More than stridulation: signal interaction and constraint in the complex vibroacoustic courtship of a cricket

More than stridulation: signal interaction and constraint in the complex vibroacoustic courtship of a cricket | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article More than stridulation: signal interaction and constraint in the complex vibroacoustic courtship of a cricket Nataša Stritih-Peljhan, Alenka Žunič-Kosi This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3971219/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 26 Nov, 2024 Read the published version in Behavioral Ecology and Sociobiology → Version 1 posted 5 You are reading this latest preprint version Abstract Crickets (Gryllidae) produce sounds by tegminal stridulation, extensively studied for its role in female attraction and choice. However, their close-range courtship song, along with additional chemical, visual, and thermal signals, fails to clarify the observed female preferences. Beyond stridulation, crickets exhibit a range of vibrational courtship behaviours that remain largely unexplored. In this study, using Acheta domesticus as a model, we present the first comprehensive analysis of the entire set of vibroacoustic courtship signals in crickets, including their interaction. Employing audio recording, laser vibrometry, and videorecording, we unveil a complex signal involving simultaneous wing stridulation, body tremulation, and leg drumming against the substrate. These signal components exhibit a pattern of regular exchange within a specific time window relative to each other. We show the tightest coupling between the two types of stridulation pulses, and between tremulation and drumming signals, supported by the linear corelation of their rates. The coupling between drumming and stridulation signals is less consistent, with the non-linear corelation between their temporal and association parameters revealing a constraint on drumming performance. Yet, drumming is performed with high accuracy relative to stridulation, unrelated to its rate. Spectral-intensity analysis indicates the closest perceptual and thus functional connection between stridulation and drumming components of the complex signal, while proposing another function for tremulation unrelated to female choice. Our data demonstrate that the information conveyed by the complex courtship display in A. domesticus is not simply proportional to that in the song, potentially providing a much more reliable basis for female choice. male quality substrate vibration sound complex signal dynamic signal insect Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 SIGNIFICANCE STATEMENT Our study delves into the vast domain of vibroacoustic signals in insects, specifically crickets, exploring the information conveyed by their complex dynamic displays. While traditional acoustic signals in crickets have received most attention, our pioneering study of the entire set of vibroacoustic signals during courtship of a field cricket ( Acheta domesticus ) unveils a complex signal involving coordinated wing stridulation, body tremulation, and leg drumming against the substrate. Notably, we reveal a performance constraint specific to one signal component, which represents a unique case in complex dynamic signalling. Also, we find no correlation between the display vigour and skill, challenging common expectations. This study not only enhances our understanding of cricket courtship but also contributes to our knowledge of complex signaling in animals. INTRODUCTION Animals often communicate using complex signals with multiple components in the same or across sensory modalities. These multicomponent and multimodal signals play a crucial role in enhancing communication by increasing the information content, improving the effectiveness of signal transmission, and influencing receiver response through the interaction between signal components (Candolin 2003 ; Hebets and Papay 2005; Hebets and McGinley 2019 ). Courtship is a prominent context where such complex signals are observed, where their primary function is to advertise the signaler’s quality and expedite mating decisions (Bastock 1967 ; Mitoyen et al. 2019 ). The females, in particular, can assess potential mates by analysing information in individual signal components, their interaction, and also the overall complexity of the signal (Candolin 2003 ; Mitoyen et al. 2019 ; Choi et al. 2022 ). In complex dynamic displays, females may select males based on their motor performance, assessing both neuromuscular capabilities and acquired skills (Byers at al. 2010; Fussani et al. 2014). The domain of vibro-acoustic signals in insects and other arthropods provides a unique perspective of complex signalling. This system allows for dynamic communication using nearly any body part, from the head to abdomen and appendages (Ewing 1989 ; Virant-Doberlet et al. 2023 ). The signals may not even require a specialised structure for their production, such as in case of vibration (tremulation) of body parts and their drumming on the substrate, and the same body part may be engaged in different signalling mechanisms (Hill 2009; Virant-Doberlet et al. 2023 ). For example, an abdomen may be vibrating, drumming, or scraping the substrate, thereby emitting mechanical energy as a unimodal signal only in one medium or as a bimodal signal into both the substrate and air (Strauβ et al. 2021; Virant-Doberlet et al. 2023 ; see also Caldwell 2014 ). Different signalling structures and mechanisms can be applied simultaneously or sequentially in various combinations (Elias et al. 2003 , 2006 ; Stritih Peljhan and Virant-Doberlet 2021; Virant-Doberlet et al. 2023 ). This versatility, from the complex unimodal to bimodal emissions, provides rich grounds for exploration in terms of complex signalling. Much of our knowledge in this area stems from study of spiders, which combine diverse vibrational signal types with visual signals in intricate performances (e.g., Elias et al. 2006 ; Gibson and Uetz 2008 ; Hebets et al. 2008; Girard et al. 2011 , 2015 ; Choi et al. 2022 ). Crickets (Grylloidea), and particularly field crickets (Gryllidae), may offer an alternative venue to study the function, evolution, and sensory basis of complex dynamic signals in-depth. These insects are one of the most common invertebrate models for studies of sexual behaviour, with the main focus on the acoustic communication and its neuronal control (Huber et al. 1989 ; Zuk and Simmons 1997 ; Robinson and Hall 2002 ; Hedwig 2014 ; Schöneich 2020). Males produce sound by rubbing (stridulation) of tegmina, which is the primary means of attracting female from a distance and the most conspicuous signal during the close-range courtship, as well. Yet, an accumulating body of evidence suggests that this final stage of partner choice is a multimodal process, as the song alone fails to explain it (Kuriwada 2023 ). In particular, the courtship song emitted upon the partner contact was not found to provide reliable information about male attributes (e.g., Wagner and Reiser 2000 ; Gray and Eckard 2001; Ręk 2012 ; Harrison et al. 2013 ), although this was presumed to be its main function (Fitzpatrick and Gray 2001 ; Gray 2005 ; Zuk et al. 2008 ). Studying additional signals, such as contact mechanosensory and chemical (revised in Stritih-Peljhan and Virant-Doberlet 2021 ), and even thermal cues in complementing sound (Erreger et al. 2018 ), has not yet fully resolved our understanding of female mating decisions in crickets. However, the exploration into cricket communication reveals a broad spectrum of vibrational behaviours that accompany the traditional acoustic signals during courtship. These behaviours include antennal, wing, whole body and abdominal vibrations, as well as drumming by palpi, legs and abdomen on the substrate, which are often displayed in concert with the song (Stritih-Peljhan and Virant-Doberlet 2021 ). Intriguingly, despite these behaviours being well documented across cricket families (e.g., Alexander 1967 ; Mays 1971 ; Bell 1980 ; Evans 1988; Dambach and Beck 1990 ; de Mello and dos Reis 1994; Preston-Mafham 2000 ), the characteristics of the emitted signals and their function remained largely unexplored. We have recently highlighted the role of these dynamic signals of crickets as functional complements to the song, indicating their potential to increase the significance of courtship both through increased energetic demands and synchronised display components (Stritih-Peljhan and Virant-Doberlet 2021 ). Simultaneously, an investigation into the vibrational channel in the pacific field cricket, Teleogryllus oceanicus , revealed a previously unknown drumming signal accompanying the song (Broder et al. 2021 ). Yet, the signal’s function remained unclear, as a follow up study showed female preference for non-drumming over drumming individuals (Wikle et al. 2023 ). This indicates the challenge of understanding the complex signals without a thorough analysis of all their components and their potential interaction. These studies also demonstrated that without the focus on substrate vibrations using specialised equipment, certain elements of the display can elude our perception. This holds true even for model cricket species, such as the Pacific field cricket, which have been studied behaviourally for decades (Horch et al. 2017 ). Based on this foundation, we aimed to explore deeper into the male vibroacoustic courtship at the example of the house cricket, Acheta domesticus , known for its simultaneous body tremulation and stridulation (Alexander 1967 ; Hack 1998 ). Neither the characteristics of this combined signal nor that of the tremulation signal alone have ever been investigated. In this species, the ambiguity surrounding the song relates to the finding that the females receive, and use, the information about the costliness of male courtship, while this information is not reflected in the song parameters (Nelson and Nolen 1987; Ręk 2012 ). More specifically, the probability of song production and the proportion of time spent singing are condition dependent, and the females prefer the individuals with a higher duty cycle of song (Nelson and Nolen 1987; Ręk 2012 ). Yet, the pulse rate as an energetically costly song parameter (Hack 1998 ) does not reflect male condition or influence female mating decisions (Nelson and Nolen 1987; Ręk 2012 ). We hypothesised that the ignorance of the complexity of the male courtship display may be the primary cause of this discrepancy. To test this, we examined characteristics of the entire set of male vibroacoustic signals, using combined audio recording, vibration recording using laser vibrometry, and videorecording. This approach revealed a previously unknown leg drumming signal as an additional display component produced concurrently with stridulation and tremulation. We analysed the frequency, intensity, and temporal characteristics of the individual components of this complex signal emitted into the substrate and air. While we focused our attention on their temporal characteristics and interaction, details on frequency and intensity provide a comprehensive view of the complex signal that enhances understanding of its perception, as well as lays ground for future interspecific comparison. The study represents a significant advance in understanding the basis of mate choice in A. domesticus and other crickets, also providing a new and unique example of complex dynamic signalling in insects and animals in general. MATERIALS AND METHODS Animals The crickets, purchased as young to mid-sized larvae from Bugs International, Irsingen, Germany, were kept in glass containers (24 x 38 x 24 cm) with Vermiculite as substrate and egg cardboard cover at 24+/- 1°C, under a reversed 12h/12h light/dark cycle. Larvae were kept in groups of between 50 and 100 individuals, and adults of up to 20 individuals. Upon their imaginal molt, crickets were separated by sex and kept in groups of 3 to 4 days age difference. To reduce their aggression, the males were individually separated into plastic containers (17 x 7 x 5 cm) at least one day prior an experiment. At all stages, the animals received food (fish food in flocks, zucchini, carrots and/or apples) and water ad libitum . Experiments were conducted with 2- to 5-weeks old adults. Recording sound and vibration We paired un unmated male and a female on a low-middle frequency loudspeaker (12.5 cm in diameter), surrounded by transparent foil to restrain the animals. The experiment lasted until copulation, or maximally 30 minutes following courtship initiation. We recorded sound and substrate vibration signals from 55 courting males, using a portable laser vibrometer (PDV 100, Polytec, Waldbronn, Germany) and an omnidirectional microphone (ECM8000, Behringer, Germany) with a preamplifier (Tube Ultragain Mic 100, Behringer, Germany). A foil for laser beam reflectance at various spots on the loudspeaker membrane allowed recording adjacent to the signaller. Sound and vibration were recorded using a Sound Blaster (Creative X-Fi Surround 5.1 pro, Singapore) in Raven Pro 1.6 (Cornell Laboratory of Ornithology, Ithaca, New York, USA) at 44 kHz sampling rate and 16-bit resolution. The vibration recording was calibrated (vibration calibrator, type 4294, Brüel and Kjær, Denmark), while absolute sound intensity was not analysed. Sound and vibration signal analysis Signal analysis was conducted in Raven Pro 1.6. (Cornell, Ithaca, USA), following selection and filtering of recordings in Audacity 3.1.3 (Audacity Team). We applied a 200 Hz high-pass filter to reduce background noise in the auditory channel. In the vibratory channel, we used a 200 Hz high-pass to remove tremulation before analysing stridulation and drumming signals, and a 250 Hz low-pass filter to remove stridulation and drumming before analysing tremulation signals. All signals were manually annotated, and Audacity was used to produce representative power spectra. To minimize observer bias, a blinded approach was used when all data were analysed. Restless females caused the courting males to frequently change position, which interrupted their tremulation and drumming activity (Suppl. Figure 1), so only parts of recordings with minimal locomotion were analysed. Here, only the sections with drumming and tremulation at a “plateau” rate were considered (Suppl. Figure 1). Temporal analysis The analysis of signal rates and interaction based on temporal pattern was performed on recordings from 15 males, each with 55–65 phrases of courtship song (see Figs. 1 , 2 ) selected from 3–6 different sections of signalling under above criteria. In case of stridulation and drumming, this included several thousand signals for the analysis (Table 1 ). Analysing such long sections was required due to variability in drumming performance and limited the analysis mostly to individuals courting reluctant females. Table 1 Spectral, intensity and temporal parameters of courtship stridulation, drumming and tremulation signal components in the auditory and vibratory channels Frequency (kHz) Amplitude Duration (ms) Rate (Hz) Vibro Audio Vibro Audio Vibro Audio mm/s m/s 2 normalized* Stridulation - ticks n.a. 18.26 (13.44–20.33) n.a. n.a. 7.31 (6,31–10,53) n.a. 24 (10) 1.66 (0.42) - pulses 3.79 (2.92–4.31) 4.31 (3.96–5.17) 0.025 (0.016–0.034) 0.56 (0.35–0.78) 1 / 22 (5) 18.48 (5.45) Drumming Cen: 2.41 (2.41–2.76) Lat: 1.03 (0.69–2.07) 2.76 (2.41–4.13) 0.787 (0.429–1.476) Cen: 17.78 (9.92–33.09) Lat: 5.12 (2.09–10.52) 1.70 (1.31–2.15) Cen: 7 (2) Lat: 14 (9–20) 6 (2) 11.31 (7.52–17.24) Tremulation 0.043 (0.038 − 0.043) n.a. 0.230 (0.160–0.345) 0.061 (0.040–0.092) n.a. n.a. n.a. 3.77 (0.43) Values represent mean (with SD) and median (with interquartile ranges) for normally and non-normally distributed data, respectively. Dominant frequency, peak amplitude, and duration were measured for n = 510 drumming and stridulation signals/pulses, and n = 340 tremulation intervals in 17 males. Rate was measured for n = 2536 drums, n = 7709 stridulation (trill) pulses, n = 913 stridulation ticks (all from 55–65 song phrases per male), and n = 112 videorecorded intervals in 15 males. Cen: central section of the loudspeaker membrane (n = 150), Lat: