Journal of Chemical Ecology, Vol. 12, No. 5, 1986
MACROMOLECULAR CUES IN MARINE SYSTEMS
DAN RITTSCHOF
and J O S E P H B O N A V E N T U R A
Duke University Marine Laboratory and Marine Biomedical Center, Beaufort, North Carolina 28516
(Received June 26, 1985; accepted August 19, 1985) Abstraet--A review of the roles of biopolymers as marine chemical cues is presented. The goal of the review is to provide a context within which to view present research and to provide insight into future research potential for macromolecules in marine chemical ecology. The roles of peptides, proteins, glycoproteins, proteoglycans, lectins, and mucopolysaccharides are discussed. Biological events mediated include: larval settlement and metamorphosis, gamete attraction, predator-prey interactions, alarm responses, feeding responses, nonfood resource acquisition, trail following, and larval-release behavior. Molecular origins, transmission, modulation, and multifunctionality of cues are discussed and illustrated with specific examples. The advantages of biopolymers, especially peptides and proteins, as specific cues in marine systems derive from their solubility, specific information content (due to the asymmetric nature of the monomer and the wordlike information content of the primary structure of the polymer), distance transmission in water by bulk flow rather than diffusion, relatively high signal-to-noise ratio, and common occurrence as structural and metabolic components of all living organisms. Key Words--Marine animals, macromolecule8, peptides, glycoprotein8, behavior, prey detection, site selection, metamorphosis, biopolymers.
INTRODUCTION C h e m i c a l m e d i a t i o n o f b e h a v i o r is w e l l k n o w n in virtually all groups o f living o r g a n i s m s . M a r i n e animals are no e x c e p t i o n . M o s t reports describing the c h e m icals w h i c h m e d i a t e these b e h a v i o r s in m a r i n e species h a v e been c o n c e r n e d with f e e d i n g (reviews: Bardach, 1974; Scheuer, 1977; D u n h a m , 1978; A t e m a , 1982). W h e r e k n o w n , these c h e m i c a l s are p r i m a r i l y l o w - m o l e c u l a r - w e i g h t c o m p o u n d s such as a m i n o acids. O n l y a few reports detail the m e d i a t i o n o f m a r i n e o r g a n i s m b e h a v i o r by m a c r o m o l e c u l a r s such as peptides, proteins, gly-
1013 0098-0331/86/0500-1013505.00/0
9 1986 Plenum Publishing Corporation
1014
RITTSCHOF AND BONAVENTURA
coproteins, proteoglycans, lectins, and mucopolysaccharides. Although the total number of reports is small, the spectrum of documented macromoleculeinduced responses is broad. The phyla of organisms displaying such responses include Polychaeta, Cnidaria, Mollusca, Ascidia, Echinodermata, and Cmstacea. Macromolecules mediate aspects of: (1) larval settlement and metamorphosis [Crisp, 1984 (review); Morse, 1984 (review); Mitchell and Kirchman, 1984 (review); Burke, 1984]; (2) gamete attraction (Miller and Tseng, 1974); (3) predator-prey interactions (Rittschof et al., 1984); (4) alarm responses (Atema and Stenzler, 1977); (5) feeding responses (Gurin and CarT, 1971; Magnum and Cox, 1971; Carr et al. 1974; Carr and Gurin, 1975; Collins, t975; Zimmer-Faust et al., 1984); (6) shell acquisition behavior in hermit crabs (Rittschof, 1980a); (7) trail following (Dimon, 1905; Hewatt, t940; Crisp, 1969; Hall, 1972; Wells and Buckley, 1972; Cook and Cook, 1975; Trott and Dimmock, 1978) and (8) larval release behavior (Rittschoff et al., 1985). Thus, macromolecules appear to play major roles in the transmission of information for the mediation of behavior and resource utilization in the marine environment. However, these roles are not the exclusive domain of macromolecules, and for the sake of perspective it is useful to note that other classes of substances function in similar roles and are equally important (for discussion, see Scheuer, 1977). The nature of aquatic systems enables use of molecules of virtually any size as cues and signals (Wilson, 1970). In aquatic systems, solubility rather than volatility is of major importance (Atema, 1982). From a chemical point of view, macromolecular cues may not have the unique and interesting features that many secondary compounds from plants and animals have. However, they can exert considerable influence on biological activity. The biological activity of macromolecular cues is based upon the information content inherent in their polymeric structure. Polymer building blocks in specific sequences are highinformation-containing macromolecules. Transformation and transduction into biological responses comes from polymers which have various levels of organization and structure, ranging from primary to quaternary. Previous authors have discussed the tenuous distinction between smell and taste in aquatic organisms (Bardach, 1975; Atema, 1982). "Noses" and "tongues" appear either scattered indiscriminately or in highly complex patterns on virtually every conceivable external surface of marine organisms. Virtually every aspect of an organism's life cycle appears to be capable of being modulated through chemoreceptors. A recent and "delightful" complication is the growing need to distinguish between taste, contact chemoreception and touch with respect to the detection of and response to macromolecules adsorbed on surfaces. Thus, the three intuitively and anatomically distinct senses of taste, touch, and smell in terrestrial vertebrates form a continuum in marine sensory systems.
MACROMOLECULAR CUES
1015
Equally delightful is the increasing evidence [specifically through the work of Morse's group at the University of California at Santa Barbara (Morse, 1984, 1985) and several groups at the University of Florida C.V. Whitney Marine Laboratory (Greenberg and Price, 1983; Derby et al., 1984)] that endocrine and neuroendocrine interactions which operate inside vertebrate bodies have external analogs that function at the interface between marine invertebrates and the environment. These analogs show great promise as model systems for the study of the effector-receptor interactions that are the basis of neuroendocrinology. This is another example of a simple model system shedding light on much more complex ones. In the sections that follow we discuss the origins, transmission, information content, modulation, mechanisms of action, and the evidence for multifunctionality of marine macromolecular cues. Our goal is to give a brief overview of perspectives, research directions, as we see them, and insight into the complex nontoxic chemical networks that are fundamental to the daily life in the marine environment.
ORIGINS OF CUES
In instances where the origin of the chemical cue is known (Crisp and Meadows, 1962; Atema and Stenzler, 1977; Rittschof, 1980a; Kirchman et al., 1982; Larman et al., 1982; Forward and Lohman, 1983; Rittschof et al., 1983; Morse, 1985), the primary function of the anatomical source of the cue is as a component of the structural or metabolic machinery of the source organism. Sources are diverse: structural proteins, photosynthetic pigments, blood proteins, and exopolymers such as egg capsule proteins and mucopolysaccharides. Thus, interspecific information transmission may be a secondary function for the cue molecule, while the primary function may be structural or metabolic. Some examples of chemicals with secondary cueing functions are: (1) algal products which cue barnacle or gastropod settlement on substrates (Strathmann et al., 1981); (2) predation of a gastropod and potential shell availability to a hermit crab (McClean, 1974); (3) feeding responses (see Introduction for references); and (4) prey or predator location. Molecules with both intra- and interspecific cueing functions will be discussed in more detail in the section on multifunctionality. Some of the more completely documented examples of origins of intraspecific molecular cues come from studies of larval settlement and feeding. Regarding cues for larval settlement, Kirchman et al. (1982) found that bacterial mucopolysaccharides promote settlement of polychaete larvae, whereas peptides associated with phycoerythrobilin, a photosynthetic pigment in red algae, promote settlement of abalone larvae (Morse et al., 1979; Morse, 1985). In
1016
RJTTSCHOF AND BONAVENTURA
snail feeding studies, Carr and Gurin (1974, 1975) provided convincing evidence that glycoproteins of over 100,000 daltons derived from oyster flesh are involved in initial events of feeding stimulation. In the other examples of intraspecific macromolecular cueing mentioned above (gametic attraction, alarm responses, predator-prey interaction, etc.), there is insufficient information to assign the cues a definite molecular type or origin. However, there is documentation that peptides originating from gastropod muscle proteins cue hermit crab shell acquisition behavior (Rittschof, 1980a). Also, there is evidence that heat-stable peptides of unknown origin are slowly released from living barnacles and cue their location to predatory snails (Williams et al., 1983; Rittschof et al., 1984). Likewise, heat-stable peptides may serve as sperm attractants in hydrozoans (Miller and Tseung, 1974), Among the molecules cueing conspecific responses, the majority that have been described are glycoproteins. Heat-stable, high-molecular-weight substances found in the blood of mud snails function as an alarm substance when released by a catastrophic event (Atema and Stenzler, 1977). Natural catastrophic events include crushing or injury of the snail during predation. Experimentally, release of alarm substances is accomplished by any procedure that promotes bleeding. Over 16 species of gastropods display alarm reactions in response to crushed conspecifics (Snyder, 1967). Heat-stable proteins promoting settlement of conspecific larvae have been extracted from homogenates of adult barnacle tissues (Larman et al.. 1982). Heat-stable peptides from living adult barnacles have similar effects on barnacle settlement (Rittschof. 1985). Finally, peptides from extracts of sand surrounding adult sand dollars (Burke, 1984) promote settlement and metamorphosis of larval sand dollars. However. the exact origin of any of the peptides in these examples has not been determined. The adhesive used by a colonial tube-building polychaete, which promotes settlement of conspecific larvae (Jensen and Morse. 1984). is an example of one interspecific larval settlement cue with a known origin. Peptide-cued conspecific larval release behavior is known in female mud crabs (Rittschof et al., 1985). In this case, small peptides released from hatching eggs ~Forward and Lohman, 1983) cause female crabs carrying eggs to pump their abdomens. The precise origin of these larval-releasing peptides is uncertain. Trail following in gastropods has received considerable attention at the ecological and behavioral level, but little attenuon has been given to this phenomenon at the molecular level. Many gastropods follow mucus trails laid down by conspecifics. The trails are known to have polarity, and in some instances they contain enough information for the discrimination of individuals of the same species from one another (Trott and Dimmock. 1978). The self/nonself recognition component has not been studied chemically, and the polarity appears to be a short-lived (hours) structural property of the mucus trail.
MACROMOLECULARCUES
1017 TRANSMISSION OF CUES
Because of the slow rate of diffusion of molecules in water, bulk water flow is important in the transport of chemical cues (Wilson, 1970; Atema, 1982). Three-dimensional odor trails (Atema, 1982) are a consequence of a slow rate of diffusion coupled to bulk water movement. These factors dictate that for most organisms detection of a chemical gradient and gradient search will not be involved in response to distant cue sources. Rheotaxis and searching in response to on-off type availablilty of cues (Van Haflen and Verway, 1958; Derby and Atema, 1980; Rittschof, 1980b; Rittschof et al., 1983; Brown and Rittschof, 1984) is a more commonly demonstrated mechanism. In a careful study of chemically mediated rheotatic responses of oyster drills (Brown and Rittschof, 1984) neither the chemical cue nor the water flow alone were effective, while any combination Of flow and cue, within a threefold range of each, elicited creeping responses by the drills. Macromolecular cues function when in solution (Carr, 1967; Atema and Stenzler, 1977; Rittschof, 1980a) much the way that any other chemicals function. A more unique feature of macromolecular cues is that many are known to function when adsorbed to or part of a surface (Morse et al., 1980; Crisp and Meadows, 1982; Kirchmann et al., 1982; Jensen and Morse, 1984; Rittschof, 1985). Often, hydrolysis of the actual source of the cue can lead to extended cueing functions. For example, small molecules like amino acids which cue feeding for fish and blue crabs are released at effective concentrations for about 12 hr from a 15-g flesh source if it is protected from consumption. In contrast, the macromolecules which cue shell acquisition in hermit crabs are generated from that same source for at least three days (Rittschof, 1980b). Macromolecules adsorbed to surfaces after release from the blood of mud snails also function to prolong behavioral responses. It is not clear whether this effect is due to partitioning of the cue between the water and substrate, or a result of partial hydrolysis of the parent compound. Nevertheless, the result is a stimulation of a specific behavior for up to 24 hr (Atema and Stenzler, 1977). In addition to macromolecules that can function as guides for trail following in snails, macromolecules implicated in larval settlement appear to function when they are adsorbed to or physically a part of a surface (Crisp and Meadows, 1962; Hidu, 1969; Morse et al., 1979; Kirchman et al., 1982; Rittschof, 1985). This particular phenomenon appears to be widespread among settling larvae. Documentation of specific surface contact requirements exists for larvae of mollusks, crustaceans, and polychaetes, ascidians (Woollacott, 1984), and bryozoans (Mihm et al., 1981). A surface mechanism of action is difficult to demonstrate experimentally because of the possibility of slow leaching or hydrolysis of the adsorbed cue. Minimally, the initial steps in the behavioral responses to
1018
RITTSCHOFANDBONAVENTURA
adsorbed molecules must be a molecular contact that intitates the response (Crisp and Meadows, 1962; Morse et al., 1979, 1980; Kirchman et al., 1982; Rittschof, 1985). This particular area of marine chemoreception is one which is at the interface between touch contact chemoreception and taste. MODULATION OF MACROMOLECULAR CUES Behavioral and physiological responses to macromolecular cues can be positively and negatively modulated by natural compounds. By themselves, modulators do not evoke responses at "natural" concentrations in the absence of the cue. For example, stimulation by the macromolecules associated with both abalone settlement (Morse, 1984, 1986) and location of prey by predatory snails (Williams et al., 1983; Rittschof and Brown, 1986) can be either facilitated or suppressed by modulatory compounds. These modulators appear to be low-molecular-weight compounds that are different in each specific instance. Morse (1984) reviews information that his group gathered on modulators that facilitate settlement of abalone larvae. Facilitators are components common in "dissolved organic material" which aid all aspects of metamorphosis in response to low concentrations of the inducer [GABA-mimetic peptide (Morse, 1985)]. Facilitators all appear to be structural analogs of GABA, which themselves possess inducing activity only at high concentrations (Morse, 1984; Trapido-Rosenthal et al., 1985). Morse (1984) makes the argument that facilitators of abalone settlement, because of their structural analogy to natural inducers, may function in any of the steps in the normal induction pathways. Facilitation (Williams et al., 1983) of responses of snails to soluble peptides from barnacles is due to micromolar concentrations of ammonium ion (Rittschof and Brown, 1985). Compounds suppressing chemotactic responses of snails to these peptides occur in the odors from the predatory snail's bivalve prey (Williams et al., 1983). Modulators with suppressant activity are poorly characterized because of the inability at this time to extract and concentrate them from seawater. However, it is known that suppressants are not amino acids or simple sugars, and that they have an apparent molecular size between 500 and 1000 daltons. Thus, chemical modulations of certain snail predator-prey interactions are expressed in several ways, including camouflaging (Fishlyn and Phillips, 1980), facilitation of the attractiveness of the odor of a prey species (Rittschof et al., 1983; Williams et al., 1983), and suppression of chemotactic behavior (Williams et al., 1983; Rittschof and Brown, 1986). MULTIPLE FUNCTIONS Evidence for multifunctionality of macromolecular cues in marine organisms is restricted at this time to preliminary investigations of peptides that orig-
MACROMOLECULAR CUES
l019
inate from barnacles and oysters (Rittschof and Brown, 1986). These peptides were discovered and isolated by virtue of the creeping response evoked in predatory snails (Rittschof et al., 1983, 1984; Rittschof et al., 1986). Peptides originating from barnacles were isolated and purified from seawater containing live intact barnacles. Detection of biological activity was done with an assay which tested the creeping response observed in inexperienced predatory snails. Soluble peptides from water bathing intact oysters were isolated and purified. The bioassay used in this study measured the creeping response in snails that had been conditioned (Wood, 1968) to respond to peptides from oysters. Although the amino acid sequences of the peptides are not yet known, chromatographic, compositional, and biological properties indicate that several distinct peptides may be present (Rittschof and Brown, 1986; Rittschof et al., 1986). In addition to their biological activity in predatory" snails, the peptides isolated from barnacles and oysters have effects on the settling stage of larval barnacles. At concentrations that can be detected in field situations (2.5 #g/ liter), barnacle peptides affect the behavior and induce metamorphosis in settling stage larvae. In this respect these peptides are similar to arthropodins (Crisp and Meadows, 1962). As is the case with arthropodins, soluble but "sticky" barnacle peptides affect larval behavior and induce metamorphosis when adsorbed onto surfaces. In contrast, "sticky" oyster peptides, presented at concentrations comparable to barnacle peptides, alter larval barnacle behavior but do not induce metamorphosis. Tests of effects of these oyster peptides on larval oysters are in progress in collaboration with researchers at the University of Maryland. Thus, there is preliminary evidence that macromolecular cues may perform more than one cueing function. In the case of barnacle peptides, there is evidence for three functions: (1) prey location by predatory snails plus (2) site selection and (3) induction of metamorphosis by barnacle larvae. In the case of oyster peptides, there is evidence for two functions: (1) prey detection by predatory snails and (2) site selection in larval barnacles. It appears likely that future work will show that macromolecules that provide information concerning the presence of specific kinds of organisms are central to the physiological ecology of those organisms. Whether adsorbed to surfaces or free in solution, macromolecular cues function to transmit specific information in marine environments. The fact that many cues are proteinaceous but heat stable suggests that higher-order macromolecular structure (secondary, tertiary, and quaternary) is less important than the covalent primary structure inherent in all biopolymers. In a peptide, for example, the " R " groups of each amino acid might function unambiguously, similar to strings of letters forming words. While odor bouquets (Bardach, 1975) of smaller molecules can perform the functions of single macromolecules, there is little evidence in marine systems other than in those areas entailing relatively
1020
RITTSCHOF AND BONAVENTURA
nonspecific responses (such as feeding) that mixtures o f odors have specific cue functions. However, as is the case in insect pheromone systems, mixtures of marine secondary metabolites may have specific functions. Advantages related to specific cueing functions are inherent in the primary structure o f macromolecules, especially peptides. In many environments peptide cues have a high signal-to-noise ratio. This is because background levels o f free peptides and amino acids (Mopper and Lindroth, 1982) are low due to the biological demand for and scavenging o f organic nitrogen, Concomitantly, rapid biological uptake combined with dilution result in short signal duration. As the size of the peptide increases, the rapid decrease in the rate o f diffusion increases the potential for transport o f effective cue concentrations over relatively long distances. Should modulating molecules be present, the change in ratio o f cue to modulator in the odor plume due to differences in rates of diffusion could be used by organisms to gain information about the distance to the source. The polar, amphoteric structure o f peptides provides high solubility in water. The linear structure and polarity (amino terminal and carboxy terminal) of peptides provide potential for unambiguous information transmission. Should the peptide originate from a repeating structure such as a marine adhesive (Waite, 1983) or blood antifreeze protein (Komatzu et al., 1970), there is remarkable potential for extended slow release function. Finally, as proteins are major metabolic and structural components of all organisms, the intact molecules and their specific degradation products are available as raw materials for the evolution o f information transmission. Acknowledgments--This was supported in part by ONR N00014-78-C-0294 and in part by NIEHS ES0-1908. The authors thank the editors and reviewers for their contributions.
REFERENCES ATEMA, J. 1982. Chemical senses, chemical signals, and feeding behavior in fishes, pp. 57-101, in J.E. Bardach, J.J. Magnuson, R.C. May, and J.M. Reinhardt (eds). Fish Behavior and Its
Use in the Capture and Culture of Fishes. International Center for Living Resource Management, Manila, Philippines. ATEMA,J., and STENZLER,D. 1977. Alarm substance of the marine mud snail. Nassarius obsoletus: Biological characterization and possible evolution. J. Chem. Ecol. 3:173-187. BARDACH,J.E. 1975. Chemoreception in aquatic animals, pp. 121-132, in D.A. Denton and J.P. Coghlan (eds.). Fifth International Symposium on Smell and Taste. Academic Press, New York. BROWN,B.B., and RITTSCHOF,D. 1984. Integration of flow and chemical cue by predatory snails. Mar. Behav. Physiol. 11:75-93. BURKE, R.D. 1984. Pheromonal control of metamorphosis in the Pacific sand dollar, Dendraster excentricus. Science 225:442-443. CARR, W.E. 1967. Chemoreception in the mud snail, Nassarius obsoletus. I. Properties of stimulatory substances extracted from shrimp. Biol. Bull. 133:106-127. CARR, W.E., and GURIN, S. 1975. Chemoreception in the shrimp. Palaeomonetes pugio: Comparative study of stimulating substances in human serum. Biol. Bull. 148:380-392.
MACROMOLECULARCUES
1021
CARR, W.E., HALL, E. and GURIN,S. 1974. Chemoreception and the role of proteins: A comparative study. Comp. Biochem. Physiol. 47A:559-566. COLLINS, A.P. 1975. Biochemical investigations of two responses involved in the feeding behavior ofAcanthasterplanci (L.). II. Isolation and characterization of chemical stimuli. J. Exp. Mar. Biol. Ecol. 17:69-86. COOK, S.B., and COOK, C.B. 1975. Directionality in the trail following response of the pulmonate limpet Siphonaria alternata. Mar. Behav. Physiol. 3:147-155. CRISP, M. 1969. Studies on the behavior of Nassarius obsoletus (Say) (Mollusca: Gastropoda). Biol. Bull. 136:335-373. CRISP, D.J. 1984. Overview of research on marine invertebrate larvae, pp. 103-126, in J.D. Costlow and R.C. Tipper (eds.). Marine Biodetedoration. Naval Institute Press, Annapolis, Maryland. CRISP, D.J., and MEADOWS,P.S. 1962. The chemical basis of gregariousness in cirripedes. Proc. R. Soc. London Ser. B. 156:500-520. DERBY, C.D., and ATEMA, J. 1980. Induced host odor attraction in the pea crab Pinnotheres maculatus. Biol. Bull. 158:26-33. DERBY, C.D., CARR, W.E., and ACHE, B.W. 1984. Purinergic olfactory cells of crustaceans: Response characteristics and similarities to internal pufinergic cells of vertebrates. J. Comp. Physiol. A. 155:341-349. DIMON, A.C. 1905. The mud snail Nassa obsoleta. Cold Spring Harbor. Monogr. 5:1-48. DUNHAM, P.J. 1978. Sex pheromones in Cmstacea. Biol. Rev. 58:555-583. FISHLYN, D.A., and PHILLIPS,D.W. 1980. Chemical camouflaging and behavioral defenses against a predatory seastar by three species of gastropods from the surf grass Phylospadix community. Biol Bull. 158:34-48. FORWARD, R.B., and LOHMAN, K.J. 1983. Control of egg hatching in the crab Rhithropanopeus harrisii (Gould). Biol. Bull. 165:154-166. GREENBERG, M.J., and PRICE, D.A. 1983. Invertebrate neuropeptides: Native and naturalized. Annu. Rev. Physiol. 45:271-288. GURIN, S., and CARR, W.E. 1971. Chemoreception in Nassarius obsoletus: The role of specific stimulatory proteins. Science 174:293-295. HALL, J.R., 1972. Intraspecific trail-following in the marsh periwinkle Littorina irrorata (Say). Veliger 16:72-75. HEEB, M.A. 1973. Large molecules and chemical control of feeding behavior in the starfish Asterias forbesi. Helgol. Wiss. Meeresunters. 24:425-435. HEWATT, W.G. 1940. Observations on the homing limpet Acmaea scraba. Am. Midl. Nat. 24:205208. HIDU, H. 1969. Gregarious settlement in the American oyster Crassostrea virginica Gmelin. Chesapeake Sci. 10:2185-2192. JENSEN, R.A., and MORSE, D.E. 1984. Intraspecific facilitation of larval recruitment: Gregarious settlement of the polychaete Phragmatopoma californica (Fewkes). J. Exp. Mar. Biol. Ecol. 83:107-126. KIRCHMAN, D., GRAHM, S., REISH D., and MITCHELL, R. 1982. Bacteria induce settlement and metamorphosis of Janua (Dexospira)basiliensis (Grebe). J. Exp. Mar. Biol. Ecol. 56:153163. KOMATZU, S.K., DEVRIES, A.L., and FEENEY, R.E. 1970. Studies of the structure of freezing point depressing glycoproteins from an antarctic fish. J. BioL Chem. 245:2909-2913. LARMAN,V.N., GABBOTT,P.A., and EAST,J. 1982. Physicochemical properties of the settlement factor proteins from the barnacle Balanus balanoides. Comp. Biochem. Physiol. 72B:329338. MAGNUM, C.P., and Cox, C.D. 1966. A feeding response to chemical stimuli in the onuphid polychaete Diopatra cuprea. Am. Zool. 6:546-547. MCCLEAN, R.B. 1974. Direct shell acquisition by hermit crabs from gastropods. Experientia 30:206-208.
