Auditory behaviour of a parasitoid fly (Emblemasoma auditrix, Sarcophagidae, Diptera)

Females of the parasitoid fly Emblemasoma auditrix find their host cicada (Okanagana rimosa) by its acoustic signals. In laboratory experiments, fly phonotaxis had a mean threshold of about 66 dB SPL when tested with the cicada calling song. Flies exhibited a frequency dependent phonotaxis when testing to song models with different carrier frequencies (pulses of 6 ms duration and a repetition rate of 80 pulses s(-1)). However, the phonotactic threshold was rather broadly tuned in the range from 5 kHz to 11 kHz. Phonotaxis was also dependent on the temporal parameters of the song models: repetition rates of 60 pulses s(-1) and 80 pulses s and pulse durations of 5-7 ms resulted in the highest percentages of phonotaxis performing animals coupled with the lowest threshold values. Thus, parasitoid phonotaxis is adapted especially to the temporal parameters of the calling song of the host. Choice experiments revealed a preference of a song model with 9 kHz carrier frequency (peak energy of the host song) compared with 5 kHz carrier frequency (electrophysiologically determined best hearing frequency). However, this preference changed with the relative sound pressure level of both signals. When presented simultaneously, E. auditrix preferred 5-kHz signals, if they were 5 dB SPL louder than the 9-kHz signal.     

The effect of mating on phonotactic behaviour in Gryllus bimaculatus (De Geer)

Abstract. Phonotaxis of G. bimaculatus females is expressed by a course-consistent, directional approach to a conspecific model calling song emitted alternatingly at sound intensities of 50–90 dB SPL and appears at the age of 6–7 days, the onset of maturation. Mating abolishes phonotaxis after about 1 h. By that time, the content of the attached spermatophore has migrated into the female's sper-matheca. Removal or emptying of the spermatheca, or severing the ventral nerve cord, fully reinstates phonotaxis, whereas ovariectomy has no effect. We suggest that mechanoreceptors record the expansion of the filled spermatheca and that the inhibitory message is communicated via the ventral nerve cord anteriorly to an unknown control centre in the brain. The loss of phonotaxis is combined with reduced locomotor activity and results in the female no longer being attracted to another calling male.     

Phonotaxis in flying crickets

The effects of two-tone stimuli on the high frequency bat-avoidance steering behavior of flying crickets (Teleogryllus oceanicus) were studied during tethered flight. Similarly, the effects of two-tone stimuli on the ultrasound sensitive auditory interneuron, Int-1, which elicits this behavior, were studied using intracellular staining and recording techniques. When a low frequency tone (3-8 kHz) was presented simultaneously with an aversive high frequency tone (in a two-tone stimulus paradigm), the high frequency avoidance steering behavior was suppressed. Suppression was optimal when the low frequency tone was between 4 and 5 kHz and about 10-15 dB louder than the high frequency tone (Figs. 2, 3). Best suppression occurred when the low frequency tone-pulse just preceded or overlapped the high frequency tone-pulse, indicating that the suppressive effects of 5 kHz could last for up to 70 ms (Fig. 4). The threshold for avoidance of the bat-like stimulus was elevated when model bat biosonar (30 kHz) was presented while the animal was performing positive phonotaxis toward 5 kHz model calling song, but only if the calling song intensity was relatively high (greater than 70-80 dB SPL) (Fig. 1). However, avoidance steering could always be elicited as long as the calling song was not more than 10 dB louder than the ultrasound (Fig. 1). This suppressive effect did not require performance of positive phonotaxis to the calling song (Fig. 2) and was probably due to the persistence of the suppressive effects of the 5 kHz model calling song (Fig. 4). The requirement for relatively high intensities of calling song suggest that the suppression of bat-avoidance by the calling song is not likely to be of great significance in nature. The high frequency harmonics of the male cricket's natural calling song overlap the lower frequency range used by insectivorous bats (10-20 kHz) and are loud enough to elicit avoidance behavior in a flying female as she closely approaches a singing male (Fig. 5). The high frequency 'harmonics' of a model calling song were aversive even if presented with a normally attractive temporal pattern (pulse repetition rate of 16 pps) (Fig. 6A). When the 5 kHz 'fundamental' was added to one of the high frequency 'harmonics', in a two-tone stimulus paradigm, this complex model calling song was attractive; the high frequency 'harmonic' no longer elicited the avoidance behavior (Fig. 6) and the animals steered toward the model CS. Thus, addition of 5 kHz to a high frequency harmonic of the calling song 'masked' the aversive nature of this stimulus.(ABSTRACT TRUNCATED AT 400 WORDS)     

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.     

