Plant phenotypic plasticity changes pollinator-mediated selection

Abstract

Many organisms change their phenotype in response to the environment, a phenomenon called phenotypic plasticity. Yet we hardly understand how such plasticity can affect biotic interactions and the resulting phenotypic selection. Here we use fast cycling Brassica rapa plants in a proof-of-concept experiment in the greenhouse to study the link between plasticity and selection. We detected strong plasticity in morphology, nectar, and floral scent in response to different soil types and aphid herbivory. We found positive selection on nectar and several morphological traits. Bumblebee-mediated selection on a principle component representing plant height, flower number, and flowering time (mPC3) differed depending on soil type and herbivory. For plants growing in richer soil, selection was stronger in the absence of herbivores, whereas for plants growing in poorer soil selection was stronger with herbivory. We showed that bumblebees visited tall plants with many flowers over-proportionally when they were rare (i.e. in plants in poor soil with herbivory), thus causing stronger positive selection on this trait-combination. We suggest that with strong plasticity under most stressful conditions, a shift in pollinator behavior may speed up adaptation to local environmental factors.