Female Promiscuity and Male Reproductive Success in Social Birds and Mammals

Abstract

The selective pressures that influence the evolution of mating systems in multimale social groups that persist throughout the breeding season may differ significantly from those that operate in one-male systems. Within this type of group, females may increase their reproductive success by mating with several males, if they can thereby induce those males to provide care for their young. Males may benefit from the presence of other males during reproduction, either through joint feeding of the young or through other cooperative activities. When males are related to each other, inclusive fitness benefits arising from the reproductive success of other males also will be important. Extending the approach of Maynard Smith (1977, 1978), I develop a model for the evolution of different mating systems within multimale groups. The analysis considers the effects on reproductive success and inclusive fitness when a male either shares mates with other males, or leaves the group and attempts to breed elsewhere. The model suggests that when promiscuity is advantageous to the female, a male should not interfere with copulations by other males when male-male cooperation is important to the survival of the young, and when subordinate males are likely to leave the group if prevented from breeding. Males should attempt to monopolize matings with a female when subordinate males are closely related to the breeders, and when they have a low probability of finding new mates if they leave the group.