Toleration games: Compensatory growth by plants in response to enemy attack is an evolutionarily stable strategy

Plants are regularly attacked by enemies such as herbivores and pathogens. Not surprisingly, plants have evolved ways of coping with these attacks. One way is to tolerate attack and compensate for lost or damaged tissue with regrowth of additional tissue. While ecological models of plant defence are common, there has been less effort to make predictions about the evolutionary stability of tolerance.

In a study recently published in AoBP, McNickle & Evans developed an evolutionary game theoretic model of tolerance to herbivory. Plants in the model have a vector strategy which includes both root and shoot production, and herbivores in the model have a scalar strategy which is time spent foraging. The evolutionarily stable strategy (ESS) is the set of root growth, shoot growth and herbivore foraging which simultaneously maximizes all player’s fitness. The model was validated experimentally using wheat, with herbivory simulated by clipping shoots during production. The model predicted that compensatory growth was often an evolutionary stable strategy whether herbivores were above- or below-ground. Plants in the experiment followed model predictions, producing more tissue than expected based on damage. When less than 15 % of new shoots were clipped the plants were able to maintain equal fitness compared to undamaged plants. These confirmative results mean that the model can be used as a new tool to predict compensatory growth as a mechanism to tolerate herbivory.