Can plants evolve tolerance mechanisms to heterospecific pollen effects? An experimental test of the adaptive potential in Clarkia species

Flowering plants do not occur alone and often grow in mixed-species communities where pollinator sharing is high and interactions via pollinators can occur at pre- and post-pollination stages. While the causes and consequences of pre-pollination interactions have been well studied little is known about post-pollination interactions via heterospecific pollen (HP) receipt, and even less about the evolutionary implications of these interactions. In particular, the degree to which plants can evolve tolerance mechanisms to the negative effects of HP receipt has received little attention. Here, we aim to fill this gap in our understanding of post-pollination interactions by experimentally testing whether two co-flowering Clarkia species can evolve HP tolerance, and whether tolerance to specific HP ‘genotypes’ (fine-scale local adaptation to HP) occurs. We find that Clarkia species vary in their tolerance to HP effects. Furthermore, conspecific pollen performance and the magnitude of HP effect...