A general model of mating behaviour with natural selection and female preference

Abstract

A model is analysed in which female mating preferences are expressed partially, depending on the frequencies of the males. A female, who has been stimulated sufficiently to mate with a male of the phenotype she prefers, will only mate with another male after a certain number of extra encounters with the others. After n of these extra encounters, females with preferences mate randomly with any male. The probability that n encounters occur depends on the frequencies of the different male phenotypes. If n = 1, the mating advantage gained by the preferred males rises slightly as their frequency increases: either natural selection against the preferred phenotypes outweighs their mating advantage and they are eliminated, or they spread through the population to fixation; stable polymorphisms cannot become established. If n > 1, the mating advantage declines with increasing frequency: stable polymorphisms can exist over a range of values of the parameters of mating preference and natural selection. As n increases, the mating advantage becomes more strongly frequency-dependent and a wider range of values of parameters gives rise to stable polymorphisms. When n > 5, the results are very close to those of models in which mating preferences are always expressed. The rates of selection and equilibrium frequencies are the same for preferred characters determined either by dominant or by recessive alleles. In the models the preferred character is either sex-limited and expressed only in males or expressed in both sexes. If it is expressed in both sexes, the effect of natural selection is doubled, and twice as many females must have the mating preference before the preferred character may start to spread through the population.