lateral section of the loudspeaker membrane (n = 360); the separation indicates significant influence of location on the measured parameter. *Amplitude of audio signal components relative to that of stridulation pulses in the same individual (median values). / - not evaluated (for stridulation pulses, which were of similar duration in both channels), n.a. - not applicable Stridulation We measured the periods, and calculated rates, of high-frequency stridulation ticks and low-frequency stridulation pulses (from in-phrase periods of the latter) and counted the number of pulses per phrase (Figs. 1 , 2 ). Drumming We applied an amplitude threshold criterion set at 10% of the average vibrational amplitude (peak) of the most intense drums within each song phrase, which reliably distinguished drumming from other impact disturbances. We measured the in-phrase periods, and calculated rates, of drum signals and counted their number per phrase (Fig. 1 ). We calculated the ratio of drums to stridulation trill-pulses emitted per phrase and refer to this ratio as “drumming efficiency”. We calculated the proportion of drums emitted in the pauses between stridulation pulses (by their peak amplitude) and labelled it “drumming accuracy”. We also calculated the proportion of drums associated with different numbers of successive stridulation pulses (Fig. 1 ). In the rare instances where two drums were emitted within the same pulse period, we treated them as a single event for the calculation of drum-pulse association. Tremulation We assessed tremulation rates, often not evident from vibration recordings (see Results), through video analysis. Utilising frame-by-frame examination (in Filmora 11, Wondershare), we counted the cycles of body motion with 0.5 cycle resolution. The analysis focused on the same recording sections (rounded to the closest second) as with other signals, with subdivision for sections longer than 7 seconds for statistical purposes. Tremulation rates were determined from 6–9 sections per male, each lasting 4–7 seconds. Spectral-intensity analysis We measured the dominant (peak) frequency (from power spectrum) and peak velocity of signals in both auditory and vibratory domain (where applicable) from 17 males. Measured was the first 30 stridulation ticks, stridulation pulses and drum signals (with no overlap) in the selections. In the same signals, we also measured signal duration. For tremulation (which did not produce discrete signals), the frequency and amplitude were measured in the periods of individual song phrases. Due to mechanical differences between the central and lateral sections of the loudspeaker membrane, we analysed the signal characteristics emitted on these sections separately. Statistics We report mean values (with SD) for normally distributed data and median values (with IQR) for non-normally distributed data, including the dominant frequency measured as a discrete variable. We assessed the nature of data distribution using the Kolmogorov-Smirnov test. For tremulation rates we applied weighted mean and SD values, considering the duration of the evaluated sections. We examined the relationships among signal temporal and association parameters using the curve estimation function (in Microsoft Excel). We assess statistical significance using Pearson’s correlation, as well as quadratic and cubic regression functions. In case of significance in more regression models, we used the simpler one. We compared the frequency and intensity characteristics of signals between the lateral and central part of the loudspeaker membrane using ANOVA and reported them separately in cases where a significant difference was found. We conducted all statistical tests using SPSS 14.0 (Chicago, SPSS Inc.). RESULTS The complex vibroacoustic signal The stridulatory song of A. domesticus males (Fig. 2 ) represents only one component of a much more complex vibroacoustic courtship signal. We demonstrate the emission of a complex signal by simultaneous action of wing stridulation, body tremulation and leg drumming against the substrate (Fig. 3 , Suppl. Video 1). Our experimental recordings, along with many more observations of the males courting not in standardized conditions, affirm that this signal combination represents a consistent pattern of male courtship behaviour. Drumming and tremulation occur in a close association during the display, with some delay following song initiation. In the initial courtship bout, the median occurrence of the first leg drum was in the second song phrase (IQR 1. – 5. phrase), 1.24 s (IQR 0.43–2.94) after the initial stridulation tick (n = 27). Afterwards, several additional seconds were typically required for drumming and tremulation to reach their plateau rates (Suppl. Figure 1). In this complex signal, the components emitted by stridulation, drumming and tremulation occur in a pattern of regular exchange, described in more detail below. Stridulation The stridulatory courtship song is composed of repetitive elements, called phrases, each containing one high frequency pulse or 'tick', followed by a series of low frequency pulses in the 'trill' (Fig. 2 ); the latter with a considerable component both in the substrate and air (Figs. 3 , 4 ). On average, a phrase contained 9.30 (SD 2.10; n = 929, N = 15) trill pulses (called ‘pulses’ in the following manuscript). The pulses occurred at a mean rate of 18.48 Hz (SD 5.45; Table 1 ), with the variation between 14.66 Hz (SD 3.70, n = 623) and 22.59 Hz (SD 6.44, n = 523) among males. The ticks occurred at a mean rate of 1.66 Hz (SD 0.42 Hz; Table 1 ), with the variation between 1.13 Hz (SD 0.25, n = 64), and 2.05 Hz (SD 0.36, n = 65) among males. The rates of ticks and pulses were linearly correlated (Pearson’s correlation, r = 0.722, P = 0.002; Fig. 6 a), maintaining a stereotyped phrase structure across rates. Drumming Drumming is performed mostly by forelegs, and to a lesser extent also by midlegs, each leg typically producing more consecutive drums. Yet, attributing these signals to individual leg movements was in most cases not possible due to the limited 24-frame rate of video recordings. However, in a sequence where the count of identified drum signals aligned between video and audio recordings, the forelegs accounted for 82% and midlegs to 18% of the signals (n = 43). Each foreleg produced up to four and each midleg up to two consecutive signals. The impact of each leg against the substrate produced a transient pulse with the amplitude peak in the first few milliseconds and a progressive decay. These signals had a broadband frequency structure in both auditory and vibratory domain (Figs. 3 , 4 ). Their rate was highly variable, both within and between individuals. The median (in-phrase) drum rate of the entire sample was 11.31 Hz (IQR 7.52–17.24; n = 2536, N = 15) and ranged from 6.42 Hz (IQR 4.15–8.82, n = 130) to 16.18 Hz (IQR 10.45–22.73, n = 243) among males (see also Fig. 6 c). Association of drumming and stridulation Drumming predominantly occurs during the trill periods of the song (Figs. 3 , 5 a), mostly with drums emitted individually in the pauses following the pulses. This accuracy of drumming in the pauses was 0.84 (SD 0.22; n = 3408, N = 15) overall and ranged from 0.73 (SD 0.21; n = 308) to 0.94 (SD 0.10; n = 220) among the males (see also Fig. 6 g). Most drums were emitted in association with the second pulse, and their occurrence progressively decreased with subsequent pulses in the trill (Fig. 5 a). Very rarely, a drum was emitted immediately following the tick (Fig. 5 a). Most drums were separated by a pause of at least one pulse period, and the likelihood of drum occurrence in association with successive pulses, decreased exponentially with their number in such a series (Fig. 5 b). The efficiency of drums to associate with each pulse in a trill was generally low and variable, with an average of 0.40 (SD 0.17, n = 929) and ranging from 0.26 (SD 0.16, n = 55) to 0.54 (SD 0.18, n = 65) among males (see also Fig. 6 e). A substantial part of its variability within individuals was related to its fluctuation between directly subsequent phrases (Suppl. Figure 2). Full efficiency was achieved extremely rarely; only three males emitted a drum after each trill pulse in one of the phrases analysed (i.e., in 0.3% of the total, n = 929; see also Fig. 6 e). The association between drumming and stridulation rates shows the best and statistically significant fit when modelled as a quadratic function (with pulses: F (2, 12) = 8.158, P = 0.006 / F (2, 12) = 4.042, P = 0.045 for mean / median drumming rates, Fig. 6 c; with ticks: F (2, 12) = 13.520, P < 0.001 / F (2, 12) = 5.955, P = 0.016 for mean / median drumming rates). The peak drumming rate occurs when the stridulation rate approximates the sample median (Fig. 6 c, see also Table 1 ). The association between drumming efficiency and stridulation rate exhibits an initial brief rise followed by a consistent decline of its upper-bound values (for method see Podos 1997 ). This negative trend is statistically significant (Pearson’s correlation, r = − 0.8579, P = 0.028; Fig. 6 e). While the complete set of values shows the best fit to quadratic function, this fit is not statistically significant ( F (2,12) = 0.734, P = 0.5; Fig. 6 e). Drumming accuracy exhibits no dependence on drumming rate or efficiency (Pearson’s correlation r = 0.018–0.089, P = 0.752–0.946; Fig. 6 g). Tremulation Body tremulation occurs with rhythmic lateral movements or “swinging” of the body at a low rate, clearly notable to an observer (Suppl. Video 1). Produced was a continuous, amplitude modulated signal confined to the substrate, with most spectral energy below 100 Hz (Fig. 3 , 4 A, Table 1 ). For the most part, the amplitude peaks did not clearly correspond to the individual phases of body movement. However, in some instances, particularly with slower signaller, this correspondence was more evident (Fig. 7 ). The mean rate of tremulation movement was 3.77 Hz (SD 0.43 Hz; n = 112, N = 15), varying from 3.06 Hz (SD 0.16 Hz, n = 7) to 4.38 Hz (SD 0.23 Hz, n = 6) among males (see also Fig. 6 b). Association of tremulation with drumming and stridulation The timing and rate of tremulation were most closely associated to those of drumming (Figs. 3 , 6 b). At times, the signal’s amplitude modulation accurately represented tremulation movements; these recordings revealed the emission of drums shortly after onset, and with more efficient drummers also shortly before offset of tremulation amplitude increase (Fig. 7 ). Accordingly, we found significant linear correlation between tremulation and drumming rates (Pearson’s correlation, r = 0.682, p = 0.005 and r = 0.5123, P = 0.05, for mean and median drumming rates, respectively), with an approximate 1:2 to 1:4 relationship (Fig. 6 b). The rate of tremulation movements was significantly linearly correlated to that of stridulation ticks (Pearson’s correlation, r = 0.724, P = 0.002). In contrast, the relationship between stridulation pulse and tremulation rates was found to be more complex, with the best and statistically significant fit to a cubic function ( F (2,12) = 6.4211, P = 0.009; Fig. 6 d). Signal frequency, amplitude, and duration The median dominant frequency of stridulation (trill) pulses was 4.3 kHz in the air and 3.79 kHz in the substrate (Fig. 4 , for the IQR, see Table 1 ). Frequency composition of the substrate component was similar for the ticks (but weak and not formally analysed), with the median dominant frequency at 18.26 kHz in the air (Table 1 ). In the substrate, the median dominant frequency of drums was 1.03 kHz on the lateral and over twice higher on the central section of the loudspeaker membrane, while in the air it was 2.76 kHz with no location-related difference (Table 1 ). The dominant frequency peak of tremulation signals was almost invariably at 43 Hz. In the air, the stridulatory ticks were over 7 time more intense than pulses (Table 1 ), while the substrate component was strongest for pulses (median at 0.025 mm/s, Table 1 ). The median peak amplitude of the auditory drumming component was 1.7 times higher than that of stridulation pulses. In the substrate, drumming was by far most intense of all signals (Table 1 ). Tremulation signals had the median peak velocity at 0.23 mm/s (Table 1 ). The mean signal duration was 24 ms for the ticks and 22 ms for the pulses. Drumming signals were much shorter, and similar between the air and substrate, when emitted on the central membrane (around 6 and 7 ms, respectively), while on the lateral membrane the substrate signal was twice longer (Table 1 ). DISCUSSION Complexity of cricket courtship display In field crickets and other cricket taxa, the characteristics and function of vibrational signals, which are not only a by-product of stridulation but often complement it in a complex courtship display, have remained largely unexplored or even primarily overlooked (Stritih-Peljhan and Virant-Doberlet 2021 ). We present the first comprehensive study of the entire set of vibroacoustic signals emitted during courtship of a (field) cricket, analysing both the characteristics of the individual signals and their interaction, as potential targets of female choice. This provides novel insights into the understanding of their courtship process. We demonstrate that in addition to body tremulation, long known as part of courtship in A. domesticus and many other crickets (Alexander 1967 ; Hack 1998 ), the males also drum with the legs against the substrate during their repetitive display. So far, leg drumming was observed to accompany courtship stridulation also in the crickets Vanzoliniella sambophila (Phalangopsidae; de Mello and dos Reis 1994) and T. oceanicus (Gryllidae; Broder et al. 2021 ; Wikle et al. 2023 ). Unlike A. domesticus , however, where all three mechanisms are obligately included in the display, not all T. oceanicus males produced drumming signals, and in neither species males emitted an additional courtship signal by tremulation. Utilising three different signalling mechanisms that involve simultaneous action and coordination of different sets of body muscles in prolonged display, A. domesticus appears to represent a unique case of dynamic signalling in insects. When combining multiple vibroacoustic mechanisms, most insects produce serial signals that do not overlap in time (Virant-Doberlet et al. 2023 ). While certain species of Asopinae stink bugs (Žunič et al. 2008 ), Philloporinae bushcrickets (Korsunovskaya et al. 2020) and Drosophilinae fruit flies (Mazzoni et al. 2013 ) employ three or even four signalling mechanisms during the close-range courtship, they activate these mechanisms either subsequently or transiently combine at most two of them to produce a composite signal. Thus, alongside the intricate visual-vibratory courtship of spiders (e.g., Kozak and Uetz 2016 ) and the combined song and dance performances of birds (e.g., Miles and Fuxjager 2018), crickets provide another example of complex dynamic signalling that merits examination of signalling effort, complexity and coordination as potential factors influencing female choice. Quantity and quality aspects of the complex signal Traditionally, the components of the complex signals have been either viewed as redundant signals providing a functional backup or as signals providing multiple messages to the receiver (Møller and Pomianowski 1993; Johnstone 1996 ; Candolin 2003 ). This view changed when also considering the perceptual mechanisms of receivers (Rowe 1999 ; Hebets and Papaj 2005 ; Starnberger et al. 2014 ; Halfwerk et al. 2019 ), the interaction between signal components (Partan and Marler 1999 ; Hebets and Papaj 2005 ; Hebets et al. 2016 ), and the complexity and quality of (dynamic) displays (Byers et al. 2010 ; Fusani et al. 2014 ; Mitoyen et al. 2019 ) to gain insight into signal function and evolution. Applying these views on the complex signal of A. domesticus helped us to unravel its communicative potential beyond that of the stridulatory song. Signal costs Earlier studies on A. domesticus revealed that the females receive reliable information about male condition from the courtship display and select for the traits based on their costs, such as the time