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Citizen science has grown rapidly in popularity in recent years due to its potential to educate and engage the public while providing a means to address a myriad of scientific questions. However, the rise in popularity of citizen science has also been accompanied by concerns about the quality of data emerging from citizen science research projects. We assessed data quality in the online citizen scientist platform Chimp&See, which hosts camera trap videos of chimpanzees (Pan troglodytes) and other species across Equatorial Africa. In particular, we compared detection and identification of individual chimpanzees by citizen scientists with that of experts with years of experience studying those chimpanzees. We found that citizen scientists typically detected the same number of individual chimpanzees as experts, but assigned far fewer identifications (IDs) to those individuals. Those IDs assigned, however, were nearly always in agreement with the IDs provided by experts. We applied the data sets of citizen scientists and experts by constructing social networks from each. We found that both social networks were relatively robust and shared a similar structure, as well as having positively correlated individual network positions. Our findings demonstrate that, although citizen scientists produced a smaller data set based on fewer confirmed IDs, the data strongly reflect expert classifications and can be used for meaningful assessments of group structure and dynamics. This approach expands opportunities for social research and conservation monitoring in great apes and many other individually identifiable species., Citizen science has expanded rapidly in popularity, leading to a growing need to ensure data accuracy in citizen science research projects. We validated the accuracy of chimpanzee detection and individual identification data from the online citizen scientist platform Chimp&See, which hosts camera trap videos of chimpanzees and other species across Equatorial Africa. When comparing data from citizen scientists with those of experts who coded the same videos, we found a high level of agreement in detecting and identifying chimpanzees, although citizen scientists assigned fewer IDs overall. The resulting citizen scientist data could be used to construct a robust social network with a similar structure and network positions to that constructed from expert data coded from the same camera trap videos.

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Stable isotope analysis is an increasingly used molecular tool to reconstruct the diet and ecology of elusive primates such as unhabituated chimpanzees. The consumption of C4plant feeding termites by chimpanzees may partly explain the relatively high carbon isotope values reported for some chimpanzee communities. However, the modest availability of termite isotope data as well as the diversity and cryptic ecology of termites potentially consumed by chimpanzees obscures our ability to assess the plausibility of these termites as a C4resource. Here we report the carbon and nitrogen isotope values from 79Macrotermestermite samples from six savanna woodland chimpanzee research sites across equatorial Africa. Using mixing models, we estimated the proportion ofMacrotermesC4plant consumption across savanna woodland sites. Additionally, we tested for isotopic differences between termite colonies in different vegetation types and between the social castes within the same colony in a subset of 47 samples from 12 mounds. We found thatMacrotermescarbon isotope values were indistinguishable from those of C3plants. Only 5 to 15% ofMacrotermesdiets were comprised of C4plants across sites, suggesting that they cannot be considered a C4food resource substantially influencing the isotope signatures of consumers. In theMacrotermessubsample, vegetation type and caste were significantly correlated with termite carbon values, but not with nitrogen isotope values. LargeMacrotermessoldiers, preferentially consumed by chimpanzees, had comparably low carbon isotope values relative to other termite castes. We conclude thatMacrotermesconsumption is unlikely to result in high carbon isotope values in either extant chimpanzees or fossil hominins.

Funder: Max-Planck-Gesellschaft (Max Planck Society); doi: https://doi.org/10.13039/501100004189, Funder: Heinz L. Krekeler Foundation, Large brains and behavioural innovation are positively correlated, species-specific traits, associated with the behavioural flexibility animals need for adapting to seasonal and unpredictable habitats. Similar ecological challenges would have been important drivers throughout human evolution. However, studies examining the influence of environmental variability on within-species behavioural diversity are lacking despite the critical assumption that population diversification precedes genetic divergence and speciation. Here, using a dataset of 144 wild chimpanzee (Pan troglodytes) communities, we show that chimpanzees exhibit greater behavioural diversity in environments with more variability — in both recent and historical timescales. Notably, distance from Pleistocene forest refugia is associated with the presence of a larger number of behavioural traits, including both tool and non-tool use behaviours. Since more than half of the behaviours investigated are also likely to be cultural, we suggest that environmental variability was a critical evolutionary force promoting the behavioural, as well as cultural diversification of great apes.

