- Email: [email protected]
Evolutionary and ecological parasitology: A changing of the guard?
POINTS
IN QUESTION
ry ad Ee A Chsqing The intricate relationship between parasites and evolutionary biology (.4merican Naturalist, Ecology, their hosts has fascinated generations of biologists. Evolution, and Journtrl of Animal Ecofogy) and Parasites display an amazing array of biochemical, calculated the annual percentage of publications physiological, morphological and behavioural adap- whose main focus was some facet of parasitism. tations to their lifestyle, and the biology of hosts Special issues devoted to a single topic were excluded, has in turn been shaped to some extent by their as were papers on parasitoids since the study of these interaction with parasites. Host-parasite associaorganisms has traditionally been handled by entomologists and not pa.rasitologists. For the same tions reflect a long history of co-evolution, during which the ecology of the parasite was strongly period (1970-1993), I also surveyed the 3 main linked with that of the host. Traditionally, questions journals of parasitology (International Jaw& f&r concerning host-parasite ecology or evolution, as Parasitology, Journal of Parasitology, and Pwawell as other facets of the relationship, were sitology) and calculated the annual percentage of addressed by an ill-defined group of biologists papers focusing on either ecological or evolutionary known as parasitologists. Now, however, it seems aspects of parasitism. The results show some more or the torch is being passed on to other groups of less clear trends: the ecological/evolutionary content biologists: increasingly, ecological and evolutionary of parasitology journals increased in the early 19x0s aspects of parasitism are being studied by ecologists to reach a plateau, while the parasitological content and evolutionary biologists who had previously only of ecological/evolution,ary journals appears to be paid marginal attention to parasites. This changing presently on the rise (Fig. 1). Perhaps similar trends could be seen in the abstracts of papers presented at state of affairs has been the focus of recent popular articles (Rennie, ScientiJic American January 1992, parasitology, ecology, and evolutionary biology 258: 123-133; Holmes, New Scientist 6 November conferences over the past 20 years. Recent emphasis 1993, 140: 30-33). Some key papers appear to have in parasitology journals has been on immunology. opened the eyes of these other biologists to the parasite control and anthelminthic resistance, importance of parasites. For instance, Anderson & May’s (Journal of Animal Ecology 1978, 47: 219247; Nature 1979, 280: 361-367, 455461) models convinced many that parasites could regulate host population abundance as surely as predation, competition or abiotic factors, and Hamilton & Zuk (Science 1982, 218: 384387) took the sexual selection world by storm with their hypothesis on the role of parasites in host mate choice and the evolution of secondary sexual characteristics. Such publications brought parasites all the publicity they Year had always deserved. The “changing of the guard” in the study of Fig. 1. Trends in publications from 1970 to 1993. The percentageof parasitology articles, i.e. published in paraecological and evolutionary aspects of parasitism should be reflected by recent trends in the content of sitology journals. that address ecological/evolutionary issues (black circles) is contrasted with the percentage of journals of ecology, evolutionary biology, and ecological/evolutionaryarncles, i.e. published in journals of parasitology. I surveyed all papers published between ecology or evolutionary biology, that deal with parasites 1970 and 1993 in 4 leading journals of ecology and (open circles). 861
862
R. Poulin
biochemistry, molecular biology, taxonomy and phylogenetics; only phylogenetics relates more or lessdirectly to evolution/ecology. The trends describedabove have 2 possiblemeanings:either the focusof parasitologyhasnot followed the trends of other fields in recent years, or parasitologistsare increasinglypublishingtheir work in the journals of other disciplines.What is changing, the focusof parasitologyor that of journals?To what extent does the content of parasitology journals reflect what parasitologistsdo? The answerdepends on how one defines a parasitologist. If everyone studying parasitesqualify as parasitologists,whatever their background and where they publish their work, then the focusof parasitologyhasnot changed but its researchers are turning to new outletsfor their results.On the other hand, if we use a more strict definition of parasitologistsand include only those with a solid educational background on hostparasite interactions and who publish in journals within the discipline,then the study of ecologicaland evolutionary issuesmay be taken over by other branches of biology. My personal opinion is that there are growing numbersof biologistsnot formally trained in parasitology who realise the potential importance of parasitesin evolutionary and ecological interactions, and who join the ranks of those working on parasitism.
I sit on a fence between disciplines, working exclusively on parasitism but using approaches borrowed from ecology and evolutionary biology. While I am pleasedto seeparasitesbecominga hot topic, I also appreciatethe potential pitfalls awaiting non-specialistsventuring to study parasites. For instance,the much-citedHamilton & Zuk hypothesis of parasite-mediated sexual selection has been criticized for oversimplifying or ignoring basic parasite biology (e.g. Cox, Nature 1989, 341: 289; McLennan & Brooks, Quarterly Review of Biology 1991, 66: 255-286; Poulin & Vickery, Behavioral Ecology and Sociobiology 1993, 33: 429436). Such misconceptionsabout parasitescan lead to a whole body of theory being built upon erroneousassumptions. It is therefore essentialthat trained specialists maintain an active role in the study of the evolution and ecology of host-parasiteassociations.This may sound as a plea to parasitologists,but is rather a recommendationto ensure that evolutionary and ecological parasitology remain based on factual knowledge. ROBERT POULIN Department of Zoology, University of Otago, P.O. Box 56, Dunedin, New Zealand.
