Publications

2019
Hohmann Gottfried, Linda Vigilant, Roger Mundry, Verena Behringer, and Martin Surbeck. 5/2019. “Aggression by male bonobos against immature individuals does not fit with predictions of infanticide.” Aggressive behavior, 45, 3, Pp. 300-309. Publisher's Version
Ammie K. Kalan, Gottfried Hohmann, Mimi Arandjelovic, Christophe Boesch, Maureen S. McCarthy, Anthony Agbor, Samuel Angedakin, Emma Bailey, Cosma Wilungula Balongelwa, Mattia Bessone, Gaëlle Bocksberger, Sally Jewel Coxe, Tobias Deschner, Marie-Lyne Després-Einspenner, Paula Dieguez, Barbara Fruth, Ilka Herbinger, Anne-Céline Granjon, Josephine Head, Yves Aka Kablan, Kevin E. Langergraber, Albert Lotana Lokasola, Giovanna Maretti, Sergio Marrocoli, Menard Mbende, Jennifer Moustgaard, Paul Kouame N’Goran, Martha M. Robbins, Joost van Schijndel, Volker Sommer, Martin Surbeck, Nikki Tagg, Jacob Willie, Roman M. Wittig, and Hjalmar S. Kühl. 2019. “Novelty Response of Wild African Apes to Camera Traps.” Current Biology, 29, 7, Pp. 1211 - 1217.e3. Publisher's VersionAbstract
Summary Temperament and personality research in humans and nonhuman animals measures behavioral variation in individual, population, or species-specific traits with implications for survival and fitness, such as social status, foraging, and mating success [1, 2, 3, 4, 5]. Curiosity and risk-taking tendencies have been studied extensively across taxa by measuring boldness and exploration responses to experimental novelty exposure [3, 4, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]. Here, we conduct a natural field experiment using wildlife monitoring technology to test variation in the reaction of wild great apes (43 groups of naive chimpanzees, bonobos, and western gorillas across 14 field sites in Africa) to a novel object, the camera trap. Bonobo and gorilla groups demonstrated a stronger looking impulse toward the camera trap device compared to chimpanzees, suggesting higher visual attention and curiosity. Bonobos were also more likely to show alarm and other fearful behaviors, although such neophobic (and conversely, neophilic) responses were generally rare. Among all three species, individuals looked at cameras longer when they were young, were associating with fewer individuals, and did not live near a long-term research site. Overall, these findings partially validate results from great ape novelty paradigms in captivity [7, 8]. We further suggest that species-typical leadership styles [16] and social and environmental effects, including familiarity with humans, best explain novelty responses of wild great apes. In sum, this study illustrates the feasibility of large-scale field experiments and the importance of both intrinsic and extrinsic factors in shaping animal curiosity. Video Abstract
2017
Martin Surbeck, Christophe Boesch, Cédric Girard-Buttoz, Catherine Crockford, Gottfried Hohmann, and Roman M. Wittig. 2017. “Comparison of male conflict behavior in chimpanzees (Pan troglodytes) and bonobos (Pan paniscus), with specific regard to coalition and post-conflict behavior.” American Journal of Primatology, 79, 6, Pp. e22641. Publisher's VersionAbstract
Coalitions among males during within group conflicts have a strong influence on the competitive and social environment within social groups. To evaluate possible variation in the occurrence of such coalitions in our closest relatives, chimpanzees and bonobos, we compared male aggression and coalitionary behavior in two natural communities, one of each species, with a similar size and composition. Furthermore we compared affiliative behavior that might be related to coalition formation among males. We found higher frequencies of aggression and a greater likelihood to form coalitions during within-group conflicts among wild male chimpanzees at Taï compared to wild male bonobos at LuiKotale. The species differed in the predominant sex of the male coalition partners, with male bonobos forming coalitions more often with females, while male chimpanzees formed coalitions more often with other males. Compared to male bonobos, male chimpanzees showed higher rates of grooming and tended to reconcile more conflicts with other males. Overall our results showed lower frequencies of reconciliation among bonobos than those described in captivity and at artificial feeding sites. These findings add to the evidence that male cooperation and conflict resolution are potentially very different in bonobos and chimpanzees, despite the fact that these two species are closely related, live in multi-male, multi-female communities with a high degree of fission-fusion dynamics and have female-biased migration patterns. Given the correlation between aggressive, cooperative and some affiliative patterns within the species in our study, we hypothesize that the fitness benefits of male relationships are greater in chimpanzees compared to bonobos.
