Vocal communication in a neotropical treefrog, Hyla ebraccata: Advertisement calls

We studied the vocal communication of Hyla ebraccata in central Panama. The advertisement call of this species consists of a pulsed buzz-like primary note which may be given alone or followed by 1–4 secondary click notes. Primary notes are highly stereotyped, showing little variation within or0 among individuals in dominant frequency, duration, pulse repetition rate or rise time. Males calling in isolation give mostly single-note calls. They respond to playbacks of conspecific calls by increasing calling rates and the proportion of multi-note calls, and by giving synchronized calls 140–200 ms after the stimulus begins. Responses to conspecific advertisement calls are usually given immediately after the primary note of the leading call, but the primary note of the response often overlaps with the click notes of the leading call. Experiments with synthetic signals showed that males synchronize to any type of sound of the appropriate frequency (3 kHz), regardless of the fine structure of the stimulus. Playbacks of synthetic calls of variable duration showed that males do not synchronize well to calls less than 150 ms long, but they do to longer calls (200–600 ms). The variance in response latency increased with increasing stimulus duration, but modal response times remained at around 140–200 ms. Similar results were obtained in experiments withsynthetic calls having a variable number of click notes. Males showed no tendency to increase the number of click notes in their calls in response to increasing stimulus duration or increasing number of clicks in the stimulus. Females preferred three-note to one-note calls in two-choice playback experiments, whether these were presented in alternation, or with the one-note call leading and the three-note call following. Females showed no preference for leader or follower calls when both were one-note. When two-note calls were presented with the primary note of the follower overlapping the click note of the leader, females went to calls in which click notes were not obscured. Our results indicate that male H. ebraccata respond to other males in a chorus in ways which enhance their ability to attract mates.     

Sound production in the whitemouth croaker and relationship between fish size and disturbance call characteristics

The whitemouth croaker produces two different sounds using extrinsic sonic muscles: (1) male advertisement calls during the spawning season and (2) disturbance calls, produced by both sexes. The advertisement call, related to courtship, was recorded in the field and from two marked spawning males of 28 and 30.5 cm L_T in the laboratory. It consists of individual pulses with average durations of 19.7 ms and 17.8 ms for the two males respectively, interpulse intervals of 496 ms and 718 ms, and dominant frequencies of 280 Hz and 316 Hz. Pulses are emitted in bouts of one to three min duration. Disturbance calls consist of a burst of pulses produced at short intervals, and the pulse duration, interpulse interval and dominant frequency of the pulses average 19.8 ms, 17.1 ms, and 363 Hz, respectively. Dominant frequency and interpulse interval decrease and pulse duration increases with fish size. Sound characteristics change markedly in young of the year individuals (lower than 25 cm L_T) after which they appear to stabilize. Higher dominant frequency in the advertisement than in the disturbance call and the relationship of dominant frequency to pulse duration suggest that dominant frequency is determined as a forced response to muscle contraction parameters rather than by the natural frequency of the swimbladder.     

Changes in the Frequency Structure of a Mating Call Decrease Its Attractiveness to Females in the Cricket Frog Acris crepitans blanchardi

In many species, females often prefer male signals that are more complex than in nature or beyond the range of calls naturally produced by conspecific males in spectral, temporal and amplitude features. In this study we examined both the ability of females to recognize signals outside the normal range of spectral frequency variation seen in male advertisement calls, and the influence of increasing call complexity by adding spectral components to enhance the attractiveness of a male advertisement call in the cricket frog Acris crepitans blanchardi, while keeping its amplitude constant. We used two different natural male call groups and created the following synthetic call groups: with a dominant frequency at 3500 Hz, i.e. at the normal dominant frequency with a frequency band within the sensitivity range of the inner ear basilar papilla; with a dominant frequency at 700 Hz, i.e. outside the normal range of variation and with a frequency band outside the sensitivity range of the basilar papilla but within the range of the amphibian papilla; with two dominant frequencies, one at 700 Hz and another at 3500 Hz, stimulating the basilar and amphibian papilla simultaneously. In double choice experiments we tested all combinations of the three call groups, and we tested the 3500 Hz call groups against the same natural call groups. Additionally, we tested the 700 Hz call groups against white noise to see whether these signals are meaningful in mate choice. Females preferred 3500 Hz call groups over all other call groups. The synthetic call group was as attractive to females as the same natural call group. The 700 Hz call group was not meaningful in mate choice. The combined (700 Hz + 3500 Hz) call group was significantly less attractive to females than the 3500 Hz call group. Thus, making a call more spectrally complex without increasing its overall amplitude decreases its attractiveness to cricket frog females.     

