Contexts and consequences of takeovers in hamadryas baboons: Female parity, reproductive state, and observational evidence of pregnancy loss.

Abstract

The evolutionary consequences of sexual selection and sexual conflict are epitomized in the hamadryas baboon, a species characterized by strong sexual dimorphism and intense male-male competition. Hamadryas males coerce individual females into reproductively exclusive one-male units via aggressive takeovers, and infants involved in such takeovers are at least four times more likely to be killed (or otherwise die) after takeovers compared to other times. Here we examine female reproductive state before and after takeovers to further investigate the determinants of takeovers and their impact on female reproduction. Our data set consists of 162 takeovers over a period of 20 years in a population of wild hamadryas baboons at Filoha, Ethiopia. Results show that, in contrast to their polygynandrous relatives, hamadryas males show no bias with regard to female reproductive state at the time of the takeover, but are more likely to take over nulliparous compared to multiparous females. In addition, these results reinforce previous findings demonstrating the high likelihood of infant loss after hamadryas takeovers and suggest that females may use an additional strategy of pregnancy termination to curtail investment in offspring that are very likely to die anyway. Thus, hamadryas males may target females with high future reproductive value and hamadryas females may employ counterstrategies to help mitigate the effects of sexual coercion and infanticide on their own fitness.