Theoretical aspects of sexual selection: Variation in threshold of female mating response

Abstract

Two different models of mating behaviour may give rise to sexual selection of male phenotypes (O’Donald 1977, 1978). Some females may differ in the thresholds at which they respond to the courtship of different males. The males may also differ in the intensity of their courtship and thus stimulate the females to mate after longer or shorter periods of courtship. Both of these mechanisms give rise to similar formulations of the males’ probabilities of mating. Suppose some females have lower thresholds of response to the particular male phenotypes they prefer to mate with. They only mate with other males after having been stimulated to the level of a higher threshold: they need more courtship before mating with another phenotype of male. Thus they express their mating preference by encountering one of the males they prefer before they have been stimulated to the level of the higher threshold. At the higher threshold they mate at random among the males. We can thus describe female mating preferences in the terms of this model. O’Donald (1978) analysed models in which proportions of females have preferences towards different genotypes or phenotypes. In these models, the same number, n, of extra encounters suffices to raise the females’ level of stimulation from the lower to the higher threshold, irrespective of the genotype or phenotype the females prefer. But if the thresholds vary between females with different preferences, the number of the extra encounters will also vary. If proportions, a and y of the females prefer male phenotypes A and B respectively, then the overall frequencies of matings with these males will be as follows: