Models of sexual and natural selection in polygamous species

Abstract

SUMMARYThe 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.

Models of selective mating and the initiation of the Fisherian process

“…While previous studies of absolute preference in polygamous populations (e.g. O'Donald 1973;Bell 1978;Karlin 1978;Andersson 1982;Maynard Smith 1985) could either follow the evolution of the secondary sexual trait, assuming that the associated preference does not evolve, or study the joint evolution of the traits only numerically, the present paper provides a complete coevolutionary analysis that is not constrained to a simulation study. It also generalizes the previous treatments by allowing the probability, m 2 , of selective mating to vary, and more importantly, this seems to be the first to show in explicit terms that the absolute preference model alone can cause the initiation of a Fisherian process.…”

“…It seems, however, that this may in part be an artifact due to the unrealistic nature of the absolute preference model. Its mathematical properties are also discussed in detail by O'Donald (1973). With this mating rule the males take part in the same number of preferential matings when they are rare as when they are common (see equation (2)); individually, therefore, they mate more often when they are rare.…”

“…15;Svensson 1996 for a review). It should also be noted that the mating rule has a formal resemblance to ordinary assortative mating (O'Donald 1973;Karlin 1978). It has been argued that assortative mating or interaction of individuals occurs in socially or spatially structured populations (e.g.…”

“…While this model was rather rarely employed in the analyses based on polygamous mating (Bell 1978;Andersson 1982;Maynard Smith 1985; see also Karlin 1978), the special case m 2 = 1 has been the standard rule under monogamy (Bell 1978;O'Donald 1980;Andersson 1982Andersson , 1986. Although this rule may lead to an unrealistic situation such as an extreme monopolization of mates by a very small number of individuals (O'Donald 1973;Maynard Smith 1985) some empirical backgrounds have also been reported (O'Donald 1977b; see also § 3).…”

“…With this mating rule preferring individuals choose mates with the ornament with a certain probability m 2 (0 m 2 1), and mate randomly with a probability 1 − m 2 ; hence m 2 designates the strength of the preference. O'Donald (1973) employed this mating rule to study the evolution of the male ornament in polygynous populations. While this model was rather rarely employed in the analyses based on polygamous mating (Bell 1978;Andersson 1982;Maynard Smith 1985; see also Karlin 1978), the special case m 2 = 1 has been the standard rule under monogamy (Bell 1978;O'Donald 1980;Andersson 1982Andersson , 1986.…”