Work

Subglottal pressure and fundamental frequency control in contact calls of juvenile Alligator mississippiensis

Year: 2011

Type: article

Abstract: Vocalization is rare among non-avian reptiles, with the exception of the crocodilians, the sister taxon of birds. Crocodilians have a complex vocal repertoire. Their vocal and respiratory system is not well understood but appears to consist of a combination of features that are also found in the extremely vocal avian and mammalian taxa. Anatomical studies suggest that the alligator larynx is able to abduct and adduct the vocal folds, but not to elongate or shorten them, and is therefore lacking a key regulator of frequency, yet alligators can modulate fundamental frequency remarkably well. We investigated the morphological and physiological features of sound production in alligators. Vocal fold length scales isometrically across a wide range of alligator body sizes. The relationship between fundamental frequency and subglottal pressure is significant in some individuals at some isolated points, such as call onset and position of maximum fundamental frequency. The relationship is not consistent over large segments of the call. Fundamental frequency can change faster than expected by pressure changes alone, suggesting an active motor pattern controls frequency and is intrinsic to the larynx. We utilized a two-mass vocal fold model to test whether abduction and adduction could generate this motor pattern. The fine-tuned interplay between subglottal pressure and glottal adduction can achieve frequency modulations much larger than those resulting from subglottal pressure variations alone and of similar magnitude, as observed in alligator calls. We conclude that the alligator larynx represents a sound source with only two control parameters (subglottal pressure and vocal fold adduction) in contrast to the mammalian larynx in which three parameters can be altered to modulate frequency (subglottal pressure, vocal fold adduction and length/tension).

Source: Journal of Experimental Biology

DOI: 10.1242/jeb.051110

Authors: Tobias Riede, Isao T. Tokuda, C. G. Farmer

Institutions: University of Utah, Ritsumeikan University

Language: English

Topic: Animal Vocal Communication and Behavior

Subfield: Ecology, Evolution, Behavior and Systematics

Field: Agricultural and Biological Sciences

Domain: Life Sciences

Open Access status: hybrid

Funders: Japan Society for the Promotion of Science, National Institute on Deafness and Other Communication Disorders

Awards: Mechanisms for producing complex sounds , Construction of three-dimensional nonlinear speech production model and analysis of pathological voice, Oscillator network modeling of the circadian rhythms and its application to their control, Entrainment ability maximization in nonlinear oscillators by using calculus of variations, and its applications to practical design problems, A Simulator for Sound Production in Airways