Plasticity of the phonotactic selectiveness of four species of chirping crickets (Gryllidae): Implications for call recognition

Earlier studies of phonotaxis by female crickets describe this selective behavioural response as being important in the females' choices of conspecific males, leading to reproduction. In the present study, moderate (30+) to very large data sets of phonotactic behaviour by female Acheta domesticus L., Gryllus bimaculatus DeGeer, Gryllus pennsylvanicus Burmeister and Gryllus veletis Alexander demonstrate substantially greater plasticity in the behavioural choices, as made by females of each species, for the syllable periods (SP) of model calling songs (CS) than has been previously described. Phonotactic choices by each species range from the very selective (i.e. responding to only one or two SPs) to very unselective (i.e. responding to all SPs presented). Some females that do not respond to all SPs prefer a range that includes either the longest or shortest SP tested, which fall outside the range of SPs produced by conspecific males. Old female A. domesticus and G. pennsylvanicus are more likely to be unselective for SPs than are young females. Each species includes females that do not respond to a particular SP when responding to CSs with longer and shorter SPs. The results suggest that the plasticity of phonotactic behaviour collectively exhibited by the females of each species does not ensure that choices of a male's CS effectively focus the female's phonotactic responses on CSs that represent the conspecific male. The phonotactic behaviour collectively exhibited by females of each species does not readily fit any of the models for selective processing by central auditory neurones that have been proposed to underlie phonotactic choice.     

Response properties of the prothoracic AN2 auditory interneurone to model calling songs in the cricket Gryllus bimaculatus

Sound processing properties for calling song (CS) models, as described for the prothoracic L3 auditory neurone in Acheta domesticus, are investigated for the homologous auditory neurone 2 (AN2) in female Gryllus bimaculatus De Geer. AN2 of G. bimaculatus responds selectively to the syllable period (SP) of models of a male CS. The selectiveness of this response parallels the selectivity of phonotaxis females perform in response to the same SPs. Both, the responses of AN2 and female behaviour show clear interindividual variability. The SP‐selective responses of AN2 result from an SP‐dependent reduction in the spiking to subsequent syllables of the model CSs, measured as the percentage decrement. This SP‐dependent response does not primarily result from inbuilt properties of the AN2 membrane. Rather, it is dependent on inhibitory input to the AN2. However, clear inhibitory postsynaptic potentials in dendritic recordings of the AN2 are not encountered. This immediate response of AN2 to CSs is followed by an increased rate of tonic firing between stimulus CSs, which is termed the prolonged response, and is dependent on the carrier frequencies that make up the male CSs. With stimulation on the contralateral side of the soma of AN2s, more than 50% of AN2s exhibit a prolonged response. However, with stimulation from the ipsilateral side of the soma, most AN2s exhibit a prolonged response. The prolonged response of AN2 at 5 kHz may be even more sensitive than the immediate response. Thus, the AN2 neurone could provide a basis for phonotaxis that is selective for both the SPs and the carrier frequencies of potentially attractive calling songs.     

The L3 neuron and an associated prothoracic network are involved in calling song recognition by female crickets

In young virginAcheta domesticus females, the spiking response of the prothoracic L3 auditory interneuron discriminates between calling songs (CSs) with phonotactically attractive and unattractive syllable periods (SPs), which parallels phonotactic discrimination. Presentation of a CS with an originally attractive SP, but with the intensity modulated so as to minimize L3's selective response, results in a CS with little phonotactic attractiveness. Conversely, a CS with an originally unattractive SP becomes much more attractive when the CS is intensity modulated in ways that duplicate L3's selective response. L3's discriminatory response to CS SP deteriorates with age, in parallel with decreased phonotactic selectiveness (females, older than 14 days, typically are unselective for CS SPs). SP-selective processing, which was not apparent in these old L3s, is immediately restored by removing the contralateral ear. SP-specific information is resident in a network of neurons within the prothoracic ganglion that results in the SP selective responses of the L3 neuron in young females. Changes in the SP-selective responses of the L3 neuron are highly correlated with corresponding changes in the female's phonotactically selective behavior.     

