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Chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) are humans’ closest living relatives. The two sister species shared a common evolutionary history until about one million years ago. Yet, despite their evolutionary closeness, chimpanzees and bonobos differ in a number of important ways. One of the most striking differences is the discrepancy in the reliance on tool use in wild populations of Pan. Chimpanzees are renowned for their extensive use of tools in a wide variety of contexts, including feeding, self-maintenance, and social contexts. Bonobos, on the other hand, use surprisingly few tools in the wild, and none in feeding. The tool use difference between the two species of Pan remains one of the most challenging topics in the study of our closest living relatives. In this chapter, I will provide an overview of what we know about bonobo tool use in the wild, and specifically how tool use at the study site of Wamba in the Democratic Republic of Congo compares to other long-term bonobo study sites. Moreover, I will summarize a number of comparative studies on wild bonobos and chimpanzees, which have aimed to elucidate the drivers of the tool use dichotomy between the two species. Lastly, I will discuss future research directions in the study of tool use in our ape relatives.

Primate social organizations, or grouping patterns, vary significantly across species. Behavioral strategies that allow for flexibility in grouping patterns offer a means to reduce the costs of group living. Chimpanzees (Pan troglodytes) have a fission‐fusion social system in which temporary subgroups (“parties”) change in composition because of local socio‐ecological conditions. Notably, western chimpanzees (P. t. verus) are described as showing a higher degree of bisexual bonding and association than eastern chimpanzees, and eastern female chimpanzees (P. t. schweinfurthii) are thought to be more solitary than western female chimpanzees. However, reported comparisons in sociality currently depend on a small number of study groups, particularly in western chimpanzees, and variation in methods. The inclusion of additional communities and direct comparison using the same methods are essential to assess whether reported subspecies differences in sociality hold in this behaviorally heterogeneous species. We explored whether sociality differs between two communities of chimpanzees using the same motion‐triggered camera technology and definitions of social measures. We compare party size and composition (party type, sex ratio) between the western Gahtoy community in the Nimba Mountains (Guinea) and the eastern Waibira community in the Budongo Forest (Uganda). Once potential competition for resources such as food and mating opportunities were controlled for, subspecies did not substantially influence the number of individuals in a party. We found a higher sex‐ratio, indicating more males in a party, in Waibira; this pattern was driven by a greater likelihood in Gahtoy to be in all‐female parties. This finding is the opposite of what was expected for eastern chimpanzees, where female‐only parties are predicted to be more common. Our results highlight the flexibility in chimpanzee sociality, and caution against subspecies level generalizations.

We respond to the commentary by Tennie and Call (2023) on the article by Koops et al. (2022) in Nature Human Behaviour titled ‘Field experiments find no evidence that chimpanzee nut cracking can be independently innovated.’ Koops et al. (2022) showed that chimpanzee nut cracking is not a so-called ‘latent solution.’ Chimpanzees (Pan troglodytes verus) in the Nimba Mountains (Guinea) did not crack nuts when presented with nuts and stones in ecologically valid field experiments. In their Commentary, Tennie and Call (2023) argued that the experiments were inconclusive for two reasons: 1) the chimpanzees were not motivated to treat the nuts as food, and 2) the chimpanzees were not within the appropriate ‘sensitive learning period.’ In our response, we argue that Tennie and Call (2023) incorrectly use the term ‘motivation’ to mean ‘willingness to eat the nut’, which requires existing knowledge of the edibility of the nuts. We also point out that it is unnatural and uninformative to inject nuts with honey to motivate the chimpanzees to eat them, as suggested by Tennie and Call (2023). Finally, we highlight that Koops et al. (2022) tested appropriately aged subjects (N=32 immatures). Moreover, we argue that there is no evidence to suggest that there is a strictly sensitive learning period restricted to juvenility. Finally, we emphasize the need for researchers doing experiments in captivity to visit their study species in the wild, and for field researchers to be involved in efforts to design ecologically valid experiments in captivity.

