Mechanisms of Anxiety-Like Behavior in the Great Ramshorn Snail (Planorbarius corneus)

Abstract

Like vertebrate animals, some invertebrates have been shown to exhibit anxiety-like behavior while in apparatus that allow choice between sheltered, darkened spaces and open, lit spaces. The behavioral mechanisms by which invertebrates accomplish anxiety-like behavior, and whether those mechanisms are similar across species, has not been fully studied. Across three experiments, we investigated possible behaviors (photokinesis, phototaxis, and sheltering) that Great Ramshorn snails (Planorbarius corneus) could use to accomplish anxiety-like behavior while in presence of the odor of a predatory fish. In experiment one, we used a light/dark preference box to demonstrate reduced preference for exposed and lit areas caused by the predator odor. In experiment two, we used an open field apparatus to demonstrate an increase in refuge-seeking (time spent near a wall) in diffusely lit but not dark environments caused by predator odor. In the same experiment we saw no effect of predator odor on photokinesis (difference in movement speed in a lit versus dark environment). In experiment three, we conducted a second open field study with a directional light source and found no evidence of phototaxis (movement direction with respect to light), and no effect of predator odor on phototaxis. Thus, in our studies we found evidence for refuge-seeking as a mechanism for anxiety-like behavior in the presence of predator odor and little evidence for perhaps more computationally simple strategies of increased photokinesis and phototaxis.