1022
RITTSCHOF AND BONAVENTURA
M1HM, J.W., BANTA,W.C., and LOEB, G.I. 1981. Effects of adsorbed organic and primary fouling films on bryozoan settlement. J. Exp. Mar. Biol. Ecol. 54:167-179. MILLER, R.L., and TSENG, C.Y. 1974. Properties and partial purification of the sperm attractant of Tubularia. Am. Zool. 14:467-486. MITCHELL, R., and KmCItMAN,D. 1984. The microbial ecology of marine surfaces, pp. 49-56, in J.D. Costlow and R.C. Tipper (eds.). Marine Biodeterioration. Naval Institute Press Annapolis, Maryland. MOPPER, K., and LINDROTH, P. 1982. Diel and depth variations in dissolved free amino acids and ammonium in the Baltic Sea determined by shipboard HPLC analysis. Limnol. Oceanogr. 27:336-347. MORSE, D. 1984. Biochemical control of larval recruitment and marine fouling, pp. 134-140, in Marine Biodeterioration. J.D. Costlow and R.C. Tipper, (eds.) Naval Institute Press, Annapolis, Maryland. MORSE, D. 1985. Neurotransmitter-mimetic inducers of larval settlement and metamorphosis. Bull. Mar. Sci. 37:697-706. MORSE, D.E., HOOKER, N., DUNCAN, H., and JENSEN, L. 1979. 3,-aminobutyric acid, a neurotransmitter, induces planktonic abalone larva to settle and begin metamorphosis. Science 204:405-410. MORSE, D.E., TEGNER, M., DUNCAN,H., HOOKER,N., TREVELYAN,G. and CAMERON,A. 1980. Induction of settling and metamorphosis of planktonic molluscan (Holiotis) larvae. III. Signaling by metabolites of intact algae is dependent on contact, pp. 67-86, in D. M~iller-Schwarze and R.M. Silverstein (eds.). Chemical Signals: Vertebrates and Aquatic Invertebrates. Plenum Press, New York. RITTSCHOF, D. 1980a. Enzymatic production of small molecules attracting hermit crabs to simulated gastropod predation sites. J. Chem. Ecol. 6(4):665-675. RITTSCHOF, D. 1980b. Chemical attraction of hermit crabs and other attendants to gastropod predation sites. J. Chem, Ecol. 6:103-118. RITTSCHOF, D. 1985. Oyster drills and the frontiers of chemical ecology: Unsettling ideas. Bull. Amer. Malac. Union. Spec. Ed. 1:111-116. R1TTSCHOF, D., and BROWN,A.B. 1986. Modification of predatory snail chemotaxis by substances in bivalve prey odors. Malacology. In press. RITTSCHOF, D., WILLIAMS,L.G., BROWN, B., and CARRIKER,M.R. 1983. Chemical attraction of newly hatched oyster drills. Biol. Bull. 164:493-505. RITTSCHOF, D., SHEPHERD, R., and WILLIAMS, L.G. 1984. Concentration and preliminary characterization of a chemical attractant of the oyster drill, Urosalpinx cinerea. J. Chem. EcoL 10:63-79. RITTSCHOF, D., FORWARD,R.B., JR., and MOTT, D.D. 1985. Larval release in the crab Rhithropanopeus harrisii (Gould): Chemical cues from hatching eggs. Chem. Senses. 10:567-577. RITTSCHOF,D., SHEPHERD,R,G., and WAr,D, E. 1986. Characterization of peptides that attract oyster drills to barnacle and oyster prey. In preparation. SHELTON, R.G., and MACKIE, A.M. 1971. Studies on the chemical preferences of the shore crab, Carcinus maenas (L). J. Exp. Mar. Biol. Ecol. 7:41-49. SCHEUER, P.J. 1977. Chemical communication in marine invertebrates. Bioscience 27:664-668. SNYDER,N.F. 1967. An alarm reaction of aquatic gastropods to intraspecific extract. Cornell Agric. St. 403:1-122. STRATHMANN,R.R., BRANSCOMB,E.S., and VEDDER,K. 198t. Fatal errors in set as a cost of dispersal and the influence of intertidal flora on set of barnacles. Oecologia 48:13-18. TRAPIDO-ROSENTHAL, H.G., and MORSE, D.E. 1985. L-c~, c0-Diamino acids facilitate induction of settlement and metamorphosis in larvae of a gastropod mollusc (Haliotis rufescens). J. Comp. Physiol. B. 155:403-414. TROTT, T.J., and DIMOCK, R.V., JR. 1978. Intraspecific trail following by the mud snail, lilyanassa obsoleta. Mar. Behav. Physiol. 5:91-101.
MACROMOLECULAR CUES
1023
VAN HAFTEN,J.L., and VERWAY,J. 1958. The role of water currents in orientation in marine animals. Ext. Arch. Neederland. Zool. 13:493-499. WAITE, J.H. 1983. Evidence for a repeating 3, 4-dihydroxyphenylalanine- and hydroxyprolinecontaining decapeptide in the adhesive protein of the mussel, Mytilus edulis L. J. Biol. Chem. 258:2911-2915. WELLS, M.J., and BUCKLEY,S.K. 1972. Snails and trails. Anim. Behav. 20:345-355. WILLIAMS, L.G., RITTSCHOF, D., BROWN, B., and CARRIKER, M.R. 1983. Chemotaxis of oyster drills Urosalpinx cinerea to competing prey odors. Biol. Bull. 64:536-548. WILSON, E.O. 1970. Chemical communication within animal species, pp. 133-155, in E. Sondheimer and J.B. Simeone (eds.). Chemical Ecology. New York, Academic Press. WOOD, L. 1968. Physiological and ecological aspects of prey selection by the marine gastropod Urosalpinx cinerea (Prosobranchia: Muricidae). Malacologica 6:26%320. WOOLLACOTT,R.M. 1984. Environmental factors in bryozoan settlement, pp. 149-154, in J.D. Costlow and R.C. Tipper (eds.). Marine Biodeterioration. Naval Institute Press, Annapolis, Maryland. ZIMMER-FAUST, R.K., MmHEL, W.C., TYRE, J.C., and CASE, J.F. 1984. Chemical induction in California spiny lobster, Panulirus interruptus (Randall): Responses to molecular weight fractions of abalone. J. Chem. Ecol. 10:957-971.
