Individual variation in male vocal traits and female mating preferences in Bufo americanus

We investigated the amount of variation in mating behaviour between and within individual male and female American toads, because both sources of trait variation can influence the course of sexual selection. Males varied in all four call parameters investigated (dominant call frequency, pulse rate, call rate and call duration). Individual males lowered the dominant frequency of their call when they interacted vocally with nearby males. Dominant call frequency was more highly correlated with body size in vocally interacting males than in non-interacting males. Pulse rate of calls primarily varied with water temperature. Call rate and call duration showed the most variation of the four call properties, but this variation was unrelated to male morphology or social interactions. Females varied in three aspects of mating behaviour: two measures of pair formation and their preference for dominant frequency of male calls. The body size of paired males varied between females both in pairings initiated by either sex and in pairings initiated only by females. Males chosen by females were usually larger than average, although age and prior breeding experience of females did not affect mate choice. Playback experiments indicated that female preference for calls of low dominant frequency depended on the temporal patterning of alternative calls presented. Each of the four male vocal properties showed significant repeatability, but only one of the three aspects of female mating behaviour was repeatable. We discuss how different degrees of repeatability in sexual traits of males and females may influence the action and detection of sexual selection in this and other species. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.     

Females prefer leading males: relative call timing and sexual selection in katydid choruses

Females of several acoustic insects and anurans have recently been shown to orient preferentially to the leading of two identical male calls presented in close succession. We studied this phenomenon via two-choice phonotaxis trials in the neotropical katydid Neoconocephalus spiza and found that females avoided male calls occurring during an interval beginning immediately after the onset of a leading call. This avoidance occurred whether or not the following call was overlapped by the leader, indicating that the mechanism of preference for leading calls may represent a psychoacoustic precedence effect rather than simple call masking. We also found that females preferred leading calls as long as the amplitude of the following call was not more than 2 dB higher than the leader. Under certain circumstances, preferences for leading calls remained when females were presented with a sequence of four calls. Thus, preferences for leading calls probably influence a male's attractiveness and mating success in complex natural choruses: females are expected to orient towards males producing leading calls regardless of call length (and the probability of overlapping a following call), when the leading call is up to 1.5 times as distant as a follower, and when succeeded by multiple followers. We suggest that female preferences for leading male calls represent sensory biases that originated in contexts unrelated to sexual selection. None the less they currently play an important role in sexual selection and influence individual male signalling behaviour, and thus chorus structure. Copyright 1998 The Association for the Study of Animal Behaviour.     

Behavioral assessment of acoustic parameters relevant to signal recognition and preference in a vocal fish

Acoustic signal recognition depends on the receiver's processing of the physical attributes of a sound. This study takes advantage of the simple communication sounds produced by plainfin midshipman fish to examine effects of signal variation on call recognition and preference. Nesting male midshipman generate both long duration (> 1 min) sinusoidal-like "hums" and short duration "grunts." The hums of neighboring males often overlap, creating beat waveforms. Presentation of humlike, single tone stimuli, but not grunts or noise, elicited robust attraction (phonotaxis) by gravid females. In two-choice tests, females differentiated and chose between acoustic signals that differed in duration, frequency, amplitude, and fine temporal content. Frequency preferences were temperature dependent, in accord with the known temperature dependence of hum fundamental frequency. Concurrent hums were simulated with two-tone beat stimuli, either presented from a single speaker or produced more naturally by interference between adjacent sources. Whereas certain single-source beats reduced stimulus attractiveness, beats which resolved into unmodulated tones at their sources did not affect preference. These results demonstrate that phonotactic assessment of stimulus relevance can be applied in a teleost fish, and that multiple signal parameters can affect receiver response in a vertebrate with relatively simple communication signals.     

Spectral preferences and the role of spatial coherence in simultaneous integration in gray treefrogs (Hyla chrysoscelis).