A quantitative analysis of behavioral selectivity for pulse rise-time in the gray treefrog, Hyla versicolor

The selectivity of female phonotactic responses to synthetic advertisement calls was tested in choice situations. Preferences based on differences in the linear rise-time of synthetic pulses depended on intensity and carrier frequency. When the carrier frequency was 1.1 kHz, simulating the low-frequency peak in the advertisement call, females preferred alternatives with slower rise-time pulses that differed by 5 ms at playback levels of 75 dB SPL and higher. A rise-time difference of 10 ms was discriminated at 65 dB SPL. When the carrier frequency was 2.2 kHz, simulating the high-frequency peak in the call, females discriminated a 5-ms difference in rise-time only at 85 dB SPL. Females showed no preference when the difference was 10 ms at lower playback levels. The difference in the thresholds (about 15–20 dB) for discriminating differences in rise-time at the two carrier frequencies was greater than the difference in behavioral thresholds for these two frequencies (about 10 dB). This result suggests that rise-time discrimination can be mediated solely by the neural channel mainly tuned to the low-frequency peak in the call. Females probably assess differences in rise-time by comparing the first few pulses of each call rather than by averaging over the entire call. Accepted: 30 March 1999     

Acoustically induced call modification in the white-lipped frog,Leptodactylus albilabris

The vocalization behaviour of Leptodactylus albilabris was investigated using field playback experiments. To assess the response of males to pre-recorded natural ‘chirp’ (advertisement call) and natural ‘chuckle” (aggressive call) stimuli of gradually increasing broadcast intensity, three parameters (intensity, dominant frequency and repetition rate) of the chirp call were analysed. Of the males tested, 69% showed a significant increase in chirp intensity with increased levels of both stimulus types. In response to playback of the chirp stimulus, males actively modified the dominant frequency of their chirp calls over a mean range of 91·42 Hz, and in one case as much as 400 Hz. Moreover, 12 of 17 males shifted the frequency of their call towards the dominant frequency of the chirp stimulus (2175 Hz) by either increasing or decreasing the dominant frequency of their chirp calls. In response to the natural chuckle stimulus, 83% of the males showed either a decrease or no significant change in the dominant frequency of their chirps. All eight males for which both the chirp frequency and intensity were analysed and that showed an increase in chirp intensity also showed a concomitant increase in chirp dominant frequency. These results are the first to document quantitatively the plasticity of advertisement call intensity and dominant frequency in an anuran. The possible effects of advertisement call modification on male mating success in L. albilabris is discussed.     

Female Preferences for Call Traits and Male Mating Success in the Neotropical Frog Physalaemus enesefae

Female preferences for male call traits may affect male mating success and the evolution of exaggerated secondary sexual traits. We used phonotaxis experiments to examine female preferences in the frog Physalaemus enesefae in relation to variation in male call duration, dominant frequency, intercall interval and amplitude (dB SPL). Females preferred long calls, low and average dominant frequency calls, short intercall intervals and more intense calls. We compared the patterns of female preferences with those of acoustic variation among males to test the prediction that properties with low within‐male variation are associated with stabilizing or weakly directional female preferences, whereas properties with high within‐male variation are associated with directional preferences. Females had weakly directional preferences for the dominant frequency of the call and strongly directional preferences for call duration and call rate. We also determined whether the temporal relationship between calls influenced preferences based on the dominant frequency of the call. Preferences for low‐frequency over high‐frequency calls disappeared when calls partially overlapped. Females preferred the leading call regardless of its dominant frequency. We also investigated mating patterns in the field. There was size‐assortative mating, as male and female body sizes snout‐vent length (SVL) were positively correlated. In addition, differences in the frequency distributions of body length (SVL) between mated and unmated males approached significance; lower SVL classes were underrepresented among mated males. These patterns may reflect female preferences for lower dominant frequency calls, as there is a negative correlation between male mass and the dominant frequency of the call.     

