Ecogenomics of indirect plant-mediated interactions in food webs up to the fourth trophic level
02 / 2011 - 02 / 2015
Plants respond to herbivory with the production of herbivore-induced plant volatiles (HIPV) that attract carnivorous enemies of herbivores. These HIPV have traditionally been studied for plant-herbivore-carnivore interactions, although it is known that they affect other community members as well. Food-web ecology has shown that plant responses to herbivory constitute a major force in structuring insect communities. Intriguingly, our recent work has shown that hyperparasitoids (4th trophic level), that lay their eggs in pupae of primary parasitoids (3rd trophic level) can exploit HIPV produced by plants (1st trophic level) in response to damage done by parasitized herbivores (2nd trophic level). Hyperparasitoids can discriminate between the plant volatiles emitted in response to parasitized herbivores versus plant volatiles emitted in response to unparasitized herbivores and thus, they can use plant cues to locate their victims, i.e. parasitoids within herbivores. We will study the mechanisms that underlie the trophic interaction network that provides hyperparasitoids with cues to locate their otherwise inconspicuous hosts and how this allows hyperparasitoids to smell reproductive success from plant-derived cues, using ~omics tools. We specifically aim to identify: (I) the nature of changes that various primary parasitoids cause in caterpillars while their larvae feed on the herbivore host and whether this leads to changes in the composition of oral secretions of caterpillars. (II) the nature of changes that oral secretions of parasitized caterpillars induce in the plants on which the caterpillars are feeding. And (III) to what level of specificity hyperparasitoids can use plant-derived cues that signal host presence to hyperparasitoids. The proposed research will be the first to address indirect plant-mediated effects that extend to the fourth trophic level in insect communities. This will be done through an ecogenomics approach. Preliminary data provide a firm basis for the proposal and constitute the first evidence that hyperparasitoids use volatile cues derived from complex interactions of their primary parasitoid host with herbivores and plants. To reveal the underlying mechanisms of this phenomenon, our proposed study will combine transcriptomic and metabolomic approaches in plants, with proteomics and metabolomics on herbivorous insects and behavioural responses of hyperparasitoids in laboratory and field assays. Transcriptomic tools that are developed for a molecular model organism (Arabidopsis thaliana) will be applied to a non-model plant (Brassica oleracea) to study the complex interaction network of an ecological community with consumers up to the fourth trophic level. Furthermore, the comparison of proteomic and metabolic changes in the oral secretions of a number of congeneric caterpillar species upon parasitism with the same parasitoid species allows us to investigate adaptations of the herbivores to parasitism. Although the two primary parasitoid species are known to attack the three herbivore species, they have distinct preference for different herbivore hosts and thereby also exert different levels of selection on adaptations of herbivore species to these parasitoids. These adaptations may be reflected in the content of their oral secretions of these caterpillars when they are attacked by parasitoids. A comparative approach on the herbivore and the plant level may reveal whether hyperparasitoids can use general cues that originate from their primary parasitoid hosts even when these are developing in different herbivore species. The studies combine laboratory studies on underlying mechanisms and field studies to verify the observed interactions in an ecological setting.