Some population genetic models combining sexual selection with assortative mating

Abstract

Sexual selection can be defined in terms of mating preferences which favour particular genotypes or phenotypes and which are expressed at the same level in all females without any degree of assortment in the matings. In this paper, population genetic models are analysed in which assortative mating is combined with sexual selection. If separate mating preferences for each of three genotypes at a locus give rise to sexual selection and if each genotype may also mate assortatively, then a wide range of conditions entails the establishment of a unique, globally stable equilibrium which coincides with the equilibrium for assortative mating alone. Under certain other conditions, however, one of two different stable equilibria will be established dependent on the parameters of both sexual selection and assortative mating. This multiplicity of equilibria cannot arise in models involving either sexual selection or assortative mating alone. If females prefer either dominant or recessive phenotypes, then the advent of sexual selection prohibits the fixation that would occur by assortative mating alone: the effect of sexual selection is to ensure that a globally stable equilibrium will be established. In the combined model, therefore, sexual selection for a dominant trait exerts a greater effect on the final outcome than assortative mating. However, in contradistinction to the model with dominance, assortative mating usually determines the outcome when genotypes are preferred and assort separately.