The perceptual analysis of acoustic scenes may often require the integration of simultaneous sounds arising from a single source. Few studies have investigated the cues that promote simultaneous integration in the context of acoustic communication in nonhuman animals. This study of Cope's gray treefrog (Hyla chrysoscelis) examined female preferences based on spectral features of conspecific male advertisement calls to test the hypothesis that cues related to common spatial origin promote the perceptual integration of simultaneous signal elements (harmonics). The typical advertisement call comprises two harmonically related spectral peaks near 1.1 kHz and 2.2 kHz. Females generally exhibited preferences for calls with two spatially coherent harmonics over alternatives with just one harmonic. When given a choice between a spatially coherent call (both harmonics originating from the same speaker) and a spatially incoherent call (each harmonic from different spatially separated speakers), females preferentially chose the former in the same relative proportions in which it was chosen over single-harmonic alternatives. Preferences for spatially coherent calls over spatially incoherent alternatives did not appear to result from greater difficulty localizing the spatially incoherent sources. These results are consistent with the hypothesis that spatial coherence promotes perceptual integration of simultaneous signal elements in frogs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The function of Barbary macaque copulation calls

In a wide variety of animal species, females produce vocalizations specific to mating contexts. It has been proposed that these copulation calls function to incite males to compete for access to the calling female. Two separate advantages of inciting male-male competition in this way have been put forward. The first suggests that as a result of calling, females are only mated by the highest ranking male in the vicinity (indirect mate choice hypothesis). The second proposes that copulation calling results in a female being mated by many males, thus promoting competition at the level of sperm (sperm competition hypothesis). In this paper, I give results from the first experimental study to test these hypotheses. Playback was used to examine the function of copulation calls of female Barbary macaques (Macaca sylvanus) in Gibraltar. Although rank did not affect lone males' likelihood of approaching copulation calls, when playbacks were given to pairs of males only the higher ranking individual approached. Moreover, females were mated significantly sooner after playback of their copulation call than after playback of a control stimulus. These results suggest that the copulation calls of female Barbary macaques play a key role in affecting patterns of male reproductive behaviour, not only providing an indirect mechanism of female choice, but also promoting sperm competition by reducing the interval between copulations. Potential fitness benefits of inciting male-male competition at these two levels are discussed.     

Changes in mating vocalizations over the ejaculatory series in rats (Rattus norvegicus).

Rats (Rattus norvegicus) produce ultrasonic calls during mating. We examined changes in the structure and pattern of such vocalizations over the ejaculatory series. In Experiment 1, vocalizations were recorded from 11 pairs of rats through 3 ejaculatory series and analyzed spectrographically. We classified 4 categories of call by spectral frequency and duration. Calls of low frequency, long duration, and high intensity occurred more often shortly before the ejaculation and were associated with mounting without intromission, a behavior that often occurs shortly before ejaculation. The high-frequency calls did not vary in number across the series. In Experiment 2, vocalizations were recorded from males paired with devocalized females. Males produced all vocalization patterns produced by pairs in Experiment 1. Results suggest that most pre-ejaculatory calls are produced by males and may potentially affect female sexual behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Communication among hamsters by high-frequency acoustic signals: I. Physical characteristics of hamster calls.

In Exp I, 2 random-bred (Lak:LVG) female hamsters emitted high-frequency sounds at average intensities of 53 db (SPL). These calls tended to be 80–200 msec long and to emphasize frequencies of 34–42 kHz. However, female "ultrasounds" typically included rapid fluctuations in frequency and amplitude. In Exp II, male hamsters also emitted high-frequency vocalizations, with dominant frequencies of 32–38 kHz and average durations of 70–250 msec. Although male cells generally included fewer rapid changes in amplitude and frequency than did female calls, male call structures depended on contextual factors. Calls produced by males in the presence of estrous females tended to have lower minimum frequencies, higher maximum frequencies, longer durations, and fewer rapid frequency changes than calls by solitary males. These results show that both sex differences and situational factors influence the structures of hamster ultrasounds. The frequency and amplitude changes typical of calls by females and solitary males should facilitate the localization of a calling individual over moderate distances. Calls by males in the presence of females should be more difficult to localize and might operate over shorter distances to serve a different social function. (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of male pre-ejaculatory vocalizations on female receptive behavior in the rat (Rattus norvegicus).

