Evolution of female choosiness and mating frequency: effects of mating cost, density and sex ratio

Abstract

Choice for mate quality and number of mates are key components of female mating strategies. We investigated how selection on female choosiness also influences number of matings in various ecological conditions. In our individual-based model, females choose their first mate according to an evolving acceptance threshold and then mate with males of increasing quality (trade-up choice). We simulated evolution of this threshold under various conditions of density, sex ratio and mating cost. Thresholds rapidly evolve towards a small set of values that depend on the tested parameters. Consistent with intuitive predictions, choosier females are selected when either number of encounters with males or mating cost is high. Selection results in most females sharing the same threshold. Variation in female mating patterns remains because some variation in thresholds is maintained, at least by mutations, and because of random events affecting number of matings. Our model indicates that mating cost strongly affects evolution of female choosiness and mating frequency. Moreover, it influences the relative importance of other factors: when mating cost is low, selection on acceptance thresholds is weak and relatively more females use thresholds that differ from the norm. In that context, mate quality is therefore the most important factor affecting female reproductive success. When mating cost is high, females evolve thresholds such that both the cost of multiple mating and the risk of remaining unmated become as important as mate quality. High mating cost, by selecting for high choosiness, also leads to females mating with fewer males.