Western chimpanzees (Pan troglodytes verus) are Critically Endangered and Guinea is a key stronghold for this subspecies. However, Guinea is also rich in minerals with some of the highest‐grade iron‐ore deposits in the world. Specifically, the Nimba Mountains, home to western chimpanzees, is one of the sites under consideration for mining activities. To assess the impact of mining activities in the area, we used non‐invasive genetic sampling to estimate chimpanzee population size, sex ratio, community composition, and range boundaries on the western flank of the massif. The level of genetic diversity and affinity between communities was estimated and recommendations for future genetic censusing provided. Between 2003 and 2018, we collected 999 fecal samples of which 663 were analyzed using a panel of 26 microsatellites. We identified a minimum of 136 chimpanzees in four communities, with evidence of migratory events, a high level of shared ancestry and genetic diversity. We assessed sampling intensities and capture rates for each community. Saturation was reached in two communities with sampling between 3.2 and 4.3 times the estimated number of chimpanzees. Our findings highlight the utility of genetic censusing for temporal monitoring of ape abundance, as well as capturing migratory events and gauging genetic diversity and population viability over time. We recommend genetic sampling, combined with camera trapping, for use in future Environmental and Social Impact Assessments, as these methods can yield robust baselines for implementing the mitigation hierarchy, future biomonitoring and conservation management.

We review the main ecological and socio-cognitive hypotheses explaining the origin and evolution of tool use in primates. Whereas it is clear that recent studies have deepened our understanding of tool use in several domains, a more integrated approach will be necessary to further advance the field and place this information into a broader evolutionary context. We suggest a combined Comparative Socio-ecological and Developmental Approach (CSDA), which incorporates phylogenetic and ontogenetic perspectives with the ecological and socio-cognitive drivers of tool use as a means to clarify the integrated mechanisms that promote the emergence and maintenance of tool-using skills in primates, including humans

Chimpanzees (Pan troglodytes) harbor rich assemblages of malaria parasites, including three species closely related to P. falciparum (sub-genus Laverania), the most malignant human malaria parasite. Here, we characterize the ecology and epidemiology of malaria infection in wild chimpanzee reservoirs. We used molecular assays to screen chimpanzee fecal samples, collected longitudinally and cross-sectionally from wild populations, for malaria parasite mitochondrial DNA. We found that chimpanzee malaria parasitism has an early age of onset and varies seasonally in prevalence. A subset of samples revealed Hepatocystis mitochondrial DNA, with phylogenetic analyses suggesting that Hepatocystis appears to cross species barriers more easily than Laverania. Longitudinal and cross-sectional sampling independently support the hypothesis that mean ambient temperature drives spatiotemporal variation in chimpanzee Laverania infection. Infection probability peaked at ~24.5 °C, consistent with the empirical transmission optimum of P. falciparum in humans. Forest cover was also positively correlated with spatial variation in Laverania prevalence, consistent with the observation that forest-dwelling Anophelines are the primary vectors. Extrapolating these relationships across equatorial Africa, we map spatiotemporal variation in the suitability of chimpanzee habitat for Laverania transmission, offering a hypothetical baseline indicator of human exposure risk.

Chimpanzees live in fission-fusion social organizations, which means that party size, composition, and spatial distribution are constantly in flux. Moreover, chimpanzees use a remarkably extensive repertoire of vocal and nonvocal forms of communication, thought to help convey information in such a socially and spatially dynamic setting. One proposed form of nonvocal communication in chimpanzees is buttress drumming, in which an individual hits a tree buttress with its hands and/or feet, thereby producing a low-frequency acoustic signal. It is often presumed that this behavior functions to communicate over long distances and is, therefore, goal-oriented. If so, we would expect chimpanzees to exhibit selectivity in the choice of trees and buttresses used in buttress drumming. Selectivity is a key attribute of many other goal-directed chimpanzee behaviors, such as nut-cracking and ant dipping. Here, we investigate whether chimpanzees at the Seringbara study site in the Nimba Mountains, Guinea, West Africa, show selectivity in their buttress drumming behavior. Our results indicate that Seringbara chimpanzees are more likely to use larger trees and select buttresses that are thinner and have a greater surface area. These findings imply that tree buttress drumming is not a random act, but rather goal-oriented and requires knowledge of suitable trees and buttresses. Our results also point to long-distance communication as a probable function of buttress drumming based on selectivity for buttress characteristics likely to impact sound propagation. This study provides a foundation for further assessing the cognitive underpinnings and functions of buttress drumming in wild chimpanzees.

