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, and a stronger association between flower size and nectar content (honest signalling), 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.