Can Plants evolve stable Alliances with the Enemies' Enemies ?

Background/Question/Methods   Evidence is accumulating that plants betray herbivores to their predators by releasing chemical signals. Can such plant-predator alliances be expected to evolve in the face of mutant strategies expressed by individuals at each of the three trophic levels ?

Results/Conclusions   I will first show that there is genetic variation including mutants that may disrupt these alliances (e.g. plants calling for help, yet harbouring no or only few herbivores). Then, I will ask how these mutants may alter the course of evolution in tritrophic systems. The picture emerging from mathematical analysis is that alliances build up and break down due to frequency-dependent selection on plants to send (dis-)honest signals. This would imply that chemical languages of plants are not stable unless the time scale at which populations of the herbivores'enemies learn is fast enough. I will close by defending the view that populations of these enemies do not learn fast enough even when they do at the individual level. The take-home message is therefore that tritrophic systems are prone to exhibit waves of alliance build-up and break-down.