Male competition and speciation： expanding our framework for speciation by sexual selection

Introduction Sexual selection is a powerful source of rapid evolutionary change, and there is a long-standing hypothesis that it can cause reproductive isolation. However, our understanding of speciation by sexual selection is largely limited to mechanisms by which sexual selection via female mate choice can drive divergence （i.e., when male mating signals and female preferences for those signals diversify; Panhuis et al. 2001; Maan and Seehausen 2011）. Male competition for mates--Darwin＇s second mechanism of sexual selection-can also favor rapid and dramatic phenotypic and genotypic changes, yet it has been all but overlooked in speciation research （Darwin 1859, 1871; Seehausen and Schluter 2004;