Journal o f Chemical Ecology, VoL 8, No. 7, 1982
Letter to the Editor
IS K A I R O M O N E A V A L I D A N D U S E F U L T E R M ?
Since it was first proposed by Brown et al. (1970), the term " k a i r o m o n e " has been the subject of criticisms but also has found warm supporters. Most of the debate has been summarized by Weldon (1980), who advocated its maintenance in the nomenclature of chemical ecology. However, as Weldon missed my own criticisms of the term (Pasteels, 1973, 1976), I would like to repeat them here and answer some of Weldon's arguments without necessarily developing all the issues already discussed by him. As is the case for others (see Weldon, 1980, for detailed literature), I feel uneasy with the term for two main reasons. First, I cannot agree with its present definition, and second, I am unsure of its usefulness. Kairomone was defined by Brown et al. (1970) as "a transpecific chemical messenger, the adaptative benefit of which falls on the recipient rather than on the emitter." They immediately added: "Kairomones are, in fact, commonly nonadaptive or maladaptive to the transmitter." I cannot subscribe to this definition and above all to the last statement, which I find unsound on biological grounds. To take a caricatural analogy, it would be equivalent to say that since mosquitoes and fleas like human blood, blood is nonadaptive or maladaptive to man. Most of the compounds used by predators or parasites to find their prey or host have obvious adaptive value, e.g., as pheromones or allomones, as already pointed out by Blum (1974, 1977, 1980). Even if the adaptive value is not obvious, as for incidental metabolites, the compounds are more than often the result of metabolic processes which are adaptive. Besides, if maladaptive at the individual level, "kairomones" could still be adaptive at kin or any kind of supraindividual level and thus be selected through kin or other kinds of cooperative selection. Indeed, adaptive value is very hard to measure, most of the time multidimensional, and certainly cannot be judged on the basis of a single interaction. On pure logic, I am inclined to say that so-called "kairomones" are in fact, most of the time, globally not maladaptive. If so, they would be eliminated through selection. Many predator-prey or host-parasite interactions are, however, rather stable. In particular, very specific interactions, 1079 0098-033 t / 82/0700-1079503.00/0 9 1982 Plenum Publishing Corporation
1080
LETTER TO THE EDITOR
which are those mediated by specific signals (i.e., "kairomones"), are characterized by great stability. Thus if kairomone is to be kept in the nomenclature of chemical ecology, it should be defined without any reference to its "maladaptive" value to the emitter. A definition like a chemical cue used by some organisms to exploit others would be acceptable. Even with such a definition, is kairomone an useful term? This is of course a much more subjective question. As in all kinds of classification, there are "splitters" and "lumpers." I am a lumper. Weldon (1980) defended the usefulness of kairomone as opposed to allornone (sensu Nordlund and Lewis, 1976) for two main reasons. First, Weldon advocated that "the d i s t i n c t i o n . . , is a real and useful one since it amounts to specifying who has taken the adaptive measure, the emitter or the receiver." I am not convinced by the argument. To take another caricatural analogy, we do not feel it is necessary to adaptively differentiate a digestive tract when considering that it is adapted to digest a prey, or when considering that a parasite has been adapted to live and reproduce in it. Since this holds, of course, for any kind of structure and organ, why not for chemicals? Moreover, as recognized by Weldon, a third term now must be added ("synomone," Norlund and Lewis, 1976) for chemicals mediating mutualistic interactions. I am afraid that by adding more terms, we render chemical ecology more confusing for the nonspecialists, even biologists, without necessarily rendering it more clear for the specialists. Secondly, Weldon found the distinction between kairomones and allomones to be heuristic since "making distinctions between them demands precise consideration of the interactions betweeen organisms and the consequences for participants." On the contrary, I believe that a narrow labeling of a compound could obscure its real ecological meaning by giving too much emphasis to a single interaction. Duffey (1976) has listed 46 different terms already used to designate chemical interactions between organisms, and he missed 11 terms proposed by Kirschenblatt (1962). Also, Dindal (I 975) listed, from the literature, 26 terms used to specify different types of interindividual relationships, many of them possessing synonyms, and he further divided these terms into subcategories with still other names. Not surprisingly, there is no simple parallelism between the two classifications! We badly need simplicity and stability for the nomenclature of chemical ecology, and it is time to strive for some international agreement, remembering that no classification can be perfect. Being a lumper, I am inclined to use "allomone" for all interspecific signals as opposed to "pheromone" which designates intraspecific signals. To cover both, as well as chemical signals coming from the abiotic environment, I