Temperature coupling in cricket acoustic communication

Summary Temperature effects on calling song production and recognition were investigated in the North American field cricket, Gryllus firmus. Temporal parameters of field-recorded G. firmus calling song are strongly affected by temperature. Chirp rate and syllable rate increase, by factors of 4 and 2, respectively, as linear functions of temperature over the range in which these animals sing in the field (12°–30 °C). Temperature affects syllable duration to a lesser extent, and does not influence calling song carrier frequency. Female phonotactic preference, measured on a spherical treadmill in the laboratory, also changes with temperature such that warmer females prefer songs with faster chirp and syllable rates. Best phonotaxis, measured as accuracy of orientation to the sound source, and highest walking velocity, occur in response to temperature-matched songs at 15°, 21°, and 30 °C. Experiments under semi-natural conditions in an outdoor arena revealed that females perform phonotaxis at temperatures as low as 13 °C. Taken together, the song and phonotaxis data demonstrate that this communication system is temperature coupled. A strategy is outlined by which temperature coupling may be exploited to test hypotheses about the organization of neural networks subserving song recognition.Abbreviations CP chirp period - SP syllable period - SD syllable duration     

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     

Phonotaxis in <Emphasis Type="Italic">Hyla versicolor</Emphasis> (Anura,Hylidae): the effect of absolute call amplitude

The influence of call amplitude on phonotaxis in female Hyla versicolor was studied using a no-choice paradigm. One set of experiments estimated effects of stimulus amplitude on phonotaxis toward a synthetic model of a conspecific call. The response strength increased with amplitude from the behavioral threshold (37–43 dB SPL) up to 79 dB SPL and then decreased at higher amplitudes. Females approached the loudspeaker with short walking bouts (1 s duration) occurring immediately after call presentations. Increase in response strength was attributed to an increasing proportion of calls that elicited such walking bouts, whereas the decrease at high amplitudes resulted from decreasing distance covered per bout. The quality of orientation remained constant for all above-threshold amplitudes. A second set of experiments tested the selectivity for interval duration and pulse duration at amplitudes of 55, 70, and 85 dB SPL. Selectivity for both parameters was similar at 70 and 85 dB SPL, but tended to increase at 55 dB SPL. The results suggest that selective phonotaxis in H. versicolor is not adapted for long-distance communication. This finding differs from those of comparable studies of acoustic insects.     

Phonotactic response of female crickets on the Kramer treadmill: methodology, sensory and behavioural implications

Since population-level variation in female mating preferences can shape intraspecific communication systems within the context of sexual selection it is essential to quantify these preferences and their sources of variation. We calculated individual female response functions for four male calling song traits in the field cricket Gryllus bimaculatus, by performing untethered phonotaxis measurements on a spherical locomotor compensator (Kramer treadmill). Firstly, we quantify the population-level sources of phonotactic variation and correct for factors that adversely affect this measurement. Secondly, we develop methodology for the characterisation of individual female phonotactic response functions suitable for population-level analyses and demonstrate the applicability of our method with respect to recent literature on Orthopteran acoustic communication. Phonotaxis towards a preferred stimulus on different occasions is highly repeatable, with lower repeatabilities away from the most preferred signal traits. For certain male signal traits, female preference and selectivity are highly repeatable. Although phonotactic response magnitude deteriorated with age, preference functions of females remained the same during their lifetimes. Finally, the limitations of measuring phonotaxis using a spherical locomotor compensator are described and discussed with respect to the estimation of the selectivity of female response.     

Prolonged response to calling songs by the L3 auditory interneuron in female crickets (Acheta domesticus): possible roles in regulating phonotactic threshold and selectiveness for call carrier frequency

