GASTROPOD CHEMORECEPTION

Abstract

Summary(I). Gastropods use chemoreception for a wide variety of behaviours including feeding, homing, escape from predators and a variety of social and reproductive behaviours. Chemoreception is used to locate distant food sources, and to discriminate between potential foods. Responses to chemical food stimuli result from a combination of innate and experiential factors. Gastropods use chemical cues in mucus trails to home. They also home by direct olfactory orientation. Reproductive behaviour in a variety of gastropods appears to involve chemical cues. Evidence exists for pheromones controlling aggregation and mating. Numerous gastropods use chemical cues to avoid or escape from predators.(2). Amino acids appear as likely candidates for attractants and phagostimulants for gastropod feeding. Macromolecules are probably also involved. Amino acids have also been shown to stimulate reproductive behaviours in certain gastropods, thus suggesting a pheromonal function. However, the significance of this finding to the behaviour of the organisms in the field has yet to be evaluated. Saponins have been implicated as the active substances found in sea stars that elicit escape responses of marine gastropods. Choline esters may play a homologous role in gastropod—prey and gastropod‐predator interactions.(3). Gastropods can apparently use a number of different methods to orient to olfactory cues. These include anemotaxis or rheotaxis, klinotaxis and tropotaxis.(4). The major chemosensory organs of gastropods have been identified. They include the anterior and posterior tentacles and lips of terrestrial pulmonates; the cephalic tentacles, the lips and buccal cavity lining, and possibly the osphradium of aquatic pulmonates; the cephalic and mantle tentacles, the anterior margin of the foot, the siphon tip, and the osphradium of prosobranchs; and the rhinophores, tentacles, oral veil and osphradium of opisthobranchs.(5). Many of the organs named above have been examined by both light and electron microscopy. The most common anatomical organization includes bipolar primary sensory cells with cell bodies located subepithelially, and a distal dendrite extending to the free surface. Often a peripheral ganglion is located deep to the sensory epithelium. It is unclear whether axons of the sensory cells project directly to the central ganglion or by way of interneurones located in the peripheral ganglia.(6). The dendritic specializations of the sensory cells vary considerably. Most bear cilia or a combination of cilia and microvilli. The functional significance of the variation in the types of sensory endings is unknown, although the chemosensory epithelia also respond to other sensory modalities, and it is often difficult to ascribe any one cell type to any one modality. Species‐specific variations may also complicate the picture.(7). Prospects for and importance of future studies on gastropod chemoreception are discussed.