Social organization and space use of a wild mandrill (Mandrillus sphinx) group

Socially bonded females face more sexual coercion in a female-philopatric primate

Sexual coercion is a manifestation of sexual conflict increasing male mating success while inflicting costs to females. Although previous work has examined inter-individual variation in male sexually coercive tactics, little is known about female counter-strategies. We investigated whether social bonding mitigates the extent of sexual coercion faced by female mandrills (Mandrillus sphinx), as a putative mechanism linking sociality to fitness. Surprisingly, females faced the most coercion from those males with whom they formed the strongest bonds, while the strength of a female-male bond was also positively correlated with coercion from all other males. Finally, greater social integration in the female network was positively correlated with coercion, through a direct 'public exposure' mechanism and not mediated by female reproductive success or retaliation potential. Altogether, this study shows that neither between- nor within-sex bonds are protective against sexual coercion and identifies, instead, a hidden cost of social bonding.

Mother-to-daughter transmission of hygienic anti-parasite behaviour in mandrills

Social animals are particularly exposed to infectious diseases. Pathogen-driven selection pressures have thus favoured the evolution of behavioural adaptations to decrease transmission risk such as the avoidance of contagious individuals. Yet, such strategies deprive individuals of valuable social interactions, generating a cost-benefit trade-off between pathogen avoidance and social opportunities. Recent studies revealed that hosts differ in these behavioural defences, but the determinants driving such inter-individual variation remain understudied. Using 6 years of behavioural and parasite data on a large natural population of mandrills (Mandrillus sphinx), we showed that, when parasite prevalence was high in the population, females avoided grooming their conspecifics' peri-anal region (PAR), where contagious gastro-intestinal parasites accumulate. Females varied, however, in their propensity to avoid this risky body region: across years, some females consistently avoided grooming it, while others did not. Interestingly, hygienic females (i.e. those avoiding the PAR) were less parasitized than non-hygienic females. Finally, age, dominance rank and grooming frequency did not influence a female's hygiene, but both mother-daughter and maternal half-sisters exhibited similar hygienic levels, whereas paternal half-sisters and non-kin dyads did not, suggesting a social transmission of this behaviour. Our study emphasizes that the social inheritance of hygiene may structure behavioural resistance to pathogens in host populations with potential consequences on the dynamics of infectious diseases.

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.

Mandrill mothers associate with infants who look like their own offspring using phenotype matching

Behavioral discrimination of kin is a key process structuring social relationships in animals. In this study, we provide evidence for discrimination towards non-kin by third-parties through a mechanism of phenotype matching. In mandrills, we recently demonstrated increased facial resemblance among paternally related juvenile and adult females indicating adaptive opportunities for paternal kin recognition. Here, we hypothesize that mandrill mothers use offspring's facial resemblance with other infants to guide offspring's social opportunities towards similar-looking ones. Using deep learning for face recognition in 80 wild mandrill infants, we first show that infants sired by the same father resemble each other the most, independently of their age, sex or maternal origin, extending previous results to the youngest age class. Using long-term behavioral observations on association patterns, and controlling for matrilineal origin, maternal relatedness and infant age and sex, we then show, as predicted, that mothers are spatially closer to infants that resemble their own offspring more, and that this maternal behavior leads to similar-looking infants being spatially associated. We then discuss the different scenarios explaining this result, arguing that an adaptive maternal behavior is a likely explanation. In support of this mechanism and using theoretical modeling, we finally describe a plausible evolutionary process whereby mothers gain fitness benefits by promoting nepotism among paternally related infants. This mechanism, that we call 'second-order kin selection', may extend beyond mother-infant interactions and has the potential to explain cooperative behaviors among non-kin in other social species, including humans.

Sex and dominance: How to assess and interpret intersexual dominance relationships in mammalian societies

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 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 intra- and 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.

