Precipitation predictability drives evolution of drought tolerance in Papaver rhoeas

Current climate change leads to an increase in the frequency and intensity of droughts and to a decreased precipitation predictability. The few studies investigating plant evolutionary responses to contrasting predictability regimes showed that intrinsic precipitation predictability shapes plant phenotypic variation, drives evolution of phenotypic plasticity, and can vary in strength and direction of selection. This suggests that the selection pressure induced by decreased precipitation predictability may lead to plants coping better with severe drought events. To investigate this unsolved question, we performed a common-garden experiment applying control, short-term and long-term drought treatments on seedlings of Papaver rhoeas (Papaveraceae) whose progenitors experienced less versus more precipitation predictability treatments for three consecutive generations. In addition, to assess whether competition modulates plant responses, half of the plants were grown together with the widespread herbaceous plant Galium album (Rubiaceae). In the presence of long drought episodes, plants whose progenitors experienced less predictable precipitation survived longer than those whose progenitors experienced more predictable precipitation. Furthermore, plants whose progenitors experienced less predictable precipitation had lower biomass, which is likely to reduce water loss via transpiration, and, across all drought treatments, they showed lower root investment. Altogether our results indicate that lower precipitation predictability promotes drought tolerance rather than a drought-avoidance strategy to their offspring. Overall, our experiment highlights that precipitation predictability is an important driver of plant evolution, potentially shifting evolutionary trajectories of plants under increasing intensity of drought events.