Meeting Abstract
The mechanical properties of tissues in appendages play a key role in vertebrate locomotion. For fishes, fin ray stiffness has been proposed to be associated with locomotor behavior. Here we explore this idea in the wrasses (Labridae), a clade that employs pectoral fin-based propulsion with kinematics ranging from drag-based rowing to lift-based flapping. We predicted that wrasses employing a flapping swimming behavior have stiffer fins than those employing a rowing behavior. To describe the flexural stiffness of the pectoral fins more broadly and to test this hypothesis, we quantified intrinsic pectoral fin ray flexural stiffness in similar sized fins of two closely related species, the flapping Gomphosus varius and the rowing Halichoeres bivittatus. The proximal portions of G. varius’s fin rays were significantly stiffer than those of H. bivittatus. However, there is not a simple dichotomy in fin stiffness between these two species. We found a consistent spatial arrangement of fin stiffness between the two species. The flexural stiffness of each species’ pectoral fin decreases along each ray’s proximodistal axis as well as across the fin’s chord from the leading to trailing edge. The flexural stiffness along the length of a given fin ray rapidly declined in G. varius but only gradually declined in H. bivittatus. The distal thirds of the fin rays did not differ significantly in flexural stiffness between these species. We develop a stiffness field profile across the fin surface that will allow us to explore how the flexible fin rays of H. bivittatus and the proximally stiffer fin rays of G. varius might impact fin deformation and proprioceptive feedback during swimming.
