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 and chacma baboons, 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 exert mate choice. 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. These results indicate that sexual intimidation is widespread in sexually dimorphic and group-living mammals, can co-occur with female mate choice, and is most costly to the most attractive females.

Socially Bonded Females Face More Sexual Coercion in a Female-Philopatric Primate

“…Similarly, the results of our path analysis did not support the 'retaliation' indirect path: female centrality did not predict rank and rank did not mediate the effect of centrality on coercion. Finally, in contrast to previous results 47 (see also Table 3) our path analysis suggested that female rank is not associated with coercion (Table 4), calling for future studies using, for example, more finegrained estimations of female rank, to clarify this association, or lack thereof.…”

“…However, unlike hamadryas baboons or bottlenose dolphins, male mandrills rarely, if ever, use overt physical restraint, sequestering or 'herding' behaviors toward females; but they rather coerce females using milder aggressive tactics. 47 While directional grooming of females toward males may be less easily enforced by males than spatial proximity, a recent study in sexually coercive chacma baboons (Papio ursinus) 7 indicates that females may regularly groom males as an appeasement strategy. 56 In mandrills, females have been occasionally observed to groom males after receiving aggression from them (NS personal observation), suggesting that a similar appeasement strategy might explain our results.…”

“…While a male mandrill might repel rivals during short mate-guarding bouts in the few days around ovulation in the mating season, he might not gain any additional benefits from protecting a female outside these bouts. Finally, given that the highest-ranking males are also the most coercive in mandrills, 47 a male would likely face high risks-regardless of his own rank-when confronting these high-ranking coercers to protect his female partner. Instead of a protective effect, we unexpectedly found that female mandrills sharing stronger bonds with their top grooming partner received more coercion from other males, but the reasons for that are not yet clear.…”

“…Previous results have shown that higher-ranking female mandrills receive significantly more male aggression and that higher-ranking males are more coercive. 47 In our models described below we therefore used both female and male rank as control variables, retrieved from the intersexual hierarchy (based on both within and between-sex interactions) because high-ranking females occasionally outrank some males. 49…”

“…Following previous results on sexual coercion in mandrills, we calculated sexual coercion, for each female-male dyad and each mating season, as the total number of male aggressive events towards the female recorded during a period starting at the male's arrival in the group that year iScience Article (for immigrant males) or at the arrival of the first immigrant male in the group that year (for resident males) and ending on the first day of the swelling phase of a female's estrus cycle. 47 Although all male-to-female aggression events during this period might not reflect exclusively sexual coercion, we grouped them under the term 'sexual coercion' throughout the manuscript because of their correlation with male mating success. 47 Conversely, we did not consider male-to-female aggression during the swelling phase as sexual coercion because it did not correlate with male mating success 47 and thus, did not fall within the definition of sexual coercion.…”