Chimpanzees Research Articles

Relative facial width, and its association with canine size and body mass among chimpanzees and bonobos: Implications for understanding facial width-to-height ratio expression among human populations.

Facial width-to-height ratio (fWHR) has been widely investigated in the context of its role in visual communication, though there is a lack of consensus about how fWHR serves as a social signal. To better understand fWHR variation in a comparative context, we investigate the associations between fWHR and canine crown height (CCH) and body mass, respectively, among two chimpanzee subspecies (Pan troglodytes schweinfurthii, Pan troglodytes troglodytes) and bonobos (Pan paniscus). We collected landmark data from 3D surface models of 86 Pan cranial specimens to quantify fWHR and upper CCH, and to estimate body mass. We used Spearman's r and Kruskal-Wallis tests to test for significant relationships among variables, and to assess sexual dimorphism. There is an inverse relationship between fWHR and CCH in both sexes of Pan, however there are interpopulation differences in the relationship between fWHR and CCH among Pan taxa. Pan paniscus have relatively wide faces and small canine crowns, and wide faces in Pan t. schweinfurthii males may be driven by body size constraints. Pan troglodytes and Pan paniscus show fWHR dimorphism, and Pan paniscus have significantly higher fWHRs than do either Pan troglodytes subspecies. Our findings indicate that CCH and facial breadth may serve subtly different signaling functions among Pan taxa. Further research into the circumstances in which wide faces evolved among chimpanzees and bonobos will likely afford deeper insights into the function of relatively wide faces in the context of visual signaling among humans and our extinct hominin relatives.

Bio-characteristics, tissue expression of miR-375 in hypothalamic-pituitary-ovarian axis and its regulation in reproduction-related diseases

Our study concentrated on the expression of miRNA-375 in the hypothalamic-pituitary-gonadal axis of female Hu sheep. The investigation involved cloning the precursor sequence of miR-NA-375, followed by comparison with database entries and subsequent Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses. In our approach, we obtained ovaries, thalamus, cerebellum, brain, uterus, pituitary gland, hypothalamus, and pineal gland from fertile but nonpregnant Hu ewes. MiRNA extraction kit was used to extract miRNA from the above eight tissues. Real-time fluorescent quantitative polymerase chain reaction was used to evaluate the role of miR-375 in the hy-pothalamic-pituitary-gonadal axis. The results of miR-375 precursor sequence cloning were compared with those of Anopheles gambiae, Apis mellifera, Bos taurus, Drosophila melanogaster, Danio rerio, Fugu rubripes, Gallus gallus, Homo sapiens, Monodelphis domestica, Macaca mulatta, Mus musculus, Pan troglodytes, Rattus norvegicus, Tetraodon nigroviridis, Xenopus tropicalis miR-375 in miRBase database. It was found that oar-miR-375 was highly conserved. Notably, miR-375 expression in the pineal gland was significantly higher (p < 0.01) than that in the ovaries, thalamus, cerebellum, brain, uterus, pituitary gland, hypothalamus. The study also involved predicting miR-375 target genes. GO and KEGG enrichment analyses of these predicted target genes revealed that miR-375 is involved in 182 biological processes, affects 186 cellular components, and participates in 184 molecular functions. In terms of pathway enrichment, miR-375 was linked to nine pathways, including the Hippo, Wnt, and mTOR signaling pathways. This study has validated the interaction between miR-375 and its target gene FZD4, which can be recognized and bound to produce effects. These findings lead to the inference that miR-375 may play a crucial regulatory role in sheep reproduction through the Hippo pathway and Wnt pathway, laying a foundation for further exploration of miR-375’s role in this domain.

Flexibility of Gestural Production in Captive Groups of Chimpanzees (Pan troglodytes), Sumatran Orangutans (Pongo abelii), and Siamangs (Symphalangus syndactylus)

