recognition in location processes.     

Male–male interactions and male mating success in the leafhopper Aphrodes makarovi

In mating systems based on substrate‐borne vibrations, sexual communication often involves a reciprocal exchange of species‐ and sex‐specific vibrational signals and male is searching for a stationary female. In the leafhopper Aphrodes makarovi, female reply is essential for successful location of the female and its variable duration directly affects male's costs associated with signalling and searching. We studied male and female behaviour in a trio situation (two males and one female), and our results show that male–male competition had important effects on male mating success. Females replied equally to advertisement calls emitted by the winning and losing males and mated with the first male that located them, regardless of his investment in calling effort. Males eavesdropped to male–female duet maintained by the rival, and the winners were better at exploiting female replies to the rival's advertisement calls by silently approaching the female. To interfere with the ongoing male–female duet, males also emitted masking signals overlapping the latter part of the female reply. More overlapped female replies were registered in response to the losers and masking signals most likely delay the rival in reaching the female. Our study shows that a comprehensive understanding of male mating success and female preferences in vibrational duetting systems requires also investigations in more complex settings that more realistically represent the situation in nature.     

Disruption of the reproductive behaviour of Scaphoideus titanus by playback of vibrational signals

Scaphoideus titanus Ball (Hemiptera: Cicadellidae: Deltocephalinae) is the vector of the grapevine disease Flavescence dorée. In S. titanus the male–female duet (MFD), based on species-specific vibrational signals, is essential for successful copulation. The female reply within a duet is a single pulse that is coupled with the male pulse with constant latency. It has been shown that a rival male can interrupt an existing duet by emitting disruptive noise signals. We tested whether the reproductive behaviour of S. titanus can be disrupted by the playback of intra-specific and synthesized vibrational signals. Tested males responded to the playback of an MFD with typical rivalry behaviour. Such behaviour includes silent search for a duetting female (satellite behaviour) and/or emission of disruptive signals. These signals were emitted either after exchange of male–female pulses or after two male pulses coupled by latency corresponding to the female response window. The onset of male disruptive signals overlapped with a female pulse. We suggest that the intruder's disruptive signals can mask the female reply and confuse courting males. Playback of disruptive vibrational signals reduced the level of male calling and interrupted an established MFD that consequently resulted in a significantly reduced number of copulations. These results indicate that the vibrational communication channel is open to interference either from abiotic environmental noise or from signals produced by sexual competitors or heterospecifics. The present study also suggests that a detailed understanding of leafhopper behaviour is essential for trying new approaches in the development of more environmentally friendly control practices.     

Duetting in insects – does call length influence reply latency?

A meta-analysis of the duetting patterns of insect taxa that signal by bioluminescence, substrate vibration, or sound was used to test the prediction that call length by the initiating male influences the latency of reply of the female. There was a significant and positive relationship between these two measures. Although tests on the entire dataset did not consider phylogeny, when all members of one sub-family of bushcricket, the Phaneropterinae, were isolated there was a significant and positive relationship between call length and reply latency. Two explanations are suggested. First, the female must wait for the conclusion of a long and potentially variable message; there is uncertainty as to when the call has finished before she can reply. Second, is the requirement of the female to process information; a longer male call, with more information requires more processing than a brief call. The authors suggest that long reply latencies may be vulnerable to intrusion by competing mates. One defensive tactic of potential female partners is to insert a trigger pulse that indicates to the female when the long and complex call has concluded. This behaviour may be considered as acoustic mate guarding and one example is given of this behaviour.     

Insect duets: underlying mechanisms and their evolution

Abstract. Duetting between the sexes in insects involves the use of airborne acoustic signals, substrate vibration and bioluminescence. Unlike avian duets, in which females may initiate the interaction, among insects the duet starts with the male, and the female usually provides a brief reply. Insect duets are characterized by low variance in the reply latency of the female (the time between a key element in the male call and the onset of the female's response). Duetting is reviewed principally in Orthoptera but also in Plecoptera, Hemiptera, Neuroptera and bioluminescence in the Coleoptera. The mechanisms of the duet are examined first, followed by evolution and the associated change in searching strategies of each sex. As defined, the duet has distinct temporal characteristics and these are compared with acoustic interactions among males in those species that exhibit male–male synchrony and alternation. For insects, the key element of a duet for species' recognition is low variance in the reply latency of females. In cases in which the male's initiating signal is extremely short, reply latencies become indicators of species' recognition. However, in those species in which the initiating male call is under selection through female choice, the male call is predictably longer and occasionally more complex. Under these circumstances, reply latencies often increase, creating an opportunity for alternative male tactics. When alternative tactics exist in nature, males may decrease the intensity of their call, insert a trigger pulse that signals to the female the end of its complex call, or males may even add a masking signal that obscures the competing signal.     