MACROMOLECULAR CUES IN MARINE SYSTEMS
DAN RITTSCHOF
and J O S E P H B O N A V E N T U R A
Duke University Marine Laboratory and Marine Biomedical Center, Beaufort, North Carolina 28516
(Received June 26, 1985; accepted August 19, 1985) Abstraet--A review of the roles of biopolymers as marine chemical cues is presented. The goal of the review is to provide a context within which to view present research and to provide insight into future research potential for macromolecules in marine chemical ecology. The roles of peptides, proteins, glycoproteins, proteoglycans, lectins, and mucopolysaccharides are discussed. Biological events mediated include: larval settlement and metamorphosis, gamete attraction, predator-prey interactions, alarm responses, feeding responses, nonfood resource acquisition, trail following, and larval-release behavior. Molecular origins, transmission, modulation, and multifunctionality of cues are discussed and illustrated with specific examples. The advantages of biopolymers, especially peptides and proteins, as specific cues in marine systems derive from their solubility, specific information content (due to the asymmetric nature of the monomer and the wordlike information content of the primary structure of the polymer), distance transmission in water by bulk flow rather than diffusion, relatively high signal-to-noise ratio, and common occurrence as structural and metabolic components of all living organisms. Key Words--Marine animals, macromolecule8, peptides, glycoprotein8, behavior, prey detection, site selection, metamorphosis, biopolymers.
INTRODUCTION C h e m i c a l m e d i a t i o n o f b e h a v i o r is w e l l k n o w n in virtually all groups o f living o r g a n i s m s . M a r i n e animals are no e x c e p t i o n . M o s t reports describing the c h e m icals w h i c h m e d i a t e these b e h a v i o r s in m a r i n e species h a v e been c o n c e r n e d with f e e d i n g (reviews: Bardach, 1974; Scheuer, 1977; D u n h a m , 1978; A t e m a , 1982). W h e r e k n o w n , these c h e m i c a l s are p r i m a r i l y l o w - m o l e c u l a r - w e i g h t c o m p o u n d s such as a m i n o acids. O n l y a few reports detail the m e d i a t i o n o f m a r i n e o r g a n i s m b e h a v i o r by m a c r o m o l e c u l a r s such as peptides, proteins, gly-
1013 0098-0331/86/0500-1013505.00/0
9 1986 Plenum Publishing Corporation
1014
RITTSCHOF AND BONAVENTURA
coproteins, proteoglycans, lectins, and mucopolysaccharides. Although the total number of reports is small, the spectrum of documented macromoleculeinduced responses is broad. The phyla of organisms displaying such responses include Polychaeta, Cnidaria, Mollusca, Ascidia, Echinodermata, and Cmstacea. Macromolecules mediate aspects of: (1) larval settlement and metamorphosis [Crisp, 1984 (review); Morse, 1984 (review); Mitchell and Kirchman, 1984 (review); Burke, 1984]; (2) gamete attraction (Miller and Tseng, 1974); (3) predator-prey interactions (Rittschof et al., 1984); (4) alarm responses (Atema and Stenzler, 1977); (5) feeding responses (Gurin and CarT, 1971; Magnum and Cox, 1971; Carr et al. 1974; Carr and Gurin, 1975; Collins, t975; Zimmer-Faust et al., 1984); (6) shell acquisition behavior in hermit crabs (Rittschof, 1980a); (7) trail following (Dimon, 1905; Hewatt, t940; Crisp, 1969; Hall, 1972; Wells and Buckley, 1972; Cook and Cook, 1975; Trott and Dimmock, 1978) and (8) larval release behavior (Rittschoff et al., 1985). Thus, macromolecules appear to play major roles in the transmission of information for the mediation of behavior and resource utilization in the marine environment. However, these roles are not the exclusive domain of macromolecules, and for the sake of perspective it is useful to note that other classes of substances function in similar roles and are equally important (for discussion, see Scheuer, 1977). The nature of aquatic systems enables use of molecules of virtually any size as cues and signals (Wilson, 1970). In aquatic systems, solubility rather than volatility is of major importance (Atema, 1982). From a chemical point of view, macromolecular cues may not have the unique and interesting features that many secondary compounds from plants and animals have. However, they can exert considerable influence on biological activity. The biological activity of macromolecular cues is based upon the information content inherent in their polymeric structure. Polymer building blocks in specific sequences are highinformation-containing macromolecules. Transformation and transduction into biological responses comes from polymers which have various levels of organization and structure, ranging from primary to quaternary. Previous authors have discussed the tenuous distinction between smell and taste in aquatic organisms (Bardach, 1975; Atema, 1982). "Noses" and "tongues" appear either scattered indiscriminately or in highly complex patterns on virtually every conceivable external surface of marine organisms. Virtually every aspect of an organism's life cycle appears to be capable of being modulated through chemoreceptors. A recent and "delightful" complication is the growing need to distinguish between taste, contact chemoreception and touch with respect to the detection of and response to macromolecules adsorbed on surfaces. Thus, the three intuitively and anatomically distinct senses of taste, touch, and smell in terrestrial vertebrates form a continuum in marine sensory systems.
MACROMOLECULAR CUES
1015
Equally delightful is the increasing evidence [specifically through the work of Morse's group at the University of California at Santa Barbara (Morse, 1984, 1985) and several groups at the University of Florida C.V. Whitney Marine Laboratory (Greenberg and Price, 1983; Derby et al., 1984)] that endocrine and neuroendocrine interactions which operate inside vertebrate bodies have external analogs that function at the interface between marine invertebrates and the environment. These analogs show great promise as model systems for the study of the effector-receptor interactions that are the basis of neuroendocrinology. This is another example of a simple model system shedding light on much more complex ones. In the sections that follow we discuss the origins, transmission, information content, modulation, mechanisms of action, and the evidence for multifunctionality of marine macromolecular cues. Our goal is to give a brief overview of perspectives, research directions, as we see them, and insight into the complex nontoxic chemical networks that are fundamental to the daily life in the marine environment.