Seasonality in daily movement patterns of mandrills revealed by combining direct tracking and camera traps

Movement is a fundamental characteristic of animals, but challenging to measure noninvasively. Noninvasive methods for measuring travel have different weaknesses, so multiple techniques need to be applied multiple techniques for reliable inferences. We used two methods, direct tracking and camera trapping, to examine the variation in time and seasonal differences in movement rates of mandrills (Mandrillus sphinx), an elusive primate that lives in large groups in central Africa. In a 400-km2 rainforest area in Moukalaba-Doudou National Park, Gabon, we tracked unidentified groups 46 times from 2009 to 2013. We systematically placed 157 terrestrial camera traps in the same area from 2012 to 2014 and recorded groups 309 times. Generalized additive mixed models (GAMMs) of the tracking data indicated that the group travel speed varied with time and season. In the fruiting season, the movement rate fluctuated with time in a bimodal pattern, whereas in the nonfruiting season, it increased monotonously with time. The predicted day range was longer in the fruiting season (6.98 km) than in the nonfruiting season (6.06 km). These seasonal differences suggest responses to changes in food resources and temperature. Camera-trap detection rates showed similar temporal and seasonal patterns to the tracking data, allowing us to generalize our findings to the population level. Moreover, cameras never detected mandrills at night, and we observed that they slept high in trees and hardly moved until the next morning, all suggesting their strict avoidance of nighttime movement. This study demonstrated the significance of the multiple-method approach in drawing robust conclusions on temporal patterns of animal movement.

Social complexity and the fractal structure of group size in primate social evolution

Compared to most other mammals and birds, anthropoid primates have unusually complex societies characterised by bonded social groups. Among primates, this effect is encapsulated in the social brain hypothesis: the robust correlation between various indices of social complexity (social group size, grooming clique size, tactical behaviour, coalition formation) and brain size. Hitherto, this has always been interpreted as a simple, unitary relationship. Using data for five different indices of brain volume from four independent brain databases, we show that the distribution of group size plotted against brain size is best described as a set of four distinct, very narrowly defined grades which are unrelated to phylogeny. The allocation of genera to these grades is highly consistent across the different data sets and brain indices. We show that these grades correspond to the progressive evolution of bonded social groups. In addition, we show, for those species that live in multilevel social systems, that the typical sizes of the different grouping levels in each case coincide with different grades. This suggests that the grades correspond to demographic attractors that are especially stable. Using five different cognitive indices, we show that the grades correlate with increasing social cognitive skills, suggesting that the cognitive demands of managing group cohesion increase progressively across grades. We argue that the grades themselves represent glass ceilings on animals' capacity to maintain social and spatial coherence during foraging and that, in order to evolve more highly bonded groups, species have to be able to invest in costly forms of cognition.

Natural infection of free-ranging mandrills (Mandrillus sphinx) by enteroviruses and astroviruses in southern Gabon

Enteroviruses (Picornaviridae) and astroviruses (Astroviridae) cause various diseases in humans and animals, including in non-human primates (NHPs). Some enteroviruses and astroviruses detected in NHPs are genetically related to those infecting humans, indicating the occurrence of interspecies transmissions. In this study, we screened 200 fecal samples of 56 free-ranging mandrills (Mandrillus sphinx) by nested reverse transcription-PCR with primers targeting the VP1 and RdRp genes, to evaluate the diversity of enterovirus and astrovirus infection, respectively, and the associated zoonotic risk. Overall, ten samples from six mandrills were enterovirus-positive (5%), and three samples from three mandrills were astrovirus-positive (1.5%). This is the first evidence of astrovirus infection in mandrills. Phylogenetic analyses based on the VP1 sequences revealed that all ten enterovirus sequences were part of the species Enterovirus J, suggesting low zoonotic risk. Phylogenetic analysis of the three astrovirus sequences showed that they all belonged to the Mamastrovirus genus. Two astrovirus sequences were highly divergent from all human astrovirus sequences (63.4-73% nucleotide identity), while one sequence (AstV-5) suggested cross-species transmission from humans to mandrills. Additional studies are needed to better characterize the identified astroviruses and to confirm whether mandrills are host of astroviruses than can be transmitted to humans.

Seasonality and interindividual variation in mandrill feeding ecology revealed by stable isotope analyses of hair and blood