Martin Surbeck, Sally Coxe, and Albert Lotana Lokasola. 2017. “ Lonoa: The Establishment of a Permanent Field Site for Behavioural Research on Bonobos in the Kokolopori Bonobo Reserve.” Pan Africa News, 24, 2, Pp. 13-15.
Martin Surbeck, Kevin E. Langergraber, Barbara Fruth, Linda Vigilant, and Gottfried Hohmann. 2017. “Male reproductive skew is higher in bonobos than chimpanzees.” Current Biology, 27, 13, Pp. R640 - R641. Publisher's VersionAbstract
Summary The two closest living relatives of humans, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes), share many traits that are common in humans but rare in other mammals, including societies with high fission–fusion dynamics, male philopatry, female dispersal and extensive social bonding among unrelated individuals [1]. The major difference between these two species is that male aggression is more frequent and intense in male-dominated chimpanzees than in bonobos, where the highest-ranking individuals are female [1]. One potential explanation is that because periods of female sexual receptivity and attractiveness are more extended in bonobos [2], males compete less intensely for each mating opportunity. This would reduce the strength of selection for traits that lead to success in direct contest competition between males and in sexual coercion of females, thus increasing the potential for female choice [3]. Accordingly, it has been predicted that the influence of male dominance rank on reproductive success and the extent of male reproductive skew should be lower in bonobos than in chimpanzees [1]. Although relevant for understanding the evolution of the unusual levels of egalitarianism and cooperation found in human hunter-gatherers [4], comparative analyses in the genus Pan have been limited by the scanty paternity data available for wild bonobos [5]. Here, we show using the largest sample of paternity data available that, contrary to expectation, male bonobos have a higher reproductive skew and a stronger relationship between dominance rank and reproductive success than chimpanzees.
Martin Surbeck, Cédric Girard-Buttoz, Christophe Boesch, Catherine Crockford, Barbara Fruth, Gottfried Hohmann, Kevin E. Langergraber, Klaus Zuberbühler, Roman M. Wittig, and Roger Mundry. 2017. “Sex-specific association patterns in bonobos and chimpanzees reflect species differences in cooperation.” Royal Society Open Science, 4, 5, Pp. 161081. Publisher's VersionAbstract
In several group-living species, individuals' social preferences are thought to be influenced by cooperation. For some societies with fission–fusion dynamics, sex-specific association patterns reflect sex differences in cooperation in within- and between-group contexts. In our study, we investigated this hypothesis further by comparing sex-specific association patterns in two closely related species, chimpanzees and bonobos, which differ in the level of between-group competition and in the degree to which sex and kinship influence dyadic cooperation. Here, we used long-term party composition data collected on five chimpanzee and two bonobo communities and assessed, for each individual of 10 years and older, the sex of its top associate and of all conspecifics with whom it associated more frequently than expected by chance. We found clear species differences in association patterns. While in all chimpanzee communities males and females associated more with same-sex partners, in bonobos males and females tended to associate preferentially with females, but the female association preference for other females is lower than in chimpanzees. Our results also show that, for bonobos (but not for chimpanzees), association patterns were predominantly driven by mother–offspring relationships. These species differences in association patterns reflect the high levels of male–male cooperation in chimpanzees and of mother–son cooperation in bonobos. Finally, female chimpanzees showed intense association with a few other females, and male chimpanzees showed more uniform association across males. In bonobos, the most differentiated associations were from males towards females. Chimpanzee male association patterns mirror fundamental human male social traits and, as in humans, may have evolved as a response to strong between-group competition. The lack of such a pattern in a closely related species with a lower degree of between-group competition further supports this notion.