Search behaviour of two hemipteran species using vibrational communication

The ability of conspecifics to recognize and locate each other in the environment depends on the efficiency of intraspecific communication. We compared the mate searching strategies of southern green stinkbug Nezara viridula (male searches for a continuously calling female) and the leafhopper Aphrodes makarovi (partners form a precisely coordinated duet). Males of both species were tested on plants in playback experiments. One leaf was vibrated with unaltered conspecific female signals or with various conspecific signals using modified temporal parameters. The results showed that the onset of searching was faster in A. makarovi than in N. viridula. Changes in temporal parameters of female replies had negative effect on the searching behaviour of A. makarovi. Males located the source of longer female replies faster than the short female call and they failed to locate the source of a female reply with temporal parameters outside the species-specific values. In contrast, in N. viridula, searching males successfully located also the source of a female song with parameters outside the species-specific values. The results are discussed with regard to male behavioural strategies in species with different vibrational communication systems and different male mating investment.     

Acoustic satellite behaviour in the Australian bushcricket Elephantodeta nobilis (Phaneropterinae, Tettigoniidae, Orthoptera)

Male and female Elephantodeta nobilis duet with the female responding to the male's long and complex call. The duetting male's call consisted of four parts, described here as parts A, B, C and D. We found that the female replied 570 ms after the male's D pulse, which followed the extended part B and short click of part C. Noncalling males were attracted to the duet and often used satellite tactics by inserting a volley of clicks 200 ms before the alpha male's D pulse. Satellite males used part C of the alpha male song to cue their own call and this inserted call induced females to reply earlier compared with the alpha male call alone. Alpha males often extended their calls with additional D-type calls and so we examined the effectiveness of these calls as countermeasures to satellite calling. There was no influence of this alpha strategy on the satellite's propensity to call although more calls from the alpha male did cause the female to reply more frequently. We also examined the effect of relative intensity of alpha and satellite calls on the female's reply. Reduced satellite intensity increased the variance in the timing of the female response. Finally, we tested the effectiveness of the satellite's call on female phonotaxis within a two-speaker arena. Although females preferred the alpha male they were nevertheless attracted to the satellite calls regardless of the latter's relative intensity. We discuss the possible role of satellite calling as a novel conditional strategy. Copyright 2000 The Association for the Study of Animal Behaviour.     

Vibrational communication and mating behaviour of Dichelops melacanthus (Hemiptera: Pentatomidae) recorded from loudspeaker membranes and plants

Vibrational communication is important for successful mating in various stink bugs species. The vibrational signals from males and females of Dichelops melacanthus Dallas (Hemiptera: Pentatomidae) are recorded from a nonresonant substrate (i.e. a loudspeaker membrane) to characterize the temporal and spectral properties of these vibrational signals, as well as on a resonant substrate (i.e. bean plants) to obtain information about how these signals are altered when they are transmitted through the plants. On the loudspeaker membrane, D. melacanthus males and females emit only one male or one female song, respectively. However, when the insects are placed on bean leaves, a more complex repertoire is recorded, with three different songs for each sex. The first female and male songs appear to have calling functions and the third male and female songs are emitted during courtship. The second female and male songs are emitted after the first song, although their functions in mating behaviour are not clear. The identified repertoire is similar to those of other Neotropical stink bugs, starting with songs 1 and 2 and developing into song 3. Frequency modulation is observed in the female songs recorded from the loudspeaker membrane and the plants. The signals recorded from plants present higher harmonic peaks compared with the signals recorded from the loudspeaker membrane. The presence of species and sex‐specific songs during mating confirms the important role of vibrational communication in mate location and recognition. The temporal and spectral characteristic signals are influenced by the substrate used to record the songs emitted by D. melacanthus.     

Genetic control and evolution of acoustic signals in planthoppers (Homoptera: Delphacidae)

Acoustic signals are part of the specific mate recognition system of planthoppers. The genetic control of acoustic signal characters was studied in the planthopperRibautodelphax imitans. Artificial selection for interpulse interval in the female call revealed a large additive genetic component for this polygenic character. Other female call characters showed a correlated response. Some male call characters also appeared to be genetically correlated with the female character selected for, despite the rather different structure of male and female calls. Parent-offspring regression provided significant heritability estimates for those male call characters that also responded to artificial selection in the female call, one of which appeared to be influenced by sex-linked genes. It is argued that the differentiation of this mate recognition system in planthopper populations and species could be the result of founder effects, enabled by the genetic plasticity of the call characters and the existence of a wing length dimorphism in these animals.     

