Behavioral and neural activity during magnetic stimulation of Tritonia tetraquetra imply conditional magnetotactic response

Abstract

A variety of species are known to sense and respond to the geomagnetic field for navigation. The sea slug Tritonia tetraquetra (a.k.a. Tritonia diomedea) has been shown to respond to the magnetic field through both behavior and electrophysiological experiments. However, it remains unclear by which mechanism this sensory information is integrated into motor commands. Additionally, the purpose for a response to magnetic stimuli has yet to be determined. While it is hypothesized that the sea slug sometimes uses a cue-switching mechanism to navigate, ultimately relying on the magnetic field for orientation, laboratory experiments thus far have failed to demonstrate this behavior. The experiments here sought to test this cue-switching hypothesis by demonstrating a response to a local distortion in the geomagnetic field. However, the behavioral response observed was an increased turning frequency upon loss of an initial attractive odor, independent of magnetic distortion, which is inconsistent with the hypothesized straight, geomagnetic-guided crawling. Additionally, in electrophysiological experiments ciliary motor neurons Pd5 and Pd6, as well as sensory nerve CeN1, failed to demonstrate a response to rotations of the magnetic field, despite previous evidence that these units are involved in T. tetraquetra’s magnetic response. These results, when compared with previously demonstrated responses, may imply conditional parameters under which detection and use of the magnetic field are employed, or may be due to population differences.