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International audience; 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 use behavioural data on juvenile primates who 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 association remained stable; (2) mothers did not decrease their probability to initiate proximity or affiliation with their juvenile; and (3) juveniles initiated proximity and affiliation more frequently toward 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 in the post-weaning period, during which more subtle maternal resources, such as maternal attention, could be at stake in sibling competitive relationships.

International audience; The causes and consequences of being in a particular dominance position have been illuminated in various animal species, and new methods to assess dominance relationships and to describe the structure of dominance hierarchies have been developed in recent years. Most research has focused on same-sex relationships, however, so that intersexual dominance relationships and hierarchies including both sexes have remained much less studied. In particular, different methods continue to be employed to rank males and females along a dominance hierarchy, and sex biases in dominance are still widely regarded as simple byproducts of sexual size dimorphism. However, males and females regularly compete over similar resources when living in the same group, and sexual conflict takes a variety of forms across Frontiers in Ecology and Evolution 01 frontiersin.org Kappeler et al. 10.3389/fevo.2022.918773 societies. These processes affect the fitness of both sexes, and are mitigated by intersexual hierarchies. In this study, we draw on data from free-ranging populations of nine species of mammals that vary in the degree to which members of one sex dominate members of the other sex to explore the consequences of using different criteria and procedures for describing intraand intersexual dominance relationships in these societies. Our analyses confirmed a continuum in patterns of intersexual dominance, from strictly male-dominated species to strictly female-dominated species. All indices of the degree of female dominance were well correlated with each other. The rank order among same-sex individuals was highly correlated between the intra-and intersexual hierarchies, and such correlation was not affected by the degree of female dominance. The relative prevalence of aggression and submission was sensitive to variation in the degree of female dominance across species, with more submissive signals and fewer aggressive acts being used in societies where female dominance prevails. Thus, this study provides important insights and key methodological tools to study intersexual dominance relationships in mammals.

Mechanistic models suggest that individuals’ memories could shape home range patterns and dynamics, and how neighbors share space. In social species, such dynamics of home range overlap may be affected by the pre-dispersal memories of immigrants. We tested this “immigrant knowledge hypothesis” in a wild population of chacma baboons (Papio ursinus). We predicted that overlap dynamics with a given neighboring troop’s home range should reflect males’ adaptive interests in overlap when the alpha male had immigrated from this neighboring troop but less so when the alpha male originated from elsewhere. We used data collected between 2005 and 2013 on two neighboring troops in Namibia, comprising GPS records of daily ranges, male natal origins, daily females’ reproductive status, and a satellite index of vegetation growth. We found support for our prediction in line with male reproductive strategies but not in line with foraging conditions. In periods with a higher relative number of fertile females over adult males in the focal troop, male baboons would benefit from reducing overlap with their neighbors to mitigate the costs of between-troop mating competition. This was indeed observed but only when the alpha male of the focal troop was an immigrant from that neighboring troop, and not with alpha males of other origins, presumably due to their different knowledge of the neighboring troop. Our findings highlight the role of reproductive competition in the range dynamics of social groups, and suggest that spatial segregation between groups could increase through the combination of dispersal and memory.

The evolutionary benefits of reproductive seasonality are often measured by a single-fitness component, namely offspring survival. Yet different fitness components may be maximized by different birth timings. This may generate fitness trade-offs that could be critical to understanding variation in reproductive timing across individuals, populations and species. Here, we use long-term demographic and behavioural data from wild chacma baboons ( Papio ursinus ) living in a seasonal environment to test the adaptive significance of seasonal variation in birth frequencies. We identify two distinct optimal birth timings in the annual cycle, located four-month apart, which maximize offspring survival or minimize maternal interbirth intervals (IBIs), by respectively matching the annual food peak with late or early weaning. Observed births are the most frequent between these optima, supporting an adaptive trade-off between current and future reproduction. Furthermore, infants born closer to the optimal timing favouring maternal IBIs (instead of offspring survival) throw more tantrums, a typical manifestation of mother–offspring conflict. Maternal trade-offs over birth timing, which extend into mother–offspring conflict after birth, may commonly occur in long-lived species where development from birth to independence spans multiple seasons. Our findings therefore open new avenues to understanding the evolution of breeding phenology in long-lived animals, including humans.

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.

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.

International audience; 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

In social species, female mating strategies can be constrained by both male and female groupmates through sexual conflict and reproductive competition, respectively. This study tests if females adjust their sexual behaviour according to the presence of male and female bystanders in wild chacma baboons ( Papio ursinus ) and assesses their relative importance. Our results show that oestrous females initiate fewer copulations in the presence of adult male bystanders, irrespective of whether they are mate-guarded or not. This inhibitory effect probably reflects a response to indirect sexual coercion by males, whose close proximity may dissuade females to initiate copulations with rival males to avoid punishment and/or aggressive mating interference. By contrast, females initiate more matings with their mate-guard in the presence of higher-ranking female bystanders, which may reflect an attempt to secure bodyguard services from their mate when they feel threatened. These results emphasize the importance of intra- and intersexual conflicts in shaping female sexual behaviour in this promiscuous society.

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.

The critical role of major histocompatibility complex (MHC) genes in disease resistance, along with their putative function in sexual selection, reproduction and chemical ecology, make them an important genetic system in evolutionary ecology. Studying selective pressures acting on MHC genes in the wild nevertheless requires population-wide genotyping, which has long been challenging because of their extensive polymorphism. Here, we report on large-scale genotyping of the MHC class II loci of the grey mouse lemur (Microcebus murinus) from a wild population in western Madagascar. The second exons from MHC-DRB and -DQB of 772 and 672 individuals were sequenced, respectively, using a 454 sequencing platform, generating more than 800,000 reads. Sequence analysis, through a stepwise variant validation procedure, allowed reliable typing of more than 600 individuals. The quality of our genotyping was evaluated through three independent methods, namely genotyping the same individuals by both cloning and 454 sequencing, running duplicates, and comparing parent–offspring dyads; each displaying very high accuracy. A total of 61 (including 20 new) and 60 (including 53 new) alleles were detected at DRB and DQB genes, respectively. Both loci were non-duplicated, in tight linkage disequilibrium and in Hardy–Weinberg equilibrium, despite the fact that sequence analysis revealed clear evidence of historical selection. Our results highlight the potential of 454 sequencing technology in attempts to investigate patterns of selection shaping MHC variation in contemporary populations. The power of this approach will nevertheless be conditional upon strict quality control of the genotyping data. peerReviewed

Erratum to: Immunogenetics (2012) 64:895 – 913 DOI 10.1007/s00251-012-0649-6 The original version of this article unfortunately contains an error in author's name in the original publication. The name Peter M. Kappeler Peter should be corrected as Peter M. Kappeler.