Female Acheta domesticus track acoustical and visual targets with different walking modes

ABSTRACT. Female Acheta domesticus L. were tested for tracking model calling songs with different syllable periods on the Kramer treadmill in the dark, under homogenous light, and in the presence of a visually attractive target (black square) positioned either perpendicular to or in front of the invisible acoustical target. The females exhibited tracking of the two targets by different walking modes.     

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.     

Attractiveness of the maleAcheta domestica calling song to females

Summary FemaleAcheta domestica did not discriminate between pairs of model calling songs (CSs) which differed only in syllable period (SP; Fig. 1). The females selected the louder CS (Fig. 2) or the CS with a faster chirp rate (CR; Fig. 3) when presented with pairs of otherwise identical CSs. A CS with an SP of 50 ms (modal for the male's CS) was preferred when it was 5 dB louder than one with a 60-ms SP while a CS with a 60-ms SP was only consistently chosen when it was 10 dB louder than a CS with a 50-ms SP (Fig. 4). A more intense CS was preferred by the females regardless of whether its CR was faster or slower than that of the CS produced at a lower intensity (Fig. 6). When CSs with SPs of 50 or 60 ms had several different CRs, the females that made a significant choice preferred a CS with a 50-ms SP regardless of whether it was produced at a faster or slower CR (Figs. 7, 8). No significant selection between CSs with 40- and 50-ms SPs resulted when they were produced at different intensities (Fig. 5) or CRs (Fig. 9). Females only significantly chose a CS with a 50-ms SP over those with 40 ms SPs when the 50-ms-SP CS was louder and produced at a different CR (Fig. 10). From these results, it was apparent that SP, intensity, and CR all influenced a female's choice of a CS, and thus the male producing it. However, our results indicate that SP was the most important feature influencing the female's choice and that intensity was more effective than CR.Abbreviations CR chirp rate - CS calling song - POD polar orientation diagram - SP syllable period     

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

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

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.     

Responses and song pattern copying of Omega-type I-neurons in the cricket,Gryllus bimaculatus,at different prothoracic temperatures

Summary Omega-type I-neurons (ON/1) (Fig. 1A) were recorded intracellularly with the prothoracic ganglion kept at temperatures of either 8–9°, or 20–22° or 30–33 °C and the forelegs with the tympanal organs kept at ambient temperature (20–22 °C). The neurons were stimulated with synthetic calling songs (5 kHz carrier frequency) with syllable periods (SP in ms) varying between 20 and 100, presented at sound intensities between 40 and 80 dB SPL. The amplitude and duration of spikes as well as response latency decreased at higher temperatures (Figs. 1 B, 2, 6). At lower prothoracic temperatures (8–9 °C) the neuron's responses to songs with short SP (20 ms) failed to copy single syllables, or with moderate SP (40 ms) copied the syllable with low signal to noise ratio (Fig. 3). The auditory threshold of the ON/1 type neuron, when tested with the song model, was temperature-dependent. At 9° and 20 °C it was between 40 and 50 dB SPL and at 33 °C it was less than 40 dB SPL (Fig. 4). For each SP, the slope of the intensity-response function was positively correlated with temperature, however, at low prothoracic temperatures the slope was lower for songs with shorter SPs (Fig. 5). The poor copying of the syllabic structure of the songs with short SPs at low prothoracic temperatures finds a behavioral correlate because females when tested for phonotaxis on a walking compensator responded best to songs with longer SPs at a similar temperature.Abbreviations epsps excitatory postsynaptic potentials - ON/1 omega-type I-neuron - SP syllable period - SPL sound pressure level     

Processing of model calling songs by the prothoracic AN2 neurone and phonotaxis are significantly correlated in individual female Gryllus bimaculatus

Syllable period (SP) selective calling song processing has been demonstrated for the prothoracic, AN2 auditory neurone that correlates very well with SP‐selective phonotaxis by female cricket Gryllus bimaculatus De Geer. Both SP‐selective processing by the AN2 and the phonotactic behaviour of the female exhibit substantial plasticity. Thus, the question remains as to whether the selective responses of the AN2 neurone and the selective behaviour of the female match in an individual female. The present study is designed to answer that question. The SP‐selective phonotactic behaviour of individual females is evaluated, followed immediately by measuring the SP‐selective responses of the same female's AN2 neurone. Very significant correlations are found between the selective responses of the AN2 neurone and the same female's selective behaviour. In 208 possible comparisons (26 females, eight behavioural and neuronal tests each), 186 resulted in matches between behaviour and neuronal processing. Dividing the SP‐selective females into two groups (one group that responded phonotactically to the shortest SP tested and a second group that did not respond to this SP) resulted in significantly more selective responses to this shortest SP by the AN2 neurone in the females that responded phonotactically to the SP than for the females who did not respond to the shortest SP. The behavioural responses by these two groups to the other SPs tested are shown to be essentially identical.     

