MECHANISM OF TONGUE PROTRACTION DURING PREY CAPTURE IN THE SPADEFOOT TOAD SPEA-MULTIPLICATA (ANURA, PELOBATIDAE)

Recent studies have used muscle denervation experiments to examine the function of muscles during feeding in frogs. By comparing the results of denervation experiments among taxa, it is possible to identify evo lutionary changes in muscle function. The purpose of this study was to examine the function of jaw and tongue muscles during prey capture in Spea multiplicata, a representative of the superorder Mesobatrachia. All members of this group possess a disjunct hyoid apparatus. We predi cted that Spea would possess a novel mechanism of tongue protraction o n the basis of its hyoid morphology. High-speed video motion analysis and muscle denervation were used to study the feeding behavior and mec hanism of tongue protraction in Spea. Although Spea possesses a relati vely long tongue, its feeding behavior is similar to that of short-ton gued frogs of similar body size. Denervation of the m, submentalis had no effect on feeding behavior. When the m. geniohyoideus was denervat ed, the tongue pad was raised and moved forward slightly, but did not leave the mouth. When the m. genioglossus was denervated, the tongue p ad was raised slightly, but no forward movement of the tongue occurred . A similar result was obtained after the mm. genioglossus and geniohy oideus were denervated simultaneously Thus, both the mm. genioglossus and geniohyoideus are necessary for normal tongue protraction in Spea. In contrast, only the m. genioglossus is necessary for normal tongue protraction in archaeobatrachians and neobatrachians. We hypothesize t hat the disjunct hyoid is responsible for the greater role of hyoid mo vement during feeding in mesobatrachians. (C) 1995 Wiley-Liss, Inc.