Neuroethology of odour-based navigation in aquatic gastropods

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My long-term goal is to understand how animals use multiple navigation strategies to move, focusing on odour-based navigation in gastropods. Researchers have spent considerable effort to understand how animals respond to attractive odour plumes by crawling upstream, following the flow to an odour source. Yet, in nature, flow directions frequently change. We know much less about the consequences of this flow variability on animal navigation. My first objective is to explore how slow-moving slugs and snails cope with flow variability at two different levels: one that should be tracked, and another that likely should be ignored. First, as bulk flow direction shifts, so do odour plumes, and animals must track these shifts to find odour sources. My students and I will use field video recording and current meters to explore how responsive the nudibranch Tritonia diomedea is to shifting flows of varying degrees, empirically determining the time scale over which the slugs determine bulk flow direction. Second, depending on flow speeds, an odour plume carried by unchanging bulk flow will involve turbulence - smaller scale variations in flow direction generated by water movement across the substrate. If so, the animals should avoid following this local flow variation, responding only to the underlying bulk flow direction. For these experiments, we will use the freshwater snail Lymnaea stagnalis to test their responses to local turbulence. From the work on both species, we will learn how the animals may differentiate between changes in bulk flow direction versus changes from turbulent flow. My second objective is to lay a foundation to explore how the animals' nervous system produces these behaviours. The experimental amenability and simpler nervous system of gastropods allow us to determine the roles of single neurons in cue detection and the subsequent control mechanisms of the animals' crawling. However, there remains a substantial gap in our understanding of the sensory systems involved in navigation. Thus, my students and I will use a variety of methods to document the anatomy of the nervous system in the animals' sense organs. My third objective is to focus specifically on the function of the sensory neurons and circuits that detect and process flow direction in T. diomedea. This sensory processing must serve as a key input into the brain circuits that control navigation, yet we know very little about the detection of flow direction in any animal. Our results will guide future aspects of my research program studying the neural circuits that produce the different navigational strategies in gastropods. Moreover, by comparing results from across the animal kingdom, we can achieve a broader understanding of the neural mechanisms underlying both navigation and other behaviours. Finally, through this research, my students will learn a variety of fundamental skills and transferable techniques they can apply in their academic or professional careers.