89.5 Friday, Jan. 6 Diversity of cranial morphology and jaw biomechanics in tetraodontiform fishes MCCORD, CHARLENE, L.; Univ. of Chicago email@example.com
The multiply subdivided adductor mandibulae muscles of tetraodontiform fishes provide an excellent model upon which to explore the biomechanical consequences of differential morphology. This work describes and compares the diversification of cranial shape, macro-architecture of the adductor mandibulae muscles, and basic jaw biomechanics of tetraodontiform fishes. A landmark protocol was developed to outline cranial shape and highlight functional elements of the skull for 150 representative fish specimens from six families within the order Tetraodontiformes. Homologous landmarks were located during dissections, photographed, digitized, and then assessed using standard Procrustes geometric morphometric analyses. Morphospace plots of phylogenetically independent contrasts reveal cranial shape-based clustering patterns that mirror family-level phylogenetic groupings. Each family falls out in a significantly different region of morphospace, with fishes from the family Tetraodontidae exhibiting the most divergent morphology overall. The primary axis of shape variation scales to differences in the position of the adductor mandibulae 1 subdivisions, the length of the cranium, and the size of the jaws. In order to elucidate some of the potential biomechanical consequences of the evident geometric diversity of tetraodontiform skulls, mechanical advantage of the jaws was calculated and the mass of each adductor mandibulae subdivision was measured. Intra-familial variation of adductor mandibulae muscle mass and mechanical advantage of the jaws is evident, but is negligible compared to inter-familial disparity. Fishes from the family Tetraodontidae demonstrate the most deviant scaled adductor mandibulae muscle masses and upper jaw mechanical advantage. These results suggest multiple origins of several different morphological and biomechanical strategies through the evolution of the Tetraodontiformes. Project funded by EAPSI Fellowship-1107759, NSF DEB-0844745 and NSF DGE-0903637.