Meeting Abstract
67.2 Tuesday, Jan. 6 Intraspecific scaling of bite-force generation in a durophagous turtle, Sternotherus minor minor PFALLER, Joseph B*; ERICKSON, Gregory M; Florida State Univ., Tallahassee; Florida State Univ., Tallahassee jpfaller@bio.fsu.edu
Among vertebrates, ontogenetic shifts towards more durable prey (durophagy) are common. Such transitions require the development of a feeding apparatus with sufficient morphology to generate and sustain high bite forces. Bite-force generation has been shown to increase with significant positive allometry relative to head dimensions. Nevertheless, to our knowledge, no detailed, quantitative study has examined the intrinsic biomechanical anatomy of an ontogenetic series to explain such allometric increases in bite force. The loggerhead musk turtle (Sternotherus minor minor) is a simple, yet relevant, model to explore this phenomenon. Adult S. m. minor develop hypertrophied heads and expanded beak surfaces; changes that reflect an ontogenetic diet shift toward durophagy and an ecologically relevant increase in bite force. Bite-force generation was measured from a growth series of 72 S. m. minor (range = 5 N – 162 N), and was found to increase with significant positive allometry relative to body (e.g., carapace length; scaling coefficient = 2.9) and head dimensions (e.g., head length; scaling coefficient = 2.6). Of these, a growth series of 30 individuals was dissected and detailed osteological and myological measurements were made to develop a biomechanical model of bite-force generation throughout ontogeny. To evaluate the accuracy of our model, we tested it against actual bite forces measured for individual turtles. Allometric increases in adductor mass and pennation angles, and an allometric decrease in fiber lengths, contributed to an allometric increase in the total cross-sectional area of the adductor musculature. These changes were matched by a relative increase in the mechanical advantage of the jaw system, and collectively explain the significant positive allometry in bite-force generation in this taxon.
