Differential behavior of ampullary subunits in the electrosensory system of the scalloped hammerhead shark (Sphyrna lewini)

M.S. University of Hawaii at Manoa 2012.Includes bibliographical references.The electrosensory system of elasmobranchs consists of discrete networks of gelfilled canals that connect to a specific subgroup of a subcutaneous structure called an ampulla. This project tested the functional subgroup hypothesis that predicts functional differences among the ampullary subgroups using the scalloped hammerhead shark, Sphyrna lewini. To examine electroorientation behavior, the reaction of sharks to electrical dipoles was digitally recorded on video. After control trials, sharks then had certain ampullary pore fields blocked with non-conductive petroleum jelly and again exposed to the same dipoles to observe potential changes in orientation behavior. The entire cephalofoil and either the right or left half of the cephalofoil were blocked in trials to determine the efficacy of the treatment protocol. The Buccal (BUC) and Superficial Ophthalmic anterior (SOa) ampullary pores were then inactivated. The BUC and SOa pore fields were chosen for study due to their location on the cephalofoil and pore number (the SOa includes more than half the pore field). The majority of sharks oriented to the dipole less than 12cm away and at an angle of less than 40 degrees from the dipole axis. Sharks with blocked BUC pores demonstrated fewer orientations to the simulated prey field (p = 0.008), although they still fed and swam normally. The manipulated sharks also showed decrease spiral behavior in relation to the other orientation types, and increased their overshoot behavior with blocked SOa pores. Thus, the functional subunit hypothesis is supported by this study and the entire ampullary pore field was demonstrated to be necessary for proper orientation within a dipole field