AbstractAcross species, communication systems may differ in their levels of flexibility, but comparisons are challenging, because flexibility is not operationalized in a consistent way. In this study, we investigated different aspects of flexibility in the gestural communication systems of 7 groups of captive apes (N = 53), including 19 chimpanzees (Pan troglodytes), 16 Sumatran orangutans (Pongo abelii), and 18 siamangs (Symphalangus syndactylus). We operationalized flexibility in four different ways: (i) the use of one gesture type across several contexts (i.e., contextual flexibility), (ii) the use of many gesture types in the same context (i.e., pragmatic flexibility), (iii) the production of one gesture type with different limbs and/or toward different target locations (i.e., morphological flexibility), and (iv) the ability to combine different signals into a sequence in different orders (i.e., combinational flexibility). Comparisons across individuals and species revealed variation in contextual and morphological flexibility. In particular, contextual flexibility increased with age and was overall higher in chimpanzees than siamangs. Moreover, morphological flexibility increased with social integration and was highest in siamangs and lowest in orangutans. Overall, variation largely reflected differences in social experience and possibly in the socioecological characteristics of the species. Our findings suggest that contextual and morphological flexibility might be good candidates to study interindividual and interspecific variation in primate gestural production.

Roads and Woody Vegetation Structure Are Associated With Chimpanzee (Pan troglodytes) Occurrence at Its Northern Range Limit

ABSTRACTAimThe purported defining features of chimpanzee (Pan troglodytes) biogeography are sometimes simplistic and contradictory, yet we rely on these metrics to shape conservation and management planning for this endangered ape. We analysed the cover and configuration of woody vegetation at the northern margins of the species' range in Senegal to elucidate key predictors of chimpanzee biogeography.LocationSoutheastern Senegal.TaxaWestern chimpanzee (Pan troglodytes verus).MethodsWe combined reconnaissance surveys and interviews with published accounts of chimpanzee presence to verify previous estimates of the range limits of the species. High‐resolution, multispectral satellite images were used to quantify the configuration of trees and shrubs at each site. Woody vegetation cover and physiognomy, river density and road density were compared within and outside of the species range with generalised linear mixed models.ResultsOur surveys and interviews support the current estimates of the northern limits of the species range. Chimpanzee‐occupied sites had more patchily‐distributed vegetation, greater patch edge complexity, and slightly higher river density than unoccupied sites. Unoccupied sites had more woody vegetation cover and higher road density. Of all predictors, roads had the highest impact on chimpanzee occupancy.Main ConclusionsIn line with previous findings, anthropogenic modifications of the landscape had a strong impact on chimpanzee occupancy, but surprisingly, woody vegetation cover was negatively associated with chimpanzee occupancy in this region. Instead, more specific metrics of vegetation configuration were positively associated with chimpanzee site occupancy, indicating that precise measures are needed for assessing chimpanzee biogeography at the landscape scale.

Comparative Study of the Genetic Similarity of Aquaporins through In Silico Genetic Analysis of Homo sapiens, Jaculus jaculus, Pan troglodytes, and Mus musculus

Our study aims to compare the nucleotide sequences of specific aquaporin genes (AQPs) by analysing and studying the possible similarities and differences of a number of animal species using the NCBI website, BLAST, MEGA, and MAFFT. As a practical application of modern methods and tools in molecular analysis through informatics tools. This study shows that comparing the nucleotide sequences of aquaporin genes between different species can reveal important evolutionary advances and fundamental biological adaptations. The differences and similarities discovered between humans (Homo sapiens), chimpanzees (Pan troglodytes), gerbils (Jaculus jaculus) and house mice (Mus musculus) highlight the delicate balance between genetic conservation and adaptation to different environments, enhancing our deep understanding of the molecular mechanisms that regulate water balance in different organisms.

Idiosyncratic gesture use in a mother-infant dyad in chimpanzees (Pan troglodytes schweinfurthii) in the wild

One promising method to tackle the question, “In which modality did language evolve?” is by studying the ontogenetic trajectory of signals in human’s closest living relatives, including chimpanzees (Pan troglodytes). Concerning gestures, current debates centre on four different hypotheses: “phylogenetic ritualization”, “social transmission through imitation”, “ontogenetic ritualization”, and “social negotiation”. These differ in their predictions regarding idiosyncratic gestures, making such occurrences a crucial area of investigation. Here, we describe a novel and potential idiosyncratic behaviour — ‘hand-on-eye’ — which was initially observed in one mother-infant dyad in a community of chimpanzees living in the wild. We systematically investigated the form, sequential organisation, intentionality, usage, function, and distribution of the behaviour over a five-year period. The results showed that ‘hand-on-eye’ was nearly exclusively deployed in a single mother-infant dyad, was accompanied by hallmarks of intentionality, and served to initiate or resume joint dorsal travel. Although the behaviour was observed once in each of three other mother-infant dyads, these lacked the same frequency and hallmarks of intentionality. ‘Hand-on-eye’ thus qualifies as an idiosyncratic gesture. The proposed developmental pathway gives support to both the “ontogenetic ritualization” and “social negotiation” hypotheses. It also stresses the crucial need for longitudinal approaches to tackle developmental processes that are triggered by unique circumstances and unfold over relatively long time windows.