Sound production and mating in a waterboatman, Palmacorixa nana (Heteroptera: Corixidae)

Both male and female Palmacorixa nana stridulate by rubbing fields of pegs on the fore femora over thickened flanges on the maxillary plates. I sugges that the head is the sound-radiating structure and is driven into oscillation when its edges are plucked by rows of femoral pegs. P. nana males produce spontaneous, courtship, mounting and copulatory signals. The latter tow signals are produced by a new mechanism which constitutes only the third record of inter-individual stridulation in insects. The known acoustic behaviour of the female is limited to a signal indicating readiness to mate. Mating behaviour was observed and copulatory success found not to rely on a complete exchange of acoustic signals. Comparison of data from several sources indicates that corixids capable of singing can either have an obligatory or optional exchange of signals.     

Divergence in Female Duetting Signals in the Enchenopa binotata Species Complex of Treehoppers (Hemiptera: Membracidae)

Sexual communication often involves signal exchanges between the sexes, or duetting, in which mate choice is expressed through response signals. With both sexes acting as signalers and receivers, variation in the signals of males and females may be important for mate choice, reproductive isolation, and divergence. In the Enchenopa binotata species complex – a case study of sympatric speciation in which vibrational duetting may have an important role – male signals are species‐specific, females choose among males on the basis of signal traits that reflect species and individual differences, and female preferences have exerted divergent selection on male signals. Here, we describe variation in female signals in the E. binotata species complex. We report substantial species differences in the spectral and temporal features of female signals, and in their timing relative to male signals. These differences were similar in range to differences in male signals in the E. binotata complex. We consider processes that might contribute to divergence in female signals, and suggest that signal evolution in the E. binotata complex may be influenced by mate choice in both sexes.     

Evolution and Diversity of Vibrational Signals in Mantophasmatodea (Insecta)

Vibrational communication for species identification and mate location is widespread among insects. We investigated the vibrational communication signals of 13 species of the insect order Mantophasmatodea (Heelwalkers). Males and females produce percussive signals by tapping their abdomens on the substrate to locate conspecific mates. We show that male and female calls are of similar general structure but differ in temporal characteristics. Using a principal component analysis, we demonstrate that most species can be distinguished by their calls only. Mapping the calls onto an existing molecular phylogenetic tree reveals a slow diverging drift of male call pattern but no specific trend. For females, a trend from faster towards slower pulse repetition times is indicated. Two sympatric species, Karoophasma biedouwense and Viridiphasma clanwilliamense (Austrophasmatidae), exhibit very different call parameters. The latter species produces calls rather different from all other investigated species, which might hint at reproductive character displacement.     

Vibrational playbacks and microscopy to study the signalling behaviour and female physiology of Philaenus spumarius

The meadow spittlebug Philaenus spumarius, vector of the bacterium Xylella fastidiosa, relies on vibrational communication to accomplish mating: the female calls to establish a duet with a male. A deeper knowledge of the species’ reproductive biology and behaviour would provide useful information for developing control techniques based on principles of ‘biotremology’, which studies the vibrational behaviour of animals. Playback tests were conducted on single females and male–female pairs of P. spumarius from June to October 2018, and the features of the recorded calling signals were analysed using a wavelet decomposition. Dissections were performed on females to evaluate the relationship between calling activity and ovarioles development. From August onwards, females started to emit calling signals and to develop ovarioles. Female calling activity, duration of their chirps and their responsiveness to mating increased as the season progressed, and they were correlated with ovarioles’ development and presence of mature eggs. Hence, the ovarian maturation represents a key factor in association with the development of the sexual behaviour of P. spumarius females. Conversely, males produced advertisement signals soon after adult eclosion in May, but these signals were not involved in the pair formation process. Mating was achieved only when males produced courtship signals in response to female calling signals and established with them vibrational duets starting from August. Here, we provide new information regarding the P. spumarius’ ethology and hypothesize that potential mating disruption techniques should consider the insect physiology and be applied when both sexes are responsive to mating signals.     

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.     

