ZEPNEWSKI, E.D.*; NISHIKAWA, K.C.; Northern Arizona University; Northern Arizona University: Does collagen fiber angle affect prey capture kinematics in inertial elongators?

Inertial elongation is one of three non-exclusive feeding mechanisms that frogs use to protract their tongues. It is a ballistic mechanism in which the tongue is projected out of the mouth using angular momentum produced by rapid mouth opening. In this study, feeding behavior was compared between two different species of inertial elongators, Rana pipiens and Bufo woodhousii. Prey capture was studied using high-speed digital imaging (250 Hz) and kinematic analysis. Although both use inertial elongation, results showed significant differences between Bufo and Rana. Bufo showed faster lower jaw and tongue velocities and greater tongue extensions. Mean tongue elongation for B. woodhousii was 210% while R. pipiens showed 130% mean tongue elongation. While both species appear to be anatomically similar, subtle morphological changes may account for behavioral differences. In particular, the angle of the collagen fibers surrounding the tongue musculature may affect tongue protraction mechanics. Collagen fibers oriented at an angle greater than 54° 44′ will facilitate elongation while fibers oriented at an angle less than 54° 44′ will facilitate shortening. Scanning Electron Microscopy was used to examine the epimysial connective tissue surrounding the main protracting musculature of both species. B. woodhousii was shown to have a mean collagen fiber angle of 73.6 &deg. R. pipiens showed a significantly lower collagen fiber angle of 60.8 &deg. These data indicate that the collagen fibers surrounding the tongue protraction musculature may have evolved towards higher angles in Bufo, to facilitate greater elongation.