Meeting Abstract

2.1  Friday, Jan. 4  Structure-function relationships in the pectoral fin of freshwater stingray Potamotrygon orbignyi BLEVINS, E.L.; Harvard University eblevins@fas.harvard.edu

To achieve the characteristic undulations of rajiform locomotion, the pectoral fins of batoid fishes must be flexible and well-controlled, to generate, accommodate, and modulate the propulsive wave. Batoids have dramatically diverged from their shark-like ancestors in both fin use and structure, but lack the mechanical linkages that provide control in the pectoral fins of actinopterygian fishes. By integrating an understanding of 3-D swimming kinematics with the pectoral fin morphology of freshwater stingray Potamotrygon orbignyi, I connect aspects of structure and function in the fin of an undulatory rajiform swimmer. The morphology of skeletal and muscular fin elements differs across fin chord and span, creating regional variations that correlate with the swimming kinematics of P. orbignyi. Anterior regions of the pectoral fin, which form a stable leading edge during swimming, are structurally stiffened by a more robust fin skeleton, with the potential for active stiffening from a pennate arrangement of muscle fibers. Structure predisposes mid-disc and posterior regions of the fin to greater flexibility; these same regions show the greatest amplitudes during undulation. Comparisons with the fins of a representative actinopterygian fish (bluegill sunfish Lepomis macrochirus) and shark (dogfish Squalus acanthias), reveal structural convergence between stingrays and actinopterygians in fin ray branching and segmentation. The repetition of fin elements during the evolution of batoid pectoral fins created the potential for this convergence, as well as for regional specialization within the fin, with structural features connecting pectoral fin morphology and undulatory performance.