The influence of female viability differences on the evolution of mate choice

When females choose a mate, they may do so on the basis of some arbitrary character or they may prefer a trait that provides them with some direct or indirect benefit. One class of models of female choice, collectively referred to as the 'handicap principle', states that preferred ornaments act as markers of underlying heritable male fitness. 'Handicap' models have proved to be of great importance in explaining how female mating preferences can coevolve with male ornaments by an augmented form of the 'Fisherian process'. We suggest that differences in heritable female (Darwinian) fitness might affect the evolution of female mating preferences. Although little experimental evidence currently exists, it is entirely plausible that female fitness affects the expression of mating preferences. For example, fitter females might undertake more rigorous searches for rare, preferred males. In order to determine whether differences in female fitness can influence sexual selection by female choice, a model is presented in which mating preferences are more likely to be expressed by females of higher fitness. Results of the model show how specific female preferences for arbitrary, disadvantageous male characters can easily evolve, even if choice itself is costly. In many of these cases, the Fisherian process alone would not be sufficient to cause coevolution of preference and preferred character. Polymorphisms in male characters may also be maintained in the fitter female models. Some of the models show extreme and unusual fluctuations in the frequencies of male characters and female preferences before equilibrium is reached. Differences in female fitness may have important influences on sexual selection by female choice.