L3, an auditory interneuron in the prothoracic ganglion of female crickets (Acheta domesticus) exhibited two kinds of responses to models of the male's calling song (CS): a previously described, phasically encoded immediate response; a more tonically encoded prolonged response. The onset of the prolonged response required 3-8 sec of stimulation to reach its maximum spiking rate and 6-20 sec to decay once the calling song ceased. It did not encode the syllables of the chirp. The prolonged response was sharply selective for the 4-5 kHz carrier frequency of the male's calling songs and its threshold tuning matched the threshold tuning of phonotaxis, while the immediate response of the same neuron was broadly tuned to a wide range of carrier frequencies. The thresholds for the prolonged response covaried with the changing phonotactic thresholds of 2- and 5-day-old females. Treatment of females with juvenile hormone reduced the thresholds for both phonotaxis and the prolonged response by equivalent amounts. Of the 3 types of responses to CSs provided by the ascending L1 and L3 auditory interneurons, the threshold for L3's prolonged response, on average, best matched the same females phonotactic threshold. The prolonged response was stimulated by inputs from both ears while L3's immediate response was driven only from its axon-ipsilateral ear. The prolonged response was not selective for either the CS's syllable period or chirp rate.     

Cricket phonotaxis: localization depends on recognition of the calling song pattern

Summary Calling song with a carrier frequency of 5 kHz evokes positive phonotaxis in female crickets,Gryllus bimaculatus, when presented at an azimuth. In contrast, a continuous tone of 4.7 kHz in the same position when paired with calling song from above leads to negative phonotaxis. Under open-loop conditions, when a tethered animal runs on a paired tread wheel, characteristic curves are produced with the stable equilibrium point towards or away from the stimulus, respectively (Fig. 3).In order to understand this sign reversal at the neuronal level, directional characteristics of the ascending acoustic inter neurons AN1 and AN2 were measured using extracellular recordings from the cervical connectives.Taking the mean spike rate of the interneurons as a measure for their excitation, the function relating response magnitude to stimulus direction for calling song corresponds well to the behavioural characteristic curve (Fig. 5). The response function obtained using a continuous tone with simultaneous presentation of calling song from above is similar (Fig. 5) and hence does not correspond to the inverse behavioural characteristic curve.However, consideration of the extent to which the temporal parameters of the calling song (syllables and chirps) are reflected in the neuronal response (amplitudes of the Fourier components) leads to characteristic curves for AN1 and AN2 which are in good agreement with the behaviour for stimulation with calling song as well as for the continuous tone experiment (Fig. 8). In addition, the neural response curves correspond to the behaviour in showing smaller amplitudes when a continuous tone rather than the calling song is presented on the horizon (Fig. 8).From these data we conclude that the activity in interneurons AN1 and AN2 does not directly guide orientation in mating behaviour but first is filtered by a mechanism tuned to the frequency of syllables and/or chirps. According to this hypothesis recognition of conspecific song and localization proceed sequentially inGryllus.     

The influence of auditory and visual experience on the phonotactic behavior of the cricket,Gryllus bimaculatus

Female crickets lacking experience with phonotaxis to conspecific calling song respond to trains of continuously repeated sound pulses (trill), whereas experienced females do not. In the present study such inexperienced crickets were tested for their responsiveness to trills of pulse repetition periods from 30 to 70 ms on a Y- shaped maze. Stimulation with a repetition period of 30 ms led to unexpectedly low phonotactic and exploratory activity. Initial stimulation with trills of 30- ms repetition period drastically reduced the responsiveness of inexperienced animals to conspecific calling song and other attractive stimuli. Effects of visual stimulation on the phonotactic behavior of female crickets are demonstrated. Threatening visual stimuli changed the behavior of experienced animals to a state that resembles that of inexperienced animals. The relevance of these observations is discussed with respect to the development of the auditory pattern recognition mechanism in crickets.     

Temperature coupling in cricket acoustic communication

Acoustic communication in Gryllus firmus is temperature-coupled: temperature induces parallel changes in male calling song temporal pattern, and in female preference for song. Temperature effects on song production and recognition networks were localized by selectively warming head or thorax or both head and thorax of intact crickets, then eliciting aggression song production (males) or phonotaxis to synthetic calling song (females). Because male song is produced by a thoracic central pattern generator (CPG), and because head ganglia are necessary for female song recognition, measurements of female phonotaxis under such conditions may be used to test the following competing hypotheses about organization of the song recognition network: 1. A set of neurons homologous to the male song CPG exist in the female, and are used as a template that determines preferred values of song temporal parameters for song pattern recognition (the common neural elements hypothesis), and 2. temporal pattern preference is determined entirely within the head ganglia. Neither selective warming of the head nor of the thorax was effective in changing female song preference, but simultaneous warming of head and thorax shifted preference toward a faster song in most preparations, as did warming the whole animal by raising ambient temperature. These results suggest that phonotactic preference for song temporal pattern is plurisegmentally determined in field crickets. Selective warming experiments during aggression song production in males revealed that syllable period is influenced but not completely determined by thoracic temperature; head temperature is irrelevant. The song CPG appears to receive some rate-setting information from outside the thoracic central nervous system.     

