Physical factors affecting the cost and efficiency of sound production in the treefrog Hyla versicolor (original) (raw)
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Animal behaviour, 2010
One strategy for coping with the constraints on acoustic signal reception posed by ambient noise is to signal louder as noise levels increase. Termed the 'Lombard effect', this reflexive behaviour is widespread among birds and mammals and occurs with a diversity of signal types, leading to the hypothesis that voice amplitude regulation represents a general vertebrate mechanism for coping with environmental noise. Support for this evolutionary hypothesis, however, remains limited due to a lack of studies in taxa other than birds and mammals. Here, we report the results of an experimental test of the hypothesis that male grey treefrogs increase the amplitude of their advertisement calls in response to increasing levels of chorus-shaped noise. We recorded spontaneously produced calls in quiet and in the presence of noise broadcast at sound pressure levels ranging between 40 dB and 70 dB. While increasing noise levels induced predictable changes in call duration and rate, males did not regulate call amplitude. These results do not support the hypothesis that voice amplitude regulation is a generic vertebrate mechanism for coping with noise. We discuss the possibility that intense sexual selection and high levels of competition for mates in choruses place some frogs under strong selection to call consistently as loudly as possible.
Ethology Ecology and Evolution
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The Advertisement Call of the European Treefrogs (Hyla arborea): A Multilevel Study of Variation
Ethology, 2002
In this study, we analysed the patterns of variation of the European treefrog's advertisement call at four levels of organization: within individuals, within populations, among populations of the same species, and among dierent species of the same clade. At the within-individual level, call acoustic properties are distinguished into static and dynamic properties. At the withinpopulation level, two sources of call variation were analysed: temperature and body size. Temperature aects both temporal and spectral properties of the call. Body size mostly aects spectral properties. At the between-population level, calls do not show signi®cant dierences with respect to temporal properties, but they do dier in two spectral (and stereotyped) properties: the fundamental frequency and the dierence in amplitude between dominant and fundamental frequencies. Finally, at the between-species level, call dierences are much more conspicuous: they involve both spectral and temporal and both static and dynamic properties. At all four levels, body size is associated with call variation, explaining 11% of the dierences among populations of the same species and 73% of the dierences among species of the same clade. On the basis of these results, we hypothesize that patterns of variation of call acoustic properties, their constraints, and their biological functions are intrinsically associated. We discuss the role that such an association might play in the evolution of acoustic signals.
Calling energetics of a neotropical treefrog, Hyla microcephala
1989
We investigated the calling energetics of Hyla microcephala, a neotropical treefrog with an unusually complex vocal repertoire. Males respond to the calls of other individuals by adding secondary click notes to their calls, thereby increasing the total number of notes given per minute. Rates of oxygen consumption of males calling in metabolic chambers were 0.41-2.80 ml O2/(g-h), corresponding to calling rates of 205-6330 notes/h. Note rate explained 95% of the variance in metabolic rate; the effect of variation in body size and temperature was small. Data from playback experiments with males in the field showed that note rate increased as as the number of notes in a stimulus call increased, and this resulted in substantial increases in the cost of calling. Average metabolic rates for males in the field were about 1.7 ml O2/(g" h), for a net cost of calling of about 20 J/h for an average-size male. However, estimated metabolic rates varied by more than 300% and were strongly influenced by the proximity and calling activity of other males in the chorus. Male H. microeephala appear to conserve energy by reducing calling rates when only a few males are active and increasing calling efforts only when vocal competition among males is intense.
Journal of Herpetology, 2013
We evaluated the hypothesis that adjustments in call duration made by male Gray Treefrogs render their calls less easily masked in noise and so facilitate communication with females in choruses. We also tested whether shifts in male call duration and rate can be elicited through changes in the level of filtered background noise. We found that males increased the number of pulses in their calls while lowering call rate with elevations in noise level in a fashion similar to that reported during broadcasts of calls. In phonotaxis tests with females using unmodulated or modulated background noise and calls (10, 20, 30, or 40 pulses long) presented at either unequal or equal rates, we failed to find significant differences in noise levels at call recognition thresholds for calls of different duration. However, calls were detected more easily (i.e., noise levels at recognition thresholds were higher) when the noise background was modulated as compared to unmodulated. Our results and those of an earlier study by our laboratory indicate that changes in vocal behavior made by males of Hyla versicolor in response to changes in the calling of other males and background noise within choruses likely do not function to lessen the problems of signal detection or degradation due to interference. Accordingly, a small advantage accruing to males because of an inherent, albeit context-dependent, female preference for long calls (even at low call rates) may account for the dynamic calling behavior of male Gray Treefrogs.