Both male and female rats (Rattus norvegicus) emit ultrasounds during copulation. Bursts of ultrasounds from males that occur as ejaculation approaches are lower in frequency, longer in duration, and louder than those that appear earlier in the ejaculatory series. We attempted to determine if these pre-ejaculatory calls affect female sexual behavior. The behavior of females paired with devocalized males was compared with that of females paired with intact males, and in a second experiment tape-recorded vocalizations were played to females paired with devocalized males. Females were less receptive when paired with devocalized males; they were less likely to remain stationary when males attempted to mount. Playback of both types of calls restored female immobility toward control levels, although pre-ejaculatory calls were more effective than mating ones. Pre-ejaculatory calls restored running and trailing levels somewhat toward control level but to a lesser extent than female immobility. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A test of the acoustic adaptation hypothesis in four species of marmots

Acoustic signals must be transmitted from a signaller to a receiver during which time they become modified. The acoustic adaptation hypothesis suggests that selection should shape the structure of long-distance signals to maximize transmission through different habitats. A specific prediction of the acoustic adaptation hypothesis is that long-distance signals of animals in their native habitat are expected to change less during transmission than non-native signals within that habitat. This prediction was tested using the alarm calls of four species of marmots that live in acoustically different habitats and produce species-specific, long-distance alarm vocalizations: yellow-bellied marmot, Marmota flaviventris; Olympic marmot, M. olympus; hoary marmot, M. caligata; and woodchuck, M. monax. By doing so, we evaluated the relative importance the acoustic environment plays on selecting for divergent marmot alarm calls. Representative alarm calls of the four species were broadcast and rerecorded in each species' habitat at four distances from a source. Rerecorded, and therefore degraded alarm calls, were compared to undegraded calls using spectrogram correlation. If each species' alarm call was transmitted with less overall degradation in its own environment, a significant interaction between species' habitat and species' call type would be expected. Transmission fidelity at each of four distances was treated as a multivariate response and differences among habitat and call type were tested in a two-way MANOVA. Although significant overall differences in the transmission properties of the habitats were found, and significant overall differences in the transmission properties of the call types were found, there was no significant interaction between habitat and call type. Thus, the evidence did not support the acoustic adaptation hypothesis for these marmot species. Factors other than maximizing long-distance transmission through the environment may be important in the evolution of species-specific marmot alarm calls. (c) 1998 The Association for the Study of Animal Behaviour.     

Receptivity of the female rat (Rattus norvegicus) after male devocalization: A ventral perspective.

Male rats (Rattus norvegicus) emit at least two patterns of vocalization during copulation, the mating call and the pre-ejaculatory call. Both calls promote immobility of the female during lordosis, but the pre-ejaculatory calls are more effective. We undertook, through ventral observations of the mating pair, to determine if the female failed to assume or maintain the lordosis posture when mounted by a devocalized male and also to determine if the devocalized male was providing adequate stimulation to induce receptive behavior. Females were more likely to move away from the devocalized males before assuming the full lordosis posture. Furthermore, they were more likely to move away before the males had a chance to engage in intromissive behavior. However, when the females remained immobile along enough for the males to achieve a mount or intromission, there was little difference in the behavior of either animal that resulted from the devocalization of the male. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Geographic variation in the calls of wild chimpanzees: a reassessment

Male chimpanzees produce a species-typical call, the pant hoot, to communicate to conspecifics over long-distances. Calls given by males from the well-known Gombe and Mahale populations typically consist of four different phases: an introduction, build-up, climax, and let-down. Recent observations suggest that chimpanzees living in the Kibale National Park, Uganda, consistently give calls that lack a build-up and are thus qualitatively distinguishable acoustically from those made by other East African conspecifics. We analyzed additional recordings from Mahale and Kibale to re-examine geographic variation in chimpanzee calls. Results indicate that males from both sites produce pant hoots containing all four parts of the call. Calls made by chimpanzees from the two populations, however, differ in quantitative acoustic measures. Specifically, males at Kibale initiate their calls with significantly longer elements and build-up over briefer periods at slower rates than individuals from Mahale. Kibale males also deliver acoustically less variable calls than chimpanzees at Mahale. Although climax elements do not differ between populations in any single acoustic feature, discriminant function analysis reveals that acoustic variables can be used in combination to assign calls to the correct population at rates higher than that expected by chance. Ecological factors related to differences in habitat acoustics, the sound environment of the local biota, and body size are likely to account for these observed macrogeographic variations in chimpanzee calls.     

Sex differences in the incidence and sonographic characteristics of antipredator ultrasonic cries in the laboratory rat (Rattus norvegicus).