Extractive Foraging and Grasping Postures in Sanctuary-Housed Chimpanzees (Pan Troglodytes)

Extractive Foraging and Grasping Postures in Sanctuary-Housed Chimpanzees (Pan Troglodytes)

Deep genetic substructure within bonobos.

Establishing the genetic and geographic structure of populations is fundamental, both to understand their evolutionary past and preserve their future. Nevertheless, the patterns of genetic population structure are unknown for most endangered species. This is the case for bonobos (Pan paniscus), which, together with chimpanzees (Pan troglodytes), are humans' closest living relatives. Chimpanzees live across equatorial Africa and are classified into four subspecies,1 with some genetic population substructure even within subspecies. Conversely, bonobos live exclusively in the Democratic Republic of Congo and are considered a homogeneous group with low genetic diversity,2 despite some population structure inferred from mtDNA. Nevertheless, mtDNA aside, their genetic structure remains unknown, hampering our understanding of the species and conservation efforts. Mapping bonobo genetic diversity in space is, however, challenging because, being endangered, only non-invasive sampling is possible for wild individuals. Here, we jointly analyze the exomes and mtDNA from 20 wild-born bonobos, the whole genomes of 10 captive bonobos, and the mtDNA of 136 wild individuals. We identify three genetically distinct bonobo groups of inferred Central, Western, and Far-Western geographic origin within the bonobo range. We estimate the split time between the central and western populations to be ∼145,000 years ago and genetic differentiation to be in the order of that of the closest chimpanzee subspecies. Furthermore, our estimated long-term Ne for Far-West (∼3,000) is among the lowest estimated for any great ape lineage. Our results highlight the need to attend to the bonobo substructure, both in terms of research and conservation.

Examining the Long-term Retention of Associative Stimulus Relations in Chimpanzees (Pan troglodytes)

Examining the Long-term Retention of Associative Stimulus Relations in Chimpanzees (Pan troglodytes)

Phylo-Epigenetics in Phylogeny Analyses and Evolution.

Long-standing, continuous blurring and controversies in the field of phylogenetic interspecies relations, associated with insufficient explanations for dynamics and variability of speeds of evolution in mammals, hint at a crucial missing link. It has been suggested that transgenerational epigenetic inheritance and the concealed mechanisms behind play a distinct role in mammalian evolution. Here, a comprehensive sequence alignment approach in hominid species, i.e., Homo sapiens, Homo neanderthalensis, Denisovan human, Pan troglodytes, Pan paniscus, Gorilla gorilla, and Pongo pygmaeus, comprising conserved CpG islands of housekeeping genes, uncover evidence for a distinct variability of CpG dinucleotides. Applying solely these evolutionary consistent and inconsistent CpG sites in a classic phylogenetic analysis, calibrated by the divergence time point of the common chimpanzee (P. troglodytes) and the bonobo or pygmy chimpanzee (P. paniscus), a "phylo-epigenetic" tree has been generated, which precisely recapitulates branch points and branch lengths, i.e., divergence events and relations, as they have been broadly suggested in the current literature, based on comprehensive molecular phylogenomics and fossil records of many decades. It is suggested here that CpG dinucleotide changes at CpG islands are of superior importance for evolutionary developments. These changes are successfully inherited through the germ line, determining emerging methylation profiles, and they are a central component of transgenerational epigenetic inheritance. It is hidden in the DNA, what will happen on it later.

Epidemiological Consequences of Individual Centrality on Wild Chimpanzees.