spent singing, while this information is not reflected in song parameters (Nelson and Nolen 1987; Ręk 2012 ). Our study sheds light on this discrepancy, demonstrating that stridulation is only one of three components of the complex signal, whose joint costs do not appear to be simply proportional to that of stridulation. This is indicated through the non-linear correlation between stridulation vs. drumming and tremulation rates, suggesting that the females would not be able to assess male quality solely from one signal parameter (as to the redundant signal hypothesis; Candolin 2003 ). This is a relevant argument since drumming and body tremulation are known to be energetically demanding behaviours, the latter significantly costlier than stridulation (data from A. domesticus : Hack 1997 ; bushcrickets: Römer et al. 2010 ; spiders: Kotiaho et al. 1998 ). The complex signal can thus serve as a much more honest indicator of male condition then courtship stridulation alone, which generally lacks condition dependence in crickets (Wagner and Reiser 2000 ; Gray and Eckadt 2001; Ręk 2012 ). This aspect of honesty may be considered especially relevant in crickets, since courtship with multiply mated females can last for hours (Fleishmann and Sakaluk 2004), so only males in good condition may be expected to sustain the energy demands for optimal display performance (Grafen 1990 ). Performance constraint Our study reveals that the courtship signal of A. domesticus involves periodic coupling (synchrony) among stridulation, drumming, and tremulation signal components, occurring in a pattern of regular exchange. This coupling is particularly consistent between stridulation ticks and pulses, on one hand, and between tremulation and drumming signals, on the other, as evidenced also from the linear correlation of their rates. Drumming and tremulation also tend to mirror the pattern of stridulation. Stridulation, as the primary signal in the display, sets the 'template' to be matched one-to-one (in the trill) by drumming, and at a lower rate by tremulation. However, this matching is generally achieved with low efficiency and high variability, and the occurrence of one drum per pulse is extremely rare, indicating challenges in drumming performance. The nonlinear correlation with stridulation rates indicates a specific constraint on drumming performance, with an upper limit at rates around 18 Hz and an efficiency of 0.55 in association with trill pulses. This constraint does not affect tremulation, whose complex dependence on the stridulation pulse (but not tick) rate may be considered a consequence of its tight coupling with drumming. Similar performance constraints are known from other species due to trade-offs between intrinsically linked signal parameters that are difficult to produce simultaneously. In songbird vocal performance, high signal rates decrease the ability to produce high bandwidth signals, stemming from sensorimotor and physical constraints of their vocal and respiratory apparatus (Podos 1997 ; Goller et al. 2022). In gray treefrogs, male call rate and call duration covary negatively, which has been attributed to the high energetic costs combined with temporal constraints of signal production (Reichert and Gerhardt 2012 ; Ward et al. 2013 ). The mutual constraints inherent in these examples are evident through a negative correlation across the entire range of signal parameter expression. By contrast, the constraint in A. domesticus is specific to drumming and only manifests after reaching a specific effort threshold. This represents a specific and novel case of performance constraint in the complex signalling of animals. The nature of this constraint in the cricket may be, in part, mechanistic, as the leg’s neuromuscular apparatus is also utilised for body support and tremulation. Drumming may be also energetically constrained, but not primarily due to the costs of the complex signal; this limitation may arise from the lack of physiological adaptations in leg muscles for rapid repetitive contractions. In this context, the high proportion of pauses in the drumming rhythm dictated by stridulation, as well as the involvement of both forelegs and midlegs in drumming, may be seen as the necessity for frequent rest periods that avoid anaerobic metabolism, and therewith fatigue and damage to leg muscles (see Mowles et al. 2014). Performance quality through signal interaction In complex signalling involving locomotor activities, the signaller’s quality is conveyed not just through the vigour of performance, but also through the skill of combining challenging motor actions in a coordinated manner (Byers et al. 2010 ; Fusani et al. 2014 ). In A. domesticus , we observed precise timing in the exchange of stridulation, drumming and tremulation signal components, each occurring in a specific time window relative to the others. Given that these components rely on the activity of distinct parts of the neuro-muscular system, specifically the wings and the legs, their precise coordination is essential for such signaling. We evaluated drumming accuracy, as the proportion of drums emitted in pauses between stridulation pulses, as an apparent aspect of coordination quality. Despite this parameter generally demonstrated high performance, it varied largely between individuals, thus providing a putative basis for female choice. The skill of the motor performance is generally relevant for the female, as it reflects neuromuscular capabilities that are considered a reliable indicator of male genetic quality and developmental stability (Byers et al. 2010 ; Mitoyen 2019). Interestingly, we found that drumming accuracy did not correlate with drumming rate or its efficiency to associate with stridulatory pulses. This is intriguing, as trade-offs between parameters reflecting quality and quantity of motor performance can generally be expected, as recently demonstrated in acrobatic mating displays of a songbird (Manica et al. 2017 ). Hence, if female preferences in crickets rely on both courtship display vigor and skill, they might be even less evident when considering stridulation as its only relevant component. Also, evaluating the performance skill goes beyond simple summation of information in the individual components; it requires evaluation of their interaction through sensory integration (Hebets and Papaj 2005 ; Halfwerk et al. 2019 ). Functional insights through spectral-intensity analysis Analysing complex multimodal signals from the view of detection and integration facilitates understanding of their function and evolution (Halfwerk et al. 2019 ). Applied to the components of the complex signal by A. domesticus , this approach supports the tightest functional connection between sensory inputs from drumming and stridulation, while also suggesting a potentially distinct function for tremulation. Stridulation and drumming as one percept We have demonstrated that stridulation and drumming produce similar, higher frequency signals with simultaneous components both in the substrate and air. Crickets have specialised sensory organs detecting such signals; the leg subgenual organ for vibrations (with peak sensitivity at 0.5–1.5 kHz; Kühne et al. 1984 ) and the foreleg tympanal organ for sound (sensitive above 2 kHz; Imaizumi and Pollack 1999). While the vibrational component of stridulation was weak and spectrally above the subgenual organ’s detection range (making its significance questionable), the acoustic component of drumming (peaking between 2.5–4 kHz) was even louder than stridulation, so it must have been well audible to the female. Audible drumming was also recorded in a phalangopsid cricket courting on dry leaves (de Mello and dos Reis 1994), but it may be much less intense on natural substrates with lower stiffness, like soil. However, its vibration component, in our recordings at least 25 dB above threshold of the cricket subgenual organ (Kühne et al. 1984 ), can be considered effective in various environments (see also Elias and Mason 2014 , for the generalist properties of vibratory drumming signals). This vibratory input by drumming will converge with the auditory input by stridulation at two sensory levels of cricket. First, at the level of the subgenual organ sensilla, some of which exhibit bimodal sensitivity to high-frequency vibration and low-frequency sound (Kühne et al. 1984 ). Secondly, at the level of interneurons in the ventral nerve cord, with inputs from specialised auditory and vibratory sensilla (Wiese 1981 ; Kühne et al. 1984 ). This suggests a close functional connection between drumming and stridulation signals, being either perceived as same modality signals or integrated into a common bimodal percept already at the low level of sensory processing in crickets. In line with our insights from temporal analysis, this emphasises the potential significance of the combined stridulation and drumming in the context of female choice. Tremulation We show that, due to mainly horizontal body movements of the male, the rate of tremulation signal is not easily discernible to the female in the vertical component of substrate motion (detected by the laser vibrometer), which is most important in vibration detection (Strauβ et al. 2019). Although insects can detect horizontal substrate vibration (Strauβ et al. 2019), a low-mass insect may not effectively generate such signals on many substrates. Because crickets are nocturnal (Yamano et al. 2001 , for A. domesticus ), tremulation movement also cannot be visually perceived by females. In addition, the vibratory signal had most of the energy content below 100 Hz. This is typical of insect tremulation regardless of substrate type (Žunič et al. 2008 , Stritih and Čokl 2012 ; Stritih and Čokl 2014 ). Besides the inputs directed to complex processing, such stimuli are also detected by the proprioceptive sensilla of the insect body and legs, triggering reflex responses (Stritih and Čokl 2014 ; Strauβ et al. 2021). The primary function of tremulation may thus not be in signalling male quality. It may be rather inducing female (attentive) immobility, as commonly observed with male tremulation during courtship interruption and mate guarding of crickets (Evans 1988; Sakaluk 1991 ; Brown 1999 ; Su and Rentz 2000 ). Both spectral and intensity properties of vibratory tremulation signal in our study (around 0.5 m/s 2 at 50 Hz) are adequate for the proposed function. These intensities largely exceed the threshold of cricket silencing (freezing) response to vibration, as observed in G. campestris (Dambach 1989 ), but remain below the threshold of a vibrational startle response with similar properties among Orthoptera (Stritih and Čokl 2014 ). However, the continuous nature of tremulation during courtship of A. domesticus differs from its occurrence in sporadic bursts during guarding and courtship interruption of crickets. Such a signal may not be optimised for silencing females due to the potential habituation of their response, leaving the function of this complex signal component ambiguous. Conclusions We provide the first comprehensive description of the complete set of vibroacoustic signals constituting courtship display in a species of Gryllidae. This reveals the complexity and synchronisation between multiple signalling mechanisms, including a drumming signal that went completely unnoticed despite decades of study of this model species. Along with the recent discovery of drumming in the Pacific filed cricket (Broder et al. 2021 ), this calls for revisiting cricket courtship behaviour, with a specific focus on vibrational signals that may complement stridulation. The courtship behaviour of A. domesticus stands out as a unique example of complex dynamic signaling in insects, utilising three different vibroacoustic mechanisms in parallel. We demonstrate that the information conveyed to the female through this complex signal extends well beyond that provided by stridulation alone. This encompasses a performance constraint that likely played a crucial role in the signal’s evolution. Exploring the fitness-related value of different parameters of this complex signal and associated female preferences remain obvious next steps in our future research. Declarations Acknowledgements The authors thank Andreas Stumpner (Göttingen) for his comments and suggestions on an earlier version of the manuscript. Funding The authors received financial support from the Slovenian Research and Innovation Agency (Research Core Funding P1–0255). Ethics approval The study did not require ethics review and approval according to Slovenian (Invertebrates; Animal Protection Act, Official Journal of the Republic Slovenia, No 38/13, 21/18-ZNOrg, 92/20 and 159/21) and EU legislation (Directive 2010/63/EU of the European Parliament and of the Council on the protection of animals used for scientific purposes) requirements. The experimental procedures used did not include manipulation associated with pain. The males used in experiments were euthanised by freezing at -20°C and stored in ethanol. All other animals in the stock were provided with food and water until they died naturally. Competing interests The authors declare no competing interests. Data availability statement All data generated and analysed during this study have been uploaded to Zenodo with the DOI: 10.5281/zenodo.10143458 (Zenodo.org). Access to these files will be activated upon paper acceptance. 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A rapidly evolving cricket produces percussive vibrations: how, who, when, and why, Behavioral Ecology , 34(4), 631–64. Yamano, H., Watari, Y., Arai, T., Takeda, M. 2001 Melatonin in drinking water influences a circadian rhythm of locomotor activity in the house cricket, Acheta domesticus . Journal of Insect Physiology, 47(8) , 943–949. Supplementary Files SupplementaryFig1.pdf Suppl. Fig. 1 Initiation and dynamics in the emission of the complex signal. Presented is two-channel recording of sound (audio) and substrate vibration (vibro). The recording shows inclusion of signals by drumming and tremulation with some delay to stridulation (song). Contrasting the song, the rate of these signals increases for several seconds before reaching a 'plateau'. In this recording, male drumming and tremulation were repeatedly interrupted (as indicated by arrows) by female movement, inducing the male to follow her. Note that stridulation was much less affected by the male locomotion. SupplementaryFig2.pdf Suppl. Fig. 2 Variation in drumming efficiency over the successive phrases of courtship song. Shown are three example individuals, with high, medium, and low drumming efficiency. Data from different sections of recording are shown in different colours. Full and dashed black lines indicate their mean and SD values, respectively SupplementaryVideo1.mp4 Suppl. Video 1 The complex courtship display of A. domesticus . The male is signalling on the lateral section of the loudspeaker membrane. Specially in this recording, its position was constrained by an additional foil-barrier surrounding the central section of the membrane. Recording by the laser vibrometer, made close to the signaller (on the lateral membrane just outside the field of view), was driven to the camera and can be heard on the video Cite Share Download PDF Status: Published Journal Publication published 26 Nov, 2024 Read the published version in Behavioral Ecology and Sociobiology → Version 1 posted Editorial decision: Major Revisions Needed 25 Apr, 2024 Reviewers agreed at journal 21 Mar, 2024 Reviewers invited by journal 17 Mar, 2024 Editor assigned by journal 29 Feb, 2024 First submitted to journal 25 Feb, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3971219","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":280512350,"identity":"e682095b-04e4-4bba-8839-9a7942692d63","order_by":0,"name":"Nataša Stritih-Peljhan","email":"data:image/png;base64,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","orcid":"https://orcid.org/0000-0002-9021-8235","institution":"National Institute of Biology: Nacionalni institut za biologijo","correspondingAuthor":true,"prefix":"","firstName":"Nataša","middleName":"","lastName":"Stritih-Peljhan","suffix":""},{"id":280512351,"identity":"88cef5c6-d9fc-46b1-a34a-59d215962cfd","order_by":1,"name":"Alenka Žunič-Kosi","email":"","orcid":"","institution":"National Institute of Biology: Nacionalni institut za biologijo","correspondingAuthor":false,"prefix":"","firstName":"Alenka","middleName":"","lastName":"Žunič-Kosi","suffix":""}],"badges":[],"createdAt":"2024-02-20 00:50:20","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3971219/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3971219/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00265-024-03530-y","type":"published","date":"2024-11-26T15:58:06+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":52973960,"identity":"eca4e601-2fdf-4939-9a5a-bf857e502030","added_by":"auto","created_at":"2024-03-19 08:53:59","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":98855,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic representation of stridulation and drumming signals in a song phrase, depicting the evaluated temporal and association parameters\u003c/p\u003e","description":"","filename":"Fig1.png","url":"https://assets-eu.researchsquare.com/files/rs-3971219/v1/43a5008d611fb66ab13d3878.png"},{"id":52973962,"identity":"2b2012b6-71ec-4974-9a48-e28057fe6fa2","added_by":"auto","created_at":"2024-03-19 08:54:00","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1197931,"visible":true,"origin":"","legend":"\u003cp\u003eThe stridulatory courtship song of \u003cem\u003eA. domesticus\u003c/em\u003e.