Liza R. Moscovice, Pamela Heidi Douglas, Laura Martinez-Iñigo, Martin Surbeck, Linda Vigilant, and Gottfried Hohmann. 2017. “Stable and fluctuating social preferences and implications for cooperation among female bonobos at LuiKotale, Salonga National Park, DRC.” American Journal of Physical Anthropology, 163, 1, Pp. 158-172. Publisher's VersionAbstract
Abstract Objectives Female bonobos (Pan paniscus) are characterized as highly affiliative and cooperative, but few studies have quantified the strength and stability of female intra-sexual relationships or explored how variation in social relationships influences cooperation. We measure female social preferences, identify causes of variation in preferences, and test whether variation in social preferences predicts food sharing or coalitionary support. Methods Data were collected over 3 years from females in the Bompusa community at LuiKotale, DRC. We measured genetic relatedness and constructed social preference indices for party association, proximity, grooming, GG-rubbing and aggression. We identified preferred social partners based on permutation tests and measured stability using Mantel tests. We used factor analysis to identify inter-relationships between preference indices and used LMMs to test whether variation in social preferences was explained by relatedness, rank differences, having dependent young or co-residency time. We used GLMMs to test whether variation in social preferences predicted food sharing or coalitionary support. Results All females had preferred non-kin partners for proximity, grooming or GG-rubbing, but only grooming preferences were stable across years. Association indices were higher among lactating females, and aggression was lower among females with longer co-residency times. The factor analysis identified one factor, representing proximity and GG-rubbing preferences, labeled behavioral coordination. Dyads with higher levels of behavioral coordination were more likely to share food. Conclusions Female bonobos exhibit stable, differentiated grooming relationships outside of kinship and philopatry. Females also exhibit flexible proximity and GG-rubbing preferences that may facilitate cooperation with a wider range of social partners.
2016
Vicky M. Oelze, Pamela Heidi Douglas, Colleen R. Stephens, Martin Surbeck, Verena Behringer, Michael P. Richards, Barbara Fruth, and Gottfried Hohmann. 2016. “The Steady State Great Ape? Long Term Isotopic Records Reveal the Effects of Season, Social Rank and Reproductive Status on Bonobo Feeding Behavior.” PLOS ONE, 11, 9, Pp. 1-17. Publisher's VersionAbstract
Dietary ecology of extant great apes is known to respond to environmental conditions such as climate and food availability, but also to vary depending on social status and life history characteristics. Bonobos (Pan paniscus) live under comparatively steady ecological conditions in the evergreen rainforests of the Congo Basin. Bonobos are an ideal species for investigating influences of sociodemographic and physiological factors, such as female reproductive status, on diet. We investigate the long term dietary pattern in wild but fully habituated bonobos by stable isotope analysis in hair and integrating a variety of long-term sociodemographic information obtained through observations. We analyzed carbon and nitrogen stable isotopes in 432 hair sections obtained from 101 non-invasively collected hair samples. These samples represented the dietary behavior of 23 adult bonobos from 2008 through 2010. By including isotope and crude protein data from plants we could establish an isotope baseline and interpret the results of several general linear mixed models using the predictors climate, sex, social rank, reproductive state of females, adult age and age of infants. We found that low canopy foliage is a useful isotopic tracer for tropical rainforest settings, and consumption of terrestrial herbs best explains the temporal isotope patterns we found in carbon isotope values of bonobo hair. Only the diet of male bonobos was affected by social rank, with lower nitrogen isotope values in low-ranking young males. Female isotope values mainly differed between different stages of reproduction (cycling, pregnancy, lactation). These isotopic differences appear to be related to changes in dietary preference during pregnancy (high protein diet) and lactation (high energy diet), which allow to compensate for different nutritional needs during maternal investment.
2015
Martin Surbeck and Gottfried Hohmann. 2015. “Social preferences influence the short-term exchange of social grooming among male bonobos.” Animal cognition, 18, 2, Pp. 573-579. Publisher's VersionAbstract
The emotional mediation hypothesis proposes a mediating role of social bonds in the exchange of services. This model predicts that the form of short-term exchange of services depends on the relationship between the individuals involved. Here, we test this prediction in the exchange of grooming among males in a wild bonobo community for which close relatedness could be excluded. As bonobo males hardly engage in food sharing or agonistic support, grooming is mainly exchanged for grooming. While overall grooming, both given and received, correlates across dyads and within sessions, the form of grooming exchange within a given session differs according to dyadic association preferences. Individuals with a higher tendency to associate, ergo more familiar individuals, exhibit larger time differences and reduced reciprocation in consecutive grooming bouts than less familiar individuals. These results support the idea that emotional components are involved in the exchange of services between unrelated individuals.
