Meeting Abstract
When a typical vertebrate bites, bite out-lever and gape angle are two behaviorally and ecologically relevant variables expected to influence bite-force performance. With an increase in bite out-lever (i.e., distance from jaw joint to location of bite on tooth row), the law of the lever indicates that bite force should decrease following a linear relationship with a predictable slope. For gape angle, empirical data from mammals generally indicate that bite force should increase with decreasing gape angle. To examine the effects of bite out-lever and gape angle on bite force in lizards, we conducted experiments in which the jaw-adductor muscles of euthanized brown anoles (Anolis sagrei) were stimulated directly while bite force was measured with a double-cantilever beam force transducer. Comparing our empirical results with a model we developed, we found that bite force in the brown anole follows the law of the lever. With respect to gape angle, the results of a separate set of experiments show that bite force is greatest at small gape angles. The generality of these results is uncertain, given that many species of lizards exhibit various forms of cranial kinesis. Cranial kinesis, including streptostyly (i.e., mobility of quadrate bone) observed in anoles, may affect jaw muscle levers, lines-of-action, and muscle length-tension properties during biting. Therefore, in species that show considerable cranial kinesis, basic lever mechanics may not be entirely predictive of how bite out-lever or gape angle affect bite force. The results of this study can serve as a basis for comparison to other species of lizards with various types and degrees of cranial kinesis.