ORIGINS OF CUES
In instances where the origin of the chemical cue is known (Crisp and Meadows, 1962; Atema and Stenzler, 1977; Rittschof, 1980a; Kirchman et al., 1982; Larman et al., 1982; Forward and Lohman, 1983; Rittschof et al., 1983; Morse, 1985), the primary function of the anatomical source of the cue is as a component of the structural or metabolic machinery of the source organism. Sources are diverse: structural proteins, photosynthetic pigments, blood proteins, and exopolymers such as egg capsule proteins and mucopolysaccharides. Thus, interspecific information transmission may be a secondary function for the cue molecule, while the primary function may be structural or metabolic. Some examples of chemicals with secondary cueing functions are: (1) algal products which cue barnacle or gastropod settlement on substrates (Strathmann et al., 1981); (2) predation of a gastropod and potential shell availability to a hermit crab (McClean, 1974); (3) feeding responses (see Introduction for references); and (4) prey or predator location. Molecules with both intra- and interspecific cueing functions will be discussed in more detail in the section on multifunctionality. Some of the more completely documented examples of origins of intraspecific molecular cues come from studies of larval settlement and feeding. Regarding cues for larval settlement, Kirchman et al. (1982) found that bacterial mucopolysaccharides promote settlement of polychaete larvae, whereas peptides associated with phycoerythrobilin, a photosynthetic pigment in red algae, promote settlement of abalone larvae (Morse et al., 1979; Morse, 1985). In
1016
RJTTSCHOF AND BONAVENTURA
snail feeding studies, Carr and Gurin (1974, 1975) provided convincing evidence that glycoproteins of over 100,000 daltons derived from oyster flesh are involved in initial events of feeding stimulation. In the other examples of intraspecific macromolecular cueing mentioned above (gametic attraction, alarm responses, predator-prey interaction, etc.), there is insufficient information to assign the cues a definite molecular type or origin. However, there is documentation that peptides originating from gastropod muscle proteins cue hermit crab shell acquisition behavior (Rittschof, 1980a). Also, there is evidence that heat-stable peptides of unknown origin are slowly released from living barnacles and cue their location to predatory snails (Williams et al., 1983; Rittschof et al., 1984). Likewise, heat-stable peptides may serve as sperm attractants in hydrozoans (Miller and Tseung, 1974), Among the molecules cueing conspecific responses, the majority that have been described are glycoproteins. Heat-stable, high-molecular-weight substances found in the blood of mud snails function as an alarm substance when released by a catastrophic event (Atema and Stenzler, 1977). Natural catastrophic events include crushing or injury of the snail during predation. Experimentally, release of alarm substances is accomplished by any procedure that promotes bleeding. Over 16 species of gastropods display alarm reactions in response to crushed conspecifics (Snyder, 1967). Heat-stable proteins promoting settlement of conspecific larvae have been extracted from homogenates of adult barnacle tissues (Larman et al.. 1982). Heat-stable peptides from living adult barnacles have similar effects on barnacle settlement (Rittschof. 1985). Finally, peptides from extracts of sand surrounding adult sand dollars (Burke, 1984) promote settlement and metamorphosis of larval sand dollars. However. the exact origin of any of the peptides in these examples has not been determined. The adhesive used by a colonial tube-building polychaete, which promotes settlement of conspecific larvae (Jensen and Morse. 1984). is an example of one interspecific larval settlement cue with a known origin. Peptide-cued conspecific larval release behavior is known in female mud crabs (Rittschof et al., 1985). In this case, small peptides released from hatching eggs ~Forward and Lohman, 1983) cause female crabs carrying eggs to pump their abdomens. The precise origin of these larval-releasing peptides is uncertain. Trail following in gastropods has received considerable attention at the ecological and behavioral level, but little attenuon has been given to this phenomenon at the molecular level. Many gastropods follow mucus trails laid down by conspecifics. The trails are known to have polarity, and in some instances they contain enough information for the discrimination of individuals of the same species from one another (Trott and Dimmock. 1978). The self/nonself recognition component has not been studied chemically, and the polarity appears to be a short-lived (hours) structural property of the mucus trail.
MACROMOLECULARCUES
1017 TRANSMISSION OF CUES
Because of the slow rate of diffusion of molecules in water, bulk water flow is important in the transport of chemical cues (Wilson, 1970; Atema, 1982). Three-dimensional odor trails (Atema, 1982) are a consequence of a slow rate of diffusion coupled to bulk water movement. These factors dictate that for most organisms detection of a chemical gradient and gradient search will not be involved in response to distant cue sources. Rheotaxis and searching in response to on-off type availablilty of cues (Van Haflen and Verway, 1958; Derby and Atema, 1980; Rittschof, 1980b; Rittschof et al., 1983; Brown and Rittschof, 1984) is a more commonly demonstrated mechanism. In a careful study of chemically mediated rheotatic responses of oyster drills (Brown and Rittschof, 1984) neither the chemical cue nor the water flow alone were effective, while any combination Of flow and cue, within a threefold range of each, elicited creeping responses by the drills. Macromolecular cues function when in solution (Carr, 1967; Atema and Stenzler, 1977; Rittschof, 1980a) much the way that any other chemicals function. A more unique feature of macromolecular cues is that many are known to function when adsorbed to or part of a surface (Morse et al., 1980; Crisp and Meadows, 1982; Kirchmann et al., 1982; Jensen and Morse, 1984; Rittschof, 1985). Often, hydrolysis of the actual source of the cue can lead to extended cueing functions. For example, small molecules like amino acids which cue feeding for fish and blue crabs are released at effective concentrations for about 12 hr from a 15-g flesh source if it is protected from consumption. In contrast, the macromolecules which cue shell acquisition in hermit crabs are generated from that same source for at least three days (Rittschof, 1980b). Macromolecules adsorbed to surfaces after release from the blood of mud snails also function to prolong behavioral responses. It is not clear whether this effect is due to partitioning of the cue between the water and substrate, or a result of partial hydrolysis of the parent compound. Nevertheless, the result is a stimulation of a specific behavior for up to 24 hr (Atema and Stenzler, 1977). In addition to macromolecules that can function as guides for trail following in snails, macromolecules implicated in larval settlement appear to function when they are adsorbed to or physically a part of a surface (Crisp and Meadows, 1962; Hidu, 1969; Morse et al., 1979; Kirchman et al., 1982; Rittschof, 1985). This particular phenomenon appears to be widespread among settling larvae. Documentation of specific surface contact requirements exists for larvae of mollusks, crustaceans, and polychaetes, ascidians (Woollacott, 1984), and bryozoans (Mihm et al., 1981). A surface mechanism of action is difficult to demonstrate experimentally because of the possibility of slow leaching or hydrolysis of the adsorbed cue. Minimally, the initial steps in the behavioral responses to
1018
RITTSCHOFANDBONAVENTURA
adsorbed molecules must be a molecular contact that intitates the response (Crisp and Meadows, 1962; Morse et al., 1979, 1980; Kirchman et al., 1982; Rittschof, 1985). This particular area of marine chemoreception is one which is at the interface between touch contact chemoreception and taste. MODULATION OF MACROMOLECULAR CUES Behavioral and physiological responses to macromolecular cues can be positively and negatively modulated by natural compounds. By themselves, modulators do not evoke responses at "natural" concentrations in the absence of the cue. For example, stimulation by the macromolecules associated with both abalone settlement (Morse, 1984, 1986) and location of prey by predatory snails (Williams et al., 1983; Rittschof and Brown, 1986) can be either facilitated or suppressed by modulatory compounds. These modulators appear to be low-molecular-weight compounds that are different in each specific instance. Morse (1984) reviews information that his group gathered on modulators that facilitate settlement of abalone larvae. Facilitators are components common in "dissolved organic material" which aid all aspects of metamorphosis in response to low concentrations of the inducer [GABA-mimetic peptide (Morse, 1985)]. Facilitators all appear to be structural analogs of GABA, which themselves possess inducing activity only at high concentrations (Morse, 1984; Trapido-Rosenthal et al., 1985). Morse (1984) makes the argument that facilitators of abalone settlement, because of their structural analogy to natural inducers, may function in any of the steps in the normal induction pathways. Facilitation (Williams et al., 1983) of responses of snails to soluble peptides from barnacles is due to micromolar concentrations of ammonium ion (Rittschof and Brown, 1985). Compounds suppressing chemotactic responses of snails to these peptides occur in the odors from the predatory snail's bivalve prey (Williams et al., 1983). Modulators with suppressant activity are poorly characterized because of the inability at this time to extract and concentrate them from seawater. However, it is known that suppressants are not amino acids or simple sugars, and that they have an apparent molecular size between 500 and 1000 daltons. Thus, chemical modulations of certain snail predator-prey interactions are expressed in several ways, including camouflaging (Fishlyn and Phillips, 1980), facilitation of the attractiveness of the odor of a prey species (Rittschof et al., 1983; Williams et al., 1983), and suppression of chemotactic behavior (Williams et al., 1983; Rittschof and Brown, 1986). MULTIPLE FUNCTIONS Evidence for multifunctionality of macromolecular cues in marine organisms is restricted at this time to preliminary investigations of peptides that orig-
