Ar. Kraaijeveld et Hcj. Godfray, TRADE-OFF BETWEEN PARASITOID RESISTANCE AND LARVAL COMPETITIVE ABILITY IN DROSOPHILA-MELANOGASTER, Nature, 389(6648), 1997, pp. 278-280
The extent to which an organism is selected to invest in defences agai
nst pathogens and parasites depends on the advantages that ensue shoul
d infection occur, but also on the, costs of maintaining defences in t
he absence of infection. the presence of heritable variation in resist
ance suggests that costs exist, but we know very little about the natu
re or magnitude of these costs in natural populations of animals(1). A
powerful technique for identifying trade-offs between fitness compone
nts is the study of correlated responses to artificial selection(2,3).
We have selected Drosophila melanogaster for improved resistance agai
nst an endoparasitoid, Asobara tabida. Endoparasitoids are insects who
se larvae develop internally within the body of other insects, eventua
lly killing them, although their hosts can sometimes survive attack by
mounting a cellular immune response(4-6). We found that reduced larva
l competitive ability in unparasitized D. melanogaster is a correlated
response to artificial selection for improved resistance against A. t
abida. The strength of selection for competitive ability and parasitoi
d resistance is likely to vary temporally and spatially, which may exp
lain the observed heritable variation in resistance.