LETTER TO THE EDITOR
1081
advocate the use of the term "ecomone," first coined by Florkin (1965; see also Florkin and Schoffeniels, 1969, and Pasteels, 1977). Ecomone is used here as a synonym of semiochemical (Law and Regnier, 1971), a term better known by the Anglo-Saxon scientists. My only preference for ecomone (which has priority) is that is does not need to be translated into a foreign language. After all, although English is becoming the main language for scientific literature, teaching is still performed in national languages. As I state above, several of my arguments are more subjective than objective, and I am ready to change my mind and attitude for the sake of stability, if a general consensus could be reached. JACQUES M. PASTEELS Collectif de Bio-dcologie
Facultd des Sciences UniversitO libre de Bruxelles 1050 B r u s s e l s , B e l g i u m
REFERENCES BLUM, M.S. 1974, Deciphering the communicative Rosetta stone. Bull. Entomol. Soc. Am. 20:30-35. BLUM, M.S. 1977. Behavioural responses of Hymenoptera to pheromones and allomones, pp. 149-167, in H. H. Shorey and J.J. McKelvey Jr. (eds.). Chemical Control of Insect Behavior: Theory and Application. Wiley & Sons, New York. BLUM, M.S. 1980. Arthropods and ecomones: Better fitness through ecological chemistry, pp. 207-222, in R. Gilles (ed.). Animals and Environmental Fitness. Pergamon Press, Oxford. BROWN, W.L., Jr., EISNER, T., and WHITTAKER, R.H. 1970. Allomones and kairomones: Transpecific chemical messengers. Bio. Sci. 20:21-22. DINDAL, D.L. 1975. Symbiosis: Nomenclature and proposed classification. Biologist 57:129-142. DUFFEY, S.S. 1977. Arthropod allomones: Chemical effronteries and antagonists. Proc. 15th Int. Congr. Entomol. Washington, D.C. pp. 323-394. FLORKIN, M. 1965. Approaches mol6culaires de l'int6gration ~cologogique. Probl~mes de terminologie. Bull. Cl. Sci. Acad. R. Belg. 51:239-256. FLORKIN, M., and SCHOFEENIELS,E. 1969. Molecular Approaches to Ecology, Academic Press, New York. KIRSCHENBLATT,J. 1962. Terminology of some biologically active substances and validity of the term "pheromone." Nature 195:916-917. LAW, J.H., and REGNIER, F.E. 1971. -Pheromones. Annu. Rev. Biochem. 40:533-548. NORDLUND, D.A., and LEWIS, W.J. 1976. Terminology of chemical releasing stimuli in intraspecific and interspecific interactions, at. Chem. Ecol. 2:211-220. PASTEELS,J.M. 1973. Ecomones: Messages chimiques des 6cosyst~mes. Ann. Soc. R. Belg. pp. 103-117. PASTEELS,J.M. 1977. Evolutionary aspects in chemical ecology and chemical communication. Proc. 15th Int. Congr. EntomoL Washington, D.C. pp. 281-293. WELDON, P.J. 1980. In defense of "kairomone" as a class of chemical releasing stimuli. J. Chem. Ecol. 6:719-725.
Letter to the Editor
IS K A I R O M O N E A V A L I D A N D U S E F U L T E R M ?
Since it was first proposed by Brown et al. (1970), the term " k a i r o m o n e " has been the subject of criticisms but also has found warm supporters. Most of the debate has been summarized by Weldon (1980), who advocated its maintenance in the nomenclature of chemical ecology. However, as Weldon missed my own criticisms of the term (Pasteels, 1973, 1976), I would like to repeat them here and answer some of Weldon's arguments without necessarily developing all the issues already discussed by him. As is the case for others (see Weldon, 1980, for detailed literature), I feel uneasy with the term for two main reasons. First, I cannot agree with its present definition, and second, I am unsure of its usefulness. Kairomone was defined by Brown et al. (1970) as "a transpecific chemical messenger, the adaptative benefit of which falls on the recipient rather than on the emitter." They immediately added: "Kairomones are, in fact, commonly nonadaptive or maladaptive to the transmitter." I cannot subscribe to this definition and above all to the last statement, which I find unsound on biological grounds. To take a caricatural analogy, it would be equivalent to say that since mosquitoes and fleas like human blood, blood is nonadaptive or maladaptive to man. Most of the compounds used by predators or parasites to find their prey or host have obvious adaptive value, e.g., as pheromones or allomones, as already pointed out by Blum (1974, 1977, 1980). Even if the adaptive value is not obvious, as for incidental metabolites, the compounds are more than often the result of metabolic processes which are adaptive. Besides, if maladaptive at the individual level, "kairomones" could still be adaptive at kin or any kind of supraindividual level and thus be selected through kin or other kinds of cooperative selection. Indeed, adaptive value is very hard to measure, most of the time multidimensional, and certainly cannot be judged on the basis of a single interaction. On pure logic, I am inclined to say that so-called "kairomones" are in fact, most of the time, globally not maladaptive. If so, they would be eliminated through selection. Many predator-prey or host-parasite interactions are, however, rather stable. In particular, very specific interactions, 1079 0098-033 t / 82/0700-1079503.00/0 9 1982 Plenum Publishing Corporation
1080
LETTER TO THE EDITOR
