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

Specialisation into different ecological niches can participate to species divergence and co-existence in sympatry. Here, we focus on the partitioning into different timings of reproductive activities during the day, as observed in many insect species living in sympatry. We thus investigate the evolution of the reproductive activity timing of individuals within populations, using a comprehensive stochastic model, employing a Doob-Gillespie-like simulation process. We model 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 explore 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. It also shows how genetic incompatibilities fuel the differentiation among populations with divergent temporal niches, but may impair their coexistence. We then compare our results on the evolution of daily temporal niches to a previous model investigating the evolution of seasonal phenology and show the significant effect of overlapping vs. non-overlapping generations on the evolution of daily vs. seasonal niches. Our model therefore highlights male-male competition as an important factor shaping the evolution of diel niches, that may fuel sympatric speciation.