Anthocyanin impacts multiple plant-insect interactions in a carnivorous plant

Although there are many hypothesized ecological functions of plant
coloration, they have only partly been 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,
i.e. 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 context, 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.