\u003cstrong\u003e \u003c/strong\u003eThe song consists of repetitive elements called 'phrases', each with a single high frequency pulse called the 'tick' (T), followed by a series of low frequency pulses (p) of lower amplitude, called the 'trill'. The phrase indicated on the left is shown at an expanded scale on the right. Presented is the recording immediately after the initiation of the song before the inclusion of drumming and tremulation. Signal amplitude is in arbitrary units\u003c/p\u003e","description":"","filename":"Fig2.png","url":"https://assets-eu.researchsquare.com/files/rs-3971219/v1/9554d84d4309900eac3b05cc.png"},{"id":52973958,"identity":"2b3cc82a-8be9-4e23-9934-1fc2c8f8a272","added_by":"auto","created_at":"2024-03-19 08:53:59","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":2480142,"visible":true,"origin":"","legend":"\u003cp\u003eThe complex vibroacoustic signal emitted by stridulation, drumming and tremulation in \u003cem\u003eA. domesticus\u003c/em\u003e. Presented is a two-channel recording of sound (audio) and substrate vibration (vibro), when the male was signaling on a loudspeaker membrane. T: stridulation ticks; p: stridulation pulses; arrows (dr): leg drumming against the substrate (each strike producing a transient signal); tr: body tremulation (producing a continuous, amplitude modulated signal). Note the occurrence of drums in the pauses between stridulation pulses, along with the general increase in tremulation amplitude. Signal amplitude is shown in arbitrary units, with 1 corresponding to 0.579 mm/s in the vibration channel\u003c/p\u003e","description":"","filename":"Fig3.png","url":"https://assets-eu.researchsquare.com/files/rs-3971219/v1/867a75e4ea42835626c5561f.png"},{"id":52973957,"identity":"e61819ce-bcd2-4ccd-84c8-8e32e93cd56e","added_by":"auto","created_at":"2024-03-19 08:53:59","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":261395,"visible":true,"origin":"","legend":"\u003cp\u003eSample spectra of the various signal components in the substrate and air. The left side illustrates the vibratory and the right side the auditory components of tremulation, drumming and stridulation (trill) pulse signals. The spectral peaks of these examples align with the median dominant frequency of the sample. Their relative intensities illustrate differences between the median values of the vibration velocity / sound intensity of the signals. trem: tremulation; drum-l: drumming on the lateral section of the loudspeaker, drum-c: drumming on the central section of the loudspeaker; strid - stridulation pulse\u003c/p\u003e","description":"","filename":"Fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-3971219/v1/4044e7c6985086cff0d45a56.png"},{"id":52973961,"identity":"051a3d66-c9a4-4c2b-9bad-a89f4c001227","added_by":"auto","created_at":"2024-03-19 08:53:59","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":158056,"visible":true,"origin":"","legend":"\u003cp\u003eTemporal association of stridulation and drumming components of the complex signal.\u003cstrong\u003e \u003c/strong\u003ea) The proportion of drums associated with each of the successive stridulation pulses per phrase in the individual males (n = 119 – 314, N = 15). The x-axis represents the phrase structure with a tick and the mean (+1) number of low-frequency pulses in the trill. b) The proportion of drums in the associations with a different number of successive stridulation pulses, without an intercalated pause of one pulse interval, in individual males (n = 119 – 314, N=15)\u003c/p\u003e","description":"","filename":"Fig5.png","url":"https://assets-eu.researchsquare.com/files/rs-3971219/v1/4ad47346d9726ae7c84c8292.png"},{"id":52973966,"identity":"3d82e70e-95ed-4a5b-8bd4-c89d368261f3","added_by":"auto","created_at":"2024-03-19 08:54:00","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":503917,"visible":true,"origin":"","legend":"\u003cp\u003eThe relationships between the temporal and association parameters of the complex signal.\u003cstrong\u003e \u003c/strong\u003ePresented are means from individual males, and medians in (d) (due to non-normal data distribution), together with regression lines of best fit by the least-square analysis. In (e), maximal values (white circles, right scale) are also depicted along with their regression line. \u003cem\u003eR\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e = 0.5217 (a), 0.465 (b), 0.4033 (c), 0.6365 (d), 0.1120 (e), 0.1266 (f), 0.0011 (g)\u003c/p\u003e","description":"","filename":"Fig6.png","url":"https://assets-eu.researchsquare.com/files/rs-3971219/v1/2a80a76d332bfe7a9f44b625.png"},{"id":52973959,"identity":"c67dc101-7d75-4d65-a521-bbbcec6799b4","added_by":"auto","created_at":"2024-03-19 08:53:59","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":805119,"visible":true,"origin":"","legend":"\u003cp\u003eTemporal association of tremulation and drumming components of the complex signal. An example vibration recording with a more strongly pronounced amplitude modulation in the tremulation signal. The tremulation rate, calculated from the peaks (indicated by asterisks), matches the one determined from the video of the same section. Note the consistent occurrence of leg drums shortly after the onset, and occasionally just before the offset, of tremulation amplitude increase. Full and empty arrows indicate leg drums above and below the amplitude threshold, respectively. The signal amplitude is shown in arbitrary units, with 1 corresponding to 0.157 mm/s\u003c/p\u003e","description":"","filename":"Fig7.png","url":"https://assets-eu.researchsquare.com/files/rs-3971219/v1/3f9f5671e8cfffd9ebacdf12.png"},{"id":70388703,"identity":"ee7f5c51-796f-4017-a2f9-77f8f48ddac9","added_by":"auto","created_at":"2024-12-02 17:27:01","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6450024,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3971219/v1/7e01168f-2ced-483e-b7c6-0987f64ba42c.pdf"},{"id":52973965,"identity":"03c30e88-b16b-4c1b-b496-1908b3b83c94","added_by":"auto","created_at":"2024-03-19 08:54:00","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":164384,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSuppl. Fig. 1\u003c/strong\u003e Initiation and dynamics in the emission of the complex signal. Presented is two-channel recording of sound (audio) and substrate vibration (vibro). The recording shows inclusion of signals by drumming and tremulation with some delay to stridulation (song). Contrasting the song, the rate of these signals increases for several seconds before reaching a 'plateau'. In this recording, male drumming and tremulation were repeatedly interrupted (as indicated by arrows) by female movement, inducing the male to follow her. Note that stridulation was much less affected by the male locomotion.\u003c/p\u003e","description":"","filename":"SupplementaryFig1.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3971219/v1/5914acf30a384f34d9387c80.pdf"},{"id":52973964,"identity":"d4a7ae9b-3bbf-4c95-aae5-1397c5bd0575","added_by":"auto","created_at":"2024-03-19 08:54:00","extension":"pdf","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":205604,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSuppl. Fig. 2\u003c/strong\u003e Variation in drumming efficiency over the successive phrases of courtship song. Shown are three example individuals, with high, medium, and low drumming efficiency. Data from different sections of recording are shown in different colours. Full and dashed black lines indicate their mean and SD values, respectively\u003c/p\u003e","description":"","filename":"SupplementaryFig2.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3971219/v1/e53ee0aa9022601b20c815fe.pdf"},{"id":52973963,"identity":"35770a64-872e-46e1-85da-99906a2d3671","added_by":"auto","created_at":"2024-03-19 08:54:00","extension":"mp4","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":8199653,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSuppl. Video 1\u003c/strong\u003e The complex courtship display of \u003cem\u003eA. domesticus\u003c/em\u003e.\u003cstrong\u003e \u003c/strong\u003eThe male is signalling on the lateral section of the loudspeaker membrane. Specially in this recording, its position was constrained by an additional foil-barrier surrounding the central section of the membrane. Recording by the laser vibrometer, made close to the signaller (on the lateral membrane just outside the field of view), was driven to the camera and can be heard on the video\u003c/p\u003e","description":"","filename":"SupplementaryVideo1.mp4","url":"https://assets-eu.researchsquare.com/files/rs-3971219/v1/1d737183781da2f75ab33423.mp4"}],"financialInterests":"","formattedTitle":"More than stridulation: signal interaction and constraint in the complex vibroacoustic courtship of a cricket","fulltext":[{"header":"SIGNIFICANCE STATEMENT ","content":"\u003cp\u003eOur study delves into the vast domain of vibroacoustic signals in insects, specifically crickets, exploring the information conveyed by their\u0026nbsp;complex dynamic displays. While traditional acoustic signals in crickets have received most attention, our pioneering study of the entire set of vibroacoustic signals during courtship of a field cricket (\u003cem\u003eAcheta domesticus\u003c/em\u003e) unveils a complex signal involving coordinated wing stridulation, body tremulation, and leg drumming against the substrate. Notably, we reveal a performance constraint specific to one signal component, which represents a unique case in complex dynamic signalling. Also, we find no correlation between the display vigour and skill, challenging common expectations. This study not only enhances our understanding of cricket courtship but also contributes to our knowledge of complex signaling in animals.\u003c/p\u003e"},{"header":"INTRODUCTION","content":"\u003cp\u003eAnimals often communicate using complex signals with multiple components in the same or across sensory modalities. These multicomponent and multimodal signals play a crucial role in enhancing communication by increasing the information content, improving the effectiveness of signal transmission, and influencing receiver response through the interaction between signal components (Candolin \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Hebets and Papay 2005; Hebets and McGinley \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Courtship is a prominent context where such complex signals are observed, where their primary function is to advertise the signaler\u0026rsquo;s quality and expedite mating decisions (Bastock \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e1967\u003c/span\u003e; Mitoyen et al. \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). The females, in particular, can assess potential mates by analysing information in individual signal components, their interaction, and also the overall complexity of the signal (Candolin \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Mitoyen et al. \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Choi et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In complex dynamic displays, females may select males based on their motor performance, assessing both neuromuscular capabilities and acquired skills (Byers at al. 2010; Fussani et al. 2014).\u003c/p\u003e \u003cp\u003eThe domain of vibro-acoustic signals in insects and other arthropods provides a unique perspective of complex signalling. This system allows for dynamic communication using nearly any body part, from the head to abdomen and appendages (Ewing \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e1989\u003c/span\u003e; Virant-Doberlet et al. \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The signals may not even require a specialised structure for their production, such as in case of vibration (tremulation) of body parts and their drumming on the substrate, and the same body part may be engaged in different signalling mechanisms (Hill 2009; Virant-Doberlet et al. \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). For example, an abdomen may be vibrating, drumming, or scraping the substrate, thereby emitting mechanical energy as a unimodal signal only in one medium or as a bimodal signal into both the substrate and air (Strauβ et al. 2021; Virant-Doberlet et al. \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; see also Caldwell \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Different signalling structures and mechanisms can be applied simultaneously or sequentially in various combinations (Elias et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2003\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Stritih Peljhan and Virant-Doberlet 2021; Virant-Doberlet et al. \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). This versatility, from the complex unimodal to bimodal emissions, provides rich grounds for exploration in terms of complex signalling. Much of our knowledge in this area stems from study of spiders, which combine diverse vibrational signal types with visual signals in intricate performances (e.g., Elias et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Gibson and Uetz \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Hebets et al. 2008; Girard et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Choi et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eCrickets (Grylloidea), and particularly field crickets (Gryllidae), may offer an alternative venue to study the function, evolution, and sensory basis of complex dynamic signals in-depth. These insects are one of the most common invertebrate models for studies of sexual behaviour, with the main focus on the acoustic communication and its neuronal control (Huber et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e1989\u003c/span\u003e; Zuk and Simmons \u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Robinson and Hall \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Hedwig \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Sch\u0026ouml;neich 2020). Males produce sound by rubbing (stridulation) of tegmina, which is the primary means of attracting female from a distance and the most conspicuous signal during the close-range courtship, as well. Yet, an accumulating body of evidence suggests that this final stage of partner choice is a multimodal process, as the song alone fails to explain it (Kuriwada \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). In particular, the courtship song emitted upon the partner contact was not found to provide reliable information about male attributes (e.g., Wagner and Reiser \u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Gray and Eckard 2001; Ręk \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Harrison et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2013\u003c/span\u003e), although this was presumed to be its main function (Fitzpatrick and Gray \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Gray \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Zuk et al. \u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Studying additional signals, such as contact mechanosensory and chemical (revised in Stritih-Peljhan and Virant-Doberlet \u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), and even thermal cues in complementing sound (Erreger et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), has not yet fully resolved our understanding of female mating decisions in crickets.