Grooming Between Male Chimpanzees at Ngogo,Kibale National Park. I. Partner Number and Diversity and Grooming Reciprocity

Allogrooming serves many social functions in primates. Grooming can help individuals to service social relationships generally, sometimes reciprocally, and may be particularly important in the development and maintenance of alliances. However, time constraints limit the number of partners with whom one individual can groom enough to maintain cooperative relationships. As a result, the size of its grooming network may reach an asymptote as the size of its group increases, and it may distribute its grooming less equally among potential partners. Chimpanzees live in multimale, fission-fusion communities; males are philopatric, and commonly associate and groom with each other. Males form within-community alliances that influence dominance rank and access to mates, and allies groom with each other regularly; males also cooperate in aggression between communities. The chimpanzee community at Ngogo, in Kibale National Park, Uganda, is unusually large and has more males than any other known community. Field data show that adult Ngogo males groomed far more with other adult males than with females or with adolescent males, in contrast to a previous report (Ghiglieri, 1984). Adolescent males groomed adults much more than the reverse; males groomed and were groomed by females about equally. Individual males groomed mostly with a small number of other males. On average, males at Ngogo had only slightly more male grooming partners overall and had the same number of important partners as those of males in a much smaller community in the Mahale National Park, Tanzania, and they distributed their grooming less equitably. These results fit those expected if limits on available grooming time cause males to have a loyalty problem as the number of potential grooming and alliance partners increases. Despite differences in the extent and equitability of their grooming networks, males at both Ngogo and Mahale showed reciprocity in grooming. Grooming reciprocity has been demonstrated for captive chimpanzee males, but the Ngogo findings are the first demonstrations of reciprocity in wild communities.     

Neighbouring chimpanzee communities show different preferences in social grooming behaviour

Grooming handclasp (GHC) behaviour was originally advocated as the first evidence of social culture in chimpanzees owing to the finding that some populations engaged in the behaviour and others do not. To date, however, the validity of this claim and the extent to which this social behaviour varies between groups is unclear. Here, we measured (i) variation, (ii) durability and (iii) expansion of the GHC behaviour in four chimpanzee communities that do not systematically differ in their genetic backgrounds and live in similar ecological environments. Ninety chimpanzees were studied for a total of 1029 h; 1394 GHC bouts were observed between 2010 and 2012. Critically, GHC style (defined by points of bodily contact) could be systematically linked to the chimpanzee''s group identity, showed temporal consistency both within and between groups, and could not be accounted for by the arm-length differential between partners. GHC has been part of the behavioural repertoire of the chimpanzees under study for more than 9 years (surpassing durability criterion) and spread across generations (surpassing expansion criterion). These results strongly indicate that chimpanzees'' social behaviour is not only motivated by innate predispositions and individual inclinations, but may also be partly cultural in nature.     

Handedness and Grooming in Pan troglodytes: Comparative Analysis Between Findings in Captive and Wild Individuals

Grooming is a complex set of motor actions, common in highly social primates. We tested for asymmetries in hand use during unimanual and bimanual allogrooming in 215 captive chimpanzees. In addition to hand use, we coded in the ethogram whether the manual grooming action co-occurred with the use of the mouth. Overall, grooming did not elicit strong handedness at the individual level, but there is a small yet significant population-level right-hand bias for bimanual grooming. Mouth use during grooming had no influence on hand use. A comparison of the findings with previously published data on handedness for grooming in wild chimpanzees suggests that wild apes are more right-handed than captive individuals are for allogrooming. Collectively, the results suggest that role differentiation of the hands is an important factor in the assessment of handedness for grooming, and perhaps additional manual actions of chimpanzees and other primates.     