IN QUESTION
ry ad Ee A Chsqing The intricate relationship between parasites and evolutionary biology (.4merican Naturalist, Ecology, their hosts has fascinated generations of biologists. Evolution, and Journtrl of Animal Ecofogy) and Parasites display an amazing array of biochemical, calculated the annual percentage of publications physiological, morphological and behavioural adap- whose main focus was some facet of parasitism. tations to their lifestyle, and the biology of hosts Special issues devoted to a single topic were excluded, has in turn been shaped to some extent by their as were papers on parasitoids since the study of these interaction with parasites. Host-parasite associaorganisms has traditionally been handled by entomologists and not pa.rasitologists. For the same tions reflect a long history of co-evolution, during which the ecology of the parasite was strongly period (1970-1993), I also surveyed the 3 main linked with that of the host. Traditionally, questions journals of parasitology (International Jaw& f&r concerning host-parasite ecology or evolution, as Parasitology, Journal of Parasitology, and Pwawell as other facets of the relationship, were sitology) and calculated the annual percentage of addressed by an ill-defined group of biologists papers focusing on either ecological or evolutionary known as parasitologists. Now, however, it seems aspects of parasitism. The results show some more or the torch is being passed on to other groups of less clear trends: the ecological/evolutionary content biologists: increasingly, ecological and evolutionary of parasitology journals increased in the early 19x0s aspects of parasitism are being studied by ecologists to reach a plateau, while the parasitological content and evolutionary biologists who had previously only of ecological/evolution,ary journals appears to be paid marginal attention to parasites. This changing presently on the rise (Fig. 1). Perhaps similar trends could be seen in the abstracts of papers presented at state of affairs has been the focus of recent popular articles (Rennie, ScientiJic American January 1992, parasitology, ecology, and evolutionary biology 258: 123-133; Holmes, New Scientist 6 November conferences over the past 20 years. Recent emphasis 1993, 140: 30-33). Some key papers appear to have in parasitology journals has been on immunology. opened the eyes of these other biologists to the parasite control and anthelminthic resistance, importance of parasites. For instance, Anderson & May’s (Journal of Animal Ecology 1978, 47: 219247; Nature 1979, 280: 361-367, 455461) models convinced many that parasites could regulate host population abundance as surely as predation, competition or abiotic factors, and Hamilton & Zuk (Science 1982, 218: 384387) took the sexual selection world by storm with their hypothesis on the role of parasites in host mate choice and the evolution of secondary sexual characteristics. Such publications brought parasites all the publicity they Year had always deserved. The “changing of the guard” in the study of Fig. 1. Trends in publications from 1970 to 1993. The percentageof parasitology articles, i.e. published in paraecological and evolutionary aspects of parasitism should be reflected by recent trends in the content of sitology journals. that address ecological/evolutionary issues (black circles) is contrasted with the percentage of journals of ecology, evolutionary biology, and ecological/evolutionaryarncles, i.e. published in journals of parasitology. I surveyed all papers published between ecology or evolutionary biology, that deal with parasites 1970 and 1993 in 4 leading journals of ecology and (open circles). 861
862
R. Poulin
biochemistry, molecular biology, taxonomy and phylogenetics; only phylogenetics relates more or lessdirectly to evolution/ecology. The trends describedabove have 2 possiblemeanings:either the focusof parasitologyhasnot followed the trends of other fields in recent years, or parasitologistsare increasinglypublishingtheir work in the journals of other disciplines.What is changing, the focusof parasitologyor that of journals?To what extent does the content of parasitology journals reflect what parasitologistsdo? The answerdepends on how one defines a parasitologist. If everyone studying parasitesqualify as parasitologists,whatever their background and where they publish their work, then the focusof parasitologyhasnot changed but its researchers are turning to new outletsfor their results.On the other hand, if we use a more strict definition of parasitologistsand include only those with a solid educational background on hostparasite interactions and who publish in journals within the discipline,then the study of ecologicaland evolutionary issuesmay be taken over by other branches of biology. My personal opinion is that there are growing numbersof biologistsnot formally trained in parasitology who realise the potential importance of parasitesin evolutionary and ecological interactions, and who join the ranks of those working on parasitism.
I sit on a fence between disciplines, working exclusively on parasitism but using approaches borrowed from ecology and evolutionary biology. While I am pleasedto seeparasitesbecominga hot topic, I also appreciatethe potential pitfalls awaiting non-specialistsventuring to study parasites. For instance,the much-citedHamilton & Zuk hypothesis of parasite-mediated sexual selection has been criticized for oversimplifying or ignoring basic parasite biology (e.g. Cox, Nature 1989, 341: 289; McLennan & Brooks, Quarterly Review of Biology 1991, 66: 255-286; Poulin & Vickery, Behavioral Ecology and Sociobiology 1993, 33: 429436). Such misconceptionsabout parasitescan lead to a whole body of theory being built upon erroneousassumptions. It is therefore essentialthat trained specialists maintain an active role in the study of the evolution and ecology of host-parasiteassociations.This may sound as a plea to parasitologists,but is rather a recommendationto ensure that evolutionary and ecological parasitology remain based on factual knowledge. ROBERT POULIN Department of Zoology, University of Otago, P.O. Box 56, Dunedin, New Zealand.