\u003c/p\u003e \u003cp\u003eHowever, the exploration into cricket communication reveals a broad spectrum of vibrational behaviours that accompany the traditional acoustic signals during courtship. These behaviours include antennal, wing, whole body and abdominal vibrations, as well as drumming by palpi, legs and abdomen on the substrate, which are often displayed in concert with the song (Stritih-Peljhan and Virant-Doberlet \u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Intriguingly, despite these behaviours being well documented across cricket families (e.g., Alexander \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1967\u003c/span\u003e; Mays \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e1971\u003c/span\u003e; Bell \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1980\u003c/span\u003e; Evans 1988; Dambach and Beck \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1990\u003c/span\u003e; de Mello and dos Reis 1994; Preston-Mafham \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2000\u003c/span\u003e), the characteristics of the emitted signals and their function remained largely unexplored. We have recently highlighted the role of these dynamic signals of crickets as functional complements to the song, indicating their potential to increase the significance of courtship both through increased energetic demands and synchronised display components (Stritih-Peljhan and Virant-Doberlet \u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Simultaneously, an investigation into the vibrational channel in the pacific field cricket, \u003cem\u003eTeleogryllus oceanicus\u003c/em\u003e, revealed a previously unknown drumming signal accompanying the song (Broder et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Yet, the signal\u0026rsquo;s function remained unclear, as a follow up study showed female preference for non-drumming over drumming individuals (Wikle et al. \u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). This indicates the challenge of understanding the complex signals without a thorough analysis of all their components and their potential interaction. These studies also demonstrated that without the focus on substrate vibrations using specialised equipment, certain elements of the display can elude our perception. This holds true even for model cricket species, such as the Pacific field cricket, which have been studied behaviourally for decades (Horch et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eBased on this foundation, we aimed to explore deeper into the male vibroacoustic courtship at the example of the house cricket, \u003cem\u003eAcheta domesticus\u003c/em\u003e, known for its simultaneous body tremulation and stridulation (Alexander \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1967\u003c/span\u003e; Hack \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). Neither the characteristics of this combined signal nor that of the tremulation signal alone have ever been investigated. In this species, the ambiguity surrounding the song relates to the finding that the females receive, and use, the information about the costliness of male courtship, while this information is not reflected in the song parameters (Nelson and Nolen 1987; Ręk \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). More specifically, the probability of song production and the proportion of time spent singing are condition dependent, and the females prefer the individuals with a higher duty cycle of song (Nelson and Nolen 1987; Ręk \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Yet, the pulse rate as an energetically costly song parameter (Hack \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1998\u003c/span\u003e) does not reflect male condition or influence female mating decisions (Nelson and Nolen 1987; Ręk \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). We hypothesised that the ignorance of the complexity of the male courtship display may be the primary cause of this discrepancy.\u003c/p\u003e \u003cp\u003eTo test this, we examined characteristics of the entire set of male vibroacoustic signals, using combined audio recording, vibration recording using laser vibrometry, and videorecording. This approach revealed a previously unknown leg drumming signal as an additional display component produced concurrently with stridulation and tremulation. We analysed the frequency, intensity, and temporal characteristics of the individual components of this complex signal emitted into the substrate and air. While we focused our attention on their temporal characteristics and interaction, details on frequency and intensity provide a comprehensive view of the complex signal that enhances understanding of its perception, as well as lays ground for future interspecific comparison. The study represents a significant advance in understanding the basis of mate choice in \u003cem\u003eA. domesticus\u003c/em\u003e and other crickets, also providing a new and unique example of complex dynamic signalling in insects and animals in general.\u003c/p\u003e"},{"header":"MATERIALS AND METHODS","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eAnimals\u003c/h2\u003e \u003cp\u003eThe crickets, purchased as young to mid-sized larvae from Bugs International, Irsingen, Germany, were kept in glass containers (24 x 38 x 24 cm) with Vermiculite as substrate and egg cardboard cover at 24+/- 1\u0026deg;C, under a reversed 12h/12h light/dark cycle. Larvae were kept in groups of between 50 and 100 individuals, and adults of up to 20 individuals. Upon their imaginal molt, crickets were separated by sex and kept in groups of 3 to 4 days age difference. To reduce their aggression, the males were individually separated into plastic containers (17 x 7 x 5 cm) at least one day prior an experiment. At all stages, the animals received food (fish food in flocks, zucchini, carrots and/or apples) and water \u003cem\u003ead libitum\u003c/em\u003e. Experiments were conducted with 2- to 5-weeks old adults.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eRecording sound and vibration\u003c/h2\u003e \u003cp\u003eWe paired un unmated male and a female on a low-middle frequency loudspeaker (12.5 cm in diameter), surrounded by transparent foil to restrain the animals. The experiment lasted until copulation, or maximally 30 minutes following courtship initiation. We recorded sound and substrate vibration signals from 55 courting males, using a portable laser vibrometer (PDV 100, Polytec, Waldbronn, Germany) and an omnidirectional microphone (ECM8000, Behringer, Germany) with a preamplifier (Tube Ultragain Mic 100, Behringer, Germany). A foil for laser beam reflectance at various spots on the loudspeaker membrane allowed recording adjacent to the signaller. Sound and vibration were recorded using a Sound Blaster (Creative X-Fi Surround 5.1 pro, Singapore) in Raven Pro 1.6 (Cornell Laboratory of Ornithology, Ithaca, New York, USA) at 44 kHz sampling rate and 16-bit resolution. The vibration recording was calibrated (vibration calibrator, type 4294, Br\u0026uuml;el and Kj\u0026aelig;r, Denmark), while absolute sound intensity was not analysed.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eSound and vibration signal analysis\u003c/h2\u003e \u003cp\u003eSignal analysis was conducted in Raven Pro 1.6. (Cornell, Ithaca, USA), following selection and filtering of recordings in Audacity 3.1.3 (Audacity Team). We applied a 200 Hz high-pass filter to reduce background noise in the auditory channel. In the vibratory channel, we used a 200 Hz high-pass to remove tremulation before analysing stridulation and drumming signals, and a 250 Hz low-pass filter to remove stridulation and drumming before analysing tremulation signals. All signals were manually annotated, and Audacity was used to produce representative power spectra. To minimize observer bias, a blinded approach was used when all data were analysed.\u003c/p\u003e \u003cp\u003eRestless females caused the courting males to frequently change position, which interrupted their tremulation and drumming activity (Suppl. Figure\u0026nbsp;1), so only parts of recordings with minimal locomotion were analysed. Here, only the sections with drumming and tremulation at a \u0026ldquo;plateau\u0026rdquo; rate were considered (Suppl. Figure\u0026nbsp;1).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eTemporal analysis\u003c/h2\u003e \u003cp\u003eThe analysis of signal rates and interaction based on temporal pattern was performed on recordings from 15 males, each with 55\u0026ndash;65 phrases of courtship song (see Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) selected from 3\u0026ndash;6 different sections of signalling under above criteria. In case of stridulation and drumming, this included several thousand signals for the analysis (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Analysing such long sections was required due to variability in drumming performance and limited the analysis mostly to individuals courting reluctant females.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSpectral, intensity and temporal parameters of courtship stridulation, drumming and tremulation signal components in the auditory and vibratory channels\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eFrequency (kHz)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c6\" namest=\"c4\"\u003e \u003cp\u003eAmplitude\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003eDuration (ms)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eRate (Hz)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eVibro\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAudio\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003eVibro\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eAudio\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eVibro\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eAudio\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003emm/s\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003em/s\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003enormalized*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eStridulation\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003e- ticks\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003en.a.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e18.26\u003c/p\u003e \u003cp\u003e(13.44\u0026ndash;20.33)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003en.a.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003en.a.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e7.31\u003c/p\u003e \u003cp\u003e(6,31\u0026ndash;10,53)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003en.a.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e24\u003c/p\u003e \u003cp\u003e(10)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e1.66\u003c/p\u003e \u003cp\u003e(0.42)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e- pulses\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.79\u003c/p\u003e \u003cp\u003e(2.92\u0026ndash;4.31)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.31\u003c/p\u003e \u003cp\u003e(3.96\u0026ndash;5.17)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.025\u003c/p\u003e \u003cp\u003e(0.016\u0026ndash;0.034)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.56\u003c/p\u003e \u003cp\u003e(0.35\u0026ndash;0.78)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e22\u003c/p\u003e \u003cp\u003e(5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e18.48\u003c/p\u003e \u003cp\u003e(5.45)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eDrumming\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCen: 2.41\u003c/p\u003e \u003cp\u003e(2.41\u0026ndash;2.76)\u003c/p\u003e \u003cp\u003eLat: 1.03\u003c/p\u003e \u003cp\u003e(0.69\u0026ndash;2.07)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.76\u003c/p\u003e \u003cp\u003e(2.41\u0026ndash;4.13)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.787\u003c/p\u003e \u003cp\u003e(0.429\u0026ndash;1.476)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCen: 17.78 (9.92\u0026ndash;33.09)\u003c/p\u003e \u003cp\u003eLat: 5.12\u003c/p\u003e \u003cp\u003e(2.09\u0026ndash;10.52)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.70\u003c/p\u003e \u003cp\u003e(1.31\u0026ndash;2.15)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eCen:\u003c/p\u003e \u003cp\u003e7 (2)\u003c/p\u003e \u003cp\u003eLat: 14\u003c/p\u003e \u003cp\u003e(9\u0026ndash;20)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e6\u003c/p\u003e \u003cp\u003e(2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e11.31\u003c/p\u003e \u003cp\u003e(7.52\u0026ndash;17.24)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eTremulation\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.043\u003c/p\u003e \u003cp\u003e(0.038 \u0026minus;\u0026thinsp;0.043)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003en.a.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.230\u003c/p\u003e \u003cp\u003e(0.160\u0026ndash;0.345)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.061\u003c/p\u003e \u003cp\u003e(0.040\u0026ndash;0.092)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003en.a.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003en.a.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003en.a.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e3.77\u003c/p\u003e \u003cp\u003e(0.43)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"9\"\u003eValues represent mean (with SD) and median (with interquartile ranges) for normally and non-normally distributed data, respectively. Dominant frequency, peak amplitude, and duration were measured for n\u0026thinsp;=\u0026thinsp;510 drumming and stridulation signals/pulses, and n\u0026thinsp;=\u0026thinsp;340 tremulation intervals in 17 males. Rate was measured for n\u0026thinsp;=\u0026thinsp;2536 drums, n\u0026thinsp;=\u0026thinsp;7709 stridulation (trill) pulses, n\u0026thinsp;=\u0026thinsp;913 stridulation ticks (all from 55\u0026ndash;65 song phrases per male), and n\u0026thinsp;=\u0026thinsp;112 videorecorded intervals in 15 males. Cen: central section of the loudspeaker membrane (n\u0026thinsp;=\u0026thinsp;150), Lat: lateral section of the loudspeaker membrane (n\u0026thinsp;=\u0026thinsp;360); the separation indicates significant influence of location on the measured parameter. *Amplitude of audio signal components relative to that of stridulation pulses in the same individual (median values). / - not evaluated (for stridulation pulses, which were of similar duration in both channels), n.a. - not applicable\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eStridulation\u003c/h2\u003e \u003cp\u003eWe measured the periods, and calculated rates, of high-frequency stridulation ticks and low-frequency stridulation pulses (from in-phrase periods of the latter) and counted the number of pulses per phrase (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eDrumming\u003c/h2\u003e \u003cp\u003eWe applied an amplitude threshold criterion set at 10% of the average vibrational amplitude (peak) of the most intense drums within each song phrase, which reliably distinguished drumming from other impact disturbances. We measured the in-phrase periods, and calculated rates, of drum signals and counted their number per phrase (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). We calculated the ratio of drums to stridulation trill-pulses emitted per phrase and refer to this ratio as \u0026ldquo;drumming efficiency\u0026rdquo;. We calculated the proportion of drums emitted in the pauses between stridulation pulses (by their peak amplitude) and labelled it \u0026ldquo;drumming accuracy\u0026rdquo;. We also calculated the proportion of drums associated with different numbers of successive stridulation pulses (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). In the rare instances where two drums were emitted within the same pulse period, we treated them as a single event for the calculation of drum-pulse association.