FEMALE CHOICE FOR AN INDICATOR OF MALE SIZE IN THE SONG OF THE BLACK-HORNED TREE CRICKET,OECANTHUS NIGRICORNIS (ORTHOPTERA: GRYLLIDAE: OECANTHINAE)

The calling song of male crickets, including Oecanthus nigricornis (Walker), attracts females for mating and provides a model system of sexual communication. We give the first conclusive identification of a feature of cricket song that is both attractive to females and indicates a phenotypic feature (body size) that determines male mating success and female reproductive benefits. We do this by first testing for correlations between song characteristics and aspects of male phenotype that are hypothesized to indicate male quality. We show that song is a reliable indicator of male size and male age, and that large male size is associated with increased female fecundity. We then use playbacks of synthetic songs that mimic natural variation in song parameters to study song preferences and we compare preferences under different presentation regimes to determine whether choices are based on relative song quality or some fixed criterion. Females show a preference for the lower frequency songs produced by large males, but only during simultaneous playbacks. Thus female choice is based on the relative quality of calls that can be sampled simultaneously. These results provide strong support for the hypothesis that females use variation in calling song to assess male mate quality.     

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

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

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.     

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.     

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

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

Phonotaxis in flying crickets

The steering responses of three species of field crickets, Teleogryllus oceanicus, T. commodus, and Gryllus bimaculatus, were characterized during tethered flight using single tone-pulses (rather than model calling song) presented at carrier frequencies from 3-100 kHz. This range of frequencies encompasses the natural songs of crickets (4-20 kHz, Fig. 1) as well as the echolocation cries of insectivorous bats (12-100 kHz). The single-pulse stimulus paradigm was necessary to assess the aversive nature of high carrier frequencies without introducing complications due to the attractive properties of repeated pulse stimuli such as model calling songs. Unlike the natural calling song, single tone-pulses were not attractive and did not elicit positive phonotactic steering even when presented at the calling song carrier frequency (Figs. 2, 3, and 9). In addition to temporal pattern, phonotactic steering was sensitive to carrier frequency as well as sound intensity. Three discrete flight steering behaviors positive phonotaxis, negative phonotaxis and evasion, were elicited by appropriate combinations of frequency, temporal pattern and sound intensity (Fig. 12). Positive phonotactic steering required a model calling song temporal pattern, was tuned to 5 kHz and was restricted to frequencies below 9 kHz. Negative phonotactic steering, similar to the 'early warning' bat-avoidance behavior of moths, was produced by low intensity (55 dB SPL) tone-pulses at frequencies between 12 and 100 kHz (Figs. 2, 3, and 9). In contrast to model calling song, single tone-pulses of high intensity 5-10 kHz elicited negative phonotactic steering; low intensity ultrasound (20-100 kHz) produced only negative phonotactic steering, regardless of pulse repetition pattern. 'Evasive', side-to-side steering, similar to the 'last-chance' bat-evasion behavior of moths was produced in response to high intensity (greater than 90 dB) ultrasound (20-100 kHz). Since the demonstration of negative phonotactic steering did not require the use of a calling song temporal pattern, avoidance of ultrasound cannot be the result of systematic errors in localizing an inherently attractive stimulus when presented at high carrier frequencies. Unlike attraction to model calling song, the ultrasound-mediated steering responses were of short latency (25-35 ms) and were produced in an open loop manner (Fig. 4), both properties of escape behaviors.(ABSTRACT TRUNCATED AT 400 WORDS)     

The effects of calling song spacing and intensity on the attraction of flying crickets (orthoptera: Goryllidae: Nemobiinae)

Previous studies have shown that sexually signaling males across different taxa show stereotyped spacing behavior that may be related to aspects of their signals, such as intensity. However, few studies have shown that the separation between signaling males affects their relative attractiveness. Using two sound traps broadcasting the calling song of the cricketEunemobius carolinus, we show that the separation, relative intensity, and absolute intensity of the calling songs influence calling song attractiveness. For calling songs separated by 5 m, the proportion of individuals attracted to the higher intensity song increased as the relative intensity difference of the two songs increased from 3 to 6 dB. For calling songs that differed by 6 dB, relative attraction to the less intense song decreased with decreasing song separation. These two results are consistent with the predictions of a model (Forrest and Raspet, 1994) that suggests that dense spacing is more costly for less powerful singers and that this cost increases with increasing differences in relative intensity. When the relative intensity of the songs was held constant (6 dB), we found that discrimination between songs decreases as the song absolute intensity increases. In particular, a greater proportion of individuals was attracted to the high-intensity song when the songs were broadcast at 103 and 97 dB than when the songs were broadcast at 109 and 103 dB. Unlike mammals and birds, the ability ofE. carolinus to discriminate between songs that differ in intensity may decrease as the absolute intensity increases. This may mean that females are less discriminating when they are closer to singing males.     

