The eco-evolutionary landscape of power relationships between males and females

In animal societies, control over resources and reproduction is often biased towards one sex. Yet, the ecological and evolutionary underpinnings of male-female power asymmetries remain poorly understood. We outline a comprehensive framework to quantify and predict the dynamics of male-female power relationships within and across mammalian species. We show that male-female power relationships are more nuanced and flexible than previously acknowledged. We then propose that enhanced reproductive control over when and with whom to mate predicts social empowerment across ecological and evolutionary contexts. The framework explains distinct pathways to sex-biased power: coercion and male-biased dimorphism constitute a co-evolutionary highway to male power, whereas female power emerges through multiple physiological, morphological, behavioural, and socioecological pathways

The submissive pattern of postconflict affiliation in asymmetric relationships: a test in male and sexually coerced female baboons

Reconciliation, or postconflict (PC) affiliation between former opponents, is a widespread conflict management strategy in animal societies, so-named for its relationship repair function. However, another possibility is that PC affiliation reflects a submissive response of victims towards aggressors to limit conflict escalation when the power imbalance between the opponents is large. Here we investigated this hypothesis in a highly asymmetric relationship context: heterosexual wild chacma baboon, Papio ursinus, dyads involving sexually receptive females, where sexual coercion by males is common. We found several lines of support for the submissive hypothesis in the context of sexual coercion. First, rates of sexual and nonsexual PC affiliative interactions in these dyads exhibited significant and comparable increases compared to baseline conditions (ca. three-fold). Second, the baseline strength of the heterosexual social bond (outside of an aggressive context) did not predict the likelihood of sexual and nonsexual PC affiliation. Third, mate-guarded females, who could not escape the proximity of their aggressor (and faced high risks of renewed aggression), exhibited the most PC affiliation with males. Finally, most PC affiliation sequences contained at least one sexual act, and the first sexual affiliative act was primarily initiated by females via presenting. This suggests that female victims affiliate in a submissive way by displaying sexual compliance to aggressive males. Nevertheless, we cannot exclude the co-occurrence of ‘true’ reconciliation: a quarter of PC affiliations between males and receptive females were exclusively nonsexual, and the first general affiliative act was equally initiated by males and females. Overall, our results suggest a mixed PC affiliation strategy in which submission may play an important role in highly asymmetric relationships and indicate that the function of PC affiliation may vary from submission to reconciliation depending on the species, dyads, individuals and conflicts under consideration. Future research on PC interactions would usefully consider this full spectrum

Developmental transitions in body color in chacma baboon infants: Implications to estimate age and developmental pace

OBJECTIVES: In many primates, one of the most noticeable morphological developmental traits is the transition from natal fur and skin color to adult coloration. Studying the chronology and average age at such color transitions can be an easy and noninvasive method to (a) estimate the age of infants whose dates of birth were not observed, and (b) detect interindividual differences in the pace of development for infants with known birth dates. MATERIALS AND METHODS: Using a combination of photographs and field observations from 73 infant chacma baboons (Papio ursinus) of known ages, we (a) scored the skin color of six different body parts from pink to gray, as well as the color of the fur from black to gray; (b) validated our method of age estimation using photographic and field observations on an independent subset of 22 infants with known date of birth; and (c) investigated ecological, social, and individual determinants of age-related variation in skin and fur color. RESULTS: Our results show that transitions in skin color can be used to age infant chacma baboons less than 7 months old with accuracy (median number of days between actual and estimated age = 10, range = 0-86). We also reveal that food availability during the mother's pregnancy, but not during lactation, affects infant color-for-age and therefore acts as a predictor of developmental pace. DISCUSSION: This study highlights the potential of monitoring within- and between-infant variation in color to estimate age when age is unknown, and developmental pace when age is known

