Interaction with insects is known to drive evolution of plant diversity. However, the effects of different selective agents (such as pollinators and herbivores) tend to be studied in isolation, precluding a full understanding of how they interact to influence plant evolution. Now, a study in Science reveals that the combined presence of pollinators and herbivores alters the evolutionary trajectories of many plant traits and that plants can rapidly evolve to reduce trade-offs between different selective pressures.
Ramos and Schiestl performed experimental evolution on four different treatment groups of fast-cycling Brassica rapa plants: pollinators (Bombus terristris bumblebees) only; herbivores (Pieris brassicae caterpillars) only; both bees and caterpillars; and neither insect (the control group); with groups lacking bees pollinated by hand. After eight generations, a range of floral, defence and mating phenotypes were measured and compared between treatments. Even after this short timescale, significant differences were detected between groups. Notably, flowers that evolved in the presence of both bees and caterpillars were less attractive than those from the bee-only group but were more attractive than those from control plants. This finding suggests a trade-off between attracting pollinators and defending against herbivores, which probably involves the reallocation of resources. Consistently, bees and caterpillars also had an interactive effect on the levels of metabolites associated with plant defence. Effects on mating strategy were also observed: herbivory reduced herkogamy (the spatial separation between sexual organs) regardless of pollination method, and increased self-compatibility and autonomous mating in bee-pollinated plants. Importantly, this latter effect is probably indirect and a result of bees spending less time on caterpillar-infested plants, highlighting that evolutionary change can be elicited by altered pollinator behaviour.
plants can rapidly evolve to reduce trade-offs between different selective pressures
The demonstration that crosstalk between selective agents leads to rapid evolution of plant traits underlines the need for a more integrative approach to investigating the evolution of diversity. As the authors note, such endeavours are particularly pertinent given the increasingly wide-ranging impact we humans have on our environment.
Ramos, S. E. & Schiestl, F. P. Rapid plant evolution driven by the interaction of pollination and herbivory. Science 364, 193–196 (2019)
About this article
Cite this article
Clyde, D. Bug battles end in compromise. Nat Rev Genet 20, 319 (2019). https://doi.org/10.1038/s41576-019-0133-3