Interchange of Grooming and Agonistic Support in Chimpanzees

We investigated the temporal relationship between grooming given and agonistic support received in a group of chimpanzees at Chester Zoo, U.K. We compared grooming levels the day before a conflict-with-support to those the day before a conflict-without-support and to baseline to investigate whether individuals groom potential supporters in anticipation of the need for support. We also compared grooming and aggression levels the day after conflicts-with-support to levels the day after conflicts-without-support and to baseline levels to determine whether chimpanzees reward individuals that support them or punish those that do not. Finally, we compared grooming and aggression levels the day after conflicts-with-unsuccessful-solicitations-for-support to those the day after conflicts-with-support and to baseline to examine the behavioral consequences of not providing support when an individual had solicited but did not receive it. Future recipients of support groomed future supporters more the day before receiving support, compared to the day before conflicts-without-support, indicating that grooming increased the likelihood of support. The relationship between prior grooming and support held true only for aggressor and not victim support and is consistent with behavior expected if chimpanzees anticipated the need for agonistic support and groomed their supporter the day before to increase the likelihood of support. We found evidence of a system of reward and punishment. Individuals experienced significantly lower rates of aggression after conflicts in which they provided support than at baseline and after conflicts in which they did not provide support. The finding was true only for aggressor support. We found no evidence that chimpanzees punished individuals whom or that they unsuccessfully solicited with aggression or a reduction in grooming. However, solicitors groomed individuals that they solicited for support significantly more after unsuccessful solicitations than after individuals provided support (but with no difference from baseline), indicating that individuals may attempt to recement their relationship after an unsuccessful solicitation. The findings are consistent with a mechanism of calculated interchange in chimpanzees.     

Grooming Between Male Chimpanzees at Ngogo,Kibale National Park. II. Influence of Male Rank and Possible Competition for Partners

Allogrooming contributes to the development and maintenance of social relationships, including those that involve alliances, in many primate species. Variation in relatedness, dominance rank, and other factors can produce variation in the value of others as grooming partners. Several models have been developed to account for variation in the distribution of grooming in relation to dominance ranks. These start from the premise that individuals are attracted to high-ranking partners, but time limits, direct competition, and prior grooming engagement between high-ranking individuals can constrain access to them. Sambrook et al. (1995) formalized some of these models and showed the importance of taking group size variation into account when assessing them. Chimpanzees form multimale communities in which males are the philopatric sex. Males commonly associate and groom with each other; they also form dominance hierarchies and form alliances that influence dominance ranks and mating success. Both male rank and the rank distance between partners are significantly correlated with the distribution of grooming between males in an extremely large chimpanzee community at Ngogo, Kibale National Park, Uganda, that has more males than any other known community. High-ranking males had more grooming partners than mid- or low-ranking males. Grooming predominantly went up the dominance hierarchy, but was also concentrated among males that were close in rank. Rank and rank distance apparently both affected grooming independently of reciprocity in grooming and independently of the frequency with which males associated in temporary parties. However, the data do not clearly indicate how constraints on access to partners might have operated. Published data from a smaller chimpanzee community at Mahale show no rank or rank distance effect on male grooming. These results and earlier, conflicting findings on the association between dominance rank and grooming in male chimpanzees indicate that variation in group size, i.e., the number of males per community, probably influences the strength of any such effects, as happens for grooming between females in several cercopithecine species. Data on coalitions at Ngogo support the argument that high-ranking males are valuable social partners, and similarity in strategies of alliance formation may influence the distribution of grooming.     

Human children rely more on social information than chimpanzees do

Human societies are characterized by more cultural diversity than chimpanzee communities. However, it is currently unclear what mechanism might be driving this difference. Because reliance on social information is a pivotal characteristic of culture, we investigated individual and social information reliance in children and chimpanzees. We repeatedly presented subjects with a reward-retrieval task on which they had collected conflicting individual and social information of equal accuracy in counterbalanced order. While both species relied mostly on their individual information, children but not chimpanzees searched for the reward at the socially demonstrated location more than at a random location. Moreover, only children used social information adaptively when individual knowledge on the location of the reward had not yet been obtained. Social information usage determines information transmission and in conjunction with mechanisms that create cultural variants, such as innovation, it facilitates diversity. Our results may help explain why humans are more culturally diversified than chimpanzees.     

The scope of culture in chimpanzees, humans and ancestral apes

More studies have focused on aspects of chimpanzee behaviour and cognition relevant to the evolution of culture than on any other species except our own. Accordingly, analysis of the features shared by chimpanzees and humans is here used to infer the scope of cultural phenomena in our last common ancestor, at the same time clarifying the nature of the special characteristics that advanced further in the hominin line. To do this, culture is broken down into three major aspects: the large scale, population-level patterning of traditions; social learning mechanisms; and the behavioural and cognitive contents of culture. Each of these is further dissected into subcomponents. Shared features, as well as differences, are identified in as many as a dozen of these, offering a case study for the comparative analysis of culture across animal taxa and a deeper understanding of the roots of our own cultural capacities.     

