BICKLEY, Thomas M.*; ANDERSON, Curt; Idaho State University; Idaho State University: Sensory and motor innervation of the tongue in hylid tree frogs

This study investigated the anatomical origins and distributions of neurons innervating the tongue musculature of the green tree frog, Hyla cinerea. Recent research on the neural control of feeding behavior in anuran amphibians has focused primarily on the leopard frog, Rana pipiens, which possesses a long protrusible tongue. It has been hypothesized that during the evolution of long protrusible tongues, the number of hypoglossal motor neurons has increased. However, Hyla represents the basal condition from which long tongues evolved. Preliminary results of this study indicate an almost 60% decrease in the number of ventrolateral hypoglossal motor neurons and a 90% decrease in the number of dorsomedial hypoglossal motor neurons compared to Rana pipiens, and suggest a smaller role for tongue protraction during feeding. However, unlike previous studies with short-tongued frogs, data presented here demonstrate sensory afferents travelling in the hypoglossal nerve and projecting to the medulla and cerebellum. These data provide further insight into the evolution of motor units and feeding morphologies, and will be compared to sister taxa that have secondarily evolved long, protrusible tongues.