Coevolution of resistance and virulence in host-parasitoid interactions
Godfray HCJ., Fellowes MDE., Kraaijeveld AR.
Parasitoids are fascinating in their own right but are also useful as experimental systems for investigating more general questions in biology. In recent years, parasitoid biologists have made important contributions to both evolutionary behavioral ecology and chemical behavioral ecology and to population ecology. Work with parasitoids has illuminated aspects of insect physiology and development, as well as the burgeoning field of non-Mendelian genetic elements. But forty years ago, parasitoid workers were at the forefront of genetics, with large numbers of mutants of Bracon hebetor (Say) and Naso-nia (then Mormoniella) vitripennis (Walker) known, most of which are now lost. Might parasitoids again be useful model system in evolutionary genetics? Allen Orr has recently made the interesting point that much of recent population genetics has been concerned with the dynamics of deleterious or near-neutral mutants (Orr, 1998). Such alleles are abundant and relatively easy to treat analytically and of great interest in the context of the neutralistselectionist debate that has dominated so much of the subject since the mid-1960s. But many interesting questions posed in the 1930s such as the nature of the genetics of adaptations have received relatively short shrift (Orr and Coyne, 1992). Orr argues that one of the reasons for this is the difficulty of finding suitable adaptations amenable to experimentation and that parasitoid resistance in Drosophila may be an excellent model system (Orr and Irving, 1997). Other questions such as the maintenance of clinal variations and the role of arms races and community structure in natural enemy interactions may also be addressed with this system. The imminent completion of the Drosophila genome project, and the gene chip and other technologies that will come in its wake, will markedly change the way biologists go about their work, and the questions that they are able to address. This is already clear and happening for geneticists, cell biologists, and developmental biologists, for whom the arguments for working with one of the classic model organisms are becoming ever more insistent. We believe that these technical advances will have nearly as great an impact on evolutionary ecologists and will change both their modus operandi and the questions that they are able to ask. We look forward to radical advances in our understanding of the genetic basis of resource-consumer coevolution, and believe that parasitoid studies will play an important role in this adventure. We finish with an open question. Do parasitoid workers need a model organism on which to concentrate their research; a species for which a detailed genetic map is available-perhaps even a full genome sequence (those serried ranks of sequencers will need something to keep them occupied once man, mouse, fly, worm, and cress are completed!)? Should that parasitoid be one of the old genetic war horses, Nasonia or Bracon; or one about which a lot is known physiologically, Campoletis, Microplitus, or Cotesia; or one of immense economic importance, Trichogramma or Encarsia? But inevitably one would also want the host, and we do already have (surely by the time this is published) Drosophila and so is there not an overwhelming argument that we should plump for a Drosophila parasitoid, even if physiologists say it is too small and ecologists say it is too difficult to study in the field? But should it be Asobara tabida (Nees) or Leptopilina boulardi Barbotin et al.?! Copyright © by Kevin M. Heinz, Raymond E. Frisbie, and Carlos E. Bográn Manufactured in the United States of America. All rights reserved.