Mandrills are large-bodied terrestrial forest primates living in particularly large social groups of several hundred individuals. Following these groups in the wild to assess differences in diet over time as well as among individuals is demanding. We here use isotope analyses in blood and hair obtained during repeated captures of 43 identified free-ranging mandrills (Mandrillus sphinx) from Southern Gabon, to test how dietary variation relates to the season as well as an individual's age and sex. We measured the stable carbon (δ¹³ C‰) and nitrogen (δ¹⁵ N‰) isotope ratios in 46 blood and 214 hair section samples as well as from a small selection of mandrill foods (n = 24). We found some seasonal isotopic effects, with lower δ¹³ C values but higher δ¹⁵ N values observed during the highly competitive long dry season compared to the fruit-rich long rainy season. Variation in δ¹³ C was further predicted by individual age, with higher δ¹³ C values generally found in younger individuals suggesting that they may consume more high canopy fruit than older individuals, or that older individuals consume more low canopy foliage. The best predictor for δ¹⁵ N values was the interaction between age and sex, with mature and reproductively active males revealing the highest δ¹⁵ N values, despite the observation that males consume substantially less animal food items than females. We interpret high δ¹⁵ N values in these mature male mandrill blood and hair sections to be the result of nutritional stress associated with intense male-male competition, particularly during mating season. This is the first study showing isotopic evidence for nutritional stress in a free-ranging primate species and may spark further investigations into male mandrill diet and energy balance.

The multidimensionality of female mandrill sociality-A dynamic multiplex network approach

The structure and dynamics of primate social groups are shaped by the social relationships of its members. These relationships are based on different types of interactions and vary in relation to the identity of the interactants and over time. Social network analysis tools represent a powerful and comprehensive method to characterise social interactions and recent methodological advances now allow the study of the multidimensionality of sociality via multilayer networks that incorporate multiple types of interactions. Here, we use a multidimensional network approach to investigate the multidimensionality of sociality of females in a captive group of mandrills. We constructed two multiplex networks based on agonistic, proximity and grooming interactions of 6-7 mature females to analyse the multidimensionality of relationships within two independent observation periods; and three multiplex networks (one for each interaction type) to examine how relationships changed between periods. Within each period, different individuals were the most central in each layer and at the multiplex level, and different layers (i.e., interaction types) contributed non-redundant information to the multilayer structure. Across periods, relationships based on the same interaction type also contained non-redundant information. These results indicate that female mandrills engage in multidimensional and dynamic relationships, suggesting that in order to represent the full complexity of relationships, networks need to be constructed from more than a single type of interaction and across time. Our results provide evidence for the potential value of the multilayer network approach to characterise the multidimensionality of primate sociality.

Unconditional care from close maternal kin in the face of parasites

Several species mitigate relationships according to their conspecifics' parasite status. Yet, this defence strategy comes with the costs of depriving individuals from valuable social bonds. Animals therefore face a trade-off between the costs of pathogen exposure and the benefits of social relationships. According to the models of social evolution, social bonds are highly kin-biased. However, whether kinship mitigates social avoidance of contagious individuals has never been tested so far. Here, we build on previous research to demonstrate that mandrills (Mandrillus sphinx) modulate social avoidance of contagious individuals according to kinship: individuals do not avoid grooming their close maternal kin when contagious (parasitized with oro-faecally transmitted protozoa), although they do for more distant or non-kin. While individuals' parasite status has seldom been considered as a trait impacting social relationships in animals, this study goes a step beyond by showing that kinship balances the effect of health status on social behaviour in a non-human primate.

Ecological, parasitological and individual determinants of plasma neopterin levels in a natural mandrill population

Investigating how individuals adjust their investment into distinct components of the immune system under natural conditions necessitates to develop immune phenotyping tools that reflect the activation of specific immune components that can be measured directly in the field. Here, we examined individual variation of plasma neopterin, a biomarker of Th1 immunity in wild mandrills (Mandrillus sphinx), who are naturally exposed to a suite of parasites, including simian retroviruses and malaria agents. We analyzed a total of 201 plasma samples from 99 individuals and examined the effect of sex, age, social rank, reproductive state and disease status on neopterin levels. We found higher neopterin concentrations in males than females, but were unable to disentangle this effect from possible confounding effects of retroviral infections, which affect nearly all adult males, but hardly any females. We further detected a non-linear age effect with heightened neopterin levels in early and late life. In addition, adult males that harbored very high parasitaemia for Plasmodium gonderi also showed high neopterin levels. There was no effect of social rank in either male or female mandrills, and no effect of female reproductive state. Taken together, these results indicate that plasma neopterin may prove useful to investigate individual variation in investment into specific immune components, as well as to monitor the dynamics of immune responses to naturally occurring diseases that elicit a Th1 immune response.

