Abstract. When species overlap with each other in space and time behavioral barriers to gene flow can act as isolating mechanisms to allow species to remain separated. An effective category of isolating mechanisms is “premating isolation”. This often involves mate choice decisions, in which the choosing sex, generally the female, discriminates between males of the incipient species based upon their traits. In general, such mating can generate sexual selection, and evolutionary force akin to natural selection, in which males with certain characteristics have greater mating success than males with other characteristics.
Because closely related species that are in geographic proximity or contact often differ showy male characters that are involved in mate choice, it has often been supposed that sexual selection can be a driving force in the speciation process. The plausibility of this hypothesis can be tested using mathematical models. I will present two different major mechanisms of mate choice that differ in the basis of how preferences are determined. By showing how the action of sexual selection differs under these mechanisms, I will explain when each mechanism is, or is not expected to promote trait divergence between species, as well as reproductive isolation.