The genetics of chutes and ladders: a community genetics approach to tritrophic interactions

Abstract

Community genetics research has firmly established that intraspecific genetic variation in single populations can have large extended ecological consequences for populations and entire communities of organisms. Here, we sought to understand the bottom‐up effects of plant genetic variation on herbivore preference and performance, and the top–down control of predators on herbivores and their joint effects on plant fitness and evolution. Following three ecological genetics field experiments we detected heritable variation in plant traits that influenced both the preference and performance of a specialist weevil on Oenothera biennis. However, the weevil's preference and performance were not genetically correlated among O. biennis plant genotypes. Although predators and parasitoids were abundant, predators had no detectable effect on weevil performance because high egg and larval mortality was caused by non‐predatory factors such as intraspecific competition. Finally, neither the specialist weevil nor predators influenced plant fitness. Our results suggest that the focal tritrophic community studied here is primarily shaped by the bottom–up effects of plant genetic variation on herbivores, while top–down effects have no clear impacts on O. biennis fitness or evolution. We suggest that future studies should incorporate plant intraspecific genetic variation as a fundamental part of tritrophic interactions including their eco‐evolutionary dynamics.