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

Abstract

Over the last decades the comparative study of the intelligence of invertebrate animals has shown the psychological complexity of these species. Although significant research has been carried out on the phyla of mollusks in gastropods and cephalopods, there has been little research concerning bivalves. Some studies have demonstrated the habituation phenomenon with a dishabituation test in clams. However, no further studies in this line of research have been developed in order to study the cognitive processes of clams and similar species. The aim of the present research was to develop a habituation procedure in the slimy clam Ruditapes decussatus by measuring the percentage of siphon withdrawal when they were exposed to a white light. In Experiment 1 a habituation-dishabituation procedure was used to study the stimulus intensity effect. A group was exposed to a 350-lm and a different group to 806-lm. Clams exposed to 350-lm showed a higher habituation than those exposed to 806-lm. Experiment 2 studied the effect of stimulus and intertrial interval (ITI) duration using a 2x2 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 higher in clams exposed to 180-sec. trials with a 5-min, ITI. Altogether, this series of experiments constitutes a first systematic demonstration of habituation in bivalves.