Detection of underwater stimuli in chambered Nautilus

The marine environment is dominated by mechanical and acoustical energies such as water currents and vibrations. To respond to a given stimulus, marine organisms must collect information from their environment and subsequently process it. One such organism that may benefit from detecting these potential signals is the deep-water cephalopod, Nautilus pompilius. Two behavioral experiments were designed to test the sensory capabilities of N. pompilius. The first experiment exposed the animals to a series of angular accelerations and rotations to test the hypothesis that these animals are able to internalize environmental cues, such as hydrodynamic flow, perhaps with the aid of a canal (Kolliker's canal) that connects their statocyst to the exterior environment through an epidermal pore (an anatomical configuration that is unique within the Class Cephalopoda only to Nautilus spp.). As a measure of response to the stimulus, the positions of the hyponomes of the animals (funnels) were recorded throughout the experimental trials and their natural responses to angular acceleration were established. Results from the Angular-Accelerations Experiment indicated that only two of the 10 animals tested responded with compensatory movements in response to the rotating stimulus in the control condition. Analysis of all the animals suggested that when the animals were exposed to treatment conditions (unilateral and bilateral applications of petroleum jelly to the area containing the epidermal pore), they responded by significantly re-positioning the hyponome either in the opposite direction (phase-shift) from that in the control condition or by maintaining the same direction but reducing the amplitude of the response. The second experiment tested the hypothesis that Chambered Nautilus are capable of responding to waterborne vibration---a sensory mechanism that had yet to be investigated. Animals were exposed to a vibrating bead that produced a range of displacements and velocities. Ventilation rate was used as a behavioral measure. Animals reduced their respiratory rate when exposed to vibrational stimuli: a decrease in respiration rate was significantly correlated to an increase in source-displacement (intensity) and source-velocity. Animals responded to stimuli in closer range by decreasing their ventilation rates even further.