CHEMICAL MEDIATION OF APPETITIVE FEEDING IN A MARINE DECAPOD CRUSTACEAN: THE IMPORTANCE OF SUPPRESSION AND SYNERGISM

The California spiny lobster, Panulirus interruptus, failed to exhibit appetitive feeding or locomotion in response to a low molecular weight fraction (< 1000 daltons) prepared from a sea water extract of muscle from abalone, a natural prey. This lack of response was caused by chemical suppressants, rather than by lack of stimulatory compounds. Excitatory responses were induced by single, low molecular weight compounds, but these responses were inhibited by suppressants which occur naturally in the muscle fraction. Amino and organic acids were found highly stimulatory to lobsters, but nucleotides and sugars were not. A mixture of monocarboxylic amino acids and dicarboxylic organic acids was much more effective in elliciting behavior than either of the constituents tested alone, at the same overall concentration. Mixtures which combined either ammonium or urea with amino or organic acids significantly reduced behavioral activity caused by these latter substances. Results indicate that tests of single chemicals cannot always reliably predict the stimulatory properties of solutions, combining even as few as two or more compounds. The stimulatory properties of complex odorants, including prey extracts, are best assessed by fractionating and then combining and testing the fractions in bioassays of factorial design.