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003eTremulation\u003c/h2\u003e \u003cp\u003eWe assessed tremulation rates, often not evident from vibration recordings (see Results), through video analysis. Utilising frame-by-frame examination (in Filmora 11, Wondershare), we counted the cycles of body motion with 0.5 cycle resolution. The analysis focused on the same recording sections (rounded to the closest second) as with other signals, with subdivision for sections longer than 7 seconds for statistical purposes. Tremulation rates were determined from 6\u0026ndash;9 sections per male, each lasting 4\u0026ndash;7 seconds.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eSpectral-intensity analysis\u003c/h2\u003e \u003cp\u003eWe measured the dominant (peak) frequency (from power spectrum) and peak velocity of signals in both auditory and vibratory domain (where applicable) from 17 males. Measured was the first 30 stridulation ticks, stridulation pulses and drum signals (with no overlap) in the selections. In the same signals, we also measured signal duration. For tremulation (which did not produce discrete signals), the frequency and amplitude were measured in the periods of individual song phrases. Due to mechanical differences between the central and lateral sections of the loudspeaker membrane, we analysed the signal characteristics emitted on these sections separately.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eStatistics\u003c/h2\u003e \u003cp\u003eWe report mean values (with SD) for normally distributed data and median values (with IQR) for non-normally distributed data, including the dominant frequency measured as a discrete variable. We assessed the nature of data distribution using the Kolmogorov-Smirnov test. For tremulation rates we applied weighted mean and SD values, considering the duration of the evaluated sections. We examined the relationships among signal temporal and association parameters using the curve estimation function (in Microsoft Excel). We assess statistical significance using Pearson\u0026rsquo;s correlation, as well as quadratic and cubic regression functions. In case of significance in more regression models, we used the simpler one. We compared the frequency and intensity characteristics of signals between the lateral and central part of the loudspeaker membrane using ANOVA and reported them separately in cases where a significant difference was found. We conducted all statistical tests using SPSS 14.0 (Chicago, SPSS Inc.).\u003c/p\u003e \u003c/div\u003e"},{"header":"RESULTS","content":"\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eThe complex vibroacoustic signal\u003c/h2\u003e \u003cp\u003eThe stridulatory song of \u003cem\u003eA. domesticus\u003c/em\u003e males (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) represents only one component of a much more complex vibroacoustic courtship signal. We demonstrate the emission of a complex signal by simultaneous action of wing stridulation, body tremulation and leg drumming against the substrate (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, Suppl. Video 1). Our experimental recordings, along with many more observations of the males courting not in standardized conditions, affirm that this signal combination represents a consistent pattern of male courtship behaviour.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eDrumming and tremulation occur in a close association during the display, with some delay following song initiation. In the initial courtship bout, the median occurrence of the first leg drum was in the second song phrase (IQR 1. \u0026ndash; 5. phrase), 1.24 s (IQR 0.43\u0026ndash;2.94) after the initial stridulation tick (n\u0026thinsp;=\u0026thinsp;27). Afterwards, several additional seconds were typically required for drumming and tremulation to reach their plateau rates (Suppl. Figure\u0026nbsp;1). In this complex signal, the components emitted by stridulation, drumming and tremulation occur in a pattern of regular exchange, described in more detail below.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eStridulation\u003c/h2\u003e \u003cp\u003e The stridulatory courtship song is composed of repetitive elements, called phrases, each containing one high frequency pulse or 'tick', followed by a series of low frequency pulses in the 'trill' (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e); the latter with a considerable component both in the substrate and air (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). On average, a phrase contained 9.30 (SD 2.10; n\u0026thinsp;=\u0026thinsp;929, N\u0026thinsp;=\u0026thinsp;15) trill pulses (called \u0026lsquo;pulses\u0026rsquo; in the following manuscript). The pulses occurred at a mean rate of 18.48 Hz (SD 5.45; Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), with the variation between 14.66 Hz (SD 3.70, n\u0026thinsp;=\u0026thinsp;623) and 22.59 Hz (SD 6.44, n\u0026thinsp;=\u0026thinsp;523) among males. The ticks occurred at a mean rate of 1.66 Hz (SD 0.42 Hz; Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), with the variation between 1.13 Hz (SD 0.25, n\u0026thinsp;=\u0026thinsp;64), and 2.05 Hz (SD 0.36, n\u0026thinsp;=\u0026thinsp;65) among males. The rates of ticks and pulses were linearly correlated (Pearson\u0026rsquo;s correlation, r\u0026thinsp;=\u0026thinsp;0.722, P\u0026thinsp;=\u0026thinsp;0.002; Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea), maintaining a stereotyped phrase structure across rates.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eDrumming\u003c/h2\u003e \u003cp\u003eDrumming is performed mostly by forelegs, and to a lesser extent also by midlegs, each leg typically producing more consecutive drums. Yet, attributing these signals to individual leg movements was in most cases not possible due to the limited 24-frame rate of video recordings. However, in a sequence where the count of identified drum signals aligned between video and audio recordings, the forelegs accounted for 82% and midlegs to 18% of the signals (n\u0026thinsp;=\u0026thinsp;43). Each foreleg produced up to four and each midleg up to two consecutive signals.\u003c/p\u003e \u003cp\u003eThe impact of each leg against the substrate produced a transient pulse with the amplitude peak in the first few milliseconds and a progressive decay. These signals had a broadband frequency structure in both auditory and vibratory domain (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Their rate was highly variable, both within and between individuals. The median (in-phrase) drum rate of the entire sample was 11.31 Hz (IQR 7.52\u0026ndash;17.24; n\u0026thinsp;=\u0026thinsp;2536, N\u0026thinsp;=\u0026thinsp;15) and ranged from 6.42 Hz (IQR 4.15\u0026ndash;8.82, n\u0026thinsp;=\u0026thinsp;130) to 16.18 Hz (IQR 10.45\u0026ndash;22.73, n\u0026thinsp;=\u0026thinsp;243) among males (see also Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eAssociation of drumming and stridulation\u003c/h2\u003e \u003cp\u003eDrumming predominantly occurs during the trill periods of the song (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea), mostly with drums emitted individually in the pauses following the pulses. This accuracy of drumming in the pauses was 0.84 (SD 0.22; n\u0026thinsp;=\u0026thinsp;3408, N\u0026thinsp;=\u0026thinsp;15) overall and ranged from 0.73 (SD 0.21; n\u0026thinsp;=\u0026thinsp;308) to 0.94 (SD 0.10; n\u0026thinsp;=\u0026thinsp;220) among the males (see also Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eg). Most drums were emitted in association with the second pulse, and their occurrence progressively decreased with subsequent pulses in the trill (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea). Very rarely, a drum was emitted immediately following the tick (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea). Most drums were separated by a pause of at least one pulse period, and the likelihood of drum occurrence in association with successive pulses, decreased exponentially with their number in such a series (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe efficiency of drums to associate with each pulse in a trill was generally low and variable, with an average of 0.40 (SD 0.17, n\u0026thinsp;=\u0026thinsp;929) and ranging from 0.26 (SD 0.16, n\u0026thinsp;=\u0026thinsp;55) to 0.54 (SD 0.18, n\u0026thinsp;=\u0026thinsp;65) among males (see also Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ee). A substantial part of its variability within individuals was related to its fluctuation between directly subsequent phrases (Suppl. Figure\u0026nbsp;2). Full efficiency was achieved extremely rarely; only three males emitted a drum after each trill pulse in one of the phrases analysed (i.e., in 0.3% of the total, n\u0026thinsp;=\u0026thinsp;929; see also Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ee). The association between drumming and stridulation rates shows the best and statistically significant fit when modelled as a quadratic function (with pulses: \u003cem\u003eF\u003c/em\u003e(2, 12)\u0026thinsp;=\u0026thinsp;8.158, \u003cem\u003eP\u003c/em\u003e =\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e0.006 / \u003cem\u003eF\u003c/em\u003e(2, 12)\u0026thinsp;=\u0026thinsp;4.042, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.045 for mean / median drumming rates, Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec; with ticks: \u003cem\u003eF\u003c/em\u003e(2, 12)\u0026thinsp;=\u0026thinsp;13.520, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001 / \u003cem\u003eF\u003c/em\u003e(2, 12)\u0026thinsp;=\u0026thinsp;5.955, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.016 for mean / median drumming rates). The peak drumming rate occurs when the stridulation rate approximates the sample median (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec, see also Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe association between drumming efficiency and stridulation rate exhibits an initial brief rise followed by a consistent decline of its upper-bound values (for method see Podos \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e1997\u003c/span\u003e). This negative trend is statistically significant (Pearson\u0026rsquo;s correlation, \u003cem\u003er\u003c/em\u003e = \u0026minus;\u0026thinsp;0.8579, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.028; Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ee). While the complete set of values shows the best fit to quadratic function, this fit is not statistically significant (\u003cem\u003eF\u003c/em\u003e(2,12)\u0026thinsp;=\u0026thinsp;0.734, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.5; Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ee). Drumming accuracy exhibits no dependence on drumming rate or efficiency (Pearson\u0026rsquo;s correlation \u003cem\u003er\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.018\u0026ndash;0.089, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.752\u0026ndash;0.946; Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eg).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eTremulation\u003c/h2\u003e \u003cp\u003eBody tremulation occurs with rhythmic lateral movements or \u0026ldquo;swinging\u0026rdquo; of the body at a low rate, clearly notable to an observer (Suppl. Video 1). Produced was a continuous, amplitude modulated signal confined to the substrate, with most spectral energy below 100 Hz (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). For the most part, the amplitude peaks did not clearly correspond to the individual phases of body movement. However, in some instances, particularly with slower signaller, this correspondence was more evident (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). The mean rate of tremulation movement was 3.77 Hz (SD 0.43 Hz; n\u0026thinsp;=\u0026thinsp;112, N\u0026thinsp;=\u0026thinsp;15), varying from 3.06 Hz (SD 0.16 Hz, n\u0026thinsp;=\u0026thinsp;7) to 4.38 Hz (SD 0.23 Hz, n\u0026thinsp;=\u0026thinsp;6) among males (see also Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eAssociation of tremulation with drumming and stridulation\u003c/h2\u003e \u003cp\u003eThe timing and rate of tremulation were most closely associated to those of drumming (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb). At times, the signal\u0026rsquo;s amplitude modulation accurately represented tremulation movements; these recordings revealed the emission of drums shortly after onset, and with more efficient drummers also shortly before offset of tremulation amplitude increase (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). Accordingly, we found significant linear correlation between tremulation and drumming rates (Pearson\u0026rsquo;s correlation, \u003cem\u003er\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.682, p\u0026thinsp;=\u0026thinsp;0.005 and \u003cem\u003er\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.5123, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.05, for mean and median drumming rates, respectively), with an approximate 1:2 to 1:4 relationship (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb). The rate of tremulation movements was significantly linearly correlated to that of stridulation ticks (Pearson\u0026rsquo;s correlation, \u003cem\u003er\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.724, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.002). In contrast, the relationship between stridulation pulse and tremulation rates was found to be more complex, with the best and statistically significant fit to a cubic function (\u003cem\u003eF\u003c/em\u003e(2,12)\u0026thinsp;=\u0026thinsp;6.4211, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.009; Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eSignal frequency, amplitude, and duration\u003c/h2\u003e \u003cp\u003eThe median dominant frequency of stridulation (trill) pulses was 4.3 kHz in the air and 3.79 kHz in the substrate (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, for the IQR, see Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Frequency composition of the substrate component was similar for the ticks (but weak and not formally analysed), with the median dominant frequency at 18.26 kHz in the air (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). In the substrate, the median dominant frequency of drums was 1.03 kHz on the lateral and over twice higher on the central section of the loudspeaker membrane, while in the air it was 2.76 kHz with no location-related difference (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The dominant frequency peak of tremulation signals was almost invariably at 43 Hz.\u003c/p\u003e \u003cp\u003eIn the air, the stridulatory ticks were over 7 time more intense than pulses (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), while the substrate component was strongest for pulses (median at 0.025 mm/s, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The median peak amplitude of the auditory drumming component was 1.7 times higher than that of stridulation pulses. In the substrate, drumming was by far most intense of all signals (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Tremulation signals had the median peak velocity at 0.23 mm/s (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe mean signal duration was 24 ms for the ticks and 22 ms for the pulses. Drumming signals were much shorter, and similar between the air and substrate, when emitted on the central membrane (around 6 and 7 ms, respectively), while on the lateral membrane the substrate signal was twice longer (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"DISCUSSION","content":"\u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003eComplexity of cricket courtship display\u003c/h2\u003e \u003cp\u003eIn field crickets and other cricket taxa, the characteristics and function of vibrational signals, which are not only a by-product of stridulation but often complement it in a complex courtship display, have remained largely unexplored or even primarily overlooked (Stritih-Peljhan and Virant-Doberlet \u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). We present the first comprehensive study of the entire set of vibroacoustic signals emitted during courtship of a (field) cricket, analysing both the characteristics of the individual signals and their interaction, as potential targets of female choice. This provides novel insights into the understanding of their courtship process.