MACROMOLECULAR CUES
l019
inate from barnacles and oysters (Rittschof and Brown, 1986). These peptides were discovered and isolated by virtue of the creeping response evoked in predatory snails (Rittschof et al., 1983, 1984; Rittschof et al., 1986). Peptides originating from barnacles were isolated and purified from seawater containing live intact barnacles. Detection of biological activity was done with an assay which tested the creeping response observed in inexperienced predatory snails. Soluble peptides from water bathing intact oysters were isolated and purified. The bioassay used in this study measured the creeping response in snails that had been conditioned (Wood, 1968) to respond to peptides from oysters. Although the amino acid sequences of the peptides are not yet known, chromatographic, compositional, and biological properties indicate that several distinct peptides may be present (Rittschof and Brown, 1986; Rittschof et al., 1986). In addition to their biological activity in predatory" snails, the peptides isolated from barnacles and oysters have effects on the settling stage of larval barnacles. At concentrations that can be detected in field situations (2.5 #g/ liter), barnacle peptides affect the behavior and induce metamorphosis in settling stage larvae. In this respect these peptides are similar to arthropodins (Crisp and Meadows, 1962). As is the case with arthropodins, soluble but "sticky" barnacle peptides affect larval behavior and induce metamorphosis when adsorbed onto surfaces. In contrast, "sticky" oyster peptides, presented at concentrations comparable to barnacle peptides, alter larval barnacle behavior but do not induce metamorphosis. Tests of effects of these oyster peptides on larval oysters are in progress in collaboration with researchers at the University of Maryland. Thus, there is preliminary evidence that macromolecular cues may perform more than one cueing function. In the case of barnacle peptides, there is evidence for three functions: (1) prey location by predatory snails plus (2) site selection and (3) induction of metamorphosis by barnacle larvae. In the case of oyster peptides, there is evidence for two functions: (1) prey detection by predatory snails and (2) site selection in larval barnacles. It appears likely that future work will show that macromolecules that provide information concerning the presence of specific kinds of organisms are central to the physiological ecology of those organisms. Whether adsorbed to surfaces or free in solution, macromolecular cues function to transmit specific information in marine environments. The fact that many cues are proteinaceous but heat stable suggests that higher-order macromolecular structure (secondary, tertiary, and quaternary) is less important than the covalent primary structure inherent in all biopolymers. In a peptide, for example, the " R " groups of each amino acid might function unambiguously, similar to strings of letters forming words. While odor bouquets (Bardach, 1975) of smaller molecules can perform the functions of single macromolecules, there is little evidence in marine systems other than in those areas entailing relatively
1020
RITTSCHOF AND BONAVENTURA
nonspecific responses (such as feeding) that mixtures o f odors have specific cue functions. However, as is the case in insect pheromone systems, mixtures of marine secondary metabolites may have specific functions. Advantages related to specific cueing functions are inherent in the primary structure o f macromolecules, especially peptides. In many environments peptide cues have a high signal-to-noise ratio. This is because background levels o f free peptides and amino acids (Mopper and Lindroth, 1982) are low due to the biological demand for and scavenging o f organic nitrogen, Concomitantly, rapid biological uptake combined with dilution result in short signal duration. As the size of the peptide increases, the rapid decrease in the rate o f diffusion increases the potential for transport o f effective cue concentrations over relatively long distances. Should modulating molecules be present, the change in ratio o f cue to modulator in the odor plume due to differences in rates of diffusion could be used by organisms to gain information about the distance to the source. The polar, amphoteric structure o f peptides provides high solubility in water. The linear structure and polarity (amino terminal and carboxy terminal) of peptides provide potential for unambiguous information transmission. Should the peptide originate from a repeating structure such as a marine adhesive (Waite, 1983) or blood antifreeze protein (Komatzu et al., 1970), there is remarkable potential for extended slow release function. Finally, as proteins are major metabolic and structural components of all organisms, the intact molecules and their specific degradation products are available as raw materials for the evolution o f information transmission. Acknowledgments--This was supported in part by ONR N00014-78-C-0294 and in part by NIEHS ES0-1908. The authors thank the editors and reviewers for their contributions.
REFERENCES ATEMA, J. 1982. Chemical senses, chemical signals, and feeding behavior in fishes, pp. 57-101, in J.E. Bardach, J.J. Magnuson, R.C. May, and J.M. Reinhardt (eds). Fish Behavior and Its
Use in the Capture and Culture of Fishes. International Center for Living Resource Management, Manila, Philippines. ATEMA,J., and STENZLER,D. 1977. Alarm substance of the marine mud snail. Nassarius obsoletus: Biological characterization and possible evolution. J. Chem. Ecol. 3:173-187. BARDACH,J.E. 1975. Chemoreception in aquatic animals, pp. 121-132, in D.A. Denton and J.P. Coghlan (eds.). Fifth International Symposium on Smell and Taste. Academic Press, New York. BROWN,B.B., and RITTSCHOF,D. 1984. Integration of flow and chemical cue by predatory snails. Mar. Behav. Physiol. 11:75-93. BURKE, R.D. 1984. Pheromonal control of metamorphosis in the Pacific sand dollar, Dendraster excentricus. Science 225:442-443. CARR, W.E. 1967. Chemoreception in the mud snail, Nassarius obsoletus. I. Properties of stimulatory substances extracted from shrimp. Biol. Bull. 133:106-127. CARR, W.E., and GURIN, S. 1975. Chemoreception in the shrimp. Palaeomonetes pugio: Comparative study of stimulating substances in human serum. Biol. Bull. 148:380-392.
MACROMOLECULARCUES
1021
CARR, W.E., HALL, E. and GURIN,S. 1974. Chemoreception and the role of proteins: A comparative study. Comp. Biochem. Physiol. 47A:559-566. COLLINS, A.P. 1975. Biochemical investigations of two responses involved in the feeding behavior ofAcanthasterplanci (L.). II. Isolation and characterization of chemical stimuli. J. Exp. Mar. Biol. Ecol. 17:69-86. COOK, S.B., and COOK, C.B. 1975. Directionality in the trail following response of the pulmonate limpet Siphonaria alternata. Mar. Behav. Physiol. 3:147-155. CRISP, M. 1969. Studies on the behavior of Nassarius obsoletus (Say) (Mollusca: Gastropoda). Biol. Bull. 136:335-373. CRISP, D.J. 1984. Overview of research on marine invertebrate larvae, pp. 103-126, in J.D. Costlow and R.C. Tipper (eds.). Marine Biodetedoration. Naval Institute Press, Annapolis, Maryland. CRISP, D.J., and MEADOWS,P.S. 1962. The chemical basis of gregariousness in cirripedes. Proc. R. Soc. London Ser. B. 156:500-520. DERBY, C.D., and ATEMA, J. 1980. Induced host odor attraction in the pea crab Pinnotheres maculatus. Biol. Bull. 158:26-33. DERBY, C.D., CARR, W.E., and ACHE, B.W. 1984. Purinergic olfactory cells of crustaceans: Response characteristics and similarities to internal pufinergic cells of vertebrates. J. Comp. Physiol. A. 155:341-349. DIMON, A.C. 1905. The mud snail Nassa obsoleta. Cold Spring Harbor. Monogr. 5:1-48. DUNHAM, P.J. 1978. Sex pheromones in Cmstacea. Biol. Rev. 58:555-583. FISHLYN, D.A., and PHILLIPS,D.W. 1980. Chemical camouflaging and behavioral defenses against a predatory seastar by three species of gastropods from the surf grass Phylospadix community. Biol Bull. 158:34-48. FORWARD, R.B., and LOHMAN, K.J. 1983. Control of egg hatching in the crab Rhithropanopeus harrisii (Gould). Biol. Bull. 165:154-166. GREENBERG, M.J., and PRICE, D.A. 1983. Invertebrate neuropeptides: Native and naturalized. Annu. Rev. Physiol. 45:271-288. GURIN, S., and CARR, W.E. 1971. Chemoreception in Nassarius obsoletus: The role of specific stimulatory proteins. Science 174:293-295. HALL, J.R., 1972. Intraspecific trail-following in the marsh periwinkle Littorina irrorata (Say). Veliger 16:72-75. HEEB, M.A. 1973. Large molecules and chemical control of feeding behavior in the starfish Asterias forbesi. Helgol. Wiss. Meeresunters. 24:425-435. HEWATT, W.G. 1940. Observations on the homing limpet Acmaea scraba. Am. Midl. Nat. 24:205208. HIDU, H. 1969. Gregarious settlement in the American oyster Crassostrea virginica Gmelin. Chesapeake Sci. 10:2185-2192. JENSEN, R.A., and MORSE, D.E. 1984. Intraspecific facilitation of larval recruitment: Gregarious settlement of the polychaete Phragmatopoma californica (Fewkes). J. Exp. Mar. Biol. Ecol. 83:107-126. KIRCHMAN, D., GRAHM, S., REISH D., and MITCHELL, R. 1982. Bacteria induce settlement and metamorphosis of Janua (Dexospira)basiliensis (Grebe). J. Exp. Mar. Biol. Ecol. 56:153163. KOMATZU, S.K., DEVRIES, A.L., and FEENEY, R.E. 1970. Studies of the structure of freezing point depressing glycoproteins from an antarctic fish. J. BioL Chem. 245:2909-2913. LARMAN,V.N., GABBOTT,P.A., and EAST,J. 1982. Physicochemical properties of the settlement factor proteins from the barnacle Balanus balanoides. Comp. Biochem. Physiol. 72B:329338. MAGNUM, C.P., and Cox, C.D. 1966. A feeding response to chemical stimuli in the onuphid polychaete Diopatra cuprea. Am. Zool. 6:546-547. MCCLEAN, R.B. 1974. Direct shell acquisition by hermit crabs from gastropods. Experientia 30:206-208.