Reproductive strategy of the Nearctic leafhopper Scaphoideus titanus Ball (Hemiptera: Cicadellidae)

Mating behaviour of Scaphoideus titanus Ball, the vector of the grapevine disease Flavescence dorée, was investigated in order to determine the role of substrate-borne vibrational signals in intra-specific communication and pair formation. Vibrational signals were recorded from grapevine leaves with a laser vibrometer. Signalling activity of single males changed throughout the day and the peak in activity was associated with twilight and early night when 'call and fly' behaviour was observed. Pair formation began with the spontaneous emission of male signals. The male calling signal consisted of a single series of pulses, partially accompanied with a 'rumble'. The male courtship phrase consisted of four consecutive sections characterized by two sound elements, pulse and 'buzz'. Female vibrational signals were emitted only in response to male signals. The female response was a single pulse that closely resembled male pulses and was inserted between pulses within the male signals. All recorded vibrational signals of S. titanus have a dominant frequency below 900 Hz. A unique feature of vibrational communication in S. titanus is well-developed intrasexual competition; males may use alternative tactics, in the form of disturbance signals, or silently approach duetting females (satellite behaviour). While the male-female duet appears to be essential for successful localization of females and copulation, it is also vulnerable to, and easily disrupted by, alternative tactics like masking.     

Mate searching in Ennya maculicornis (Membracidae: Polyglyptini) initiated by females: behavioural and acoustic descriptions

1. In treehoppers in which courtship has been studied, males initiate the search for females by periodically emitting a vibrational signal. The responses by the female are used by males as a beacon and give rise to a duet. 2. Courtship and mating of the treehopper Ennya maculicornis were characterised through the simultaneous recording of vibrational signals and the behaviour of males and females in an arena. 3. In E. maculicornis, female initiated mate searching. Females produced two types of signals during the this process: (i) a signal that preceded the approach by the male and (ii) a signal that preceded mating. Males emitted two signals associated with two stereotyped body movements: (i) a signal produced as a response to the first signal emitted by the female, involving a change in the male's locomotory mode and the approach to the female, and (ii) a signal produced after finding and holding on to the female, involving simultaneous abdomen raising and wing fluttering. These signals were repeated several times before the female emitted the second signal. The four signalling patterns were observed in all recordings in which mating was observed. When any of the signals was missing, mating did not occur. 4. Female‐biased sex ratios in E. maculicornis, along with iteroparity, are suggested to explain the initiation of mate searching behaviour by females. A comparison of data with that from other treehoppers indicates that vibrational signals and their associated behaviour are more diverse among treehoppers than has been appreciated previously.     

Modality interactions alter the shape of acoustic mate preference functions in gray treefrogs

Sexual selection takes place in complex environments where females evaluating male mating signals are confronted with stimuli from multiple sources and modalities. The pattern of expression of female preferences may be influenced by interactions between modalities, changing the shape of female preference functions, and thus ultimately altering the selective landscape acting on male signal evolution. We tested the hypothesis that the responses of female gray treefrogs, Hyla versicolor, to acoustic male advertisement calls are affected by interactions with visual stimuli. We measured preference functions for several call traits under two experimental conditions: unimodal (only acoustic signals presented), and multimodal (acoustic signals presented along with a video‐animated calling male). We found that females were more responsive to multimodal stimulus presentations and, compared to unimodal playbacks, had weaker preferences for temporal call characteristics. We compared the preference functions obtained in these two treatments to the distribution of male call characteristics to make inferences on the strength and direction of selection expected to act on male calls. Modality interactions have the potential to influence the course of signal evolution and thus are an important consideration in sexual selection studies.     

Copulatory vocalizations of female macaques (Macaca fascicularis): Variability factors analysis

In 234 copulations, male and female behavioural patterns were collected, especially the vocal pattern for the female. Moreover quantitative structural analysis was performed on 38 of these female copulatory vocalizations. A multifactorial analysis, ANAFAC, was performed to seek relations between (1) utterance of female copulatory call and male and female copulatory behaviour and (2) these patterns and the great variability of female calls. Utterance of female copulatory vocalizations is essentially due to the female’s own copulatory behaviour in periods of intense sexual activity. Long female calls are related to male ejaculation, and those “rich” in harmonics are related to visual and tactile communicatory signals exchanged by the male and the female during a mount. This analysis strongly confirms the tied bond between quality of a call and internal state of the emitter. Long calls, rich in harmonics, may serve as signals maintaining or strengthening the possibly temporary preferential relation between male and sexually receptive female.