Selective processing of calling songs by auditory interneurons in the female cricket, Gryllus pennsylvanicus: possible roles in behavior

Female crickets (Gryllus pennsylvanicus), caught in the field as nymphs, responded as adults in the laboratory with selective phonotaxis to model calling songs (CSs) that reproduced the dominant carrier frequencies and syllable periods (SPs) characteristic of the male's natural calling song. Extracellular recordings demonstrated two types of auditory interneurons in the female's cervical connectives that were very similar to the AN1 and AN2 neurons previously described in other gryllid species. The AN2 neuron responded to model CSs with a phasically encoded immediate response, and a more tonically encoded prolonged response. AN2's immediate response exhibited SP-dependent decreases (termed decrement) in its responses to sequential syllables of the CS that were greatest to CSs with the shortest SPs and diminished as SPs were lengthened, resulting in an SP-dependent habituation. Picrotoxin application transformed this SP-dependent habituation by AN2 to SP-selective responses in which the degree of decrement was greatest to SPs that were most phonotactically attractive. AN2's prolonged response was most sensitive to 5 kHz CSs and correlated with the carrier frequency tuning for the thresholds of phonotaxis by females. Thus, in females, AN2's immediate (in the presence of picrotoxin) and prolonged responses were selectively tuned to the SPs and carrier frequencies of the male's calls that were most attractive behaviorally. AN1's responses at threshold were also tuned to the dominant carrier frequencies of the male's CS.     

The effects of injecting Juvenile Hormone III into the prothoracic ganglion on phonotaxis by female crickets Gryllus bimaculatus

Nanoinjection of Juvenile Hormone III (JH III) into the prothoracic ganglion causes virgin female crickets Gryllus bimaculatus De Geer to become more phonotactically selective for the syllable periods (SPs) of model calling songs. Females responding to all, or almost all, of the SPs presented before JH III injection significantly narrow their responses to a range of SPs that is usually centered on the SPs included in the conspecific males' calling song. Control injections of acetone (i.e. the solvent for JH III) into the prothoracic ganglion do not significantly change the recipient females' phonotactic responses. Injection of JH III into the metathoracic ganglion also has no effect the females' phonotactic choices.     

Parallel effects of temperature on the male cricket calling song,phonotaxis of the female and the auditory responses of the L3 neurone

Sender–receiver coupling is a fundamental aspect of sexual communication systems, especially when the signal must travel over significant distances. In the cricket Acheta domesticus L., both the syllable period of the calling songs of males and the syllable periods that are most attractive to females are negatively correlated with temperature. However, the range of syllable periods that females respond to phonotactically extends beyond the range of males' calling songs at all temperatures tested. In habitats occupied by crickets, surface temperatures of the ground vary considerably. The cricket's body temperature changes rather quickly based on the amount of direct solar radiation encountered (7 °C in 1 min). The responses by females to calling songs with syllable periods outside of the males' range might be advantageous in countering the effects of local variations in temperature caused by variations in the microhabitat. A temperature shift in the response to syllable period of the L3 auditory neurone parallels the temperature shift seen in the phonotactic response over a similar temperature range. These similarities support the model of the involvement of L3 in the phonotactic response and its modulation by temperature.     

The effect of visual input on calling song attractiveness for female Acheta domesticus

ABSTRACT. Of twelve mature phonotactically-responsive female Acheta domesticus L., ten responded phonotactically to a wider range (30 or SO to 100 ms) of model calling song (CS) syllable periods (SP) on the Kramer treadmill in the dark than in a lighted visually structured arena (50–70 ms). When given a choice between the visually attractive target and the invisible loudspeaker, seven of the ten females that tracked a visually attractive target (black square) when presented alone in the light reduced the range of SPs they tracked phonotactically to 50–70 ms. Three of the ten females that were not strongly attracted to the visual target when presented alone, continued to respond to model calling songs with a wide range of SPs (30–100 ms) when given a choice between visual and acoustical targets under the same conditions. Two of the twelve females responded only to model calling songs with a 50–70 ms SP on the Kramer treadmill in the dark. These females did not change their choice for model calling song SPs when presented with the visually attractive target.     