Martin Surbeck, Tobias Deschner, Verena Behringer, and Gottfried Hohmann. 2015. “Urinary C-peptide levels in male bonobos (Pan paniscus) are related to party size and rank but not to mate competition.” Hormones and Behavior, 71, Pp. 22 - 30. Publisher's VersionAbstract
Within- and between-species variation in male mating strategies has been attributed to a multitude of factors including male competitive ability and the distribution of fertile females across space and time. Differences in energy balance across and within males allow for the identification of some of the trade-offs associated with certain social and mating strategies. Bonobos live in groups with a high degree of fission–fusion dynamics, there is co-dominance between the sexes and a linear dominance hierarchy among males. Males compete over access to females, breeding is aseasonal, and females exhibit sexual swellings over extended time periods. In this study we use urinary C-peptide (UCP) levels in male bonobos (Pan paniscus) obtained from 260 urine samples from a wild bonobo community, to quantify male energy balance during mate competition and levels of gregariousness in the species. Although high ranking males are more aggressive, spend more time in proximity to maximally tumescent females, and have higher mating frequencies, we found no indication that mate guarding or mate competition affected male energy balance. Our results showed a positive correlation between monthly mean UCP levels and mean party size. When traveling in large parties, high ranking males had higher UCP levels than those of the low ranking males. These results support the hypothesis that patterns of fission–fusion dynamics in bonobos are either linked to energy availability in the environment or to the energetic costs of foraging. The finding of a rank-bias in UCP levels in larger parties could also reflect an increase in contest competition among males over access to food.
2013
Grit Schubert, Linda Vigilant, Christophe Boesch, Reinhard Klenke, Kevin Langergraber, Roger Mundry, Martin Surbeck, and Gottfried Hohmann. 2013. “Co–Residence between Males and Their Mothers and Grandmothers Is More Frequent in Bonobos Than Chimpanzees.” PLOS ONE, 8, 12. Publisher's VersionAbstract
In long–lived social mammals such as primates, individuals can benefit from social bonds with close kin, including their mothers. In the patrilocal chimpanzee (Pan troglodytes spp.) and bonobo (Pan paniscus), sexually mature males reside and reproduce in their natal groups and can retain post-dependency bonds with their mothers, while immatures of both sexes might also have their paternal grandmothers available. However, quantitative information on the proportion of males and immatures that co-reside with both types of these close female relatives is limited for both species. Combining genetic parentage determination and group composition data from five communities of wild chimpanzees and three communities of wild bonobos, we estimated the frequency of co-residence between (1) mature males and their mothers, and (2) immature males and females and their paternal grandmothers. We found that adult males resided twice as frequently with their mothers in bonobos than in chimpanzees, and that immature bonobos were three times more likely to possess a living paternal grandmother than were immature chimpanzees. Patterns of female and male survivorship from studbook records of captive individuals of both species suggest that mature bonobo females survive longer than their chimpanzee counterparts, possibly contributing to the differences observed in mother–son and grandmother–immature co-residency levels. Taking into account reports of bonobo mothers supporting their sons' mating efforts and females sharing food with immatures other than their own offspring, our findings suggest that life history traits may facilitate maternal and grandmaternal support more in bonobos than in chimpanzees.
Martin Surbeck and Gottfried Hohmann. 2013. “Intersexual dominance relationships and the influence of leverage on the outcome of conflicts in wild bonobos (Pan paniscus).” Behavioral Ecology and Sociobiology volume, 67, Pp. 1767–1780. Publisher's VersionAbstract
Dominance relationships between females and males are characteristic traits of species and are usually associated with sexual dimorphism. Exploring the social and contextual circumstances in which females win conflicts against males allows one to study the conditions triggering shifting power asymmetries between the sexes. This study investigates dominance relationships in bonobos (Pan paniscus), a species in which females are thought to display social dominance despite male-biased sexual dimorphism. To identify dominance relationships among females and males, we first explored how intrasexual dominance status affects the outcome of intersexual conflicts. Second, by incorporating social and behavioral information about the context of intersexual conflicts, we tested to which extent different components of power are relevant to the observed asymmetries in the relationships. Post-hoc analyses indicate a sex-independent dominance hierarchy with several females occupying the top ranks. Our results also reveal that two factors—female leverage and motivation to help offspring—had a significant influence on the outcome of intersexual conflicts. The results of our study do not indicate an overall reduction in male aggression against females but do show lower levels of male aggression in the mating context, and an absence of male aggression toward those females displaying visual signs of elevated fecundity. This indicates that both female sexuality and male mating strategies are involved in the shifting dominance relationships between the sexes.