Pre-existing sensory biases in the spectral domain in frogs: empirical results and methodological considerations

In many species of anurans, advertisement calls excite only one of the two inner-ear organs. One prediction of the pre-existing bias hypothesis is that signal innovations that additionally excite the “untapped” organ will be more behaviorally effective than normal calls. However, recent studies have shown that females of three species with single-peaked calls that stimulate only the basilar papilla (BP) preferred single-peaked synthetic calls with a frequency typical of conspecific calls to two-peaked calls that also stimulated the amphibian papilla (AP). We report that in spring peepers (Pseudacris crucifer) that also produce single-peaked calls, females did not show a preference in choices between single-peaked and two-peaked synthetic calls. Thus, the addition of energy exciting the AP had a neutral effect on signal attractiveness. Together, these results are unsupportive of the pre-existing bias hypothesis. An alternative hypothesis is that positive fitness consequences of responding to sounds providing extraordinary spectral stimulation are required for a novel call to become established as a mate-attracting signal. Testing these ideas requires a taxonomically broader examination of responses to sounds with novel spectral complexity, and attention to some methodological details will improve the comparability of such studies.     

Passive acoustic monitoring,development of disturbance calls and differentiation of disturbance and advertisement calls in the Argentine croaker Umbrina canosai (Sciaenidae)

Disturbance and advertisement calls of the Argentine croaker Umbrina canosai were recorded from coastal Uruguayan waters. Dissections indicate typical sciaenid extrinsic swimbladder muscles present exclusively in males. Disturbance calls were produced when captive U. canosai were startled, chased with a net or grabbed by the tail. Calls were unusual for sciaenids because each pulse consisted of multiple cycles. The number of cycles per pulse and dominant frequency did not change with U. canosai size, but pulse duration and interpulse interval increased. Advertisement calls were recorded from unseen choruses in the field and confirmed with captive individuals in a large tank. Advertisement calls were recorded throughout the known range of the species in Uruguay indicating a continuous belt of spawning populations. Tank recordings of the same individuals permitted explicit comparisons between the two calls. Advertisement call pulses averaged 2·4 more cycles (11·0–8·6) although pulses of both calls were basically similar as were durations and dominant frequencies. Pulse number, however, differed markedly, averaging 13·6 and 3·4 pulses for disturbance and advertisement calls respectively. Furthermore, disturbance calls were produced as a rapid series with an interpulse interval of 26–31 ms whereas advertisement call patterns were less stereotyped and ranged from <100 to 450 ms. Multicycle pulses distinguished U. canosai from other sympatric sciaenids.     

Advertisement calls of Guenther’s frog Hylarana guentheri (Anura: Ranidae) during the breeding season

Acoustic signalling is the most important form of communication in anuran amphibians. Here we recorded and analysed the calls of 18 male Guenther’s frogs (Hylarana guentheri) from the wild during the breeding season. The advertisement calls of H. guentheri were composed of from a single note to five notes, with three-note calls the most recorded. All individuals produced calls around 600 Hz but calls ranged from 470 to 2600 Hz. Comparing the differences between individuals calls, we found within-male coefficients of variation (CV_w) of call intensity, the fundamental frequency, the first formant, the second formant, the third formant and the fourth formant were static (less than 5% variation), whereas those of note duration, call duration, call interval, numbers of pulses and dominant frequency were dynamic (larger than 15% variation). Comparisons of the call characteristics of H. guentheri in this study with other studies from China, Singapore and Vietnam found call characteristics varied greatly between the five different locations.     

