Meeting Abstract

P1.188  Saturday, Jan. 4 15:30  Loss of scent while following plume results in search-like behavior with no evidence of reliance on geomagnetic cues in the nudibranch Tritonia tetraquetra LINNEY, MD*; MURRAY, JA; Mt. Holyoke College and Friday Harbor Labs; Cal. State U. East Bay and Friday Harbor Labs james.murray@csueastbay.edu

Although the nudibranch mollusk, Tritonia tetraquetra (a.k.a. Tritonia diomedea) is known to orient to the geomagnetic field, the purpose of this behavior and much of the underlying neurobiology is still unknown. It has been hypothesized that their magnetic sense is used in response to situations when primary navigational cues (odor and flow) become undependable. In the present work, we investigated the behavioral function by putting slugs in a flow-through arena with primary navigational cues and magnetic field distortion (with a permanent magnet). Before the slugs reached the field of magnetic distortion, primary navigational cues were turned off to test for the use of the magnetic sense. In these trials, it was found that slugs changed directional heading repeatedly and significantly more (~3X more) after odor was turned off than before odor was turned off. We speculate that the slug was searching for the lost odor plume. Although this increase in turning upon loss of the scent was not entirely consistent with the sole reliance on magnetic guidance, the slugs turned 1.7X more in the distorted magnetic field compared to the normal field in the 40 s after the odor was removed, consistent with magnetic influence on orientation. Additionally, we investigated how the nervous system encodes magnetic field direction. We performed sensory nerve (Cerebral Nerve 1, CeN1) and single neuron (pedal neuron 5 and 6) recordings in semi-intact preparations with 60° clockwise and counter-clockwise magnetic field rotations. Based on previous studies we expected to see an increase in spiking after magnetic rotations. We observed some increases in the sensory nerve activity, but little change in the motor neuron activity in our limited number of trials. The sensory nerve showed more increase with counter-clockwise rotations of the magnetic field.