AimPaleoclimate reconstructions have enhanced our understanding of how past climates may have shaped present-day biodiversity. We hypothesize that habitat stability in historical Afrotropical refugia played a major role in the habitat suitability and persistence of chimpanzees (Pan troglodytes) during the late Quaternary. We aimed to build a dynamic model of changing habitat suitability for chimpanzees at fine spatio-temporal scales to provide a new resource for understanding their ecology, behaviour and evolution.LocationAfrotropics.TaxonChimpanzee (Pan troglodytes), including all four subspecies (P. t. verus, P. t. ellioti, P. t. troglodytes, P. t. schweinfurthii).MethodsWe used downscaled bioclimatic variables representing monthly temperature and precipitation estimates, historical human population density data and an extensive database of georeferenced presence points to infer chimpanzee habitat suitability at 62 paleoclimatic time periods across the Afrotropics based on ensemble species distribution models. We mapped habitat stability over time using an approach that accounts for dispersal between time periods, and compared our modelled stability estimates to existing knowledge of Afrotropical refugia. Our models cover a spatial resolution of 0.0467 degrees (approximately 5.19 km2 grid cells) and a temporal resolution of every 1,000–4,000 years dating back to the Last Interglacial (120,000 BP).ResultsOur results show high habitat stability concordant with known historical forest refugia across Africa, but suggest that their extents are underestimated for chimpanzees. We provide the first fine-grained dynamic map of historical chimpanzee habitat suitability since the Last Interglacial which is suspected to have influenced a number of ecological-evolutionary processes, such as the emergence of complex patterns of behavioural and genetic diversity.Main ConclusionsWe provide a novel resource that can be used to reveal spatio-temporally explicit insights into the role of refugia in determining chimpanzee behavioural, ecological and genetic diversity. This methodology can be applied to other taxonomic groups and geographic areas where sufficient data are available.

Primates often consume either bark or cambium (inner bark) as a fallback food to complete their diet during periods of food scarcity. Wild chimpanzees exhibit great behavioral diversity across Africa, as studies of new populations frequently reveal. Since 2014, we have been using a combination of camera traps and indirect signs to study the ecology and behavior of wild chimpanzees (Pan troglodytes verus) in Comoé National Park, Ivory Coast, to document and understand the behavioral adaptations that help them to survive in a savanna–forest mosaic landscape. We found that Comoé chimpanzees peel the bark of the buttresses of kapok tree (Ceiba pentandra) trees to eat the cambium underneath. Individuals of all sex/age classes across at least six neighboring communities peeled the bark, but only during the late rainy season and beginning of the dry season, when cambium may represent an important fallback food. Baboons (Papio anubis) also target the same trees but mainly eat the bark itself. Most of the bark-peeling wounds on Ceiba trees healed completely within 2 years, seemingly without any permanent damage. We recorded chimpanzees visiting trees in early stages of wound recovery but leaving them unpeeled. Only 6% of peeled trees (N = 53) were reexploited after a year, suggesting that chimpanzees waited for the rest of the trees to regrow the bark fully before peeling them again, thus using them sustainably. Many human groups of hunter-gatherers and herders exploited cambium sustainably in the past. The observation that similar sustainable bark-peeling behavior evolved in both chimpanzees and humans suggests that it has an important adaptive value in harsh environments when other food sources become seasonally scarce, by avoiding the depletion of the resource and keeping it available for periods of scarcity.

The social structure of primates has recently been shown to influence the composition of their microbiomes. What is less clear is how the microbiome composition of primates might influence their social behavior, either in general or with particular reference to hominins. Here we use a comparative approach to understand how microbiomes of hominins have, or might have, changed since the last common ancestor of chimpanzees and humans, roughly six million years ago. We focus on microbiomes associated with social evolution, namely those hosted or influenced by stomachs, intestines, armpits, and food fermentation. In doing so, we highlight the potential influence of microbiomes in hominin evolution while also offering a series of hypotheses and questions with regard to evolution of human stomach acidity, the factors structuring gut microbiomes, the functional consequences of changes in armpit ecology, and whether Homo erectus was engaged in fermentation. We conclude by briefly considering the possibility that hominin social behavior was influenced by prosocial microbes whose fitness was favored by social interactions among individual hominins.

Anthrax is a globally important animal disease and zoonosis. Despite this, our current knowledge of anthrax ecology is largely limited to arid ecosystems, where outbreaks are most commonly reported. Here we show that the dynamics of an anthrax-causing agent, Bacillus cereus biovar anthracis, in a tropical rainforest have severe consequences for local wildlife communities. Using data and samples collected over three decades, we show that rainforest anthrax is a persistent and widespread cause of death for a broad range of mammalian hosts. We predict that this pathogen will accelerate the decline and possibly result in the extirpation of local chimpanzee (Pan troglodytes verus) populations. We present the epidemiology of a cryptic pathogen and show that its presence has important implications for conservation.

