Evolution of specialization and ecological character displacement: metabolic plasticity matters.

An important question in evolutionary biology, especially with respect to herbivorous arthropods, is the evolution of specialization. In a previous paper, the combined evolutionary dynamics of specialization and ecological character displacement was studied, focusing on the role of herbivore foraging behaviour. In this paper, the robustness of these results is examined with respect to the assumption about the (metabolic) feeding efficiency function, changing it from a fixed to a plastic response. For part of the parameter space, the model yields qualitatively similar results: adaptive radiation of a herbivore population on a gradient of plant species into many specialized phenotypes through evolutionary branching, for basically any level of sub-optimal foraging (where plant utilisation is to some degree determined by the relative growth rate on each plant type). However, for an increased cost for specialization, the model loses its primary evolutionary equilibrium point. In this part of parameter space there is run-away selection towards the ultimate generalist strategy. Under the conditions for evolutionary branching, the model predicts host race formation and sympatric speciation in herbivorous arthropods when mating is host-plant associated.