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Reproductive seasonality is a major adaptation to seasonal cycles and varies substantially among organisms. This variation, which was long thought to reflect a simple latitudinal gradient, remains poorly understood for many species, in part due to a lacunary theoretical framework. Because seasonal cycles are increasingly disrupted by climate change, a better understanding of the ecology of reproductive seasonality could generate important insights on how climate change may affect biodiversity. The goal of this study was to investigate the drivers of evolutionary transitions towards reproductive seasonality using a realistic agent-based optimisation model simulating the life cycle of a female yellow baboon, who typically breeds year-round. Specifically, we tested the influence of three ecological traits (environmental seasonality, productivity and unpredictability) and three life-history traits (daily reproductive energy expenditure, reproductive cycle length and infant extrinsic mortality) on the intensity of reproductive seasonality. To do so, we simulated diverse reproductive phenology strategies (from non-seasonal to highly seasonal), assessed which were optimal and computed, for the set of optimal strategies, the intensity of reproductive seasonality. We then induced variation in each trait of interest and examined how it affected the intensity of reproductive seasonality. We found substantial effects of all three environmental traits: high reproductive seasonality was favoured by high environmental seasonality, low environmental productivity and low unpredictability. It was further, and most strongly, favoured by high daily reproductive energy expenditure. In contrast, there was no effect of reproductive cycle length and infant extrinsic mortality. Our modelling approach successfully disentangled the effects of environmental seasonality, productivity and unpredictability on the intensity of reproductive seasonality, which likely all contribute to generate the well-known association between latitude and reproductive seasonality. Our results further highlight the critical importance of life history pace on the evolution of reproductive seasonality. Overall, this study contributes a powerful theoretical framework and modelling tool that may apply across the life-history space, as well as sheds new light on the emergence and maintenance of non-seasonal breeding in slow-living species, including humans.

Life in social groups, while potentially providing social benefits, inevitably leads to conflict among group members. In many social mammals, such conflicts lead to the formation of dominance hierarchies, where high-ranking individuals consistently outcompete other group members. Given that competition is a fundamental tenet of the theory of natural selection, it is generally assumed that high-ranking individuals have higher reproductive success than lower-ranking individuals. Previous reviews have indicated large variation across populations on the potential effect of dominance rank on reproductive success in female mammals. Here, we perform a meta-analysis based on 444 effect sizes from 187 studies on 86 mammal species to investigate how life-history, ecology and sociality modulate the relationship between female dominance rank and fitness. As predicted, we found that (1) dominance rank is generally positively associated with reproductive success, independent of the approach different studies have taken to answer this question; and that (2) the relationship between rank and reproductive success is conditional on life-history mechanisms, with higher effects of dominance rank on reproductive output than on survival, particularly in species with high reproductive investment. Contrary to our predictions, (3) the fitness benefits to high-ranking females appear consistent across ecological conditions rather than increasing when resources decrease. Instead, we found that the social environment consistently mitigates rank differences on reproductive success by modulating female competition, with, as predicted, (4) dominant females showing higher reproductive success than subordinates in two different types of societies: first, effect sizes are highest when females live in cooperatively breeding groups composed of a single dominant female and one or more subordinate females; second, they are also elevated when females form differentiated relationships which occurs when groups are composed of unrelated females. Our findings indicate that obtaining a high ranking position in a social group consistently provides female mammals with fitness benefits, even though future studies might show lower effects given various biases in the literature we were able to access, including, but not restricted to, a publication bias. They further draw a complex landscape of the level of social inequality across mammalian societies, reflected by variation in the benefits of social dominance, which appears to be shaped by reproductive and social competition more than by ecological competition.

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.

This editorial examines the impact of sex and gender on power, status, dominance, and leadership in human and mammalian societies. It emphasizes the need for collaboration between natural and social sciences to study these topics. The research combines contributions from ecology, biology, psychology, and management to gain a deeper understanding of gender inequalities and explore ways to reduce disparities. The article discusses various studies on the effects of sex and gender on power dynamics, including the role of emotional labor in women's prosocial power and the dynamics of male-female power in non-human societies. The goal is to develop a more comprehensive and interdisciplinary understanding of gender differences in power dynamics, which could contribute to empowering women. [Extracted from the article]

This article examines the impact of sex and gender on power, dominance, and leadership in human and mammalian societies. It emphasizes the similarities in the unequal distribution of power between males and females in both human and animal societies. The article highlights the need for interdisciplinary research and collaboration between natural and social sciences to gain a comprehensive understanding of these dynamics. It explores various factors that influence women's advancement to powerful positions and the evaluation of female and male leaders. The article also discusses the evolutionary origins and flexibility of intersexual dominance in mammalian societies, with a focus on lemurs. Overall, the goal of the research is to deepen our understanding of gender and sex inequalities and generate insights into reducing disparities. [Extracted from the article]

In monotocous mammals, most individuals experience the birth of a younger sibling. This period may induce losses in maternal care and can be physiologically, energetically and emotionally challenging for the older sibling, yet has rarely been studied in wild primates. We used behavioural data collected from a natural population of mandrills to investigate changes in maternal care and mother-juvenile relationship throughout the transition to siblinghood (TTS), by comparing juveniles who recently experienced the birth of a younger sibling, to juveniles who did not. We found that the TTS was associated with an abrupt cessation of the weaning process for the juvenile, and to a decrease in maternal affiliation. Juveniles' reactions were sex-specific, as males associated less with their mother, while females tended to groom their mother more often after the birth of their sibling. Despite the substantial loss of maternal care, juveniles did not show an increase in conflict or anxiety-related behaviours. This study contributes to explain why short interbirth intervals often pose a risk to juveniles' survival in monotocous primates. Our results contrast existing studies and further highlight the importance of examining the TTS in species and populations with various life histories and ecologies., Competing Interests: We declare we have no competing interests., (© 2024 The Authors.)