Understanding the behavioral and neural basis of the geomagnetic sense of Tritonia tetraquetra

Abstract

The Earth’s magnetic field is often used by a variety of animals as a navigational tool. Animals may use their compass navigation to fix their position and determine their direction of movement. Oftentimes, a variety of complementary tools like, celestial cues may be used to assist compass navigation (Hill et al. 2012). These navigational abilities can promote reproductive success, food acquisition, and effective migration. While compass navigation and orientation behavior has been well studied in birds (Wiltschko & Wiltschko 1972), sea turtles (Lohmann 1991), and other organisms, the underlying neural basis of these behaviors is less understood. In investigating the neurophysiology of vertebrate navigation, the animal is restrained and thus limited in exhibiting typical migratory behavior. Additionally, the complexity of vertebrate brain structure makes it difficult to identify specific neurons and neural circuits involved in navigation. The large nudibranch mollusk, Tritonia tetraquetra is known to orient to the Earth’s magnetic field (Lohmann and Willows 1987). It has been hypothesized that T. tetraquetra use their magnetic sense in response to situations when primary navigational cues become undependable (Wyeth 2010). T. tetraquetra uses odor-gated rheotaxis (OGR) to detect predators, mates, and prey (Wyeth & Willows 2006). But, sometimes before the slug reaches the source of the odor, the odor plume may dissipate due to varying water flow direction. The slug may then benefit from switching to a secondary navigational tool, such as, magnetoreception (Wyeth 2010) when the odor cue is lost. T. tetraquetra is a good model for studying the behavior and neural basis of navigation and magnetic sensing. Their navigational distances are short compared to Morgan D. Linney 3 other animals, allowing behavioral experiments to be done in the lab. Additionally, they have a centralized nervous system with large orange and white neurons that make them easy to visualize and identify (Willows 1971). The majority of their neurons have been mapped and characterized. Past studies of the neural basis of T. tetraquetra magnetic sensing has begun to identify key neurons and potential uses of this navigational tool (Lohmann et al. 1991).