Factors which influence female crickets' (Acheta domesticus) phonotactic and sexual responsiveness to males

ABSTRACT. Removal of the corpora allata from sexually responsive Acheta domesticus females exhibiting direct, positive phonotaxis resulted in a decline of the directionality of phonotaxis and sexual responsiveness to males for the 3-day testing period. Phonotaxis and sexual responsiveness were restored to the level before allatectomy after topical treatment with JH III. Sexually and phonotactically responsive females, given Precocene I or II showed no change in phonotactic orientation or sexual responsiveness. Females were isolated from males just prior to the imaginal moult. After 3 weeks of isolation (1 2.5 weeks following the imaginal moult) they showed significantly better phonotaxis to the calling song than did females that had been fully exposed to males, or those which had only olfactory exposure to males. There were no significant differences among the groups in their copulatory readiness when placed directly in contact with males. Mating caused a reduction in the phonotaxis of females. Females on the day of imaginal moult responded negatively to the calling song. This negative response disappeared on the day following the imaginal moult and did not re-appear in older females. Topical application of JH III or the synthetic analogue, ZR 515 caused females to become phonotactically positive in response to the calling song on the day of, or the day following the imaginal moult.     

Experience Affects Female Responses to Male Song in the Variable Field Cricket Gryllus lineaticeps (Orthoptera, Gryllidae)

Search theory predicts that females will use information on search costs and the characteristics of potential mates to adjust their search behavior and mate choices. We examined the effect of previous acoustic experience on female mating responses in the variable field cricket Gryllus lineaticeps . Females of this species prefer calling songs with higher chirp rates to those with lower chirp rates. In this study we examined how female responses to male calling songs change with experience by measuring the responses of females to male calls over a sequence of three trials. Females in one group (group I) were exposed to a sequence of three identical low chirp rate songs and females in a second group (group II) were exposed to two identical low chirp rate songs interspersed by a high chirp rate song. Females in group I did not show a significant difference in their responses to the initial and final low chirp rate presentations, whereas females in group II showed a significantly reduced response to the final low chirp rate song. In addition, the degree to which female responses to the initial and final low chirp rate song changed differed significantly between the treatment groups. Thus acoustic experience appears to affect female mating preferences in this species; exposure to either more attractive songs or more variable songs makes normally unattractive songs even less attractive. These results suggest that females do not use a fixed-threshold search rule in which they mate with any male with a phenotype that exceeds a given threshold. Instead, G. lineaticeps females appear to use a more complex search rule in which they adjust their searching behavior based on the local distribution of male phenotypes.     

Indirect benefits for choosy female grasshoppers (Chorthippus biguttulus)?

Since direct benefits are likely to be absent in the grasshopper Chorthippus biguttulus, indirect genetic benefits are a potential explanation for costly female preference. Choosy females may improve their fitness in terms of enhanced attractiveness of sons alone or additionally by improved viability of offspring. We tested the predictions of these two hypotheses by comparing attractiveness-related song traits and viability in offspring of attractive and unattractive grasshopper males. The experiment was conducted with larvae reared under semi natural lab conditions in one year and under natural conditions in the field in the following year. If reared under natural conditions no significant differences in viability and song traits between offspring of attractive and unattractive males could be found. Offspring reared in the lab produced calling songs with a significantly more exact song rhythm when sired by attractive males than offspring of unattractive males. Offspring of attractive males should thus have a theoretical advantage in mate choice, which, however, did not translate into higher attractiveness values in acoustic female choice experiments. Therefore our experiments could not resolve whether female choice in C. biguttulus evolved according to the sexy son hypothesis. Since viability in offspring of attractive males did not differ from offspring of unattractive males, “good genes” seems unlikely to be the underlying mechanism of female choice.     

Calling song and selective phonotaxis in the field crickets,Gryllus firmus andG. pennsylvanicus (Orthoptera: Gryllidae)

The field cricket species, Gryllus firmusand G. pennsylvanicus,occur in a mosaic hybrid zone that roughly parallels the eastern slope of the Appalachian mountains in the northeastern United States. It is important to know what role, if any, the calling song plays in mate choice in sympatric and allopatric populations. In this report, we present results on the variability of calling song properties along transects across this hybrid zone. We also present the results of experiments on phonotactic selectivity of females from an allopatric population of G. firmus.The male calling song of allopatric G. firmuswas significantly slower in temporal rhythm (i. e., chirp and pulse repetition rates) and lower in pitch (i.e., dominant frequency) than that of allopatric G. pennsylvanicus.Calling song properties of males recorded in the hybrid zone varied considerably in temporal and spectral properties. In two-stimulus (choice) phonotaxis experiments, allopatric females of G. firmuspreferred synthetic calling songs with conspecific pulse repetition rates over songs that had lower and higher pulse rates. This preference persisted even when the sound pressure levels of alternative stimuli were unequal. Therefore, allopatric females of G. firmuscan discriminate between conspecific and heterospecific calling songs. Whether or not this same selectivity is present in sympatric populations remains unclear. Investigations of phonotactic selectivity in other allopatric and sympatric populations of both species are currently under way.