Anthocyanin Impacts Multiple Plant-Insect Interactions in a Carnivorous Plant

AbstractAlthough there are many hypothesized ecological functions of plant coloration, they have been only partly resolved by examining ecological hypotheses in isolation. Multiple ecological interactions may act in concert or in opposition to fix or maintain variation in plant coloration, that is, via ecological pleiotropy. To investigate the adaptive value of red plant pigment (anthocyanin) in a carnivorous plant, we compared insect prey capture, herbivore damage, and recruitment of specialist insect larvae in naturally occurring sympatric red and green color morphs of the pitcher plant Sarracenia purpurea. We integrated field and laboratory bioassays, visual modeling, chemical analysis of anthocyanins, and a long-term demographic study to investigate multiple ways anthocyanins mediate plant-insect interactions. In support of ecological pleiotropy, each morph performed better in one or more ecological contexts, providing evidence for ecological interactions exerting opposing selection on plant color and thus maintaining variation. The mixture of both ecological benefits and costs to anthocyanin production is further supported by stable color polymorphism and seed set data consistent with balancing selection. More broadly, this work reveals the impacts of a single anthocyanin compound on multiple key plant-insect interactions, demonstrating evidence for ecological pleiotropy maintaining intraspecific diversity in plant color.