Disease outbreaks are one of the key threats to great apes and other wildlife. Because the spread of some pathogens (e.g., respiratory viruses, sexually transmitted diseases, ectoparasites) are mediated by social interactions, there is a growing interest in understanding how social networks predict the chain of pathogen transmission. In this study, we built a party network from wild chimpanzees (Pan troglodytes), and used agent-based modeling to test: (i) whether individual attributes (sex, age) predict individual centrality (i.e., whether it is more or less socially connected); (ii) whether individual centrality affects an individual's role in the chain of pathogen transmission; and, (iii) whether the basic reproduction number (R0) and infectious period modulate the influence of centrality on pathogen transmission. We show that sex and age predict individual centrality, with older males presenting many (degree centrality) and strong (strength centrality) relationships. As expected, males are more central than females within their network, and their centrality determines their probability of getting infected during simulated outbreaks. We then demonstrate that direct measures of social interaction (strength centrality), as well as eigenvector centrality, strongly predict disease dynamics in the chimpanzee community. Finally, we show that this predictive power depends on the pathogen's R0 and infectious period: individual centrality was most predictive in simulations with the most transmissible pathogens and long-lasting diseases. These findings highlight the importance of considering animal social networks when investigating disease outbreaks.

Comparing cranial suture interdigitation in humans and non-human primates: unearthing links to osteopathic cranial concept.

Since William Garner Sutherland's inception of osteopathic cranial manipulative medicine (OCMM), osteopathic physicians have practiced with the knowledge that cranial sutures exhibit motion. We hypothesize that the complexity of suture interdigitation in humans may provide clues to elucidate the concept of OCMM. We compared the interdigitation of sagittal, coronal (left and right), and lambdoid (left and right) sutures in computed tomography (CT) scans of humans and five nonhuman primate species (Gorilla gorilla, Pongo pygmaeus, Pan troglodytes, Hylobates lar, and Nasalis larvatus). Human ages are evenly distributed between 10 and 65 years of age, with an equal number of males (n=16) and females (n=16) in the sample. Nonhuman primates are all females, and the sample includes juveniles (n=6) and adults (n=34). Sutures were evaluated on a scale ranging from 0 to 3 (0: fused sutures; 1: no interdigitation; 2: low complexity; and 3: representing the highest degree of interdigitation and complexity). Based on ordinary least squares linear regression, we found no significant relationship between suture interdigitation and age in humans. Chi-square tests were utilized to assess sex differences within humans, species-level differences, and differences between humans and nonhuman primates across all five sutures. Humans exhibited a statistically significant greater degree of suture complexity than all five nonhuman species across all five sutures. These findings indicate that human suture interdigitation is more complex than their closest living relatives (African apes) and other primates (Asian monkeys and apes). We theorize that this would enable subtle movement and serve to transmit forces at the cranial sutures from dietary or ethological behaviors, similar to the pattern observed in other mammals. While humans have a softer diet compared to other living primates, the uniqueness of human craniofacial growth and extended developmental period could contribute to the necessity for complex cranial sutures. More studies are needed to understand variation in human and nonhuman sutural complexity and its relationship to cranial motion.

The archaeological visibility of chimpanzee (Pan troglodytes) nut-cracking

The earliest evidence for complex tool use in the archaeological record dates to 3.3 Ma. While wooden tools may have been used by our earliest ancestors, the evidence is absent due to poor preservation. However, insights into possible early hominin wooden tool use can be gained from observing the tool-use practices of our closest living relatives, chimpanzees (Pan troglodytes). By using stone hammers used to crack various nuts, chimpanzees leave a durable material signature comprised of formal tools and associated diagnostic fragments. While the archaeological evidence of chimpanzee wooden tool use is temporary, the combination of stone hammers and wooden anvils can create a more enduring lithic record. This study explores the lithic assemblages associated with wooden and stone anvil use at nut-cracking sites in Taï National Park, Côte d'Ivoire, using technological and use-wear analyses. Our results indicate clear differences in density, fracture patterns, and use-wear in the lithic records between wooden anvil and stone anvil sites. New archaeological excavations at six chimpanzee nut-cracking sites reveal that the anvils' material directly influences the visibility of nut-cracking evidence in the archaeological record. By examining the nature of the lithic signatures associated with wooden anvil and stone anvil use by chimpanzees, we can formulate hypotheses about the probability of such behaviors being preserved and identifiable in the Plio-Pleistocene hominin archaeological record. The variability in material signatures from nut-cracking on different anvils suggests that stone anvils leave a clear archaeological record. Evidence for wooden anvil use is likely underrepresented due to the more ephemeral nature of the associated percussive damage and material signature. It may, however, still be possible, albeit challenging, to identify wooden anvil use in the archaeological record.

