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About the Cover
Cover: A major feature of locomotor evolution in teleost fishes is the transformation of the dorsal fin from its plesiomorphic form, a single soft-rayed fin (shown in red in the cladogram), to the derived morphology of a distinct spiny dorsal fin (shown in blue) in addition to the soft portion of the fin. Drucker and Lauder (pp. 2943-2958) initiated an empirical hydrodynamic study of dorsal fin function during locomotion through an analysis of wake dynamics in the bluegill sunfish Lepomis macrochirus. During both steady swimming and turning, the soft dorsal fin generates a thrust-producing wake with a central jet flow (represented schematically by the red arrow). Digital particle image velocimetry was used to calculate wake velocity fields (yellow vectors) and in vivo locomotor forces. Constructive wake interaction between dorsal and caudal fin vortices is proposed as a mechanism for enhancing thrust. The fish line drawings are modified from Nelson (1994) (Nelson, 1994. Fishes of the World, third edition. New York: John Wiley & Sons).
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