THE COEVOLUTION OF HOST-RESISTANCE AND PARASITOID VIRULENCE

Host-parasitoid interactions are abundant in nature and offer great sc ope for the study of coevolution. A particularly fertile area is the i nteraction between internal feeding parasitoids and their hosts. Hosts have evolved a variety of means of combating parasitoids, in particul ar cellular encapsulation, while parasitoids have evolved a wide range of countermeasures. Studies of the evolution of host resistance and p arasitoid Virulence are reviewed, with an emphasis on work involving D rosophila and its parasitoids. Genetic variation in both traits has be en demonstrated using isofemale line and artificial selection techniqu es. Recent studies have investigated the fitness costs of maintaining the ability to resist parasitoids, the comparative fitness of flies th at have successfully defended themselves against parasitoids, and the degree to which resistance and virulence act against one or more speci es of host or parasitoid. A number of studies have examined geographic al patterns, and sought to look for local adaptation; or have compared the traits across a range of species. Finally, the physiological and genetic basis of change in resistance and virulence is being investiga ted. While concentrating on Drosophila, the limited amount of work on different systems is reviewed, and other possible areas of coevolution in host-parasitoid interactions are briefly discussed.