A longitudinal molecular study of the ecology of malaria infections in free-ranging mandrills

Unravelling the determinants of host variation in susceptibility and exposure to parasite infections, infection dynamics and the consequences of parasitism on host health is of paramount interest to understand the evolution of complex host-parasite interactions. In this study, we evaluated the determinants, temporal changes and physiological correlates of Plasmodium infections in a large natural population of mandrills (Mandrillus sphinx). Over six consecutive years, we obtained detailed parasitological and physiological data from 100 male and female mandrills of all ages. The probability of infection by Plasmodium gonderi and P. mandrilli was elevated (ca. 40%) but most infections were chronical and dynamic, with several cases of parasite switching and clearance. Positive co-infections also occurred between both parasites. Individual age and sex influenced the probability of infections with some differences between parasites: while P. mandrilli appeared to infect its hosts rather randomly, P. gonderi particularly infected middle-aged mandrills. Males were also more susceptible to P. gonderi than females and were more likely to be infected by this parasite at the beginning of an infection by the simian immunodeficiency virus. P. gonderi, and to a lesser extent P. mandrilli, influenced mandrills’ physiology: skin temperatures and neutrophil/lymphocyte ratio were both impacted, generally depending on individual age and sex. These results highlight the ecological complexity of Plasmodium infections in nonhuman primates and the efforts that need to be done to decipher the epidemiology of such parasites.

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Longitudinal epidemiological and physiological data on Plasmodium infection obtained from a wild primate population.

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Elevated chronical infections by two species of Plasmodium.

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Contrasted dynamics of infection and physiological effects of P. gonderi and P. mandrilli.

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Elevated parasitaemia (P. gonderi) in male mandrills in primo-infection by the simian immunodeficiency virus.

Mandrills represent their own dominance hierarchy on a cardinal, not ordinal, scale

Attempts to measure dominance relationships using cardinal, rather than ordinal ranks have a long history. Nevertheless, it is still unclear if cardinal dominance ranks have an impact on the life of animals. In particular, no information is available on how individual group living animals represent their own dominance hierarchy. This can be investigated testing whether cardinal rank differences affect how animals interact with different group mates. In this study, we evaluated how mandrills (Mandrillus sphinx) interacted with group mates in relation to differences in cardinal ranks while controlling for differences in ordinal ranks. Mandrills were more likely both to avoid an approaching group mate and to direct their grooming to a group mate when differences in cardinal ranks were larger (controlling for differences in ordinal ranks). These results suggest mandrills represent their own dominance hierarchy as based on a cardinal, not an ordinal, scale.

Buccal dental-microwear and dietary ecology in a free-ranging population of mandrills (Mandrillus sphinx) from southern Gabon

Analyses of dental micro- and macro-wear offer valuable information about dietary adaptations. The buccal surface of the teeth does not undergo attrition, indicating that dental microwear may directly inform about food properties. Only a few studies have, however, investigated the environmental and individual factors involved in the formation of such microwear in wild animals. Here, we examine variation of buccal microwear patterns of mandibular molars in a large free-ranging population of mandrills (Mandrillus sphinx). We first explore the influence of seasonality and individual's sex, age and tooth macrowear-expressed as the percent of dentine exposure (PDE)-on six microwear variables. Second, we analyze the interplay between individual's diet and PDE. In a last analysis, we revisit our results on mandrills in the light of other primate's microwear studies. We show that the average buccal scratch length and the frequency of vertical buccal scratches are both higher during the long dry season compared to the long rainy season, while we observe the inverse relationship for disto-mesial scratches. In addition, females present more disto-mesial scratches than males and older individuals present higher scratch density, a greater proportion of horizontal scratches but a lower proportion of vertical scratches than young animals. PDE yields similar results than individual's age confirming earlier results in this population on the relationship between age and tooth macrowear. Because seasonality and individual characteristics are both known to impact mandrills' diet in the study population, our results suggest that buccal microwear patterns may inform about individual feeding strategies. Furthermore, PDE increases with the consumption of potentially abrasive monocotyledonous plants, independently of the individuals' age, although it is not affected by food mechanical properties. Finally, buccal scratch densities by orientation appear as relevant proxies for discriminating between different primate taxa.