An enduring question in the study of human evolution is why tool use evolved. A new study has found that stone tools improve diet quality in wild capuchin monkeys. Tools may have similarly increased the nutritional security in ancestral hominins.

Discussions of how animal culture can aid the conservation crisis are burgeoning. As scientists and conservationists working to protect endangered species, we call for reflection on how the culture concept may be applied in practice. Here, we discuss both the potential benefits and potential shortcomings of applying the animal culture concept, and propose a set of achievable milestones that will help guide and ensure its effective integration existing conservation frameworks, such as Adaptive Management cycles or Open Standards.

The drivers of divergent scleral morphologies in primates are currently unclear, though white sclerae are often assumed to underlie human hyper-cooperative behaviours. Humans are unusual in possessing depigmented sclerae whereas many other extant primates, including the closely-related chimpanzee, possess dark scleral pigment. Here, we use phylogenetic generalized least squares (PGLS) analyses with previously generated species-level scores of proactive prosociality, social tolerance (both n = 15 primate species), and conspecific lethal aggression (n = 108 primate species) to provide the first quantitative, comparative test of three existing hypotheses. The ‘self-domestication’ and ‘cooperative eye’ explanations predict white sclerae to be associated with cooperative, rather than competitive, environments. The ‘gaze camouflage’ hypothesis predicts that dark scleral pigment functions as gaze direction camouflage in competitive social environments. Notably, the experimental evidence that non-human primates draw social information from conspecific eye movements is unclear, with the latter two hypotheses having recently been challenged. Here, we show that white sclerae in primates are associated with increased cooperative behaviours whereas dark sclerae are associated with reduced cooperative behaviours and increased conspecific lethal violence. These results are consistent with all three hypotheses of scleral evolution, suggesting that primate scleral morphologies evolve in relation to variation in social environment.

Despite the large body of literature on ape conservation, much of the data needed for evidence‐based conservation decision‐making is still not readily accessible and standardized, rendering cross‐site comparison difficult. To support knowledge synthesis and to complement the IUCN SSC Ape Populations, Environments and Surveys database, we created the A.P.E.S. Wiki (https://apeswiki.eva.mpg.de), an open‐access platform providing site‐level information on ape conservation status and context. The aim of this Wiki is to provide information and data about geographical ape locations, to curate information on individuals and organizations active in ape research and conservation, and to act as a tool to support collaboration between conservation practitioners, scientists, and other stakeholders. To illustrate the process and benefits of knowledge synthesis, we used the momentum of the update of the conservation action plan for western chimpanzees (Pan troglodytes verus) and began with this critically endangered taxon. First, we gathered information on 59 sites in West Africa from scientific publications, reports, and online sources. Information was compiled in a standardized format and can thus be summarized using a web scraping approach. We then asked experts working at those sites to review and complement the information (20 sites have been reviewed to date). We demonstrate the utility of the information available through the Wiki, for example, for studying species distribution. Importantly, as an open‐access platform and based on the well‐known wiki layout, the A.P.E.S. Wiki can contribute to direct and interactive information sharing and promote the efforts invested by the ape research and conservation community. The Section on Great Apes and the Section on Small Apes of the IUCN SSC Primate Specialist Group will guide and support the expansion of the platform to all small and great ape taxa. Similar collaborative efforts can contribute to extending knowledge synthesis t

Cultural primatology focuses on the study of culture in nonhuman primates. Culture is defined as innovations that are spread and maintained between and within generations by social learning. The principal method used to establish the presence of culture in nature is the “method of exclusion.” It states that cultural processes can be inferred if a behavior has high prevalence at some sites but is absent at others, while genetic or ecological processes can be ruled out. Using this method, cultural variation was found in various primate species. A second approach to the study of animal cultures focuses on the process of social learning. In order for culture to be maintained, contact between generations and some form of oblique or horizontal transmission must exist. Culture can evolve, and complex cumulative human culture was built on a foundation similar to primate culture.