Male recognition mechanism for female responses implies a dilemma for their localisation in a phaneropterine bushcricket

The phonotactic behaviour of the duetting bushcricket Poecilimon ornatus was investigated on a walking compensator when two females responded to the male's call. Whenever two female clicks from different directions were presented within the time window, males tracked an intermediate course even when the two clicks were separated by up to 60 ms and differed widely in intensity. Thus, any signal arriving within that interval contributes to the localization of the female response. The inability of male P. ornatus to selectively track one of two females is in contrast to previous results found in other bushcricket species which track the leading of two singing animals. We suggest that the intermediate walking is a consequence of the basic ensiferan neuronal processing of song recognition and localization. Choice experiments in the natural habitat show that - earlier or later during the phonotactic path - the male tracks that female which is favoured by the unpredictable acoustic conditions in dense vegetation.     

Male recognition mechanism for female responses implies a dilemma for their localisation in a phaneropterine bushcricket.

The phonotactic behaviour of the duetting bushcricket Poecilimon ornatus was investigated on a walking compensator when two females responded to the male's call. Whenever two female clicks from different directions were presented within the time window, males tracked an intermediate course even when the two clicks were separated by up to 60 ms and differed widely in intensity. Thus, any signal arriving within that interval contributes to the localization of the female response. The inability of male P. ornatus to selectively track one of two females is in contrast to previous results found in other bushcricket species which track the leading of two singing animals. We suggest that the intermediate walking is a consequence of the basic ensiferan neuronal processing of song recognition and localization. Choice experiments in the natural habitat show that earlier or later during the phonotactic path--the male tracks that female which is favoured by the unpredictable acoustic conditions in dense vegetation.     

Modulation of syllable period‐selective phonotaxis by prothoracic neurones in crickets (Acheta domesticus): juvenile hormone,picrotoxin and photoinactivation of the ON1 neurones

Abstract In response to model calling songs (CSs), the phonotaxis of female Acheta domesticus ranges from being very selective to unselective. Within 15 min of nanoinjecting juvenile hormone III (JHIII) or picrotoxin (PTX) into the prothoracic ganglion, females become more selective for syllable period (SP) than in pre‐tests. Controls for JHIII experiments, including nanoinjection of acetone into the prothoracic ganglion or nanoinjection of JHIII into the metathoracic ganglion, do not influence selectivity. Similarly, nanoinjection of saline into the prothoracic ganglion and nanoinjection of PTX outside of the prothoracic ganglion does not change the overall selectivity of the female’s phonotaxis. These results indicate that circuits in the prothoracic ganglion modulate the SP‐selectivity of phonotaxis. Photoinactivating both of the ON1 prothoracic auditory interneurones in old females that were previously unselective for SP also results in greater SP‐selectivity during phonotaxis. Evidence suggesting that ON1 has this effect via its inhibitory input to L3 (another prothoracic auditory neurone) includes: photoinactivation of one ON1 neurone causes angular errors in the female’s orientation to CSs at 85 dB (above the threshold of the L3), stimulation with 60 dB CSs (above the threshold of ON1 but below the threshold of L3) does not induce errors in angular orientation, inactivation of ON1 in old crickets results in greater angular errors (85 dB stimulus) than it does when ON1 is inactivated in young females, and photoinactivation of ON1 increases the firing rate of the L3 neurone.     

The Responses of Duetting Antbirds to Stereo Duet Playback Provide Support for the Joint Territory Defence Hypothesis

In multiple animal taxa, including many birds and primates, members of mated pairs produce coordinated acoustic displays known as duets. By observing the behaviour of territorial animals as they respond to playback‐simulated duets of rivals, we can gain insight into the behavioural significance of vocal duets. Playback experiments, however, have been conducted across a very narrow range of duetting animals. Furthermore, many studies have been conducted with single‐speaker playback, whereas stereo‐speaker playback offers more spatially realistic simulation of duets. Moreover, by evaluating the reactions of animals to separate loudspeakers broadcasting male and female duet contributions, we can study the interactions of both males and females with same‐sex vs. opposite‐sex rivals. We used a paired experimental design to broadcast duet stimuli through a single‐speaker and a stereo‐speaker apparatus to 30 pairs of duetting barred antshrikes Thamnophilus doliatus in Costa Rica. Our goals were (1) to evaluate whether territorial antbirds respond more aggressively to male vs. female duet components and (2) to assess aggressive responses of antbirds towards single‐speaker vs. stereo‐speaker playback. Neither males nor females differentiated between the loudspeaker simulating the male vs. female duet contribution during stereo‐speaker playback trials. Barred antshrikes displayed significantly stronger responses to stereo‐speaker playback compared with single‐speaker playback. Males displayed stronger playback responses than females with closer, quicker and more vocal responses. These results provide evidence for a joint resource defence function of antbird duets given that pairs responded together with equivalent intensity to male and female simulated intruders. This is the first study to show that although duetting is an aggressive territorial signal, birds do not necessarily respond to sex‐specific components of duets. Our results support the idea that spatially realistic stereo presentation of duet stimuli is critical for experimental duet research.     

