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Reproductive seasonality is the norm in mammals from temperate regions but less common at lower latitudes, where a broad diversity of reproductive phenology strategies is observed. Our knowledge of the evolutionary determinants shaping this diversity remains fragmentary and may reflect high phenotypic plasticity in individual strategies. Here we investigated the ecological determinants and fitness consequences of variation in birth timing across the annual cycle in a social primate endemic to the Congo basin, the mandrill, Mandrillus sphinx , which breeds seasonally. We further examined traits that modulate this variation within and across individuals. We used 9 years of ecological, life history and behavioural data from a natural population to characterize patterns of environmental and reproductive seasonality. We then investigated the consequences of variation in birth timing for pre- and postnatal offspring survival and maternal interbirth intervals. Finally, we studied the influence of within- (reproductive history and age) and between-individual (social rank) traits on variation in birth timing. We found that mandrills' daily foraging time varied seasonally, with greater fluctuations for subordinate than dominant females. Birth timing was plastic, as females gave birth year round without detectable consequences for postnatal offspring survival. Giving birth within the birth peak, however, decreased interbirth intervals and probability of miscarriage. Finally, reproductive history and social rank mediated within- and between-individual variation in birth timing, respectively. Specifically, females that experienced a previous reproductive failure gave birth early in the next birthing season and dominant females bred less seasonally than subordinates, which may reflect their more even access to resources across the year. Overall, the selective pressures shaping mandrill reproductive seasonality differed from a classical scenario of seasonal fluctuations in resources limiting offspring survival. A complex interplay between social and ecological factors may thus determine within- and between-individual variation in phenology strategies of tropical and gregarious mammals. • Mandrills breed seasonally in an equatorial environment. • Dominant females breed less seasonally than subordinate ones. • Interbirth intervals are minimized when giving birth inside the birth peak. • Offspring survival is not affected by birth seasonality. • Miscarriage probabilities increase when conceiving late in the mating season. [ABSTRACT FROM AUTHOR]

Recent research reveals that female reproductive competition is common and may shape the social and reproductive strategies of female mammals. This study explores the determinants and intensity of female intrasexual conflicts in a wild promiscuous primate, the chacma baboon, Papio ursinus . We tested a suite of hypotheses to assess whether female–female aggression was primarily driven by instantaneous competition for food, mates or paternal care, or aimed at reducing future competition among offspring via reproductive suppression. Behavioural data were gathered from 53 females in two groups over two contrasting 2-year periods (2005–2006, 2013–2014): the first characterized by stability in the male dominance hierarchies, the second by instability induced by several immigration events and male take-overs. In both periods, we found that sexually receptive females received high levels of aggression from other sexually receptive females, consistent with competition over mating opportunities. In the unstable period, females exchanged higher rates of aggression than in the stable period, regardless of reproductive state, but lactating females received most aggression, consistent with higher competition over social access to male partners in response to increased infanticide risk. There was no evidence that aggression between females reflected either competition over food or reproductive suppression. These findings indicate that patterns of aggression between females fluctuate with sociodemographic factors affecting sexual and social access to males and reflect reproductive competition more closely than resource competition in this promiscuous primate society. [ABSTRACT FROM AUTHOR]

In monotocous mammals (i.e. where females produce one offspring at a time), most juveniles will experience the birth of a younger sibling in their life. Transition to siblinghood (TTS) has rarely been studied in primates, although it reflects the last step in the shift of maternal investment from one offspring to the next and could thus represent a critical moment for mother–offspring conflict and sibling competition. Here, we used behavioural data on juvenile primates that had recently experienced, or not, the birth of a younger sibling to investigate changes in mother–juvenile relationships during TTS in a wild population of chacma baboons, Papio ursinus. We show that (1) mother–juvenile spatial associations remained stable; (2) mothers did not decrease their probability of initiating proximity or affiliation with their juvenile; and (3) juveniles initiated proximity and affiliation more frequently towards their mothers, and showed more signs of anxiety, after the birth of their younger sibling. Taken together, these findings suggest that juveniles with a younger sibling solicit their mother more often and seek more maternal attention than juveniles without. Overall, mother–offspring conflict could extend into the postweaning period, during which more subtle maternal resources, such as maternal attention, could be at stake in competitive sibling relationships. • We examine the transition to siblinghood in wild chacma baboons. • Maternal behaviour does not change following the birth of a younger sibling. • But juveniles solicit their mother more often, and show more signs of anxiety. • These results suggest that weaned siblings may compete for maternal attention. [ABSTRACT FROM AUTHOR]

