FREQUENCY OF FEMALE COPULATIONS WITH MULTIPLE MALES AND SEXUAL SELECTION

Female animals often copulate with more than a single male during one fertile period. I suggest that female propensity to engage in such multimale copulations is caused by constraints on female mate choice set by the availability of males. A simple graphic model of mate choice after formation of pair bonds suggests that the probability of female engagement in copulations with multiple males should be inversely proportional to the availability of preferred mates at the time of mate choice. This problem will be present whenever males and females establish pair bonds, and the male availability constraint on female mate choice will be more important for mating systems in which males attract only a single or few females. Monogamy thus particularly often sets the stage for sexual selection via multiple matings. Male availability to females during mate choice differs between mating systems, and the relative frequency of female copulations with multiple males should be inversely related to male availability. If females attempt to adjust their precopulatory mate choice by copulating with additional males, sexual selection resulting from choice of copulation partners should reinforce precopulatory sexual selection. Patterns of male and female extrapair copulations and patterns of extrapair paternity in birds are in accordance with this scenario.