Attractiveness of the male Acheta domesticus calling song to females

1. Most crickets first demonstrated positive phonotaxis to 65 dB CSs having a 53-62 ms SP by day 3 following the imaginal molt (Fig. 3B). The onset of copulatory readiness occurred on average at 3.2 days. 2. The attractive range of SPs for most females became progressively broader as they aged (Fig. 4). Three to 4-day-old females were attracted to a smaller number of CS SPs than were 20-21 day old females (Fig. 4). 3. Older, less selective females did not typically respond to the same range of CS SPs (Fig. 6). However, they were more likely to respond to some SPs (especially 50 ms) than to others (Fig. 7). 4. The phonotactic threshold decreased from 95 dB or greater on day 0 to a mean of 55 dB by day 3, during a period of increasing JHIII biosynthesis, and thereafter remained at that level (Fig. 8). 5. During a period of maximal JHIII production, 3-5 day-old females usually responded to 4 of the 7 SPs presented (Fig. 8). Females older than 12 days were unselective for CS SP, and JHIII synthesis remained at a level below the peak production on day 4 (Fig. 8). 6. Older females, that were unselective for CS SP, became as selective as 3 to 5-day-old females within 4 days of topical application of JHIII (Figs. 9-11).     

Genotypes and their interaction effects on reproduction and mating‐induced immune activation in Drosophila melanogaster

Mating causes considerable alterations in female physiology and behaviour, and immune gene expression, partly due to proteins transferred from males to females during copulation. The magnitude of these phenotypic changes could be driven by the genotypes of males and females, as well as their interaction. To test this, we carried out a series of genotype‐by‐genotype (G × G) experiments using Drosophila melanogaster populations from two distant geographical locations. We expected lines to have diverged in male reproductive traits and females to differ in their responses to these traits. We examined female physiological and behavioural post‐mating responses to male mating traits, that is behaviour and ejaculate composition, in the short to mid‐term (48 hr) following mating. We then explored whether a sexually transferred molecule, sex peptide (SP), is the mechanism behind our observed female post‐mating responses. Our results show that the genotypes of both sexes as well as the interaction between male and female genotypes affect mating and post‐mating reproductive traits. Immune gene expression of three candidate genes increased in response to mating and was genotype‐dependent but did not show a G × G signature. Males showed genotype‐dependent SP expression in the 7 days following eclosion, but female genotypes showed no differential sensitivity to the receipt of SP. The two genotypes demonstrated clear divergence in physiological traits in short‐ to mid‐term responses to mating, but the longer‐term consequences of these initial dynamics remain to be uncovered.     

Processing of ultrasound in a bush cricket's brain

The processing and categorization of conspecific and heterospecific acoustic signals is an important task of the central nervous system. In orthopteran species, carrier frequency (besides temporal cues) is one of the major discriminators. In the bush cricket species Ancistrura nigrovittata Brunner von Wattenwyl (Phaneropteridae, Barbitistini), ultrasound has potentially different meanings and may elicit vastly different behaviours depending on the context it is perceived in. In the present study, data are presented of the morphology and neuronal responses of three local brain neurones (LBNs) that respond best to ultrasound. All neurones show dense arborizations in the lateral protocerebrum, where ascending interneurones terminate. The LBN2 and LBN9 neurones are entirely restricted to one side of the brain, whereas LBN5 crosses the midline, thereby linking both hemispheres. The response maxima for LBN2 overlap closely with the peak carrier frequencies found in a species‐specific duet, which consists of sonic (16 kHz, male), as well as ultrasonic (24–28 kHz, female) sound. By contrast, LBN9 responds only to ultrasound in the range of the female reply, whereas the male song induces exceptionally long‐lasting inhibition. The LBN5 neurone shows strongest spike activity to a broad range of ultrasonic frequencies, as long as the pulse duration remains short. All three brain neurones respond to ultrasound in a unique way and may be involved in the shaping of different behavioural outcomes.     

