Size-selective oviposition by parasitoids and the evolution of life-history timing in hosts: fixed preferences vs frequency-dependent host selection

The influence of size-selective oviposition behaviour by parasitoids on the evolution of life-history timing in their hosts was examined using an opti mization model of a two-stage life history similar to a genetic algorithm. Host populations with varying durations of early-larval development were su bjected to selection in scenarios where parasitoids had fixed preferences f or oviposition on late-stage larvae, or those where parasitoid attack was d ependent on the relative frequencies of the two life stages present in the population. Fixed preference for oviposition on late-stage larvae caused po sitive directional selection on the duration of early-larval development. S urviving individuals remained for as long as possible in the first stage of development in order to avoid parasitoid attack. Frequency-dependent paras itoid attack, in contrast. caused maintenance of variation ih the duration of early-larval development. The influence of the fitness payoffs of differ ent life stages on the plasticity of size-selective oviposition behaviour i s discussed, as are possible implications of the model results for parasito id-host population dynamics.