Mechanics and Neuromorphology of Feeding in Amphibians

Abstract

Salamanders and frogs exhibit strong similarities in their habitats, prey preferences and foraging strategies. Despite these similarities, they differ profoundly in the structure and function of the adult feeding apparatus, and in the participation of cranial and spinal nerves and nuclei in the control of feeding behavior. In frogs, the hyolingual skeleton plays no role in tongue projection. Only the tongue is projected out of the mouth under the control of the nn. trigeminus (tongue protraction) and hypoglossus (tongue protraction and retraction). In all salamanders, feeding is based on forward movement of the hyolingual apparatus, which is folded into a slender, far-reaching projectile in the most highly derived salamanders. Tongue protraction is controlled by nn. glossopharyngeus and vagus, and tongue retraction is controlled by the first and second spinal nerves. All muscles related to feeding are activated sequentially in frogs and simultaneously in salamanders. While the descending pathways to the brainstem and cervical spinal motor nuclei are similar in frogs and salamanders, differences in muscle function and activation pattern imply that the premotor reticular formation is also different. In frog tadpoles and salamander larvae, the hyobranchial apparatus plays different roles in feeding and breathing. This has led to differential loss, acquisition and change of function of musculoskeletal elements during the ontogeny and phylogeny of the adult feeding apparatus in frogs and salamanders. These differences in the musculoskeletal periphery imply that a reorganization at or above the level of the reticular formation is likely to have occurred in frogs, but not in salamanders.