Auditory pattern recognition and steering in the cricket Teleogryllus oceanicus

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

Regulation of the phonotactic threshold of the female cricket, Acheta domesticus : juvenile hormone III, allatectomy, L1 auditory neuron thresholds and environmental factors

Juvenile hormone III (JHIII), when applied to the abdomen of 1-day-old female Acheta domesticus (in quantities that would create JHIII titers in the hemolymph that were within the range measured in females of this species) caused a significant decrease in phonotactic thresholds (Fig. 1). Removal of the corpora allata from 5-day-old females with low phonotactic thresholds caused significantly increased phonotactic thresholds 2–5 days later. After a temporary increase (24 h) of, on average, about 25 dB, the phonotactic thresholds drop to about 10 dB above preallatectomy levels (Fig. 2), but remain significantly higher than controls. Application of JHIII to allatectomized females, with a mean increase in thresholds of 20 dB, results in significantly decreased thresholds (mean of about 20 dB) over the next 6 h (Fig. 3). Exposure to males 1 week before the imaginal molt causes the phonotactic thresholds of postimaginal females to drop 1–2 days significantly earlier than controls (Fig. 4). One- and 3-day-old females, phonotactically tested only once, exhibit lower thresholds in the early morning than they do in the late afternoon (Fig. 5). Five-day-old females do not exhibit such a diurnal rhythm. Phonotactically testing females more than once a day significantly influences their phonotactic thresholds (Figs. 6, 7). In 1-day-old females, with high (above 70 dB) phonotactic thresholds, the threshold of their L1 auditory interneurons can be 30 dB or more below their phonotactic threshold (Fig. 8). In females with phonotactic thresholds of 70 dB or lower, the L1 threshold is within 10 dB of their phonotactic threshold. Both JHIII and allatectomy influence phonotactic and L1 thresholds in a similar manner. Accepted: 29 September 1997     

Molecular evolution of the sex peptide network in Drosophila

Successful reproduction depends on interactions between numerous proteins beyond those involved directly in gamete fusion. Although such reproductive proteins evolve in response to sexual selection pressures, how networks of interacting proteins arise and evolve as reproductive phenotypes change remains an open question. Here, we investigated the molecular evolution of the ‘sex peptide network’ of Drosophila melanogaster, a functionally well‐characterized reproductive protein network. In this species, the peptide hormone sex peptide (SP) and its interacting proteins cause major changes in female physiology and behaviour after mating. In contrast, females of more distantly related Drosophila species do not respond to SP. In spite of these phenotypic differences, we detected orthologs of all network proteins across 22 diverse Drosophila species and found evidence that most orthologs likely function in reproduction throughout the genus. Within SP‐responsive species, we detected the recurrent, adaptive evolution of several network proteins, consistent with sexual selection acting to continually refine network function. We also found some evidence for adaptive evolution of several proteins along two specific phylogenetic lineages that correspond with increased expression of the SP receptor in female reproductive tracts or increased sperm length, respectively. Finally, we used gene expression profiling to examine the likely degree of functional conservation of the paralogs of an SP network protein that arose via gene duplication. Our results suggest a dynamic history for the SP network in which network members arose before the onset of robust SP‐mediated responses and then were shaped by both purifying and positive selection.     

Fast and reliable decisions for a dynamic song parameter in field crickets

We investigated the choice of female crickets for a dynamic song parameter (chirp rate) on a walking compensator, and the underlying neuronal basis for the choice in the form of discharge differences in the pair of AN1-neurons driving the phonotactic steering behaviour. Our analysis reveals that decisions about chirp rate in a choice situation are made fast and reliably by female crickets. They steered towards the higher chirp rate after a delay of only 2.2–6 s, depending on the rate difference between the song alternatives. In this time period, the female experienced only one to two additional chirps in the song model with the higher rate. There was a strong correlation between the accumulated AN1 discharge difference and the amount of steering towards the side with the stronger response.