Meeting Abstract
8.8 Saturday, Jan. 4 08:56 Fish Gristle: mechanical performance of IOPM ligaments among functionally diverse jaws. GRUBICH, JR; WESTNEAT, MW*; BOS, AR; The Field Museum of Natural History; The Field Museum of Natural History; American University in Cairo jgrubich@fieldmuseum.org
The motor patterns, feeding kinematics, and functional morphology of jaws have been studied in numerous reef fish taxa. However, the underlying mechanics of the ligaments and tendons that make up the critical linkages of fish feeding mechanisms have received less attention. The interopercular mandibular ligament (IOPM) provides a key functional link between the lower jaw and suspensorium in the jaw mechanisms of fishes. Here, we examine the tensile properties of this ligament among five ecomorphologically diverse reef fish species (Chlorurus gibbus, Cheilinus lunulatus, Sphyraena qenie, Plectropomus areolatus, and Epibulus insidiator) that span the continuum of feeding strategies from substrate biting to ram/suction feeding including the advent of extreme jaw protrusion. Using a materials testing machine, we tested the tensile load capacity of this ligament in each species. We used cross-sectional area of the main jaw closing muscle, the adductor mandibulae, to estimate the upper bound of maximum force transmitted through the IOPM during feeding. Our preliminary analysis shows considerable mechanical variation among species. IOPM ligaments of biting taxa show the greatest strains (e.g. C. gibbus = 54.6%, C. lunulatus =19.9%, and S. qenie = 29.6%). In contrast, suction feeding taxa that exhibit jaw protrusion had much smaller strains 3.5% and 10.7% for E. insidiator and P. areolatus, respectively. Mean stiffness of the ligament also varied more than a 325 fold from 14.65 kN/m for the excavating parrotfish C. gibbus to 4769 kN/m for the suction feeding grouper, P. areolatus. Comparing mechanical properties of fish skull linkage components offers new if not counterintuitive insights into the selective forces that have shaped the diversity of feeding strategies found in reef fishes.