Maternal strategies reflect the trade-off between offspring needs and maternal ability to invest, a concept described by the evolutionary theory of parent–offspring conflict. In mammals this conflict has often been investigated by studying weaning, the transition from maternal milk consumption to dietary independence. An investigation of individual variation in weaning can provide information on the adaptive significance of maternal strategies in relation to social and biological variables. We analysed stable nitrogen isotopes of hair samples collected from 22 mother–infant dyads in a wild population of chacma baboons, Papio ursinus , in conjunction with behavioural data on suckling, to explore the temporal dynamics of weaning, as well as the extent and determinants of individual variation in these dynamics. The weaning pattern suggested by isotope values and behavioural data were congruent. The difference between infant and mother stable nitrogen isotope values decreased faster with age in infants of low-ranking mothers, which suggests a faster progression towards weaning, perhaps due to subordinate females experiencing lower resource availability and so being less able to bear the costs of lactation over prolonged periods. Additionally, within-infant variation in stable nitrogen isotope values showed an increase with age (which was not detectable between infants), potentially highlighting the nutritional costs that weaning imposes on offspring. Our combination of isotope analysis and behavioural data from a wild population provides insight into the evolution of maternal strategies. In particular, it suggests that the quantity of care a mother can provide is affected by her rank, with subordinate females possibly not able to lactate for as long and perhaps benefiting from weaning earlier. • Time to weaning may depend on maternal and offspring characteristics • Stable isotope signatures can characterize the weaning process • In baboons, offspring of low-ranked mothers moved towards weaning more quickly • Stable isotope analysis may show signs of nutritional stress in weaning infants • Social environment can influence the weaning process and maternal strategies [ABSTRACT FROM AUTHOR]

Animals living in groups will profit most from sociality if they coordinate the timing and nature of their activities. Self-organizing mechanisms can underlie coordination in large animal groups such as insect colonies or fish schools, but to what degree these mechanisms operate in socially complex species that live in small stable groups is not well known. We therefore examined the collective departure of wild chacma baboons, Papio ursinus, from their sleeping sites. First, in line with previous observations, the departure process appeared to be coordinated through the cue of individuals ‘moving off’, with no role for specific vocal or visual signalling. Second, we employed network analyses to explore how interindividual relationships influenced departure patterns, and found that a local rule, to follow the movements of those baboons with whom they shared a close social affiliation, determined when the baboon group departed. Finally, using an agent-based model, we were able to simulate mathematically the observed patterns of collective movements based upon the emergent rule that we identified. Our study adds weight to the idea that social complexity does not necessitate cognitive complexity in the decision-making process, consistent with heuristic decision-making perspectives studied by cognitive psychologists and researchers studying self-organization in biological systems. [ABSTRACT FROM AUTHOR]

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. • Males and fertile females show increased affiliation after aggression. • The strength of the dyadic social bond does not predict postconflict affiliation. • Postconflict affiliations are most frequent in dyads involving coerced females. • A majority of postconflict affiliations are sexual, and mostly initiated by females. • Postconflict affiliation can be submissive in asymmetric relationships. [ABSTRACT FROM AUTHOR]

Male aggression towards females is a common and often costly occurrence in species that live in bisexual groups. But preferential heterosexual relationships are also known to confer numerous fitness advantages to both sexes—making it of interest to explore how aggression is managed among male–female dyads through strategies like reconciliation (i.e. postconflict affiliative reunions between former opponents). In this study, we build on the traditional postconflict matched-control (PC-MC), time rule and rate methods to validate a novel methodological approach that tests for the presence and form of reconciliation between male and female wild chacma baboons, Papio ursinus. We show that heterosexual opponents exhibit friendly postconflict reunions, further demonstrating that reconciliation occurs almost exclusively between males and pregnant/lactating females who form tight social bonds. Such 'friendships' represent stable associations offering proximate and ultimate benefits to both parties—mainly improving (future) offspring survival. This aligns our findings with the 'valuable relationship hypothesis', which predicts rates of reconciliation to increase with the fitness consequences of the opponents' bond. Moreover, patterns concerning the initiative to reconcile reveal that males are as likely as females to initiate reconciliation, suggesting that males play a heretofore underappreciated role in maintaining heterosexual friendships. Beyond proposing a multivariate methodological technique applicable to other long-term observational data sets, the present research illuminates how male–female aggression in promiscuous societies may be mitigated via relationship repair strategies like reconciliation, the balance in those efforts between partners shedding new light on the mutual investment in such bonds. • Heterosexual opponents reconcile after aggression in a promiscuous primate society. • Friends but not nonfriends reconcile, backing the valuable relationship hypothesis. • Males and their female friends are equally likely to initiate reconciliation. • Males may play an underappreciated role in maintaining heterosexual friendships. • We present a novel method to study reconciliation using observational data sets. [ABSTRACT FROM AUTHOR]