Some properties of habituation of siphon withdrawal in the slimy clam (Ruditapes decussatus)

A first approximation to the study of learning processes in bivalves is presented. A habituation procedure was developed using the slimy clam Ruditapes decussatus. The percentage of siphon withdrawal when they were exposed to a white light was measured. In Experiment 1, a habituation-discrimination procedure was used to study the stimulus intensity effect (350-lm vs 806 lm). Clams exposed to 350-lm showed a faster habituation than those exposed to 806-lm. Experiment 2 studied the effect of stimulus and intertrial interval (ITI) duration using a 2×2 design. Trials lasted 20 or 180 seconds, and the ITI lasted 5 or 10 minutes. A combined effect of these two parameters was obtained. Habituation was faster in clams exposed to 180-sec trials with a 5-min ITI. Finally, in Experiment 3 clams were trained with five blocks of five trials with a 5-min ITI. Groups differed on trial duration (20 or 180 s). The results showed a general spontaneous recovery effect that was more pronounced for the 180 s group. Also, it was found in this experimental condition a reduced response 24 hours after finishing training (long-term habituation). Altogether, this series of experiments constitutes a first systematic demonstration of habituation in bivalves.