Search Theory and Mate Choice. II. Mutual Interaction, Assortative Mating, and Equilibrium Variation in Male and Female Fitness

I have extended the sequential search model for mate choice to include situations in which "passive" mates (males in most cases) can adjust their perceived fitness in accordance with the expected fitness from the "active" searching sex (in most cases females). For example, males may adjust the intensity of their display based on the fitnesses of searching females. Increases in adjusted male fitness are expected with increases in the average fitness of the searching females. When fitness is temporally discounted, then adjusted fitness increases with increasing discount rate. The adjusted "passive" (male) fitness will be less than the average fitness in the population of "active" (female) searchers. When the passive (male) sex shows individual variation in minimal fitness requirements they will accept in the searching active (female) mates, then the passive mates and active mates will show an assortative mating equilibrium. Similarly, if the adjustments to fitness in the passive mates depend on the perceived fitness of the opposite sex, then individuals will show assortative mating. If individuals of either sex show sustained variation in search characteristics, for example, variation in search costs, the probable number of encountered individuals, and/or the temporal onset of search, then variation in the fitness distribution in each sex can be maintained. Most behavioral sources of variation can be considered some form of informational disequilibrium.