which are those mediated by specific signals (i.e., "kairomones"), are characterized by great stability. Thus if kairomone is to be kept in the nomenclature of chemical ecology, it should be defined without any reference to its "maladaptive" value to the emitter. A definition like a chemical cue used by some organisms to exploit others would be acceptable. Even with such a definition, is kairomone an useful term? This is of course a much more subjective question. As in all kinds of classification, there are "splitters" and "lumpers." I am a lumper. Weldon (1980) defended the usefulness of kairomone as opposed to allornone (sensu Nordlund and Lewis, 1976) for two main reasons. First, Weldon advocated that "the d i s t i n c t i o n . . , is a real and useful one since it amounts to specifying who has taken the adaptive measure, the emitter or the receiver." I am not convinced by the argument. To take another caricatural analogy, we do not feel it is necessary to adaptively differentiate a digestive tract when considering that it is adapted to digest a prey, or when considering that a parasite has been adapted to live and reproduce in it. Since this holds, of course, for any kind of structure and organ, why not for chemicals? Moreover, as recognized by Weldon, a third term now must be added ("synomone," Norlund and Lewis, 1976) for chemicals mediating mutualistic interactions. I am afraid that by adding more terms, we render chemical ecology more confusing for the nonspecialists, even biologists, without necessarily rendering it more clear for the specialists. Secondly, Weldon found the distinction between kairomones and allomones to be heuristic since "making distinctions between them demands precise consideration of the interactions betweeen organisms and the consequences for participants." On the contrary, I believe that a narrow labeling of a compound could obscure its real ecological meaning by giving too much emphasis to a single interaction. Duffey (1976) has listed 46 different terms already used to designate chemical interactions between organisms, and he missed 11 terms proposed by Kirschenblatt (1962). Also, Dindal (I 975) listed, from the literature, 26 terms used to specify different types of interindividual relationships, many of them possessing synonyms, and he further divided these terms into subcategories with still other names. Not surprisingly, there is no simple parallelism between the two classifications! We badly need simplicity and stability for the nomenclature of chemical ecology, and it is time to strive for some international agreement, remembering that no classification can be perfect. Being a lumper, I am inclined to use "allomone" for all interspecific signals as opposed to "pheromone" which designates intraspecific signals. To cover both, as well as chemical signals coming from the abiotic environment, I
LETTER TO THE EDITOR
1081
advocate the use of the term "ecomone," first coined by Florkin (1965; see also Florkin and Schoffeniels, 1969, and Pasteels, 1977). Ecomone is used here as a synonym of semiochemical (Law and Regnier, 1971), a term better known by the Anglo-Saxon scientists. My only preference for ecomone (which has priority) is that is does not need to be translated into a foreign language. After all, although English is becoming the main language for scientific literature, teaching is still performed in national languages. As I state above, several of my arguments are more subjective than objective, and I am ready to change my mind and attitude for the sake of stability, if a general consensus could be reached. JACQUES M. PASTEELS Collectif de Bio-dcologie
Facultd des Sciences UniversitO libre de Bruxelles 1050 B r u s s e l s , B e l g i u m
REFERENCES BLUM, M.S. 1974, Deciphering the communicative Rosetta stone. Bull. Entomol. Soc. Am. 20:30-35. BLUM, M.S. 1977. Behavioural responses of Hymenoptera to pheromones and allomones, pp. 149-167, in H. H. Shorey and J.J. McKelvey Jr. (eds.). Chemical Control of Insect Behavior: Theory and Application. Wiley & Sons, New York. BLUM, M.S. 1980. Arthropods and ecomones: Better fitness through ecological chemistry, pp. 207-222, in R. Gilles (ed.). Animals and Environmental Fitness. Pergamon Press, Oxford. BROWN, W.L., Jr., EISNER, T., and WHITTAKER, R.H. 1970. Allomones and kairomones: Transpecific chemical messengers. Bio. Sci. 20:21-22. DINDAL, D.L. 1975. Symbiosis: Nomenclature and proposed classification. Biologist 57:129-142. DUFFEY, S.S. 1977. Arthropod allomones: Chemical effronteries and antagonists. Proc. 15th Int. Congr. Entomol. Washington, D.C. pp. 323-394. FLORKIN, M. 1965. Approaches mol6culaires de l'int6gration ~cologogique. Probl~mes de terminologie. Bull. Cl. Sci. Acad. R. Belg. 51:239-256. FLORKIN, M., and SCHOFEENIELS,E. 1969. Molecular Approaches to Ecology, Academic Press, New York. KIRSCHENBLATT,J. 1962. Terminology of some biologically active substances and validity of the term "pheromone." Nature 195:916-917. LAW, J.H., and REGNIER, F.E. 1971. -Pheromones. Annu. Rev. Biochem. 40:533-548. NORDLUND, D.A., and LEWIS, W.J. 1976. Terminology of chemical releasing stimuli in intraspecific and interspecific interactions, at. Chem. Ecol. 2:211-220. PASTEELS,J.M. 1973. Ecomones: Messages chimiques des 6cosyst~mes. Ann. Soc. R. Belg. pp. 103-117. PASTEELS,J.M. 1977. Evolutionary aspects in chemical ecology and chemical communication. Proc. 15th Int. Congr. EntomoL Washington, D.C. pp. 281-293. WELDON, P.J. 1980. In defense of "kairomone" as a class of chemical releasing stimuli. J. Chem. Ecol. 6:719-725.
