The mechanism of tongue protraction in the archaeobatrachian frog Discoglossus pictus was studied using high-speed video motion analysis before and after denervation of the submentalis and genioglossus muscles. The kinematics of prey capture were compared (1) between successful and unsuccessful feeding attempts before surgery; (2) before and after denervation of the m. submentalis; and (3) before and after denervation of the m. genioglossus. Prey capture by D. pictus is similar to that of Ascaphus truei, hypothesized to be the sister group of all other living frogs. These archaeobatrachians have tongues of limited protrusibility (maximum tongue reach=0.21-0.27cm) and lunge forward with the whole body to catch prey. In Discoglossus, unsuccessful attempts to capture prey differ from successful captures in having a longer duration of most kinematic variables. These results suggest that kinematic events are postponed in unsuccessful attempts at prey capture, owing to the absence of the somatosensory feedback that results from successful prey contact. Denervation of the m. submentalis prevents mandibular bending, but does not affect tongue protraction. Denervation of the m. genioglossus significantly decreases maximum tongue reach and maximum tongue height, but does not affect mandibular bending. The m. submentalis is necessary for mandibular bending, but neither mandibular bending nor m. submentalis activity are necessary or sufficient for tongue protraction. The m. genioglossus is necessary for normal tongue protraction. It does more than stiffen and support the tongue. These results are not consistent with the current model of tongue protraction developed for the neobatrachian toad Bufo marinus. If this model withstands the denervation test in Bufo marinus, then archaeobatrachians and neobatrachians must differ in their mechanisms of tongue protraction.
Note:
Present address: Brain Research Institute FB2, University of Bremen, D-2800 Bremen, Federal Republic of Germany.
