Sexual conflict in chacma baboons, Papio hamadryas ursinus: absent males select for proactive females

We argue that, in the absence of an infanticidal threat from resident males, female chacma baboons favour polyandry because it may predispose multiple males to protect their infants from infanticide by immigrant males. This assumes that the most likely sire, or principal protector, of an infant may often be absent during its period of vulnerability, thereby creating the need for additional protection. Accordingly, we found that, on average, 47% of principal protectors were absent for at least part of an infant's vulnerable period. We predicted that, to secure additional protection, females should attempt to augment the paternity estimates of as many males as possible and, therefore, should seek to influence overall patterns of mating. In line with this prediction, we found that females actively solicited copulations from all guarding males and did so irrespective of their rank or the underlying probability of ovulation. By these means, females were able to elevate significantly the mating success, and presumably, in turn, the estimated total paternity probabilities, of these males. The apparently indiscriminate nature of the female strategy highlights how, in species where female choice is limited, females may be forced to maximize the potential of all mating opportunities afforded them by intermale competition.