Adaptive evolution can mitigate the negative effects of temperature stress on plant-pollinator interactions

Temperature stress negatively affects various aspects of plant fitness, including plant-pollinator interactions, but whether plants can overcome these adverse effects through adaptive evolution is largely unknown. Here, we conducted a six-generation evolution experiment using fast-cycling Brassica rapa plants at ambient and elevated temperatures, with bumblebee pollination. At the end of the experiment, we re-grew the evolved genotypes at different temperatures. We phenotyped the plants and conducted pollinator bioassays to assess adaptive evolution, evolutionary trait divergence, and the evolution of heat-mediated phenotypic plasticity. We found that plants that had evolved with bumblebee pollination in both temperature regimes had higher seed set than control plants, which suffered lower seed set when evolved under elevated temperatures. We also showed that the number of flowers, a trait that largely determined plant attractiveness to bumblebees and seed set, was increased in bumblebee-pollinated plants, and so was heat-induced phenotypic plasticity in flower number. Plants that evolved with high temperature showed increased UV reflection, a stronger association between flower size and nectar content (honest signaling), and reduced scent emission. Our results show that plants that evolve under pollinator-mediated selection can mitigate at least some of the negative effects of temperature stress through adaptive evolution.