Does synovigeny confer reproductive plasticity upon a parasitoid wasp that is faced with variability in habitat richness?

Abstract

Understanding the factors that constrain the reproductive success of animals and their demographics requires detailed insight into the processes of resource acquisition and allocation in relation to habitat richness. Parasitoid wasp females are valuable models in this respect because their lifetime reproductive success is closely tied to host availability. Parasitoids that manufacture eggs throughout adult life (i.e. ‘synovigenic’ species) and characteristically acquire nutrients via feeding are predicted to be plastic in their allocation to egg manufacture. Using the synovigenic parasitoid wasp Venturia canescens, we tested whether this prediction holds when females are faced with variation in the availability of both hosts and food. Laboratory experiments were conducted to determine how environmental variation affects parasitoid reproductive success and the lifetime dynamics of egg load and of major nutrient types. Our results, surprisingly, show that female V. canescens lacks a significant degree of reproductive plasticity under our experimental conditions. In particular, allocation of resources to reproduction was high irrespective of host availability. We attribute this lack of flexibility to the low energy content of V. canescens' eggs and to features peculiar to the ecology of this species. Our findings shed new light on the physiological factors that constrain parasitoid lifetime reproductive success.