Tongue function in the salamander Bolitoglossa occidentalis

Abstract

Many plethodontid salamanders feed by means of tongue projection. Aspects of this mechanism were studied in the species Bolitoglossa occidentalis under laboratory conditions. Drosophila were presented at varying controlled distances from the animal. The force and duration of tongue contact with the prey, plus the EMG activity in the tongue protractor and tongue retractor muscles, were recorded. Both force and duration of contact decreased with increasing distance of tongue projection. Various measures of protractor muscle EMG activity were independent of projection distance. Protractor and retractor muscle activities were synchronous and continued throughout the projection-retraction cycle. The latency of a ‘tongue pad to retractor muscle’ reflex was greater than the shortest durations of tongue contact. Furthermore, the longest durations of contact were always associated with the greatest forces exerted by the tongue. In the light of these findings, a model is proposed in which projection-retraction is co-ordinated by properties of the peripheral structures rather than by those of the central nervous system.