Differential associative conditioning and olfactory discrimination in the spiny lobster Panulirus argus

A differential aversive associative conditioning paradigm was used to assess the ability of the spiny lobster Panulirus argus both to associatively learn not to respond to the odorant stimulus to which it was conditioned and to discriminate between odorants. The paradigm consisted of pairing an aversive stimulus (pseudopredator) with a conditioned chemical stimulus (shrimp mixture). Four artificial mixtures (crab, mullet, oyster, and shrimp), each at 0.05 and 0.5 mM, were presented to the animals prior to, during, and following conditioning to both concentrations of the shrimp mixture. Pre- vs postconditioning changes in three types of behavioral responses (and an index based on a composite of these three behaviors) were used as indicators of learned aversions. Olfactory discrimination abilities were determined by comparing the aversion to the conditioned mixture with the aversions to the three nonconditioned mixtures. A high degree of associative learning was attained after 10 pairings of the pseudopredator with the shrimp mixture over a period of 5 test days. According to the aversion index, animals conditioned to shrimp mixture perceived crab mixture as being more similar to shrimp mixture than were mullet and oyster mixtures, but all three nonconditioned mixtures were perceived as being significantly different from the shrimp mixture. These results are in concordance with results of a cluster analysis based on the mixture compositions, which indicates that shrimp and crab mixtures are compositionally similar, while mullet and oyster mixtures are compositionally distinct from the shrimp mixture.