1022
RITTSCHOF AND BONAVENTURA
M1HM, J.W., BANTA,W.C., and LOEB, G.I. 1981. Effects of adsorbed organic and primary fouling films on bryozoan settlement. J. Exp. Mar. Biol. Ecol. 54:167-179. MILLER, R.L., and TSENG, C.Y. 1974. Properties and partial purification of the sperm attractant of Tubularia. Am. Zool. 14:467-486. MITCHELL, R., and KmCItMAN,D. 1984. The microbial ecology of marine surfaces, pp. 49-56, in J.D. Costlow and R.C. Tipper (eds.). Marine Biodeterioration. Naval Institute Press Annapolis, Maryland. MOPPER, K., and LINDROTH, P. 1982. Diel and depth variations in dissolved free amino acids and ammonium in the Baltic Sea determined by shipboard HPLC analysis. Limnol. Oceanogr. 27:336-347. MORSE, D. 1984. Biochemical control of larval recruitment and marine fouling, pp. 134-140, in Marine Biodeterioration. J.D. Costlow and R.C. Tipper, (eds.) Naval Institute Press, Annapolis, Maryland. MORSE, D. 1985. Neurotransmitter-mimetic inducers of larval settlement and metamorphosis. Bull. Mar. Sci. 37:697-706. MORSE, D.E., HOOKER, N., DUNCAN, H., and JENSEN, L. 1979. 3,-aminobutyric acid, a neurotransmitter, induces planktonic abalone larva to settle and begin metamorphosis. Science 204:405-410. MORSE, D.E., TEGNER, M., DUNCAN,H., HOOKER,N., TREVELYAN,G. and CAMERON,A. 1980. Induction of settling and metamorphosis of planktonic molluscan (Holiotis) larvae. III. Signaling by metabolites of intact algae is dependent on contact, pp. 67-86, in D. M~iller-Schwarze and R.M. Silverstein (eds.). Chemical Signals: Vertebrates and Aquatic Invertebrates. Plenum Press, New York. RITTSCHOF, D. 1980a. Enzymatic production of small molecules attracting hermit crabs to simulated gastropod predation sites. J. Chem. Ecol. 6(4):665-675. RITTSCHOF, D. 1980b. Chemical attraction of hermit crabs and other attendants to gastropod predation sites. J. Chem, Ecol. 6:103-118. RITTSCHOF, D. 1985. Oyster drills and the frontiers of chemical ecology: Unsettling ideas. Bull. Amer. Malac. Union. Spec. Ed. 1:111-116. R1TTSCHOF, D., and BROWN,A.B. 1986. Modification of predatory snail chemotaxis by substances in bivalve prey odors. Malacology. In press. RITTSCHOF, D., WILLIAMS,L.G., BROWN, B., and CARRIKER,M.R. 1983. Chemical attraction of newly hatched oyster drills. Biol. Bull. 164:493-505. RITTSCHOF, D., SHEPHERD, R., and WILLIAMS, L.G. 1984. Concentration and preliminary characterization of a chemical attractant of the oyster drill, Urosalpinx cinerea. J. Chem. EcoL 10:63-79. RITTSCHOF, D., FORWARD,R.B., JR., and MOTT, D.D. 1985. Larval release in the crab Rhithropanopeus harrisii (Gould): Chemical cues from hatching eggs. Chem. Senses. 10:567-577. RITTSCHOF,D., SHEPHERD,R,G., and WAr,D, E. 1986. Characterization of peptides that attract oyster drills to barnacle and oyster prey. In preparation. SHELTON, R.G., and MACKIE, A.M. 1971. Studies on the chemical preferences of the shore crab, Carcinus maenas (L). J. Exp. Mar. Biol. Ecol. 7:41-49. SCHEUER, P.J. 1977. Chemical communication in marine invertebrates. Bioscience 27:664-668. SNYDER,N.F. 1967. An alarm reaction of aquatic gastropods to intraspecific extract. Cornell Agric. St. 403:1-122. STRATHMANN,R.R., BRANSCOMB,E.S., and VEDDER,K. 198t. Fatal errors in set as a cost of dispersal and the influence of intertidal flora on set of barnacles. Oecologia 48:13-18. TRAPIDO-ROSENTHAL, H.G., and MORSE, D.E. 1985. L-c~, c0-Diamino acids facilitate induction of settlement and metamorphosis in larvae of a gastropod mollusc (Haliotis rufescens). J. Comp. Physiol. B. 155:403-414. TROTT, T.J., and DIMOCK, R.V., JR. 1978. Intraspecific trail following by the mud snail, lilyanassa obsoleta. Mar. Behav. Physiol. 5:91-101.
MACROMOLECULAR CUES
1023
VAN HAFTEN,J.L., and VERWAY,J. 1958. The role of water currents in orientation in marine animals. Ext. Arch. Neederland. Zool. 13:493-499. WAITE, J.H. 1983. Evidence for a repeating 3, 4-dihydroxyphenylalanine- and hydroxyprolinecontaining decapeptide in the adhesive protein of the mussel, Mytilus edulis L. J. Biol. Chem. 258:2911-2915. WELLS, M.J., and BUCKLEY,S.K. 1972. Snails and trails. Anim. Behav. 20:345-355. WILLIAMS, L.G., RITTSCHOF, D., BROWN, B., and CARRIKER, M.R. 1983. Chemotaxis of oyster drills Urosalpinx cinerea to competing prey odors. Biol. Bull. 64:536-548. WILSON, E.O. 1970. Chemical communication within animal species, pp. 133-155, in E. Sondheimer and J.B. Simeone (eds.). Chemical Ecology. New York, Academic Press. WOOD, L. 1968. Physiological and ecological aspects of prey selection by the marine gastropod Urosalpinx cinerea (Prosobranchia: Muricidae). Malacologica 6:26%320. WOOLLACOTT,R.M. 1984. Environmental factors in bryozoan settlement, pp. 149-154, in J.D. Costlow and R.C. Tipper (eds.). Marine Biodeterioration. Naval Institute Press, Annapolis, Maryland. ZIMMER-FAUST, R.K., MmHEL, W.C., TYRE, J.C., and CASE, J.F. 1984. Chemical induction in California spiny lobster, Panulirus interruptus (Randall): Responses to molecular weight fractions of abalone. J. Chem. Ecol. 10:957-971.