Genital Wounding in Chimpanzees (Pan troglodytes): Targeted Attacks or Happenstance?

Genital Wounding in Chimpanzees (Pan troglodytes): Targeted Attacks or Happenstance?

A survey of nocturnality and risk for savanna chimpanzees at Assirik, Senegal.

Chimpanzees (Pan troglodytes) in Senegal may use nocturnality to mitigate hyperthermia risk in semi-arid environments but the degree of nocturnality for such chimpanzees also in sympatry with large carnivores remains uncertain. We compared diel activity among chimpanzees and their potential predators at Assirik in Niokolo-Koba National Park and contextualized these findings relative to other unit-groups in savanna landscapes. From 2015-2018, we generated a predator inventory using multi-modal methods and monitored the diel activity of chimpanzees and predators with camera traps [ N = 2092 camera trap (CT) days]. From 2015-2023, we also surveyed for evidence of predation during recce walks. Six potential nonhuman predators occur at Assirik, including lions (Panthera leo), leopards (Panthera pardus), spotted hyenas (Crocuta crocuta), African wild dogs (Lycaon pictus), Nile crocodiles (Crocodylus niloticus), and rock pythons (Python sebae). We documented one suspected case of a predator killing a chimpanzee. Nocturnality comprised 12.7% of CT events for chimpanzees and these events were more concentrated at twilight. Chimpanzees were more active during the day, predators were more active at night, and there was substantial temporal overlap among chimpanzees and potential predators during twilight intervals. Our findings support the hypothesis that savanna chimpanzees in Senegal are active at night in response to the extremely hot environment. We hypothesize that Assirik chimpanzees experience a tension between decreasing hyperthermia and increasing predation risk during nocturnality.

Chimpanzees (Pan troglodytes) strategically manipulate their environment to deny conspecifics access to food

Humans modify their environment to grant or prevent others’ access to valuable resources, for example by using locks. We tested whether sanctuary-living chimpanzees (N = 10) would flexibly modify their environment to either allow or deny a dominant conspecific access to a shared food source by giving them the option to change a food reward’s pathway prior to releasing it. The food could end up in one of two locations: one was accessible to both the subject and a dominant conspecific, the other one was only accessible to the subject. We further manipulated the extent of inhibitory control needed for modifying the pathway by varying the subjects’ starting position. Our subjects reoriented the pathway competitively to monopolize food but changed the pathway less often in trials with high inhibitory demands. We further show how inhibitory task demands in a social context influence chimpanzees’ future planning. Our results show that chimpanzees will strategically manipulate their environment to maximize their own and deny a dominant conspecific access to food.

Nesting ecology of chimpanzee (Pan troglodytes) in the Yoko Council Forest, Centre Cameroon: assessing nest characteristics and decay rate

ABSTRACT Lack of data on the population size of chimpanzees (Pan troglodytes) in the Yoko Council Forest (YCF), located in the Centre region of Cameroon has hindered the ability to develop conservation measures. The sustainable management of this species requires reliable knowledge of their ecology, habits and resource needs. This study was conducted from February–July 2022 to assess nesting ecology and to use nest decay rates to estimate population size. The retrospective method for studying the degradation of animal indices was used. The mean nest decay rate was 77.5 days and density was estimated at 69.3 [54.9 86.7] nests/ km2 to 113 chimpanzees per km2. We also found a high preference for nests in specific forest types, with 92% of nests in marantaceous forests, and a preference for nests to be on Khaya grandifolia (Meliaceae) (28.24%) or Uapaca guinensis (Euphorbiaceae) (27.06%) trees. The preferential position for construction of chimpanzee nests was on a branch (58.82%) as opposed to in a branch fork (40.39%), which is interesting since one would assume a fork would offer more nest stability. Our study offers crucial insights that can guide policymakers in formulating targeted conservation strategies for the substantial chimpanzee population in the YCF.

Age-related physiological dysregulation progresses slowly in semi-free-ranging chimpanzees.