Temporal selectivity by single neurons in the torus semicircularis of Batrachyla antartandica (Amphibia: Leptodactylidae)

We investigated the response selectivities of single auditory neurons in the torus semicircularis of Batrachyla antartandica (a leptodactylid from southern Chile) to synthetic stimuli having diverse temporal structures. The advertisement call for this species is characterized by a long sequence of brief sound pulses having a dominant frequency of about 2000 Hz. We constructed five different series of synthetic stimuli in which the following acoustic parameters were systematically modified, one at a time: pulse rate, pulse duration, pulse rise time, pulse fall time, and train duration. The carrier frequency of these stimuli was fixed at the characteristic frequency of the units under study (n=44). Response patterns of TS units to these synthetic call variants revealed different degrees of selectivity for each of the temporal variables. A substantial number of neurons showed preference for pulse rates below 2 pulses s(-1), approximating the values found in natural advertisement calls. Tonic neurons generally showed preferences for long pulse durations, long rise and fall times, and long train durations. In contrast, phasic and phasic-burst neurons preferred stimuli with short duration, short rise and fall times and short train durations.     

Temporal selectivity for complex signals by single neurons in the torus semicircularis of Pleurodema thaul (Amphibia: Leptodactylidae)

Responses of auditory neurons in the torus semicircularis (TS) of Pleurodema thaul, a leptodactylid from Chile, to synthetic stimuli having diverse temporal patterns and to digitized advertisement calls of P. thaul and three sympatric species, were recorded to investigate their temporal response selectivities. The advertisement call of this species consists of a long sequence of sound pulses (a pulse-amplitude-modulated, or PAM, signal) having a dominant frequency of about 2000 Hz. Each of the sound pulses contains intra-pulse sinusoidal-amplitude-modulations (SAMs). Synthetic stimuli consisted of six series in which the following acoustic parameters were systematically modified, one at a time: PAM rate, pulse duration, number of pulses, and intra-pulse SAM rate. The carrier frequency of these stimuli was set at the characteristic frequency (CF) of the isolated units (n = 47). Response patterns of TS units to synthetic call variants reveal different degrees of selectivities for each of the temporal variables, with populations of neurons responding maximally to specific values found in the advertisement call of this species. These selectivities are mainly shaped by neuronal responsiveness to the overall sound energy of the stimulus and by the inability of neurons to discharge to short inter-pulse gaps. Accepted: 30 October 1996     

Spatial hearing in Cope’s gray treefrog: II. Frequency-dependent directionality in the amplitude and phase of tympanum vibrations

Anuran ears function as pressure difference receivers, and the amplitude and phase of tympanum vibrations are inherently directional, varying with sound incident angle. We quantified the nature of this directionality for Cope’s gray treefrog, Hyla chrysoscelis. We presented subjects with pure tones, advertisement calls, and frequency-modulated sweeps to examine the influence of frequency, signal level, lung inflation, and sex on ear directionality. Interaural differences in the amplitude of tympanum vibrations were 1–4 dB greater than sound pressure differences adjacent to the two tympana, while interaural differences in the phase of tympanum vibration were similar to or smaller than those in sound phase. Directionality in the amplitude and phase of tympanum vibration were highly dependent on sound frequency, and directionality in amplitude varied slightly with signal level. Directionality in the amplitude and phase of tone- and call-evoked responses did not differ between sexes. Lung inflation strongly affected tympanum directionality over a narrow frequency range that, in females, included call frequencies. This study provides a foundation for further work on the biomechanics and neural mechanisms of spatial hearing in H. chrysoscelis, and lends valuable perspective to behavioral studies on the use of spatial information by this species and other frogs.     

