Meeting Abstract

90.10  Thursday, Jan. 7  Scaling of bite-force performance in horned frogs, Ceratophrys LAPPIN, A.K.*; WILCOX, S.C.; California State Polytechnic Univ., Pomona; California State Polytechnic Univ., Pomona aklappin@csupomona.edu

Of the nearly 6,000 extant frog species, most have weak jaws that play a minor role in prey capture. A notable exception is Ceratophrys, a genus of South American frogs that use a vice-like grip of their jaws to restrain and immobilize prey. These frogs are renowned for an aggressive temperament and the ability to consume large vertebrate prey, such as rodents and other frogs, nearly their own size. We measured bite-force performance during post-metamorphic ontogeny to test the hypothesis that bite force scales isometrically with body and head size. A model of isometric scaling predicts that bite force should scale with a coefficient of 2.0 relative to linear dimensions and a coefficient of 0.66 (i.e., 2/3) relative to volumetric measures (e.g., body mass). This is based on bite force being a resultant of the forces generated by several muscles, forces that in turn are determined by the cross-sectional areas of those muscles. In Ceratophrys, bite-force performance scales with strong positive allometry with respect to body length (2.5), body mass (0.8), and external linear head dimensions (3.0-3.8). These results are in general accordance with previous studies of various amniote taxa, including lizards, turtles, and crocodylians. The pattern of positive allometry of bite force on morphology in Ceratophrys is observed even though linear head dimensions scale with negative allometry on body length (0.6-0.8) and body mass (0.21-0.26), thus indicating that head size relative to body size decreases as the frogs grow. We discuss possible explanations for this counterintuitive ontogenetic relationship between morphology and performance.