Models of sexual and natural selection in polygamous species.

Abstract

The distinction between sexual selection and assortative mating is discussed. It is argued that assortative mating might evolve as a result of sexual selection. Simple models of sexual selection show that stable polymorphisms can be established by alleles with a wide range of additive and dominant effects. In more general models, the sexual selection is determined by female mating preferences depending partly on the frequencies of the preferred genotypes. However, if the mating preferences are directly proportional to the genotypic frequencies, there is no resulting selective effect on the population. When natural selection opposes the sexual selection, the ratio of the proportion of females exercising the mating preference to the natural selective coefficient determines whether a stable polymorphism can be established or not. Semler's experiments show that male sticklebacks who develop the typical red throat colour in the breeding season have a considerable sexual advantage over those who do not develop the colour. But they are at a selective disadvantage from predators. The frequency of the red males fits the model of a recessive gene maintained by a balance of sexual and natural selection.