WYETH, R.C.*; WILLOWS, A.O.D.: Field behavior of the nudibranch mollusc, Tritonia diomedea: a baseline for the neuroethology of orientation and navigation.

Animals use a variety of senses to navigate through their environment. How do they integrate multiple senses to direct movement? The nudibranch Tritonia diomedea is an excellent candidate for investigating mechanisms of sensory integration and subsequent behavior. Although neurophysiological and behavioral aspects of mechano-, chemo-, and magnetosensation have all been investigated in this animal, little is known about how these different sensory systems are used in nature. We are characterizing the orientation and navigation of T. diomedea in their native sea pen beds using underwater timelapse video, and then attempting to correlate the observed movements with sensory cues which may be guiding the animals: conspecifics, predators, prey and water flow. We quantified T. diomedea orientation and movements with respect to the Earth’s magnetic field, water currents, and the presence or absence of upstream conspecifics. Our results suggest T. diomedea used neither currents nor an internal compass exclusively to guide their movements. Rheotaxis appeared to be used mostly in the presence of an upstream conspecific, and in particular when crawling to find a mate. This suggests a behavioral state change in the downstream animal promoting upstream crawling in search of a mate, possibly triggered by a chemical from the upstream animal. The direction of crawling at other times did not necessarily involve heading directly into currents. We found only weak evidence that the slugs follow a constant magnetic bearing (however, this does not exclude the use of magnetosensation for other types of navigation). Our results suggest that T. diomedea integrates several senses to help guide itself as it moves about its habitat.