Sound Production in the Salientia: Mechanism and Evolution of the Emitter

Frog sounds involve expulsion of air through the larynx. In mating, release, rain, and territorial calls, the air vibrates vocal cords and/or arytenoid cartilages. Sound is amplified and radiated by the distended buccal cavity and vocal sacs. Distress calls are emitted with open mouth, with minimum laryngeal modulation. The trunk is filled by inflation cycles, but air is driven out by synchronized contractions of the body wall musculature. The pressure levels are more than five times those during ventilation. In the release call of Bufo valliceps the dilatators and constrictors of the larynx fire simultaneously keeping the larynx closed. As the pulmonary pressure reaches a peak they cease firing. The arytenoids then separate and vibrate, as do the vocal cords. The dilatators terminate the sound pulse by pulling vibrators out of the air stream, hence the very sharp termination. Prolonged release call sequences include interpulse Teinflations that return air from buccal cavity to lung. Frogs apparently evolved from amphibians too small to use aspiration breathing. Vocalization represented a critical factor in their social organization and its importance locked these animals into reliance upon pulse-pumping rather than the more efficient aspiration breathing.