LAPPIN, A.K.*; NISHIKAWA, K.C.; PIEROTTI, D.J.: Isometric contractile properties of anuran jaw muscles and their relationship to feeding mechanics

All terrestrial frogs examined to date use tongue prehension to capture prey. Three categories of feeding behavior have been identified in frogs with respect to tongue performance during prey capture. Tongue performance characteristics that vary markedly among taxa in the different behavioral categories include percent elongation of the tongue, and maximum tongue velocity and acceleration during protraction. Previous research on the isometric contractile properties of the tongue protractor and retractor muscles did not reveal functional differences that explain this variation in tongue performance. One factor that may cause differences in tongue performance is the transmission of inertial forces via jaw movements during feeding. Jaw opening velocity and acceleration is greater in species that exhibit greater elongation, velocity, and acceleration of the tongue during its protraction. As a first step towards elucidating the role of jaw movements in effecting tongue protraction, we compare jaw muscle contractile properties of representatives of two feeding behavior categories. In situ experiments were performed in which muscle origins were left intact. Removal of a lower jaw section isolated muscle insertions, which were attached to a force transducer. Via direct muscle stimulation, we quantified the length-tension curve, contraction time, half-relaxation time, stimulus frequency-tension curve, and fatigability of each muscle. With these data, we test the hypothesis that jaw muscles of species with faster, more greatly elongating tongues have shorter contraction times and greater force production.