Spectral and temporal gating mechanisms enhance the clutter rejection in the echolocating bat,Rhinolophus rouxi

Summary Doppler shift compensation behaviour in horseshoe bats, Rhinolophus rouxi, was used to test the interference of pure tones and narrow band noise with compensation performance. The distortions in Doppler shift compensation to sinusoidally frequency shifted echoes (modulation frequency: 0.1 Hz, maximum frequency shift: 3 kHz) consisted of a reduced compensation amplitude and/or a shift of the emitted frequency to lower frequencies (Fig. 1).Pure tones at frequencies between 200 and 900 Hz above the bat's resting frequency (RF) disturbed the Doppler shift compensation, with a maximum of intererence between 400 and 550 Hz (Fig. 2). Minimum duration of pure tones for interference was 20 ms and durations above 40 ms were most effective (Fig. 3). Interfering pure tones arriving later than about 10 ms after the onset of the echolocation call showed markedly reduced interference (Fig. 4). Doppler shift compensation was affected by pure tones at the optimum interfering frequency with sound pressure levels down to –48 dB rel the intensity level of the emitted call (Figs. 5, 6).Narrow bandwidth noise (bandwidth from ± 100 Hz to ± 800 Hz) disturbed Doppler shift compensation at carrier frequencies between –250 Hz below and 800 Hz above RF with a maximum of interference between 250 and 500 Hz above resting frequency (Fig. 7). The duration and delay of the noise had similar influences on interference with Doppler shift compensation as did pure tones (Figs. 8, 9). Intensity dependence for noise interference was more variable than for pure tones (-32 dB to -45 dB rel emitted sound pressure level, Fig. 10).The temporal and spectral gating in Doppler shift compensation behaviour is discussed as an effective mechanism for clutter rejection by improving the processing of frequency and amplitude transients in the echoes of horseshoe bats.Abbreviations CF constant frequency - FM frequency modulation - RF resting frequency - SPL sound pressure level     

Graded Aggressive Calls in the African Painted Reed Frog Hyperolius marmoratus (Hyperoliidae)

The African painted reed frog, Hyperolius marmoratus, has a potentially complex communication system. Advertisement calls and aggressive calls, although distinct from each other, are in fact two ends of a continuum of graded calls. Playback experiments using standard advertisement calls showed that males increased the proportion of aggressive calls as the stimulus intensity was increased. In addition, three characteristics of the aggressive calls changed in response to higher playback levels. Males increased the number of pulses/call, increased call duration, and decreased dominant frequency. Aggressive calling occurred primarily during the early hours of the night, with considerable overlap with times when females were searching for mates in the chorus. Females tested in two-choice arena trials discriminated against aggressive calls in favor of advertisement calls. It is suggested that aggressive calls reduce a male's ability to attract a female and that a graded signalling system may enable males to escalate agonistic encounters with other males without rendering calls completely unattractive to females.     

Calls of the black drum (Pogonias cromis: Sciaenidae): geographical differences in sound production between northern and southern hemisphere populations

Because of apparent reproductive isolation between Northern and Southern hemisphere populations of the black drum Pogonius cromis, we tested the hypothesis that advertisement calls from a southern population would differ from known calls of North American populations. Additionally, we quantified disturbance and advertisement calls, their changes with fish size and sex, not previously examined in this species. Unlike most sciaenids, both sexes of P. cromis possess robust sonic muscles, and both produce disturbance calls when handled. However, only males produce an advertisement call used in courtship. The disturbance call consists of a variable train of short-duration pulses (average 23?ms). The duration, interpulse interval, and dominant frequency of pulses are similar in males and females and change developmentally: pulse duration and interpulse interval increase and dominant frequency decreases with fish size. Advertisement calls, recorded in the field and in captivity, are long-duration (average 184?ms) and tonal. Based on variation in fundamental frequency, which decreases with fish size, field choruses are composed of different-sized individuals. The duration of advertisement calls, about a third of those from Florida populations, suggests genetic differentiation between northern and southern populations.     