DAVID BEAUNE, FRANÇOIS BRETAGNOLLE, LOÏC BOLLACHE, Gottfried Hohmann, Martin Surbeck, and Barbara Fruth. 2013. “Seed dispersal strategies and the threat of defaunation in a Congo forest.” Biodiversity and conservation, 22, 1, Pp. 225-238. Publisher's VersionAbstract
Seed dispersal mode of plants and primary interactions with animals are studied in the evergreen Afrotropical forest of LuiKotale, at the south-western part of Salonga National Park (DR Congo). We first analysed seed dispersal strategies for (a) the plant species inventoried over a decade at the study site and (b) the tree community in 12 × 1 ha census plots. Our analyses of dispersal syndromes for 735 identified plant species show that 85 % produce fleshy fruits and rely on animals for primary seed dispersal. Trees depending on animals for primary dispersal dominate the tree community (95 %), while wind-dispersed and autochorous trees are rare in mixed tropical forests. A list of frugivorous vertebrate species of the ecosystem was established. Among the fruit-eating vertebrate species identified in the ecosystem, forest elephants and bonobos are threatened with extinction (IUCN, The IUCN red list of threatened species, 2012). Although most of the species listed previously are internationally and regionally protected, all the species we observed dispersing seeds are hunted, fished or trapped by humans in the area. With the exception of bush pigs, seed predators, mainly small-sized animals, are generally not targeted by hunters. As a consequence, we expect human pressure on key animal species to impact the plant community. We suggest defaunation to be considered as major conservation problem. Thus, not only for the sake of animal species but also for that of plant species conservation, anti-poaching measures should have priority in both “protected” and unprotected areas. Defaunation could bring a new impoverished era for plants in tropical forests.
David Baune, Francois Bretagnolle, Loic Bollache, Gottfried Hohmann, Martin Surbeck, Chloe Bourson, and Barbara Fruth. 2013. “The Bonobo–Dialium Positive Interactions: Seed Dispersal Mutualism.” American Journal of Primatology, 75, 4, Pp. 394-403. Publisher's VersionAbstract
A positive interaction is any interaction between individuals of the same or different species (mutualism) that provides a benefit to both partners such as increased fitness. Here we focus on seed dispersal mutualism between an animal (bonobo, Pan paniscus) and a plant (velvet tamarind trees, Dialium spp.). In the LuiKotale rainforest southwest of Salonga National Park, Democratic Republic of Congo, seven species of the genus Dialium account for 29.3% of all trees. Dialium is thus the dominant genus in this forest. Dialium fruits make up a large proportion of the diet of a habituated bonobo community in this forest. During the 6 months of the fruiting season, more than half of the bonobos’ feeding time is devoted to Dialium fruits. Furthermore, Dialium fruits contribute a considerable proportion of sugar and protein to bonobos’ dietary intake, being among the richest fruits for these nutrients. Bonobos in turn ingest fruits with seeds that are disseminated in their feces (endozoochory) at considerable distances (average: 1.25 km after 24 hr of average transit time). Endozoochory through the gut causes loss of the cuticle protection and tegumentary dormancy, as well as an increase in size by water uptake. Thus, after gut passage, seeds are better able to germinate. We consider other primate species as a potential seed disperser and conclude that Dialium germination is dependent on passage through bonobo guts. This plant–animal interaction highlights positive effects between two major organisms of the Congo basin rainforest, and establishes the role of the bonobo as an efficient disperser of Dialium seeds. Am. J. Primatol. 75:394-403, 2013. © 2013 Wiley Periodicals, Inc.
2012
Martin Surbeck, Tobias Deschner, Grit Schubert, Anja Weltring, and Gottfried Hohmann. 2012. “Mate competition, testosterone and intersexual relationships in bonobos, Pan paniscus.” Animal Behaviour, 83, 3, Pp. 659 - 669. Publisher's VersionAbstract
Variation in male testosterone levels across and within species is known to be related to mating systems, male dominance rank and aggression rates. When aggression enhances access to mates, dominance status and androgen levels correlate positively. Deviation from this pattern is expected when access to females is determined by factors other than male dominance or when high androgen levels interfere with nonaggressive forms of male reproductive strategies such as paternal care and pair bonding. Bonobos offer an interesting study species to test the relationship between male dominance, aggression and intersexual relationships. On the one hand, males form dominance hierarchies and compete for access to females and mating success varies with rank. On the other hand, males and females are equally dominant, male rank is not only the result of aggression, and strong intersexual relationships might be crucial to male reproductive success. We used behavioural and physiological data from wild bonobos to test relationships between behavioural correlates of mate competition and androgen levels. Aggression and rank were positively correlated, as were aggression and mating success. In the presence of potentially fertile females, male aggression increased but only low-ranking, less aggressive males showed increases in testosterone levels, which consequently tended to be negatively related to rank. High-ranking males who had lower testosterone levels and were less responsive in their testosterone increase were more often involved in friendly relationships with unrelated females. These results suggest that, in bonobos, amicable relationships between the sexes rather than aggressive interactions mediate males’ physiological reactivity during periods of mate competition.