\u003c/p\u003e \u003cp\u003eWe demonstrate that in addition to body tremulation, long known as part of courtship in \u003cem\u003eA. domesticus\u003c/em\u003e and many other crickets (Alexander \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1967\u003c/span\u003e; Hack \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1998\u003c/span\u003e), the males also drum with the legs against the substrate during their repetitive display. So far, leg drumming was observed to accompany courtship stridulation also in the crickets \u003cem\u003eVanzoliniella sambophila\u003c/em\u003e (Phalangopsidae; de Mello and dos Reis 1994) and \u003cem\u003eT. oceanicus\u003c/em\u003e (Gryllidae; Broder et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Wikle et al. \u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Unlike \u003cem\u003eA. domesticus\u003c/em\u003e, however, where all three mechanisms are obligately included in the display, not all \u003cem\u003eT. oceanicus\u003c/em\u003e males produced drumming signals, and in neither species males emitted an additional courtship signal by tremulation.\u003c/p\u003e \u003cp\u003eUtilising three different signalling mechanisms that involve simultaneous action and coordination of different sets of body muscles in prolonged display, \u003cem\u003eA. domesticus\u003c/em\u003e appears to represent a unique case of dynamic signalling in insects. When combining multiple vibroacoustic mechanisms, most insects produce serial signals that do not overlap in time (Virant-Doberlet et al. \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). While certain species of Asopinae stink bugs (Žunič et al. \u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e2008\u003c/span\u003e), Philloporinae bushcrickets (Korsunovskaya et al. 2020) and Drosophilinae fruit flies (Mazzoni et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) employ three or even four signalling mechanisms during the close-range courtship, they activate these mechanisms either subsequently or transiently combine at most two of them to produce a composite signal. Thus, alongside the intricate visual-vibratory courtship of spiders (e.g., Kozak and Uetz \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) and the combined song and dance performances of birds (e.g., Miles and Fuxjager 2018), crickets provide another example of complex dynamic signalling that merits examination of signalling effort, complexity and coordination as potential factors influencing female choice.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003eQuantity and quality aspects of the complex signal\u003c/h2\u003e \u003cp\u003eTraditionally, the components of the complex signals have been either viewed as redundant signals providing a functional backup or as signals providing multiple messages to the receiver (M\u0026oslash;ller and Pomianowski 1993; Johnstone \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e1996\u003c/span\u003e; Candolin \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). This view changed when also considering the perceptual mechanisms of receivers (Rowe \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e1999\u003c/span\u003e; Hebets and Papaj \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Starnberger et al. \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Halfwerk et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), the interaction between signal components (Partan and Marler \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e1999\u003c/span\u003e; Hebets and Papaj \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Hebets et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), and the complexity and quality of (dynamic) displays (Byers et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Fusani et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Mitoyen et al. \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) to gain insight into signal function and evolution. Applying these views on the complex signal of \u003cem\u003eA. domesticus\u003c/em\u003e helped us to unravel its communicative potential beyond that of the stridulatory song.\u003c/p\u003e \u003cdiv id=\"Sec23\" class=\"Section3\"\u003e \u003ch2\u003eSignal costs\u003c/h2\u003e \u003cp\u003eEarlier studies on \u003cem\u003eA. domesticus\u003c/em\u003e revealed that the females receive reliable information about male condition from the courtship display and select for the traits based on their costs, such as the time spent singing, while this information is not reflected in song parameters (Nelson and Nolen 1987; Ręk \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Our study sheds light on this discrepancy, demonstrating that stridulation is only one of three components of the complex signal, whose joint costs do not appear to be simply proportional to that of stridulation. This is indicated through the non-linear correlation between stridulation vs. drumming and tremulation rates, suggesting that the females would not be able to assess male quality solely from one signal parameter (as to the redundant signal hypothesis; Candolin \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). This is a relevant argument since drumming and body tremulation are known to be energetically demanding behaviours, the latter significantly costlier than stridulation (data from \u003cem\u003eA. domesticus\u003c/em\u003e: Hack \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; bushcrickets: R\u0026ouml;mer et al. \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; spiders: Kotiaho et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). The complex signal can thus serve as a much more honest indicator of male condition then courtship stridulation alone, which generally lacks condition dependence in crickets (Wagner and Reiser \u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Gray and Eckadt 2001; Ręk \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). This aspect of honesty may be considered especially relevant in crickets, since courtship with multiply mated females can last for hours (Fleishmann and Sakaluk 2004), so only males in good condition may be expected to sustain the energy demands for optimal display performance (Grafen \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e1990\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section2\"\u003e \u003ch2\u003ePerformance constraint\u003c/h2\u003e \u003cp\u003eOur study reveals that the courtship signal of \u003cem\u003eA. domesticus\u003c/em\u003e involves periodic coupling (synchrony) among stridulation, drumming, and tremulation signal components, occurring in a pattern of regular exchange. This coupling is particularly consistent between stridulation ticks and pulses, on one hand, and between tremulation and drumming signals, on the other, as evidenced also from the linear correlation of their rates. Drumming and tremulation also tend to mirror the pattern of stridulation. Stridulation, as the primary signal in the display, sets the 'template' to be matched one-to-one (in the trill) by drumming, and at a lower rate by tremulation. However, this matching is generally achieved with low efficiency and high variability, and the occurrence of one drum per pulse is extremely rare, indicating challenges in drumming performance. The nonlinear correlation with stridulation rates indicates a specific constraint on drumming performance, with an upper limit at rates around 18 Hz and an efficiency of 0.55 in association with trill pulses. This constraint does not affect tremulation, whose complex dependence on the stridulation pulse (but not tick) rate may be considered a consequence of its tight coupling with drumming.\u003c/p\u003e \u003cp\u003eSimilar performance constraints are known from other species due to trade-offs between intrinsically linked signal parameters that are difficult to produce simultaneously. In songbird vocal performance, high signal rates decrease the ability to produce high bandwidth signals, stemming from sensorimotor and physical constraints of their vocal and respiratory apparatus (Podos \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Goller et al. 2022). In gray treefrogs, male call rate and call duration covary negatively, which has been attributed to the high energetic costs combined with temporal constraints of signal production (Reichert and Gerhardt \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Ward et al. \u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). The mutual constraints inherent in these examples are evident through a negative correlation across the entire range of signal parameter expression. By contrast, the constraint in \u003cem\u003eA. domesticus\u003c/em\u003e is specific to drumming and only manifests after reaching a specific effort threshold. This represents a specific and novel case of performance constraint in the complex signalling of animals.\u003c/p\u003e \u003cp\u003eThe nature of this constraint in the cricket may be, in part, mechanistic, as the leg\u0026rsquo;s neuromuscular apparatus is also utilised for body support and tremulation. Drumming may be also energetically constrained, but not primarily due to the costs of the complex signal; this limitation may arise from the lack of physiological adaptations in leg muscles for rapid repetitive contractions. In this context, the high proportion of pauses in the drumming rhythm dictated by stridulation, as well as the involvement of both forelegs and midlegs in drumming, may be seen as the necessity for frequent rest periods that avoid anaerobic metabolism, and therewith fatigue and damage to leg muscles (see Mowles et al. 2014).\u003c/p\u003e \u003cdiv id=\"Sec25\" class=\"Section3\"\u003e \u003ch2\u003ePerformance quality through signal interaction\u003c/h2\u003e \u003cp\u003eIn complex signalling involving locomotor activities, the signaller\u0026rsquo;s quality is conveyed not just through the vigour of performance, but also through the skill of combining challenging motor actions in a coordinated manner (Byers et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Fusani et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). In \u003cem\u003eA. domesticus\u003c/em\u003e, we observed precise timing in the exchange of stridulation, drumming and tremulation signal components, each occurring in a specific time window relative to the others. Given that these components rely on the activity of distinct parts of the neuro-muscular system, specifically the wings and the legs, their precise coordination is essential for such signaling. We evaluated drumming accuracy, as the proportion of drums emitted in pauses between stridulation pulses, as an apparent aspect of coordination quality. Despite this parameter generally demonstrated high performance, it varied largely between individuals, thus providing a putative basis for female choice. The skill of the motor performance is generally relevant for the female, as it reflects neuromuscular capabilities that are considered a reliable indicator of male genetic quality and developmental stability (Byers et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Mitoyen 2019). Interestingly, we found that drumming accuracy did not correlate with drumming rate or its efficiency to associate with stridulatory pulses. This is intriguing, as trade-offs between parameters reflecting quality and quantity of motor performance can generally be expected, as recently demonstrated in acrobatic mating displays of a songbird (Manica et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Hence, if female preferences in crickets rely on both courtship display vigor and skill, they might be even less evident when considering stridulation as its only relevant component. Also, evaluating the performance skill goes beyond simple summation of information in the individual components; it requires evaluation of their interaction through sensory integration (Hebets and Papaj \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Halfwerk et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec26\" class=\"Section3\"\u003e \u003ch2\u003eFunctional insights through spectral-intensity analysis\u003c/h2\u003e \u003cp\u003eAnalysing complex multimodal signals from the view of detection and integration facilitates understanding of their function and evolution (Halfwerk et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Applied to the components of the complex signal by \u003cem\u003eA. domesticus\u003c/em\u003e, this approach supports the tightest functional connection between sensory inputs from drumming and stridulation, while also suggesting a potentially distinct function for tremulation.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec27\" class=\"Section3\"\u003e \u003ch2\u003eStridulation and drumming as one percept\u003c/h2\u003e \u003cp\u003eWe have demonstrated that stridulation and drumming produce similar, higher frequency signals with simultaneous components both in the substrate and air. Crickets have specialised sensory organs detecting such signals; the leg subgenual organ for vibrations (with peak sensitivity at 0.5\u0026ndash;1.5 kHz; K\u0026uuml;hne et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e1984\u003c/span\u003e) and the foreleg tympanal organ for sound (sensitive above 2 kHz; Imaizumi and Pollack 1999). While the vibrational component of stridulation was weak and spectrally above the subgenual organ\u0026rsquo;s detection range (making its significance questionable), the acoustic component of drumming (peaking between 2.5\u0026ndash;4 kHz) was even louder than stridulation, so it must have been well audible to the female. Audible drumming was also recorded in a phalangopsid cricket courting on dry leaves (de Mello and dos Reis 1994), but it may be much less intense on natural substrates with lower stiffness, like soil. However, its vibration component, in our recordings at least 25 dB above threshold of the cricket subgenual organ (K\u0026uuml;hne et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e1984\u003c/span\u003e), can be considered effective in various environments (see also Elias and Mason \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2014\u003c/span\u003e, for the generalist properties of vibratory drumming signals).\u003c/p\u003e \u003cp\u003eThis vibratory input by drumming will converge with the auditory input by stridulation at two sensory levels of cricket. First, at the level of the subgenual organ sensilla, some of which exhibit bimodal sensitivity to high-frequency vibration and low-frequency sound (K\u0026uuml;hne et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e1984\u003c/span\u003e). Secondly, at the level of interneurons in the ventral nerve cord, with inputs from specialised auditory and vibratory sensilla (Wiese \u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003e1981\u003c/span\u003e; K\u0026uuml;hne et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e1984\u003c/span\u003e). This suggests a close functional connection between drumming and stridulation signals, being either perceived as same modality signals or integrated into a common bimodal percept already at the low level of sensory processing in crickets. In line with our insights from temporal analysis, this emphasises the potential significance of the combined stridulation and drumming in the context of female choice.