Lifestyle has widespread effects on human health and aging. Prior results from chimpanzees (Pan troglodytes), one of humans' closest evolutionary relatives, indicate that these lifestyle effects may also be shared with other species, as semi-free-ranging chimpanzees fed a naturalistic diet show healthier values in several specific health biomarkers, compared with their sedentary, captive counterparts. Here, we examined how lifestyle factors associated with different environments affect rates of physiological aging in closely related chimpanzees. We compared physiological dysregulation, an index of biological aging, in semi-free-ranging chimpanzees in an African sanctuary versus captive chimpanzees in US laboratories. If the rate of aging is accelerated by high-calorie diet and sedentism, we predicted greater age-related dysregulation in the laboratory populations. Conversely, if costs of a wild lifestyle accelerate aging, then semi-free-ranging chimpanzees at the sanctuary, whose environment better approximates the wild, should show greater age-related dysregulation. We further tested whether dysregulation differed based on sex or body system, as in humans. We found that semi-free-ranging chimpanzees showed lower overall dysregulation, as well as lower age-related change in dysregulation, than laboratory chimpanzees. Males experienced lower dysregulation than females in both contexts, and the two populations exhibited distinct aging patterns based on body system. Our results support the conclusion that naturalistic living conditions result in healthier aging in chimpanzees. These data provide support for the proposal that lifestyle effects on human health and aging are conserved from deeper into our evolutionary history.

Comparative Analysis of Human-Chimpanzee Divergence in Brain Connectivity and its Genetic Correlates.

Chimpanzees (Pan troglodytes) are humans' closest living relatives, making them the most directly relevant comparison point for understanding human brain evolution. Zeroing in on the differences in brain connectivity between humans and chimpanzees can provide key insights into the specific evolutionary changes that might have occured along the human lineage. However, conducting comparisons of brain connectivity between humans and chimpanzees remains challenging, as cross-species brain atlases established within the same framework are currently lacking. Without the availability of cross-species brain atlases, the region-wise connectivity patterns between humans and chimpanzees cannot be directly compared. To address this gap, we built the first Chimpanzee Brainnetome Atlas (ChimpBNA) by following a well-established connectivity-based parcellation framework. Leveraging this new resource, we found substantial divergence in connectivity patterns across most association cortices, notably in the lateral temporal and dorsolateral prefrontal cortex between the two species. Intriguingly, these patterns significantly deviate from the patterns of cortical expansion observed in humans compared to chimpanzees. Additionally, we identified regions displaying connectional asymmetries that differed between species, likely resulting from evolutionary divergence. Genes associated with these divergent connectivities were found to be enriched in cell types crucial for cortical projection circuits and synapse formation. These genes exhibited more pronounced differences in expression patterns in regions with higher connectivity divergence, suggesting a potential foundation for brain connectivity evolution. Therefore, our study not only provides a fine-scale brain atlas of chimpanzees but also highlights the connectivity divergence between humans and chimpanzees in a more rigorous and comparative manner and suggests potential genetic correlates for the observed divergence in brain connectivity patterns between the two species. This can help us better understand the origins and development of uniquely human cognitive capabilities.

Sodium content in plant and insect food resources consumed by chimpanzees (Pan troglodytes schweinfurthii) in Gombe National Park, Tanzania.

Many nonhuman primate diets are dominated by plant foods, yet plant tissues are often poor sources of sodium-a necessary mineral for metabolism and health. Among primates, chimpanzees (Pan troglodytes), which are ripe fruit specialists, consume diverse animal, and plant resources. Insects have been proposed as a source of dietary sodium for chimpanzees, yet published data on sodium values for specific foods are limited. We assayed plants and insects commonly eaten by chimpanzees to assess their relative value as sodium sources. We used atomic absorption spectroscopy to determine sodium content of key plant foods and insects consumed by chimpanzees of Gombe National Park, Tanzania. Dietary contributions of plant and insect foods were calculated using feeding observational data. On a dry matter basis, mean sodium value of plant foods (n = 83 samples; mean = 86 ppm, SD = 92 ppm) was significantly lower than insects (n = 12; mean = 1549 ppm, SD = 807 ppm) (Wilcoxon rank sum test: W = 975, p < 0.001). All plant values were below the suggested sodium requirement (2000 ppm) for captive primates. While values of assayed insects were variable, sodium content of two commonly consumed insect prey for Gombe chimpanzees (Macrotermes soldiers and Dorylus ants) were four to five times greater than the highest plant values and likely meet requirements. We conclude that plant foods available to Gombe chimpanzees are generally poor sources of sodium while insects are important, perhaps critical, sources of sodium for this population.