Condition dependence of female choosiness in a field cricket

Females generally choose mates that produce the loudest, brightest or most elaborate sexual displays, and these costly male displays are predicted to be condition dependent. However, mate choice itself is a costly behaviour also expected to be condition dependent. Male fall field crickets, Gryllus pennsylvanicus, produce a conspicuous long‐distance calling song that attracts females and is condition dependent. In this study, we tested the condition dependence of female preferences (preference function and choosiness) for male calling effort in G. pennsylvanicus. We manipulated female condition by raising crickets from hatching on either a low‐ or high‐quality diet. In a series of two‐speaker phonotaxis trials, both low‐ and high‐condition females preferred playbacks reflecting greater calling effort. However, relative to low‐condition females, high‐condition females took significantly longer to make a choice, were more likely to fail to choose within the time allotted for a phonotaxis trial and significantly increased their latency to choose over the course of multiple trials. We discuss these results with respect to the possibility that female G. pennsylvanicus may be foraging for direct benefits when they choose their mates.     

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)     

Processing of Song Signals in the Cricket and its Hormonal Control

SYNOPSIS. Phonotaxis by female crickets to the calling songof males, is an important model for investigating the neuralbasis of auditory behavior. Recent advances make it possibleto explain some components of this behavior and its hormonalcontrol, at the level of identified neurons and molecular expressionwithin those neurons Tonotopically arranged afferents from the cricket's ear, projectto local and intersegmental prothoracic interneurons. Bilateralprocessing of signals and some temporal-pattern specific processingoccurs in the prothoracic ganglion and influences acoustic informationthat is sent to the brain via ascending interneurons that aredemonstrably involved in phonotaxis. High, low and band- passinterneurons in the brain continue temporal pattern processingwhich matches the selectivity of phonotaxis and may be filtersfor recognition of the calling song. Neurons descending fromthe brain and prothoracic ganglion, direct multimodal signals(including auditory) to more posterior regions, possibly theleg motor neurons that are responsible for phonotaxis Age-related changes or artificially induced changes in JuvenileHormone III levels regulate the threshold for phonotaxis inAcheta domesticus, by varying the threshold of LI, a prothoracicascending interneuron that is necessary for phonotaxis to lowintensity calling songs. Results from in situ hybridizationsuggest that this might be accomplished, in part, by controllingthe levels of nicotinic acetylcholine receptor-like mRNA expressedin LI, presumably by increasing its neurotransmitter receptordensity. L3 is a prothoracic ascending interneuron that exhibitsbandselective response properties to the syllable period ofthe calling song. L3's response is age and JHIII related, andis correlated to phonotactic selectivity. These changes in L3might be accomplished, at least in part by JHIII regulatingthe expression of nicotinic acetylcholine receptor-like mRNAin L3     

Out of phase: relevance of the medial septum for directional hearing and phonotaxis in the natural habitat of field crickets

A modified tracheal system is the anatomical basis for a pressure difference receiver in field crickets, where sound has access to the inner and outer side of the tympanum of the ear in the forelegs. A thin septum in the midline of a connecting trachea coupling both ears is regarded to be important in producing frequency-dependent interaural intensity differences (IIDs) for sound localization. However, the fundamental role of the septum in directional hearing has recently been challenged by the finding that the localization ability is ensured even with a perforated septum, at least under controlled laboratory conditions. Here, we investigated the influence of the medial septum on phonotaxis of female Gryllus bimaculatus under natural conditions. Surprisingly, even with a perforated septum, females reliably tracked a male calling song in the field. Although reduced by 5.2 dB, IIDs still averaged at 7.9 dB and provided a reliable proximate basis for the observed behavioural performance of operated females in the field. In contrast, in the closely related species Gryllus campestris the same septum perforation caused a dramatic decline in IIDs over all frequencies tested. We discuss this discrepancy with respect to a difference in the phenotype of their tracheal systems.     