Dynamics of intersexual dominance in a highly dimorphic primate

Intersexual dominance, which is measured by the probability that members of one sex elicit submission of members of the other sex during agonistic interactions, is often skewed in favor of males. However, even in sexually dimorphic species, several factors may influence intersexual dominance. Here, we use an 8-year dataset to examine the dynamics of intersexual dominance in wild-living mandrills (Mandrillus sphinx). Mandrills exhibit an extreme male-biased sexual size dimorphism but females show pronounced kin-differentiated social relationships and occasionally form coalitions against males. We established intersexual hierarchies across consecutive 6-month time blocks, representing either mating or birth seasons. Although females appeared to outrank 11% of males, they elicited male submission in only 2% of agonistic interactions against males. This discrepancy is likely due to the temporary residency of most males in the exceptionally large mandrill groups, the sexually coercive male mating strategies and the scarce number of agonistic interactions within most dyads, that may limit hierarchical inferences. In a second step, we found that the intersexual hierarchy mixes the intrasexual ones respecting their respective order. Females outranked mostly young and old males during the mating (vs. birth) season and social integration was positively correlated to dominance status in both sexes. In a third step, we found that females win more conflicts against young or old males which are closer to them in the intersexual hierarchy. These results extend our understanding of female-male dominance relationships by indicating that female mandrills occasionally outrank males who are considerably larger than them, and that a combination of demographic and social factors can influence the intersexual hierarchy

From Parasite Encounter to Infection: Multiple-Scale Drivers of Parasite Richness in a Wild Social Primate Population

Host parasite diversity plays a fundamental role in ecological and evolutionary processes, yet the factors that drive it are still poorly understood. A variety of processes, operating across a range of spatial scales, are likely to influence both the probability of parasite encounter and subsequent infection. Here, we explored eight possible determinants of parasite richness, comprising rainfall and temperature at the population level, ranging behavior and home range productivity at the group level, and age, sex, body condition, and social rank at the individual level. We used a unique dataset describing gastrointestinal parasites in a terrestrial subtropical vertebrate (chacma baboons, Papio ursinus), comprising 662 faecal samples from 86 individuals representing all age-sex classes across two groups over two dry seasons in a desert population. Three mixed models were used to identify the most important factor at each of the three spatial scales (population, group, individual); these were then standardised and combined in a single, global, mixed model. Individual age had the strongest influence on parasite richness, in a convex relationship. Parasite richness was also higher in females and animals in poor condition, albeit at a lower order of magnitude than age. Finally, with a further halving of effect size, parasite richness was positively correlated to day range and temperature. These findings indicate that a range of factors influence host parasite richness through both encounter and infection probabilities, but that individual-level processes may be more important than those at the group or population level

Editorial: Sex and gender effects on power, status, dominance, and leadership – an interdisciplinary look at human and other mammalian societies

In human societies, men tend to have more power, status, dominance, and occupy leadership positions more often than women; similarly, in animal societies, power and dominance are often unequally distributed between males and females. Despite these similarities across societies of humans and animals, the scientific study of power, status, dominance, and leadership have (for the most part) progressed in isolation, with little cross-disciplinary exchange or fertilization between the natural and social sciences. In the social sciences, an extensive body of work has investigated the relation between gender (or sometimes sex) and power, status, dominance, and leadership outcomes (e.g., Eagly & Karau, 2002; Goldin, 2014; Eagly and Heilman, 2016; Meeussen et al., 2016; Hentschel et al., 2018; Von Rueden et al., 2018; Smith et al., 2020; Eckel et al., 2021; Shen et al., in press; Heilman et al., 2024). This effort notwithstanding, many questions remain. For example, we lack a comprehensive understanding of the contexts and circumstances that favor (or undermine) women’s advancement to powerful positions, and about why and when female and male leaders are evaluated differently (Williams and Tiedens, 2016; Cardador et al., 2022). In the natural sciences, empirical investigations in mammalian societies have primarily focused on the evolutionary origins and dynamics of male-female power asymmetries. Specifically, such investigations often focus on a few taxa with female dominance, such as bonobos, lemurs, and spotted hyenas (Kappeler, 1993; Lewis, 2018; Davidian et al., 2022; Smith et al. in this Research Topic). Notably, intersexual dominance–the distribution of power and status between the sexes—is often treated as a binary (i.e., a species is described as either male-dominant or female-dominant) and as a fixed (rather than flexible) trait of a given species (Lewis, 2018; Davidian, 2022). Contrary to this view, recent studies suggest the relative power of the sexes in some animal societies may be less biased in favor of one sex and more flexible than previously assumed (Kappeler et al.). With this Research Topic, we aim to facilitate academic exchange, to learn from perspectives that typically lie outside of each of our disciplinary boundaries, to draw comparisons and insights across these perspectives, and to promote an integrative understanding of gender and sex1 inequalities in power, status, dominance, and leadership. To do so, this Research Topic combines contributions from ecology, biology, psychology, and management. It houses a collection of 21 articles, including 10 articles from the social sciences and 11 articles from the natural sciences. We hope this trans-disciplinary Research Topic will not only deepen our understanding of the roots and origins of gender and sex inequalities in humans and non-humans, but also generate new insights into possible solutions for reducing sex and gender disparities

