Problems in invertebrate chemoreception.

Abstract

C HEMORECEPTION in invertebrate animals has attracted several types of interest among biologists. Natural historians have long been impressed with the large number of cases in which responses to chemical stimuli underlie behavioral responses and important ecological relationships among invertebrates. More recently, physiologists have become aware of the invertebrates as experimental animals of choice in the study of many problems concerning the fundamental mechanisms of chemoreception. Farthest removed from direct concern with behavioral and ecological problems are those physiologists who are intrigued by the incredibly small amounts of chemicals which activate the chemoreceptors of invertebrates, and who look upon this area of sensory physiology as a promising approach to increased understanding of specific molecular interactions in living cells. Despite the breadth of this spectrum of interests, ranging from the behavior of intact organisms in their normal environments to the reactions of a few molecules within a minute part of an organism, the relevant scientific literature consists predominantly of natural history. Formidable technical problems have for a long time prevented work on any other level. Recent technological refinements, however, have made it possible to study the physiology of some primary chemoreceptor cells directly, and a rapidly increasing emphasis upon this level of physiological information can be expected. It is predominantly through accumulation of information about the physiology of the primary chemoreceptors that sound interpretations at the molecular level can ultimately be expected. Because of the new trends which appear probable in experimental work on chemoreception, this is an especially appropriate time to take stock of the past observations which suggest some of the areas in which future work might be most rewarding. The present review is directed toward two objectives. One is to analyze the bearing which the data on invertebrates have on the development of general concepts in this area of sensory physiology. In so doing, emphasis tends to fall upon similarities in the physiology of chemoreception, not only among invertebrate animals but in comparison to vertebrates as well. However, the differences in the methods by which various animals carry on a function usually are important for understanding the ways of life peculiar to the animals themselves. Since differences in the chemical senses influence host-parasite and other relationships of theoretical or economic interest, the dissimilarities as well as the similarities in chemoreception raise questions of more than anecdotal significance. The analysis of such differences and their significance is the second objective of this review. It is hoped that this type of treatment will help to retain and strengthen the connecting ideas between strictly physiological studies and the central concepts of