Responses to features of the calling song by ascending auditory interneurones in the cricket Gryllus campestris

ABSTRACT. In female Gryllus campestris L., three functional types of ascending auditory intemeurones have been studied by recording from them extracellularly in the split cervical connectives using suction electrodes. Type 1 neurones are characterized by an optimal sensitivity to the carrier frequency of the species calling song (4–5 kHz). They copy the syllable and pause structure of the call at all intensities. The patterned spike discharge is observable at least 8 dB above absolute threshold. With suprathreshold stimulation, the neurones exhibit maximal responses (number of spikes/chirp) around the carrier frequency. The intensity response curves are approximately linear in the range of 40–90 dB SPL. The envelope of each syllable is reflected by a corresponding change in the firing rate, and syllable periods of 24ms and longer are resolved. This type can be considered as a neural correlate for phonotactic behaviour of the female where the syllable period has been found to be the most important temporal parameter. Type 2 neurones are most sensitive in the range of 4–6 and 11–13 kHz. They copy the syllable and pause structure of the species calling song at low and moderate intensities. However, the spikes invade the intersyllable pauses, when stimulated with the calling song at higher intensities (above 85 dB). This is particularly apparent at the onset of a chirp series. The slope of the intensity—response curve mimics that of type 1 units. The neurones cannot follow syllable periods shorter than 32 ms. Type 3 neurones differ from types 1 and 2 by a rather broad-band sensitivity in the range of 3–16 kHz, and in copying the chirp as a whole. Even at low stimulus intensities, the intersyllable pauses are filled with spikes, and information about the syllable—pause structure is lost. Stimulation with suprathreshold intensities gives rise to a rather uniform, broad-band response without distinctive peaks. The intensity—response curve is characterized by a higher absolute threshold, and by the reduction in the response magnitude starting above 70–80 dB. These units are not suitable for copying the calling song temporal structure in detail, but would indicate the chirping rhythm. Their strong response in the range of the species courtship song carrier frequency make them suitable to copy the courtship song.     

Cues for male phonotaxis in the duetting bushcricketLeptophyes punctatissima

Summary A computer controlled setup is introduced which allows the song analysis of both male and femaleLeptophyes punctatissima during duetting in a laboratory situation. The essential acoustical parameters for the initiation of the male's phonotactic approach towards the stationary female are described. The female responds reflex-like to the male song after a remarkably short delay time of about 28 ms. The male only performs phonotaxis if he perceives the female reply above an intensity value of about 50 dB SPL and if the female response falls within a critical time window from 25 to a maximum of 55 ms after the onset of his song (Figs. 3 and 5). The sound intensity and overall time delay of the female response can be varied independently, so that the relationship between both parameters and their limitations for maximum phonotaxis distance can be described.     

Sound-pressure Levels and Song Preferences in Female Red-winged Blackbirds (Agelaius phoeniceus) (Aves,Emberizidae)

Female red-winged blackbirds (Agelaius phoeniceus) were tested for response to songs of male red-winged blackbirds differing in sound-pressure level (SPL) of playback. Subjects gave significantly more copulation-solicitation displays in response to playback of songs at 85 dB SPL than to playback of the same songs at 72 dB SPL. The strength of the preference, as judged by the ratio of response to high and low SPL playback (1.15:1), was lower than that of preferences for high SPL shown by insects and anurans. Female red-winged blackbirds responded preferentially to a conspecific song relative to a heterospecific imitation, even when the imitation was presented at an SPL 13 dB higher than that of the conspecific song. By contrast, female redwings did not maintain a preference for multiple conspecific song types over single types when the single song types were presented at the higher SPL. These results are compatible with Klump & Gerhardt's (1987) suggestion that the intensity independence of female preferences varies with the relative benefit females obtain from each preference.     

Male-male behavior and sexual dimorphism of the ear of a zaprochiline tettigoniid (Orthoptera: Tettigoniidae)

The external anatomy of the auditory system of an undescribed zaprochiline tettigoniid (Genus nov. 22 Sp. 1, Australian National Insect Collection, Canberra) shows sexual dimorphism: the male appears to have no auditory spiracle equivalent to that seen in the female. Nocturnally active males aggregate around female required nectar sources in a random manner with regard to each other. There is limited evidence, either from song interaction or from their behavior in the field, that males respond to each other by acoustic cues. Laboratory trials, testing male phonotaxis, showed that movement was random with respect to a target group of caged calling males. In the field, the only signs of agonistic behavior consisted of an increased calling rate when males were close together. Taken together, these data suggest that the male may not preceive sound in the same way as the female.