Evolution of divergent daily temporal niches shaped by male-male competition can generate sympatric speciation

Specialisation into different ecological niches is assumed as an important driver of speciation in sympatry. Here, we focused on male-male competition fuelling population divergence, without assuming any ecological specialisation. We investigated how antagonistic interactions between males can promote divergent evolution of timings of reproductive activities during the day, as observed in some closely related insect species living in sympatry. We used a multilocus, comprehensive stochastic model to investigate the evolution of (1) the timing of reproductive activity as a quantitative trait and (2) neutral loci that may generate genetic incompatibilities among divergent individuals. We specifically explored how male-male competition for female access can generate negative frequency-dependence on the timing of reproductive activities and fuel population divergence. Our simulations in finite populations highlight the strong effect of male-male competition and operational sex-ratio on the evolution of divergent temporal niches. They also show how genetic incompatibilities promote the differentiation among populations with divergent temporal niches, but may also impair their coexistence. Our model therefore highlights male-male competition as an important factor shaping the evolution of diel niches, that may fuel sympatric speciation.