On automatic class insertion with overloading

Also published in Proceedings of the 11th ACM SIGPLAN conference on Object-oriented programming, systems, languages, and applications (OOPSLA)International audienceSeveral algorithms [Cas92, MS89, Run92, DDHL94a, DDHL95, GMM95] have been proposed to automatically insert a class into an inheritance hierarchy. But actual hierarchies all include overriden and overloaded properties that these algorithms handle either very partially or not at all. Partially handled means handled provided there is a separate given function f able to compare overloaded properties [DDHL95, GMM95].In this paper, we describe a new version of our algorithm (named Ares) which handles automatic class insertion more efficiently using such a function f. Although impossible to fully define, this function can be computed for a number of well defined cases of overloading and overriding. We give a classification of such cases and describe the computation process for a well-defined set of nontrivial cases.The algorithm preserves these important properties:- preservation of the maximal factorization of properties- preservation of the underlying structure (Galois lattice) of the input hierarchy- conservation of relevant classes of the input hierarchy with their properties

Red Is Not a Proxy Signal for Female Genitalia in Humans

Red is a colour that induces physiological and psychological effects in humans, affecting competitive and sporting success, signalling and enhancing male social dominance. The colour is also associated with increased sexual attractiveness, such that women associated with red objects or contexts are regarded as more desirable. It has been proposed that human males have a biological predisposition towards the colour red such that it is ‘sexually salient’. This hypothesis argues that women use the colour red to announce impending ovulation and sexual proceptivity, with this functioning as a proxy signal for genital colour, and that men show increased attraction in consequence. In the first test of this hypothesis, we show that contrary to the hypothesis, heterosexual men did not prefer redder female genitalia and, by extension, that red is not a proxy signal for genital colour. We found a relative preference for pinker genital images with redder genitalia rated significantly less sexually attractive. This effect was independent of raters' prior sexual experience and variation in female genital morphology. Our results refute the hypothesis that men's attraction to red is linked to an implied relationship to genital colour and women's signalling of fertility and sexual proceptivity

Mother-male bond, but not paternity, influences male-infant affiliation in wild crested macaques

In promiscuous primates, interactions between adult males and infants have rarely been investigated. However, recent evidence suggests that male affiliation towards infants has an influence on several aspects of the infants’ life. Furthermore, affiliations may be associated with male reproductive strategy. In this study, we examined which social factors influenced male-infant affiliation initiated by either male or infant, in wild crested macaques (Macaca nigra). We combined behavioral data and genetic paternity analysis from 30 infants living in three wild groups in Tangkoko Reserve, Indonesia. Our results indicate that adult males and infants do not interact at random, but rather form preferential associations. The social factors with the highest influence on infant-initiated interactions were male rank and male association with the infant’s mother. While infants initiated affiliations with males more often in the absence of their mothers, adult males initiated more affiliations with infants when their mothers were present. Furthermore, males initiated affiliations more often when they were in the same group at the time the infant was conceived, when they held a high dominance rank or when they had a close relationship with the mother. Interestingly, paternity did not affect male-infant affiliation despite being highly skewed in this species. Overall, our results suggest that adult males potentially associate with an infant to secure future mating with the mother. Infants are more likely to associate with a male to receive better support, suggesting a strategy to increase the chance of infant survival in a primate society with high infant mortality