CHEMORECEPTION IN THE MUD SNAIL, NASSARIUS OBSOLETUS. II. IDENTIFICATION OF STIMULATORY SUBSTANCES 1 WILLIAM E. S. CARR 2 Department of Zoology, Duke University, Durham, North Carolina The ecological significance of chemoreception to aquatic gastropods and other aquatic invertebrates is well documented (for reviews, see Kohn, 1961 ; Hodgson, 1955). However, at the molecular level little is known about the substances which influence the behavior of these animals. Blake (1961) attempted to characterize the oyster metabolites which served as attractants to the predatory oyster drill, Urosalpinx cinerea. This work was limited primarily to studies on the physical properties of the attractants and to a series of somewhat inconclusive tests with known compounds. Frings and Frings (1965) studied the physical properties of stimulants which diffused from the food of Aplysia Juliana, but these studies did not include tests with known compounds. Brown and Noble (1960) and Brown (1961) reported that the gastropod, Bullia laevissima, would emerge from its buried position when food was near or when certain quaternary amines were present in sufficient concentrations. No attempt was made to correlate the con-centrations of compounds necessary for stimulation with the concentrations avail-able when food was placed in the water. Bailey and Laverack (1963), using electrophysiological techniques, reported that receptors in the osphradium of Buc-cinum undatum were sensitive to Mytilus extracts as well as to L-glutamic acid and trimethylamine oxide. This work did not include determinations of the relative concentrations of these compounds in the extracts and no reference was made to any response shown by the intact organism. Nassariits obsoletus was shown by Carr (1967) to be an extremely suitable animal for studies of chemoreception. This marine gastropod displays a stereo-typed response which is convenient for measuring the effectiveness of substances extracted from tissues. Carr showed that the principal response-inducing com-pounds in shrimp extracts were heat-stable, more soluble in polar than in non-polar solvents, non-volatile, of low molecular weight, stable to oxidation, stable to NH 3 , and somewhat acid-labile. Further, it was shown that the principle response-inducers were amphoteric and/or weakly basic compounds which were augmented by some acidic and/or neutral compounds(s). 1 This paper is based on a portion of a dissertation submitted to the Graduate School of Arts and Sciences of Duke University in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Zoology. These studies were conducted at the Duke University Marine Laboratory, Beaufort, N. C., and were supported by a N.I.H. Physiology Training Grant and by a Bureau of Commercial Fisheries Graduate Education Grant. The author is grateful to Dr. K. M. Wilbur, Dept. of Zoology, Duke University, for providing frequent counsel during the course of this research. The fractional ion exchange separation and the quantitative amino acid analyses reported in this paper were conducted in the laboratory of Dr. R. L. Hill, Dept. of Biochemistry, Duke University. 2 Present address: Department of Zoology, University of Florida, Gainesville, Florida 32601. 106
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