Date of Award

2018

Document Type

Thesis

Degree Name

Master of Science (M.S.)

Department

Biological Sciences

First Advisor

Marcos Gridi-Papp

First Committee Member

Zachary Stahlschmidt

Second Committee Member

Tara Thiemann

Abstract

Male túngara frogs can add a distinctive note ("chuck”) to their mating call. Production of the chuck involves vibrating a pair of laryngeal fibrous masses that is attached to the vocal cords. The muscular control of this mechanism remains unknown. Recent studies revealed a split in the laryngeal dilator muscle, which unveiled the deep dilator as a novel laryngeal muscle with unique attachments, innervation, and (likely) function. The deep dilator may position the fibrous masses for chuck production. The goals of this study were 1) to confirm the innervation of the novel muscle through electrophysiology; and 2) to determine the action of each laryngeal muscle (including the deep dilator), in isolation and in combination with one another, to elucidate the control of laryngeal function. I stimulated 32 combinations of the five laryngeal muscles electrically with 3-5 repetitions. Using suction glass electrodes, I stimulated the branches of the laryngeal nerves in excised larynges maintained in saline solution and filmed the resulting movements to measure their displacement due to stimulation. The results showed that the novel muscle is exclusively innervated by the short laryngeal nerve, a condition equivalent to that of the mammalian posterior cricoarytenoid muscle, responsible for opening the vocal cords. Also, contraction of the deep dilator muscle is required and sufficient to produce lateral displacement of the fibrous masses and, therefore, to create a chuck. This identifies the deep dilator as a key element in the evolution of call complexity in túngara frogs. Clarifying the mechanism that controls the addition of chucks to the túngara frog call is an important step in understanding the evolution of signal complexity in animal communication systems. The recognition of the mechanism may allow comparative studies to be made that can reveal why complex calling evolved in the túngara frog lineage while not in others.

Pages

56

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