Long-Evans rats (10 males and 10 females) in a burrow system responded to a cat in the open area by retreating to a burrow and emitting ultrasounds of 18–27 kHz. Females made more frequent ultrasonic cries, with longer durations of ultrasounds. In a 2nd study (19 males and 19 females), sonographic analyses confirmed the more frequent vocalizations of females and indicated that the sound pulses of females were reliably shorter in duration and of higher base frequency than those of males. Also, females emitted more pulses per pulse train with shorter within-train interpulse intervals. Six basic pulse forms were determined, and males emitted more (70%) pulses with negatively accelerated descending frequencies than females (25%). The findings indicate that female rats show qualitatively different antipredator vocalizations than do males and add to previous findings of higher levels of female antipredator defensiveness. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Communication among hamsters by high-frequency acoustic signals: II. Determinants of calling by females and males.

A previous study by the authors (see record 1978-09410-001) showed that basal rates of high-frequency vocalization by estrous female hamsters exceeded those typical of nonestrous females. In the present 6 studies with random-bred (Lak:LVG) hamsters, even higher rates of calling by estrous females were provoked by male odors (male shavings or anesthetized males). This suggested that cues which normally indicate a male's proximity can increase the rate of high-frequency calls by an estrous female. These findings are consistent with a view of female "ultrasounds" as sexual advertisements which indicate the locations, sexual receptivity, and relative passivity of estrous females to nearby male conspecifies. Male hamsters also produced ultrasounds at rates that seemed to depend on the availability of potential males. Brief exposure to an awake female stimulated male calling; however, estrous females provoked higher call rates than did nonestrous females. Exposure to anesthetized females also increased the rate of male calling, which suggests that the stimulation of male calling by awake females depends in part on female odors. These results suggest that both male and female ultrasounds are parts of a communication system that facilitates reproduction by helping to coordinate social behavior with endocrine state. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acoustical and perceptual structures of sexually dimorphic distance calls in Bengalese finches (Lonchura striata domestica).

Characterized the physical structure of distance calls by the Bengalese finch (Lonchura striata domestica) and its relation to perception. Distance calls were recorded from 12 female and 12 male Bengalese finches and analyzed; such acoustic parameters as length, bandwidth, and peak frequency were obtained, and differences between sexes on combinations of these parameters were tested and shown to be significant. To assess perceptual salience of acoustic parameters, discrimination of 4 female and 4 male calls was examined. The reaction time (RT) required to discriminate a pair of distance calls was used as a measure of similarity between the 2 calls and analyzed by a multidimensional scaling procedure to find the perceptual dimensions. The results suggest that the sex difference in Bengalese finch distance calls is easily perceived by Bengalese finches and that the males and females were not different in their perception of the calls. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of the ultrasonic vocalization of the female rat (Rattus norvegicus) in sexual behavior.

Both male and females rats vocalize ultrasonically during mating. In this article, experiments were done to examine the effects of the female's mating call on rat mating behavior. In the first experiment, females copulated with intact males before and after surgical devocalization. In the second experiment, intact females copulated twice with a male: once when they were able to hear and once when they were temporarily deafened with a medical ear mold. In the third experiment, tape recorded ultrasounds were placed in the presence of devocalized females while they were copulating with intact males. In the control condition, tape hiss was presented. In each experiment, it was observed that the female darted more if communications were disrupted (i.e., female devocalized or male deafened). Playback partially reduced darting to control levels. No other behavior was affected consistently across all experiments. Female calls might facilitate self-regulation of mating behavior, or they might focus the male's attention on her proceptive behaviors. It is also possible that the female calls could alter the stimulus properties of the male's behavior, indirectly affecting her own behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Assessment of distance to potential mates by female barking treefrogs (Hyla gratiosa).

This study investigated the cues used by female barking treefrogs, Hyla gratiosa, to assess distances to potential mates. Eight-speaker playback experiments were used to demonstrate that distance affects female choice in complex acoustic environments and to test 3 possible cues that females might use to assess distance: (a) degradation in spectral and temporal cues of calls, (b) relative call amplitude at the female's location, and (c) the rate at which the amplitude of calls increases as a female approaches a calling male. All 3 hypotheses were refuted, suggesting that females use a more complex mechanism, such as triangulation, to assess distance. Females preferred speakers with greater source amplitudes even when they had to travel further to reach those speakers. Determination of source amplitude is possible only if females can assess independently both the distance to sound sources and the amplitude of calls at the females' location. Hence, anuran amphibians may possess greater cognitive abilities than are generally attributed to them. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of acoustic cue modifications on evoked vocal response to calls in zebra finches (Taeniopygia guttata).

