Infant Mortality, Paternity Certainty, and Female Reproductive Strategies in Hamadryas Baboons

Abstract

Hamadryas differ from other Papio baboons in that their social organization centers around reproductively exclusive one-male units. Infanticide and aggression toward infants are risks for hamadryas and other baboons and, as has been suggested for other primates, these risks may have played a role in shaping female baboon reproductive strategies. One way that females may reduce aggression toward (and promote protection of) infants is by increasing paternity uncertainty through promiscuity and the incitement of male contest and sperm competition. Presentations to multiple males, postcopulation darts, and copulation calling in particular have been suggested as mechanisms whereby females may incite male competition at both the pre- and postcopulatory levels. Accordingly, a coupling of infanticide risk and multiple mating by females (and the associated male competition) characterizes many baboon societies. Another, alternate route to ensure protection against infanticide and other forms of infant mortality is association and exclusive copulation with a single protective male. Paternity certainty is probably quite high among hamadryas leader males, and protective behavior toward infants has likely been selected for. Correspondingly, compared to other baboons, female hamadryas are less promiscuous, do not frequently initiate copulation, and rarely behave in ways that might incite male-male competition. We suggest that, while all baboon females use a combination of paternity concentration and confusion to varying degrees, hamadryas baboon females in particular focus on paternity concentration rather than confusion and that this can be explained by changes in male and female reproductive strategies during the evolution of hamadryas social organization.