Martin Surbeck, Tobias Deschner, Anja Weltring, and Gottfried Hohmann. 2012. “Social correlates of variation in urinary cortisol in wild male bonobos (Pan paniscus).” Hormones and Behavior, 62, 1, Pp. 27 - 35. Publisher's VersionAbstract
Cortisol excretion in males of group living species is often associated with social rank and competition for oestrous females. Rank-related patterns of cortisol levels can be used to study mechanisms of rank maintenance and costs associated with mate competition. Bonobos (Pan paniscus) are interesting because males form a linear dominance hierarchy but are not dominant over females and therefore aggressive male–male competition over access to females alone is not considered to be a successful reproductive strategy. In this study on social correlates of urinary cortisol in wild male bonobos, we investigated the relationship between cortisol levels and several aspects of mate competition, including male rank, aggression rates, and association time with oestrous females. We found that cortisol levels correlated positively with dominance rank when oestrous females were present, but not when they were absent. This result is consistent with the idea that aggressive behaviour plays a minor role in maintenance of high rank. While aggression received from males and females explained within-individual variation in cortisol levels, it was the time spent in association with oestrous females that best explained between-individual variation in male cortisol levels. The observed increase in male cortisol may be associated with spatial proximity to oestrous females and could result from anticipated aggression from other group members, reduced feeding time in the males, or a combination of both.
2011
Vicky M. Oelze, Benjamin T. Fuller, Michael P. Richards, Barbara Fruth, Martin Surbeck, Jean-Jacques Hublin, and Gottfried Hohmann. 2011. “Exploring the contribution and significance of animal protein in the diet of bonobos by stable isotope ratio analysis of hair.” Proceedings of the National Academy of Sciences, 108, 24, Pp. 9792–9797. Publisher's VersionAbstract
In primates, age, sex, and social status can strongly influence access to food resources. In Pan, these criteria are assumed to influence access to vertebrate meat. However, the significance of meat in terms of its role in the nutrition of Pan is still debated. Here we present a study using stable carbon and nitrogen isotope ratios in hair samples from habituated, wild bonobos (Pan paniscus) to explore these issues. Over a period of 5 mo hair samples were collected from fresh bonobo nests at LuiKotale, Democratic Republic of Congo. Hair samples were assigned to known individuals and were of sufficient length to allow the evaluation of isotopic variation over several months. Samples of plant foods and sympatric fauna were also analyzed. The δ13C and δ15N results of the bonobo hair were remarkably homogeneous over time and for the group as a whole. There are no differences in diet between the sexes. Within the group of males, however, there was a positive correlation between dominance status and δ15N. The isotopic data indicate that the contribution of fauna to bonobo diet is marginal and that plant food is the dietary protein source. In only some cases did elevated δ15N hair values correlate with observed faunivory and not correspond to the δ15N measured in the dominant plant foods. Given the large variation in hunting and meat eating of Pan across the African continent, the detection of seasonal changes in faunivory by elevated δ15N values in sectioned ape hair is a promising approach.
Martin Surbeck, Roger Mundry, and Gottfried Hohmann. 2011. “Mothers matter! Maternal support, dominance status and mating success in male bonobos (Pan paniscus).” Proceedings of the Royal Society B: Biological Sciences, 278, 1705, Pp. 590-598. Publisher's VersionAbstract
Variation in male mating success is often related to rank differences. Males who are unable to monopolize oestrous females alone may engage in coalitions, thus enhancing their mating success. While studies on chimpanzees and dolphins suggest that coalitions are independent of kinship, information from female philopatric species shows the importance of kin support, especially from mothers, on the reproductive success of females. Therefore, one might expect a similar effect on sons in male philopatric species. We evaluate mating success determinants in male bonobos using data from nine male individuals from a wild population. Results reveal a steep, linear male dominance hierarchy and a positive correlation between dominance status and mating success. In addition to rank, the presence of mothers enhances the mating success of sons and reduces the proportion of matings by the highest ranking male. Mothers and sons have high association rates and mothers provide agonistic aid to sons in conflicts with other males. As bonobos are male-philopatric and adult females occupy high dominance status, maternal support extends into adulthood and females have the leverage to intervene in male conflicts. The absence of female support to unrelated males suggests that mothers gain indirect fitness benefits by supporting their sons.

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