LARSON, Peter M.; REILLY, Stephen M.: Functional morphology of feeding and gill irrigation in the anuran tadpole: Electromyography and muscle function in larval Rana catesbeiana

This study provides the first data on in vivo muscle activity patterns during feeding in a larval anuran. Data from unanaesthetized, unrestrained animals are also provided to verify results presented by Gradwell (1972) regarding muscle function during gill irrigation and hyperexpiration. Electromyographic and kinematic data were recorded from six muscles in larvae of Rana catesbeiana. Results indicate that only three of these muscles are active during gill irrigation. These include: hyoangularis, orbitohyoideus, and the anterior interhyoideus. Feeding cycles are characterized by the recruitment of three additional muscles: intermandibularis, suspensorioangularis and levator mandibulae longus superficialis. The latter two are responsible, respectively, for the wide opening and forceful closing of the mouth observed during feeding. Hyperexpiration is characterized by a reversal of water flow anteriorly out of the mouth. This hydrodynamic change occurs as a result of modulation of the timing of firing of the anterior interhyoideus, as well as recruitment of the posterior interhyoideus, which is only active during this behavior. Both of these muscles are responsible for evacuation of the buccal cavity and fire during the opening phase of hyperexpiration. Kinematic results indicate that switching from gill irrigation to feeding involves both an overall shortening of the gape cycle and a shift in gape cycle profile. Our results corroborate the findings of Gradwell (1972) and provide the first indication that transitioning from irrigation to feeding involves modulation of both gape cycle kinematics and muscle activity patterns, allowing anuran tadpoles to utilize a remarkable feeding system not found in any other vertebrate group.