Besides their song, which is usually a functionally well-defined communication signal with an elaborate acoustic structure, songbirds also produce a variety of shorter vocalizations named calls. While a considerable amount of work has focused on information coding in songs, little is known about how calls' acoustic structure supports communication processes. Because male and female zebra finches use calls during most of their interactions and answer to conspecific calls without visual contact, we aimed at identifying which calls' acoustic cues are necessary to elicit a vocal response. Using synthetic zebra finch calls, we examined evoked vocal response of male and female zebra finches to modified versions of the distance calls. Our results show that the vocal response of zebra finches to female calls requires the full harmonic structure of the call, whereas the frequency downsweep of male calls is necessary to evoke a vocal response. It is likely that both female and male calls require matching a similar frequency bandwidth to trigger a response in conspecific individuals. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Assortative mating and female clutch investment in black grouse

Variation in female behaviour has only recently received attention in studies of sexual selection. It has been suggested that females may invest differentially in their offspring in relation to the quality of their mate. This may lead to females that mate with high-quality and/or attractive males laying larger clutches. Females may also differ in their ability to choose between males. For example, females in good physical condition may make better choices. If physical condition and clutch size are positively correlated, this hypothesis could also produce a relationship between male attractiveness and female clutch size. We found, in lekking black grouse, Tetrao tetrix, that females mated to the highest ranked males laid the largest clutches. Furthermore we found, regardless of female age, a positive relationship between a measure of female condition and male rank but not between female condition and her clutch size. In addition, females in good condition visited a larger number of different male territories, and old females produced the largest clutches. Our results suggest two mechanisms to explain our findings. First, females in good physical condition tend to mate with the top males, suggesting an assortative mating pattern. Second, females mating with the highest ranked males lay larger clutches as a consequence of their choice. In general, our result calls for caution in evaluating studies that look at the consequences of mate choice. It may be that differences in female quality produce effects that may be wrongly interpreted as male quality effects. (c) 1998 The Association for the Study of Animal Behaviour.     

Acoustic interactions in broods of nestling birds (Tachycineta bicolor).

Studies of acoustic interactions in animal groups, such as chorusing insects, anurans, and birds, have been invaluable in showing how cooperation and competition shape signal structure and use. The begging calls of nestling birds are ideal for such studies, because they function both as a cooperative signals of the brood's needs and as competitive signals for parental allocation within the brood. Nonetheless, studies of acoustic interactions among nestlings are rare. Here we review our work on acoustic interactions in nestling tree swallows (Tachycineta bicolor), especially how calls are used in competition for parental feedings. Nestlings attracted parental attention and responded to acoustic interference mainly by increasing call output. However, nestlings also gave more similar calls when they called together and decreased their call bandwidth when exposed to elevated noise. We suggest that these competitive uses of calls might intensify the cooperative brood signal, affecting both parental provisioning and vocal development. Given their tremendous variation across species, begging calls offer promising opportunities for developmental and comparative studies of acoustic signaling. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Vocal development in budgerigars (Melopsittacus undulatus): Contact calls.

Budgerigars have a complex vocal repertoire, some of which develops through learning. The authors examined the course of vocal development in budgerigars from hatching to about 4 weeks postfledging (approximately 85 days old). Food-begging calls showed changes in duration, peak frequency, bandwidth, and frequency modulation with age. Within a week of fledging, each bird produced a contact call bearing a strong resemblance to a shortened version of its patterned food-begging call. By 4 weeks postfledging, budgerigar contact call repertoires often contained more than one call type, and there was clear evidence of sharing and imitation among the calls of parents, fledglings, and other social companions. Perceptual testing showed that whereas acoustic variation in the structure of developing calls decreased both within and between nestling birds, the discrimination of these calls was easier for adult birds as young birds matured. These results suggest parallels with certain aspects of language development in humans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)