Historically, research into anxiety has predominantly focused on vertebrate models, particularly rodents and humans, due to their more complex nervous systems and behavioral repertoires. By extending this research to pond snails, a simpler invertebrate model, the study provides novel insights into the fundamental mechanisms of anxiety and its modulation.
Here, we demonstrate that after being exposed to fish water, which simulates the presence of predators, pond snails (Lymnaea stagnalis) exhibit a series of sustained fear responses. These include increased aerial respiration, changes in righting behavior, and reduced escape responses. Notably, these behaviors persist even after the stressor (fish water) is removed, indicating that they likely represent an anxiety-like state rather than a simple conditioned reflex. Additionally, exposure to fish water enhances long-term memory formation for the operant conditioning of aerial respiration, suggesting that the predator scent potentially induces a state of heightened alertness, which enhances memory consolidation processes. Furthermore, when snails experience fish water alongside an appetitive stimulus (carrot), they form configural learning—a higher form of learning – where the appetitive stimulus now triggers a fear response instead of eliciting feeding.