Mandrills use olfaction to socially avoid parasitized conspecifics

The evolutionary transition from a solitary to a social lifestyle entails an elevated parasite cost because the social proximity associated with group living favors parasite transmission. Despite this cost, sociality is widespread in a large range of taxonomic groups. In this context, hosts would be expected to have evolved behavioral mechanisms to reduce the risk of parasite infection. Few empirical studies have focused on the influence of pathogen-mediated selection on the evolution of antiparasitic behavior in wild vertebrates. We report an adaptive functional relationship between parasitism and social behavior in mandrills, associated with evidence that they are able to gauge parasite status of their group members. Using long-term observations, controlled experiments, and chemical analyses, we show that (i) wild mandrills avoid grooming conspecifics infected with orofecally transmitted parasites; (ii) mandrills receive significantly more grooming after treatment that targets these parasites; (iii) parasitism influences the host's fecal odors; and (iv) mandrills selectively avoid fecal material from parasitized conspecifics. These behavioral adaptations reveal that selecting safe social partners may help primates to cope with parasite-mediated costs of sociality and that "behavioral immunity" plays a crucial role in the coevolutionary dynamics between hosts and their parasites.

Sexual Selection and the differences between the sexes in Mandrills (Mandrillus sphinx)

Sexual selection has become a major focus in evolutionary and behavioral ecology. It is also a popular research topic in primatology. I use studies of mandrills (Mandrillus sphinx), a classic example of extravagant armaments and ornaments in animals, to exemplify how a long-term, multidisciplinary approach that integrates field observations with laboratory methods can contribute to on-going theoretical debates in the field of sexual selection. I begin with a brief summary of the main concepts of sexual selection theory and the differences between the sexes. I then introduce mandrills and the study population and review mandrill life history, the ontogeny of sex differences, and maternal effects. Next, I focus on male-male competition and female choice, followed by the less well-studied questions of female-female competition and male choice. This review shows how different reproductive priorities lead to very different life histories and divergent adaptations in males and females. It demonstrates how broadening traditional perspectives on sexual selection beyond the ostentatious results of intense sexual selection on males leads to an understanding of more subtle and cryptic forms of competition and choice in both sexes and opens many productive avenues in the study of primate reproductive strategies. These include the potential for studies of postcopulatory selection, female intrasexual competition, and male choice. These studies of mandrills provide comparison and, I hope, inspiration for studies of both other polygynandrous species and species with mating systems less traditionally associated with sexual selection.

Ranging behavior drives parasite richness: A more parsimonious hypothesis

Parasitism is a ubiquitous interspecific interaction that may play an important role in the evolution of hosts and parasites, molding many aspects of their behavior and ecology. Detecting behavioral changes of hosts infected with parasites is not a straightforward task. Extrapolating from individual-level responses to group-level decision-making is still a much more complex challenge. The ranging behavior of hosts that live in social groups is a good example. Many hypotheses of the cause-effect relationship between this behavior and parasite diversity and load have been proposed. For instance, Brockmeyer et al. [2015, Am. J. Primatol. 77:1036-1048] recently suggested that the richness of protozoan parasites influences the daily path length of free-ranging mandrills. We believe that this explanation for the relationship contains several implicit assumptions. Therefore, we offer an alternative, more parsimonious hypothesis in which daily path length is the driver of parasite richness rather than its consequence. Our hypothesis only assumes that ranging farther exposes animals to a richer parasite diversity. We discuss the data required to test these alternative hypotheses and recall empirical evidence and theoretical modeling results supporting or rejecting their assumptions. We also propose a model of the expected outcomes in terms of species richness, load, intensity of infection, and within-group community similarity of non-lethal environmentally transmitted parasites in social animal groups showing distinct patterns of range use. Am. J. Primatol. 78:923-927, 2016. © 2016 Wiley Periodicals, Inc.

History of primate behavioural and ecological field research at the German Primate Center

Abstract. This paper describes the background of the first behavioural and ecological field studies on primates conducted by German primatologists in the late 1960s and early 1970s. Field research by scientists from DPZ started in the middle 1980s at a time when this was not yet considered a major task for DPZ. Establishment of field research became possible due to recommendations from institutional and departmental evaluations and the formation of a working group "Ethology and Ecology", which was later transformed into a department in the 1990s. Since then, field research has gained momentum, and has become part of the research program of other DPZ departments. The DPZ is now unique, as it runs field sites in all major areas of primate distribution. The foresight and support of Hans-Jürg Kuhn during his period as scientific director was seminal and essential for the evolution of primate field research at DPZ.