A keystone gene underlies the persistence of a food web

Matthew A. Barbour and Jordi Bascompte, Department of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland, Daniel J. Kliebenstein, Plant Sciences, University of California, Davis, Davis, CA

Background/Question/Methods
Genes encode information that determine an organism’s fitness. Yet, we do not know the extent to which genes of one species determine the persistence of interacting species in an ecological community. Here we test the effect of three plant defense genes on the persistence of an insect food web. Specifically, we used an experimental food web consisting of a plant (Arabidopsis thaliana), two species of aphids (Brevicoryne brassicae and Lipaphis erysimi), and a parasitoid wasp (Diaeretiella rapae). Interactions in this food web are partly mediated by a group of specialized metabolites called aliphatic glucosinolates. Most genetic variation in aliphatic glucosinolates is determined by loss-of-function mutations at three genes (MAM1, AOP2, and GSOH). We combined tools from genetic engineering and the structural stability of ecological communities to experimentally test the effect of these three genes on food-web dynamics.
Results/Conclusions
We found that a single allele at a single gene (AOP2) promoted coexistence by increasing the intrinsic growth rates of species across multiple trophic levels. Our discovery of a keystone gene illustrates the need to bridge between biological scales, from genes to ecosystems, to understand community persistence. In particular, our results indicate that ongoing losses of genetic diversity may induce sudden changes in the persistence and functioning of ecosystems.