Wild chimpanzees regularly use tools, made from sticks, leaves, or stone, to find flexible solutions to the ecological challenges of their environment. Nevertheless, some studies suggest strong limitations in the tool-using capabilities of chimpanzees. In this context, we present the discovery of a newly observed tool-use behavior in a population of chimpanzees (Pan troglodytes verus) living in the Bakoun Classified Forest, Guinea, where a temporary research site was established for 15 months. Bakoun chimpanzees of every age-sex class were observed to fish for freshwater green algae, Spirogrya sp., from rivers, streams, and ponds using long sticks and twigs, ranging from 9 cm up to 4.31 m in length. Using remote camera trap footage from 11 different algae fishing sites within an 85-km2 study area, we found that algae fishing occurred frequently during the dry season and was non-existent during the rainy season. Chimpanzees were observed algae fishing for as little as 1 min to just over an hour, with an average duration of 9.09 min. We estimate that 364 g of Spirogyra algae could be retrieved in this time, based on human trials in the field. Only one other chimpanzee population living in Bossou, Guinea, has been described to customarily scoop algae from the surface of the water using primarily herbaceous tools. Here, we describe the new behavior found at Bakoun and compare it to the algae scooping observed in Bossou chimpanzees and the occasional variant reported in Odzala, Republic of the Congo. As these algae are reported to be high in protein, carbohydrates, and minerals, we hypothesize that chimpanzees are obtaining a nutritional benefit from this seasonally available resource.

Obtaining reliable population size or abundance estimates of endangered species is critical for their conservation and management. Genotyping non-invasively collected samples is an effective way to gain insights into the number and grouping patterns of rare or elusive animals. In this study we used genetic capture–recapture estimators to obtain a precise estimate of the size of a western gorilla population inhabiting an intensely sampled 101 km 2 area in Loango National Park, Gabon. Using 394 putative gorilla samples collected opportunistically over a 3 year period, we identified 83 unique genotypes. We used a rarefaction curve, Bayesian estimator and two maximum-likelihood methods to estimate that between 87 and 107 individuals used the study area between February 2005 and September 2007. The confidence interval surrounding the genetic estimate was smaller than that obtained using traditional ape survey methods. In addition, genetic analysis showed that gorilla and chimpanzee faeces were identified with 98% and 95% accuracy in the field, respectively. Patterns of co-occurrence of individual gorillas suggest that at least 11 gorilla social groups and five lone silverback males lived in the study area and that several individuals transferred between groups during the 3-year study period. When properly designed and implemented as part of a long-term biomonitoring program, genetic capture-recapture should prove an invaluable tool for evaluating, even on a large-scale, the population size and dynamics of apes and other elusive species.

Compared with other African apes, eastern gorillas ( Gorilla beringei ) have been little studied genetically. We used analysis of autosomal DNA genotypes obtained from non-invasively collected faecal samples to estimate the evolutionary histories of the two extant mountain gorilla populations and the closely related eastern lowland gorillas. Our results suggest that eastern lowland gorillas and mountain gorillas split beginning some 10 000 years ago, followed 5000 years ago by the split of the two mountain gorilla populations of Bwindi Impenetrable National Park and the Virungas Massif. All three populations have decreased in effective population size, with particularly substantial 10-fold decreases for the mountain gorillas. These dynamics probably reflect responses to habitat changes resulting from climate fluctuations over the past 20 000 years as well as increasing human influence in this densely populated region in the last several thousand years.

Human ethnographic knowledge covers hundreds of societies, whereas chimpanzee ethnography encompasses at most 15 communities. Using termite fishing as a window into the richness of chimpanzee cultural diversity, we address a potential sampling bias with 39 additional communities across Africa. Previously, termite fishing was known from eight locations with two distinguishable techniques observed in only two communities. Here, we add nine termite-fishing communities not studied before, revealing 38 different technical elements, as well as community-specific combinations of three to seven elements. Thirty of those were not ecologically constrained, permitting the investigation of chimpanzee termite-fishing culture. The number and combination of elements shared among individuals were more similar within communities than between them, thus supporting community-majority conformity via social imitation. The variation in community-specific combinations of elements parallels cultural diversity in human greeting norms or chopstick etiquette. We suggest that termite fishing in wild chimpanzees shows some elements of cumulative cultural diversity.