The vocal sac as a visual cue in anuran communication: an experimental analysis using video playback

Acoustic signals produced by most anurans are accompanied by inflation of a conspicuous vocal sac. We presented female túngara frogs, Physalaemus pustulosus, with acoustic playback of the male advertisement call, synchronized with a video playback of vocal sac inflation. Females significantly preferred a stimulus combination including vocal sac inflation over an identical set of stimuli with the vocal sac inflation removed. Neither a moving rectangle bearing the gross contrast and spatiotemporal properties of the vocal sac inflation sequence, nor the image of a noncalling male significantly enhanced the attractiveness of the acoustic stimulus. Both the form and spatiotemporal properties of the vocal sac thus appear to be salient to females. The results indicate that the vocal sac can serve as a visual cue, which may account for the conspicuous pigmentation found on the vocal sacs of males in many species. Gular inflation in synchrony with a call may function to facilitate female localization of individual males in an aggregation.     

Biometric analyses as a tool for the differentiation of two coccolith species of the genus Crepidolithus (Pliensbachian,Lower Jurassic) in the Basque-Cantabrian Basin (Northern Spain)

Biometric analyses were performed on 20 Pliensbachian samples from the Santotis section (Basque-Cantabrian Basin, N Spain), in order to separate the species Crepidolithus crassus and Crepidolithus crucifer based on their size, and to evaluate the role, if any, of the paleoenvironmental conditions on C. crassus and C. crucifer size changes. In each sample, 100 specimens of both C. crassus and C. crucifer were randomly selected and imaged for taking measurements of their length and width. The length/width ratio or eccentricity was calculated for each specimen. Our results show that C. crucifer is around 2 μm longer and 1.3 μm wider than C. crassus. Based on length measurements, two groups were statistically differentiated. Crepidolithus crucifer coccoliths are longer than 8.2 μm. However, an overlap has been observed for C. crassus and C. crucifer in the 8–8.5 μm range; in these cases, central area structure and crystallographic properties are essential for species separation. A trend towards a progressive increase in the size of both taxa has been observed throughout the studied interval and no obvious relationships have been recognized between the lithology, TOC values and coccolith size. However, the size increment in both C. crassus and C. crucifer coincides with a cooling period, suggesting a potential environmental control on coccolith size.Size shifts have been recorded first in C. crassus and later in C. crucifer. Based on the sizes of both species, we speculate that the large C. crucifer, perhaps inhabited a slightly deeper portion of the photic zone and, that the diachronous size variations in the two investigated taxa could be related to the transgressive phase recorded during the Late Pliensbachian. The discrepancy between size variations of C. crassus and C. crucifer specimens in the uppermost part of the studied section might be indicative of modifications of specific portions of the photic zone. We propose that the stratification of water masses probably reduced the ecologic niche of C. crucifer that was forced to reach shallower depths by reducing its size.     

REINFORCEMENT AND REPRODUCTIVE CHARACTER DISPLACEMENT IN GASTROPHRYNE CAROLINENSIS AND G. OLIVACEA (ANURA: MICROHYLIDAE): A REEXAMINATION

Tape-recorded advertisement calls of Gastrophryne carolinensis and G. olivacea, obtained in Texas and southern Louisiana, were analyzed by means of an analogue audiospectrograph. Samples were grouped into four areas: allopatric and sympatric for G. carolinensis, and combined adjacent allopatric/shallow sympatric, and sympatric for G. olivacea. Three attributes of the advertisement call (call duration, pulse rate, and dominant frequency) were investigated, with water temperature at the calling site as the independent variable. Values for dominant frequency do not overlap between species, across the full range of recording temperatures, and those of sympatric G. carolinensis are displaced away from those of both groups of G. olivacea (which are very similar)—thus indicating a pattern of geographic variation consistent with reproductive character displacement. There is considerable overlap in the values for duration and for pulse rate of each species when considered alone, but there is only slight overlap of the scatters of points for the pairs of values. For both species, no consistent patterns of correlation were detected between the three attributes of the call and the snout–vent length of the emitter, thus reducing the likelihood that the divergence in calls is due to pleiotropic effects of body size.