The structure of affiliative relations in a primate community: Allogrooming in stumptailed macaques (Macaca arctoides)

Social grooming in 19 adult stumptailed macaques (a dominant male and 18 females) was studied by focal sampling and scanning methods. Significant individual differences were found with respect to both active and passive grooming intensity, active grooming being a more variable parameter. Individual preferences in partner choice are very strong, but among the factors examined, age was the only one influencing these preferences. Neither social rank nor kinship were significant. The proportion of active and passive contacts shows marked individual differences. Yet, there is a positive association between performed and received grooming. The “extortion hypothesis” is not supported by our results: high-ranking individuals performed on the average more, and received relatively less grooming than low-ranking ones. High grooming performance of the dominants may secure group integrity in species with a “soft” dominance style.     

A quantitative comparison of terrestrial herbaceous food consumption by Pan paniscus in the Lomako Forest,Zaire, and Pan troglodytes in the Kibale Forest,Uganda

Differences in the social organization and dental morphology of Pan paniscus (bonobos) and Pan troglodytes (chimpanzees) have been related to differences in the spatiotemporal availability of food and its exploitation. The presence of abundant terrestrial herbaceous vegetation (THV) in the bonobo's habitat and the apparent greater reliance on herbs for food has been used to explain differences in party size and, by extension, social organization. Using fecal analysis, we assess quantitatively the amount of herbaceous foods consumed by Pan paniscus in the Lomako Forest, Zaire, compared to similar data for Pan troglodytes in the Kibale Forest, Uganda. We examine this data in the context of spatiotemporal patterns of availability of herbaceous foods and fruit, as well as their nutritional content. The results support the suggestion that bonobos consume more herbaceous food than do the Kibale chimpanzees and that these foods are more prevalent in the bonobo's habitat than in the Kibale Forest. However, temporal changes in fruit availability and herb consumption, along with nutritional analyses, suggest that chimpanzees consume herbs as a fallback source of carbohydrates, whereas bonobos consume herbs as a source of protein regardless of season or fruit abundance. Available data suggest that party size while feeding on terrestrial herbs is restricted at both sites, but a determination of the relative strength of this constraint is not possible at this time. Difficulties in methods used for data collection are discussed and areas where more information is needed are highlighted. © 1994 Wiley-Liss, Inc.     

Genetic and ‘cultural’ similarity in wild chimpanzees

The question of whether animals possess ‘cultures’ or ‘traditions’ continues to generate widespread theoretical and empirical interest. Studies of wild chimpanzees have featured prominently in this discussion, as the dominant approach used to identify culture in wild animals was first applied to them. This procedure, the ‘method of exclusion,’ begins by documenting behavioural differences between groups and then infers the existence of culture by eliminating ecological explanations for their occurrence. The validity of this approach has been questioned because genetic differences between groups have not explicitly been ruled out as a factor contributing to between-group differences in behaviour. Here we investigate this issue directly by analysing genetic and behavioural data from nine groups of wild chimpanzees. We find that the overall levels of genetic and behavioural dissimilarity between groups are highly and statistically significantly correlated. Additional analyses show that only a very small number of behaviours vary between genetically similar groups, and that there is no obvious pattern as to which classes of behaviours (e.g. tool-use versus communicative) have a distribution that matches patterns of between-group genetic dissimilarity. These results indicate that genetic dissimilarity cannot be eliminated as playing a major role in generating group differences in chimpanzee behaviour.     

Decision making in grooming by Japanese macaques (Macaca fuscata)

I analyzed the temporal organization of individual Japanese macaques’ (Macaca fuscata) grooming sequences in 14 mothers and 13 offspring of different age/sex classes and 4 nonkin females. I hypothesized that preceding grooming affects subsequent grooming by the same individual. Grooming bouts were likely to be terminated as the bouts became longer when females groomed nonrelatives. Moreover, the duration of first bouts was longer than that of following bouts. These effects were also seen in grooming of mothers by their offspring > 1 year old and that of adult and adolescent female offspring by their mothers. In contrast, neither the duration of first bouts nor the number of preceding bouts had much effect on the occurrence or duration of subsequent bouts in any subject.