Sexual coercion in a natural mandrill population

Abstract

Increasing evidence indicates that sexual coercion is widespread. While some coercive strategies are conspicuous, such as forced copulation or sexual harassment, less is known about the ecology and evolution of intimidation, where repeated male aggression promotes future rather than immediate mating success with targeted females. Although known in humans, intimidation was recently reported in chimpanzees (Pan troglodytes) and chacma baboons (Papio ursinus), where males are regularly violent against females. Here, we investigate the nature of male coercive strategies in wild mandrills (Mandrillus sphinx), a primate living in large polygynandrous groups where severe male aggression towards females is rare and females can form coalitions against males. Yet, we found support for all three predictions of the sexual coercion hypothesis, namely that male aggression (1) specifically targets sexually receptive females, (2) inflicts costs to these females, and (3) increases male mating success in the long-term. These results hold true when considering only non-physical threats, or only severe aggression. Finally, we show that high-ranking females are most targeted by males, probably because of their higher reproductive performances, while high-ranking males are most coercive. These results indicate that sexual intimidation is widespread in sexually dimorphic and group-living mammals, and that males and females vary in their propensities to use, and to be exposed to sexual coercion, respectively.

Dynamics of intersexual dominance in a highly dimorphic primate

“…In particular, when females have some reproductive control (i.e., control over when and with whom to mate), as in most lemurs (Hohenbrink et al, 2016;Lewis et al, 2022), they typically have more leverage when sexually receptive because males who try to mate with them may avoid to aggress them (Lewis, 2002;Davidian et al, 2022). Yet, additional results show that sexually receptive female mandrills are not more likely to win conflicts against males compared to females in other reproductive states, possibly because they have low reproductive control due to frequent sexual coercion (Smit et al, 2022). Instead, this result may reflect demographic changes due to the influx of male mandrills in the social group at the beginning of that season.…”

“…Regarding methodological problems, mandrills live in exceptionally large groups and in dense forests with low visibility, making it difficult to observe interactions between all group members. Additionally, intersexual aggression is characterized by relatively low severity (Smit et al, 2022) and thus it might be easily overlooked outside focal observations. As a result, a majority (62%) of the intersexual dyads in our study group were never observed interacting agonistically (Supplementary Table S1), and such proportion is highest (92%) in those dyads where the female was found to outrank the male.…”

“…While alternative methods, like Elo-rating (Neumann et al, 2011), for calculating dominance hierarchies would, in theory, be better suited to establish hierarchies in such a system, they require highly resolved interaction matrices which are far too challenging to obtain in such large groups. Finally, the frequent use of sexual coercion by high-ranking male mandrills (Smit et al, 2022) may also result in asymmetrical patterns of interactions between male-dominant and femaledominant dyads, and explain why there are lower rates of interactions-and more missing data-in female-dominant than male-dominant dyads. While males may often direct aggression to subordinate females in male-dominant dyads in a context of sexual coercion (Smit et al, 2022), females may not bother about harassing those males they outrank.…”

“…Finally, the frequent use of sexual coercion by high-ranking male mandrills (Smit et al, 2022) may also result in asymmetrical patterns of interactions between male-dominant and femaledominant dyads, and explain why there are lower rates of interactions-and more missing data-in female-dominant than male-dominant dyads. While males may often direct aggression to subordinate females in male-dominant dyads in a context of sexual coercion (Smit et al, 2022), females may not bother about harassing those males they outrank. Indeed, male-dominant dyads interact agonistically over twice as often as female-dominant ones (3.3 ± 4.8 vs. 1.6 ± 1.1 times; ±SD).…”

“…Their dominance rank increases with age, peaks from 11 to 16 and falls again after 16 years (Setchell et al, 2006b). Adult males are sexually coercive (Smit et al, 2022) and mate-guard females when they display maximally turgescent sexual swellings around ovulation (Setchell et al, 2005a). Females are philopatric and form differentiated social bonds and linear matrilineal hierarchies, with maternally inherited ranks that are relatively stable across their lives .…”