Marathon callers: acoustic variation during sustained calling in treefrogs
2011
We investigated the effects of within-night sustained calling on call acoustic properties in a typical lek-breeding anuran (Hyla intermedia), in which males engage in intense acoustic competitions to attract females. We continuously recorded the calling of randomly selected males over a large portion of the nightly chorus activity and investigated the pattern of temporal variation in both fine-scale (pulse rate, call duration and rise-time) and gross-scale (call rate, call-group duration) properties.
Frequency selectivity of hearing in the green treefrog,Hyla cinerea
Journal of Comparative Physiology A, 1986
1. Frequency selectivity of hearing was measured in the green treefrog, Hyla cinerea. A psychophysical technique based on reflex modification was used to obtain masked threshold estimates for pure tones (300-5,400 Hz) presented against two levels of broadband masking noise. A pure tone (S-1) presented 200 ms prior to a reflex-eliciting stimulus (S-2) inhibited the motor reflex response to S-2. The magnitude of this reflex modification effect varied systematically with the sound pressure level (SPL) of S-1, and threshold was defined as the SPL of S-1 at which the reflex modification effect disappeared.
An Experimental Study of Acoustic Interference Between Two Species of Neotropical Treefrogs
Animal Behaviour, 1983
Hyla ebraccata and H. microcephala commonly occur together in Panama. There is considerable overlap in calling sites and spectral properties of calls in these species. H. ebraccata frequently call amidst dense choruses of H. microcephala. Choruses of the latter species are cyclical, producing fluctuating background noise levels. We recorded natural vocal interactions between these species and performed playback experiments using both recordings of H. microcephala choruses and artificially synthesized noise. Our data demonstrate that background noise generated by H. microcephala choruses causes a shift in the timing and type of calls given by nearby H. ebraccata. Males reduce their calling rates and the proportion of multi-note and aggressive calls at high chorus levels, Playbacks of filtered noise produced a similar change in calling behaviour. These changes may enhance the ability of male H. ebraccata to broadcast signals to conspecifics. Our results and those of other researchers indicate that vocal interactions in mixed species anuran choruses may have important effects on the calling behaviour of individual males.
Treefrogs adjust their acoustic signals in response to harmonics structure of intruder calls
Behavioral Ecology, 2021
Spectral properties of animal acoustic signals may help individuals to assess the characteristics of rivals and to adjust their competitive strategies in territorial disputes. Thus, we hypothesized that the distribution of energy across frequency bands in anuran calls determines behavioral responses in male–male competition. Using playback experiments, we investigated the relevance of the harmonic calls in the acoustic communication of the treefrog Dendropsophus minutus. We exposed territorial males to three synthetic acoustic stimuli composed of aggressive notes: 1) standard call (all harmonics and peak frequency corresponding to the second band); 2) inverted-energy call (all harmonics and peak frequency corresponding to the first band); and 3) concentrated-energy call (all energy contained in the second harmonic). Males responded aggressively to all stimuli, mainly by increasing the rate and duration of their aggressive notes. However, when exposed to stimuli with different harmon...
Journal of Comparative Physiology A, 2014
Our knowledge of the hearing abilities of frogs and toads is largely defined by work with a few well-studied species. One way to further advance comparative work on anuran hearing would be greater use of minimally invasive electrophysiological measures, such as the auditory brainstem response (ABR). This study used the ABR evoked by tones and clicks to investigate hearing in Cope's gray treefrog (Hyla chrysoscelis). The objectives were to characterize the effects of sound frequency, sound pressure level, and subject sex and body size on ABRs. The ABR in gray treefrogs bore striking resemblance to ABRs measured in other animals. As stimulus level increased, ABR amplitude increased and latency decreased, and for responses to tones, these effects depended on stimulus frequency. Frequency-dependent differences in ABRs were correlated with expected differences in the tuning of two sensory end organs in the anuran inner ear (the amphibian and basilar papillae). The ABR audiogram indicated two frequency regions of increased sensitivity corresponding to the expected tuning of the two papillae. Overall, there was no effect of subject size and only small effects related to subject sex. Together, these results indicate the ABR is an effective method to study audition in anurans.