Invertebrate Strategies in Comparative Learning Studies

Despite the overwhelming variety and abundance of invertebratespecies the contribution of invertebrate studies to our understandingof the behavioral and physiological bases of learning has beenminimal. Although anthropocentric biases may be responsiblefor the inordinate number of studies performed with the usuallaboratory animals, clearly a vigorous extension of the comparativeapproach in the behavioral sciences is demanded. Several featuresof the comparative approach are outlined and suggestions aremade which minimize any of its inherent difficulties. A multi-leveland polythetic approach is proposed which considers multiplecharacteristics supplemented by evidence obtained at other levelsto establish a meaningful behavioral taxonomy. Controlled systematicvariation may be used to analyze the functional relations ofthe performance of different species on the same behavioraltask. Another strategy compares simplified and complex versionsof the same system in order to assess the quantitative and qualitativerelationships between complexity and capacity. The structureof many invertebrate species renders them ideally suited tosuch analysis. Data on habituation obtained in Limulus polyphemusemploying such a paradigm is discussed. The relationships betweenelectrophysiological habituation and levels of neural complexityare clearly demonstrated. Future contributions from this preparationas well as from other invertebrate species are also discussed.