Navigational behaviour of Lymnaea stagnalis in response to chemical and flow cues

Many aquatic animals use chemical cues for navigation relative to prey and predators. Navigation strategies such as chemotaxis and chemical-gated rheotaxis vary depending on the flow conditions. Moreover, sources of attractive versus aversive chemical cues are distinct goals which may use different strategies. Navigation by the great pond snail, Lymnaea stagnalis, presents an interesting case in that they can experience a range of flow environments in nature, including no flow, laminar flow and turbulent flow. In a series of behavioural experiments, we documented movement patterns relative to both sources of attractive and aversive chemical cues in all three flow conditions. The results indicate that L. stagnalis can use chemotaxis in the absence of flow, either chemotaxis or chemical-gated rheotaxis in laminar flow and probably chemical-gated rheotaxis in turbulent flow. Since navigation behaviour also differed between light and dark conditions, visual cues are also likely to be used in parallel with chemical cues to guide navigation. Responses to aversive sources of chemical cues were categorically distinct, with no evidence of crawling away from the source. Instead, we found an increased frequency of detachment from the substrate, leading the animals to float up to the water surface. Overall, our findings provide the first evidence of an animal switching between the distinct navigation strategies required in different flow environments and set the stage for more detailed analyses of the proximate mechanisms that produce the navigation behaviours in L. stagnalis.