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec28\" class=\"Section2\"\u003e \u003ch2\u003eTremulation\u003c/h2\u003e \u003cp\u003eWe show that, due to mainly horizontal body movements of the male, the rate of tremulation signal is not easily discernible to the female in the vertical component of substrate motion (detected by the laser vibrometer), which is most important in vibration detection (Strauβ et al. 2019). Although insects can detect horizontal substrate vibration (Strauβ et al. 2019), a low-mass insect may not effectively generate such signals on many substrates. Because crickets are nocturnal (Yamano et al. \u003cspan citationid=\"CR83\" class=\"CitationRef\"\u003e2001\u003c/span\u003e, for \u003cem\u003eA. domesticus\u003c/em\u003e), tremulation movement also cannot be visually perceived by females. In addition, the vibratory signal had most of the energy content below 100 Hz. This is typical of insect tremulation regardless of substrate type (Žunič et al. \u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e2008\u003c/span\u003e, Stritih and Čokl \u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Stritih and Čokl \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Besides the inputs directed to complex processing, such stimuli are also detected by the proprioceptive sensilla of the insect body and legs, triggering reflex responses (Stritih and Čokl \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Strauβ et al. 2021).\u003c/p\u003e \u003cp\u003eThe primary function of tremulation may thus not be in signalling male quality. It may be rather inducing female (attentive) immobility, as commonly observed with male tremulation during courtship interruption and mate guarding of crickets (Evans 1988; Sakaluk \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e1991\u003c/span\u003e; Brown \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1999\u003c/span\u003e; Su and Rentz \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). Both spectral and intensity properties of vibratory tremulation signal in our study (around 0.5 m/s\u003csup\u003e2\u003c/sup\u003e at 50 Hz) are adequate for the proposed function. These intensities largely exceed the threshold of cricket silencing (freezing) response to vibration, as observed in \u003cem\u003eG. campestris\u003c/em\u003e (Dambach \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1989\u003c/span\u003e), but remain below the threshold of a vibrational startle response with similar properties among Orthoptera (Stritih and Čokl \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). However, the continuous nature of tremulation during courtship of \u003cem\u003eA. domesticus\u003c/em\u003e differs from its occurrence in sporadic bursts during guarding and courtship interruption of crickets. Such a signal may not be optimised for silencing females due to the potential habituation of their response, leaving the function of this complex signal component ambiguous.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eWe provide the first comprehensive description of the complete set of vibroacoustic signals constituting courtship display in a species of Gryllidae. This reveals the complexity and synchronisation between multiple signalling mechanisms, including a drumming signal that went completely unnoticed despite decades of study of this model species. Along with the recent discovery of drumming in the Pacific filed cricket (Broder et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), this calls for revisiting cricket courtship behaviour, with a specific focus on vibrational signals that may complement stridulation.\u003c/p\u003e \u003cp\u003eThe courtship behaviour of \u003cem\u003eA. domesticus\u003c/em\u003e stands out as a unique example of complex dynamic signaling in insects, utilising three different vibroacoustic mechanisms in parallel. We demonstrate that the information conveyed to the female through this complex signal extends well beyond that provided by stridulation alone. This encompasses a performance constraint that likely played a crucial role in the signal\u0026rsquo;s evolution. Exploring the fitness-related value of different parameters of this complex signal and associated female preferences remain obvious next steps in our future research.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors thank Andreas Stumpner (G\u0026ouml;ttingen) for his comments and suggestions on an earlier version of the manuscript.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors received financial support from the Slovenian Research and Innovation Agency (Research Core Funding P1\u0026ndash;0255).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eEthics approval\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study did not require ethics review and approval according to Slovenian (Invertebrates; Animal Protection Act, Official Journal of the Republic Slovenia, No 38/13, 21/18-ZNOrg, 92/20 and 159/21) and EU legislation (Directive 2010/63/EU of the European Parliament and of the Council on the protection of animals used for scientific purposes) requirements. The experimental procedures used did not include manipulation associated with pain. The males used in experiments were euthanised by\u0026nbsp;freezing at -20\u0026deg;C and stored in ethanol. All other animals in the stock were provided with food and water until they died naturally.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eCompeting interests\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eData availability statement\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data generated and analysed during this study have been uploaded to Zenodo with the DOI: 10.5281/zenodo.10143458 (Zenodo.org). Access to these files will be activated upon paper acceptance. Meanwhile, the data are accessible at: https://oblak.nib.si/index.php/s/PByDVuGReEH3Wap\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAdamo, S.A., Hoy, R.R. 1994. Mating behavior of the field cricket \u003cem\u003eGryllus bimaculatus\u0026nbsp;\u003c/em\u003eand its dependence on social and environmental\u003cem\u003e\u0026nbsp;\u003c/em\u003ecues. \u003cem\u003eAnimal Behaviour,\u003c/em\u003e \u003cem\u003e47\u003c/em\u003e, 857\u0026ndash;868.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eAlexander, R.D., Otte, D. 1967. The evolution of genitalia and mating behavior in the crickets (Gryllidae) and other Orthoptera. \u003cem\u003eMiscellaneous publications Museum of Zoology University of Michigan, 133\u003c/em\u003e, 1\u0026ndash;62.\u003c/li\u003e\n \u003cli\u003eBastock, M. 1967. \u003cem\u003eCourtship: An Ethological Study\u003c/em\u003e (1st ed.). Routledge.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eBell, P.D. 1980. 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Receiver psychology and the evolution of multicomponent signals.\u0026nbsp;\u003cem\u003eAnimal Behaviour 58(5)\u003c/em\u003e, 921\u0026ndash;931.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eR\u0026ouml;mer, H., Lang, A., Hartbauer, M. 2010. The signaller\u0026rsquo;s dilemma: a cost \u0026ndash; benefit analysis of public and private communication. \u003cem\u003ePLoS ONE, 5(10)\u003c/em\u003e, e13325.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eSakaluk, S.K. 1991. Post-copulatory mate guarding in decorated crickets. \u003cem\u003eAnimal Behaviour, 41(2)\u003c/em\u003e, 207\u0026ndash;216.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eSch\u0026ouml;eneich S (2020) Neuroethology of acoustic communication in field crickets - from signal generation to song recognition in an insect brain. \u003cem\u003eProgress in Neurobiology\u003c/em\u003e 194, 101882.\u003c/li\u003e\n \u003cli\u003eSimmons, L. W., Thomas, M. L., Simmons, F. W., Zuk, M. 2013. 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Wessel (Eds.) \u003cem\u003eBiotremology: Studying Vibrational Behavior\u003c/em\u003e (pp. 209\u0026ndash;233) Berlin: Springer.\u003c/li\u003e\n \u003cli\u003eStrau\u0026beta;, J., Stritih-Peljhan, N., Nieri, R., Virant-Doberlet, M., Mazzoni, V. 2021. Communication by\u0026nbsp;substrate-borne mechanical waves in insects: from basic to applied biotremology. In \u003cem\u003eAdvances in Insect\u003c/em\u003e \u003cem\u003ePhysiology: Sound Communication in Insects\u003c/em\u003e, ed. R Jurenka, pp. 189\u0026ndash;307. Cambridge,MA: Academic.\u003c/li\u003e\n \u003cli\u003eStritih, N., Čokl, A. 2012. Mating behaviour and vibratory signalling in non-hearing cave crickets reflect primitive communication of Ensifera. \u003cem\u003ePLoS ONE, 7(10)\u003c/em\u003e, e47646.\u003c/li\u003e\n \u003cli\u003eStritih, N., Čokl, A. 2014. The role of frequency in vibrational communication of Orthoptera. In: R. B., Cocroft, M., Gogala, P. S. M., Hill, A. Wessel (Eds), \u003cem\u003eStudying Vibrational Communication\u003c/em\u003e (pp. 375\u0026ndash;393). Berlin: Springer.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eStritih-Peljhan, N., Virant-Doberlet, M. 2021. Vibrational signalling, an underappreciated mode in cricket communication. \u003cem\u003eThe Science of Nature 108\u003c/em\u003e, 41.\u003c/li\u003e\n \u003cli\u003eSu, Y. N., Rentz, D. C. F. 2000. Australian Nemobiine crickets: behavioral observations and new species of \u003cem\u003eBobilla\u0026nbsp;\u003c/em\u003eOtte Alexander (Orthoptera: Gryllidae: Nemobiinae). \u003cem\u003eJournal of Orthoptera Research 9\u003c/em\u003e, 5\u0026ndash;20.\u003c/li\u003e\n \u003cli\u003eVirant-Doberlet, M., Stritih-Peljhan, N., Žunič-Kosi, A., Polajnar, J. 2023. Functional diversity of vibrational signalling systems in insects. Annual Review of Entomology. 68, 191\u0026ndash;210.\u003c/li\u003e\n \u003cli\u003eZuk, M., Simmons, L.W. 1997. Reproductive strategies of the crickets (Orthoptera: Gryllidae). In: Choe, J.C., Crespi, B.J. (Eds) \u003cem\u003eThe evolution of mating systems in insects and arachnids\u003c/em\u003e. Cambridge: Cambridge University Press.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eZuk, M., Rebar, D., Scott, S. P. 2008. Courtship song is more variable than calling song in the field cricket \u003cem\u003eTeleogryllus oceanicus\u003c/em\u003e. \u003cem\u003eAnimal Behaviour,76 (3)\u003c/em\u003e, 1065\u0026ndash;1071.\u003c/li\u003e\n \u003cli\u003eŽunič, A., Čokl, A., Virant-Doberlet, M., Millar, J. G., 2008. Communication with signals produced by abdominal vibration, tremulation, and percussion in \u003cem\u003ePodisus maculiventris\u003c/em\u003e (Heteroptera: Pentatomidae), \u003cem\u003eAnnals of the Entomological Society of America\u003c/em\u003e,\u003cem\u003e\u0026nbsp;101(6)\u003c/em\u003e, 1169\u0026ndash;1178.\u003c/li\u003e\n \u003cli\u003eWagner, W. E. \u0026nbsp;Reiser, M. G., 2000. The importance of calling song and courtship song in female mate choice in the variable field cricket. \u003cem\u003eAnimal Behaviour\u003c/em\u003e, 59, 1219\u0026ndash;1226.\u003c/li\u003e\n \u003cli\u003eWard, J. L., Love, E. K., V\u0026eacute;lez, A., Buerkle, N. P., O\u0026apos;Bryan, L. R., Bee, M. A. 2013. Multitasking males and multiplicative females: dynamic signalling and receiver preferences in Cope\u0026apos;s grey treefrog. \u003cem\u003eAnimal Behaviour, 86(2)\u003c/em\u003e, 231\u0026ndash;243.\u003c/li\u003e\n \u003cli\u003eWiese, K. 1981. Influence of vibration on cricket hearing: interaction of low frequency vibration and acoustic stimuli in the omega neuron. \u003cem\u003eJournal of Comparative Physiology A, 143\u003c/em\u003e, 135\u0026ndash;142.\u003c/li\u003e\n \u003cli\u003eWikle, A. W., Broder, E. D., Gallagher, J. H., Tinghitella, R. M. 2023. A rapidly evolving cricket produces percussive vibrations: how, who, when, and why, \u003cem\u003eBehavioral Ecology\u003c/em\u003e, 34(4), 631\u0026ndash;64.\u003c/li\u003e\n \u003cli\u003eYamano, H., Watari, Y., Arai, T., Takeda, M. 2001 Melatonin in drinking water influences a circadian rhythm of locomotor activity in the house cricket, \u003cem\u003eAcheta domesticus\u003c/em\u003e. \u003cem\u003eJournal of Insect Physiology, 47(8)\u003c/em\u003e, 943\u0026ndash;949.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"behavioral-ecology-and-sociobiology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"beas","sideBox":"Learn more about [Behavioral Ecology and Sociobiology](http://link.springer.com/journal/265)","snPcode":"265","submissionUrl":"https://www.editorialmanager.com/beas/default.aspx","title":"Behavioral Ecology and Sociobiology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"male quality, substrate vibration, sound, complex signal, dynamic signal, insect","lastPublishedDoi":"10.21203/rs.3.rs-3971219/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3971219/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eCrickets (Gryllidae) produce sounds by tegminal stridulation, extensively studied for its role in female attraction and choice. However, their close-range courtship song, along with additional chemical, visual, and thermal signals, fails to clarify the observed female preferences. Beyond stridulation, crickets exhibit a range of vibrational courtship behaviours that remain largely unexplored. In this study, using \u003cem\u003eAcheta domesticus\u003c/em\u003e as a model, we present the first comprehensive analysis of the entire set of vibroacoustic courtship signals in crickets, including their interaction. Employing audio recording, laser vibrometry, and videorecording, we unveil a complex signal involving simultaneous wing stridulation, body tremulation, and leg drumming against the substrate. These signal components exhibit a pattern of regular exchange within a specific time window relative to each other. We show the tightest coupling between the two types of stridulation pulses, and between tremulation and drumming signals, supported by the linear corelation of their rates. The coupling between drumming and stridulation signals is less consistent, with the non-linear corelation between their temporal and association parameters revealing a constraint on drumming performance. Yet, drumming is performed with high accuracy relative to stridulation, unrelated to its rate. Spectral-intensity analysis indicates the closest perceptual and thus functional connection between stridulation and drumming components of the complex signal, while proposing another function for tremulation unrelated to female choice. Our data demonstrate that the information conveyed by the complex courtship display in \u003cem\u003eA. domesticus\u003c/em\u003e is not simply proportional to that in the song, potentially providing a much more reliable basis for female choice.\u003c/p\u003e","manuscriptTitle":"More than stridulation: signal interaction and constraint in the complex vibroacoustic courtship of a cricket","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-03-19 08:53:54","doi":"10.21203/rs.3.rs-3971219/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major Revisions Needed","date":"2024-04-25T23:03:43+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2024-03-21T08:37:54+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-03-17T12:36:57+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-03-01T02:07:00+00:00","index":"","fulltext":""},{"type":"submitted","content":"Behavioral Ecology and Sociobiology","date":"2024-02-26T02:47:05+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"behavioral-ecology-and-sociobiology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"beas","sideBox":"Learn more about [Behavioral Ecology and Sociobiology](http://link.springer.com/journal/265)","snPcode":"265","submissionUrl":"https://www.editorialmanager.com/beas/default.aspx","title":"Behavioral Ecology and Sociobiology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"a5c4aed9-bf7c-4af2-9378-3eb1a8d84c73","owner":[],"postedDate":"March 19th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-12-02T17:22:12+00:00","versionOfRecord":{"articleIdentity":"rs-3971219","link":"https://doi.org/10.1007/s00265-024-03530-y","journal":{"identity":"behavioral-ecology-and-sociobiology","isVorOnly":false,"title":"Behavioral Ecology and Sociobiology"},"publishedOn":"2024-11-26 15:58:06","publishedOnDateReadable":"November 26th, 2024"},"versionCreatedAt":"2024-03-19 08:53:54","video":"","vorDoi":"10.1007/s00265-024-03530-y","vorDoiUrl":"https://doi.org/10.1007/s00265-024-03530-y","workflowStages":[]},"version":"v1","identity":"rs-3971219","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3971219","identity":"rs-3971219","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}