P2.62 Monday, Jan. 5 Flexural stiffness and composition of the propterygia of punting and non-punting batoids. MACESIC, L.J.*; SUMMERS, A.P.; KAJIURA, S.M.; Florida Atlantic Univ.; Univ. of California, Irvine; Florida Atlantic Univ. firstname.lastname@example.org
Benthic batoids perform a mode of locomotion termed punting, during which the pelvic fins are depressed into the substrate and then extended caudally to propel the body forward, while keeping the rest of the body still. Skates, which possess muscular and skeletal specializations for punting, and the lesser electric ray, Narcine brasiliensis, exhibit this true punting pattern. However, some benthic batoids, such as the Atlantic stingray, Dasyatis sabina, and the yellow-spotted stingray, Urobatis jamaicensis, have demonstrated an augmented punt, which also includes pectoral fin movements. In this study, our goal was to determine if these differing kinematic patterns relate to structural and compositional differences within the main punting skeletal element, the pelvic propterygium. In addition to the species listed above, the pelagic stingray, Pteroplatytrygon violacea, was also tested, as its life history suggests that the pelvic fins are not used for this benthic locomotion. We performed morphometric analyses, three-point bending tests, and compositional analyses. Our results show that the skate possesses propterygia with significantly higher second moments of area when compared to the other species tested. Propterygia of the true punters have approximately 80% greater flexural stiffness than the augmented punters (p<0.05). Moreover, propterygia of the augmented punters have almost twice the flexural stiffness compared to the non-punting pelagic stingray (p<0.05). For all species, we found that neither water nor mineral content are good predictors of flexural stiffness. This study demonstrates that the flexural stiffness of propterygia in benthic batoids may have evolved in order to resist the bending forces experienced during punting.