Meeting Abstract
Fin evolution has allowed for the diversification of fish morphology and subsequent exploration of new habitats. Basal bony fish have elongated body shapes where the pectoral and pelvic fins have a basal position and contribute little to thrust. Less is known about the role and evolution of median fins, especially anal and dorsal fins. We examined three species of sturgeon, gar and bowfin across ontogeny to assess diversity in median fin morphology with a geometric morphometrics approach. Larval series were used to describe timing of fin development, and to document caspase-3 function in median fin patterning. Lastly, in the lab, we swam gar and sturgeon to determine the role of median fins during steady and unsteady swimming. Geometric morphometrics was successful in separating basal fish species based on median fin morphology, although differences between species became more pronounced over ontogeny. In basal fishes, the dorsal fin is the first to undergo development, followed closely by the anal fin. Caspase-3 activity was mapped to the fin fold in the regions flanking the median fins at the beginning of fin formation. Our kinematic data show that gar and sturgeon use the dorsal and anal fins in phase to augment thrust from the caudal fin during steady swimming. During acceleration, dorsal and anal fins are also actively recruited. Despite their markedly different fin morphologies, gar and sturgeon display similar median fin kinematics, which contrast the previously described ribbon-fin kinematics of bowfin. Our study shows that basal fish rely heavily on median fins for locomotion, and diversification of fin shape might have important evolutionary implications to distribution and ecology.
