Advertisement calls, auditory tuning, and larynx and ear morphology were examined in 3 neotropical frogs, Hyla microcephala, H. phlebodes and H. ebraccata, H. microcephala has the highest call dominant frequency (6.068 kHz) and basilar papilla tuning (5.36 kHz). H. phlebodes and H. ebraccata calls have lower dominant frequencies (3.832 and 3.197 kHz respectively) and basilar papilla tuning (2.79 and 2.56 kHz). The primary call notes of H. ebraccata are longer (181.6 ms) than those of H. microcephala (95.5 ms) or H. phlebodes (87.3 ms). Morphometric analysis suggests that temporal call features differ as laryngeal musculature changes, in the process changing the overall size of the larynx. The spectral aspects of the call differ as head size, and hence the size of its resonating and radiating structures, changes, modifying the dominant frequency of calls by accentuating their higher harmonics when head size decreases. Decreasing head size decreases the size of the middle and inner ear chambers, changing the mechanical tuning of the ear in the same direction as the change in dominant frequency. These changes result in divergent spectral-temporal characteristics of both the sending and receiving portions of the acoustic communication system underlying social behavior in these frogs.

In a previous report, the authors found significant population variation in the calls of cricket frogs (Acris crepitans) that could not be explained by geographic variation in body size alone. Here we extend that work by investigating intraspecific population variation in the morphological characteristics underlying acoustic communication in male cricket frogs from several sites in Texas. We measured the volumes of laryngeal and auditory components responsible for the generation or reception of species-specific vocalizations in male frogs from eight populations. We found significant differences among populations in body size, as well as all the laryngeal and ear components we measured. With the exception of vocal cord and extracolumella volumes, the volumes of these anatomical structures differ among populations independently of body size as determined by a covariate analysis with snout-vent length as the covariate. Call dominant frequency differs among populations in a clinal pattern and head width, arytenoid cartilage, vocal cord and dilator muscle volume show a similar pattern when the residuals of the regression of morphological component on SVL are assessed for this trend. The results show that both larynx and ear structures can change in size independently of body size, yielding significant geographic variation in the behavioral and physiological expressions of the acoustic communication system underlying mate choice.Copyright 1998 The Linnean Society of London

Vocalizations of Boophis madagascariensis (Rhacophoridae) males were recorded in a mid-elevation rain forest in eastern Madagascar. Call notes made by males of this species were classi®ed into 28 types. This represents the largest known call repertoire of any amphibian. The calls range widely in spectral characteristics from a narrowband, nearly pure-tone to broadband`rip' notes, to even broader band, pulsatile`iambic' notes consisting of up to 23 pulses. Even considering all`iambic' notes as variants of one type, there remain eight distinct call notes produced by this species. Morphological analysis of the vocal musculature of B. madagascariensis revealed no obvious adaptations for unusual glottal¯exibility or function. Playback studies using a subset of the call notes as stimuli were carried out in the animals' natural habitat to determine the functional signi®cance of several of the call notes. At the lowest playback levels, there was a signi®cant tendency for males to produce rip notes in immediate response to either rip or iambic note stimuli. At the higher playback levels, we identi®ed one sequence of iambic notes that consistently evoked a signi®cant iambic note response from males. A permutation test on call note transitions during spontaneous calling revealed that call note pairs occurred inconsistently and unpredictably. The evolutionary signi®cance of an extended vocal repertoire, matched counter-calling and a random call note production scheme is discussed.

Vocalizations of Boophis madagascariensis (Rhacophoridae) males were recorded in a mid-elevation rain forest in eastern Madagascar. Call notes made by males of this species were classi®ed into 28 types. This represents the largest known call repertoire of any amphibian. The calls range widely in spectral characteristics from a narrowband, nearly pure-tone to broadband`rip' notes, to even broader band, pulsatile`iambic' notes consisting of up to 23 pulses. Even considering all`iambic' notes as variants of one type, there remain eight distinct call notes produced by this species. Morphological analysis of the vocal musculature of B. madagascariensis revealed no obvious adaptations for unusual glottal¯exibility or function. Playback studies using a subset of the call notes as stimuli were carried out in the animals' natural habitat to determine the functional signi®cance of several of the call notes. At the lowest playback levels, there was a signi®cant tendency for males to produce rip notes in immediate response to either rip or iambic note stimuli. At the higher playback levels, we identi®ed one sequence of iambic notes that consistently evoked a signi®cant iambic note response from males. A permutation test on call note transitions during spontaneous calling revealed that call note pairs occurred inconsistently and unpredictably. The evolutionary signi®cance of an extended vocal repertoire, matched counter-calling and a random call note production scheme is discussed.

The sexually dimorphic vocal characteristics of Rana pipiens release calls suggest that there may be differences in the anatomical components of the larynx. The volumes of the arytenoid cartilage, surrounding muscle masses, vocal cords, supporting bronchial process, and the release-call amplitudes of six males and five females were measured in same-sized animals and sexual differences assessed. No qualitative differences in laryngeal morphology were observed, but all features measured except vocal cords were significantly larger in males. The implications of an increased laryngeal size are discussed in relation to differences previously observed in the vocalizations of this and other species and in relation to prior suggestions regarding the developmental basis of anuran sexual dimorphisms.