Ecological versus Sexual Selection Models of Sympatric Speciation: A Synthesis

Sympatric speciation is a composite phenomenon requiring both ecological differentiation and the evolution of a mating structure that induces reproductive isolation. Ecological and sexual selection models have addressed these two aspects of sympatric speciation separately. We briefly discuss the recent results of these models and argue that the evolution of ecological and mating strategies are mutually dependent processes rather than independent phenomena corresponding to incompatible views of sympatric speciation. Then, we consider a combined model incorporating ecological interactions and sexual selection. In this model, sympatric speciation is initiated by simultaneous evolutionary branching of ecological strategy, leading to ecological differentiation, and mating strategies, resulting in assortative mating. Both types of evolutionary branching can be understood as the outcome of a competition process in which individuals compete for a spectrum of either ecological resources or mating opportunities. Speciation is completed when a linkage disequilibrium between ecological and mating types splits the population into two ecologically differentiated and reproductively isolated groups. Using a combined analytical and individual-based simulation approach, we illustrate the different dynamical regimes and characterize the necessary conditions for sympatric speciation in the model.