Wild Chimpanzees Research Articles

Comparing Methods for Assessing Chimpanzee (Pan troglodytes schweinfurthii) Party Size: Observations, Camera Traps, and Bed Counts from a Savanna\u2013Woodland Mosaic in the Issa Valley, Tanzania

Studying animal grouping behavior is important for understanding the causes and consequences of sociality and has implications for conservation. Chimpanzee (Pan troglodytes) party size is often assessed by counting individuals or extracted indirectly from camera trap footage or the number of nests. Little is known, however, about consistency across methods for estimating party size. We collected party size data for wild chimpanzees in the Issa valley, western Tanzania, using direct observations, camera traps, and nest counts over six years (2012–2018). We compared mean monthly party size estimates calculated using each method and found that estimates derived from direct observations were weakly positively correlated with those derived from camera traps. Estimates from nest counts were not significantly correlated with either direct observations or camera traps. Overall observed party size was significantly larger than that estimated from both camera traps and nest counts. In both the dry and wet seasons, observed party size was significantly larger than camera trap party size, but not significantly larger than nest party size. Finally, overall party size and wet season party size estimated from camera traps were significantly smaller than nest party size, but this was not the case in the dry season. Our results reveal how data collection methods influence party size estimates in unhabituated chimpanzees and have implications for comparative analysis within and across primate communities. Specifically, future work must consider how estimates were calculated before we can reliably investigate environmental influences on primate behavior.

Consequences of maternal loss before and after weaning in male and female wild chimpanzees

The mother-offspring relationship is paramount in most mammals and infant survival often depends on maternal investment. In species with prolonged periods of development or co-residence, mothers may continue to influence their offspring’s outcomes beyond nutritional independence with benefits biased towards the philopatric sex. Chimpanzees (Pan troglodytes) are long-lived mammals with a protracted period of immaturity during which offspring continue to travel with their mothers. In contrast to most mammals, chimpanzees are also typically male philopatric. Here, we use over 50 years of demographic data from two communities in Gombe National Park, Tanzania, to examine the survival and longevity of both male and female chimpanzees that experienced maternal loss during three different age categories. Males who were orphaned between the ages of 0–4.99 years, 5–9.99 years, and 10–14.99 years all faced significantly lower survival than non-orphans and died earlier than expected. Females faced similarly reduced survival probabilities when orphaned between 0–4.99 and 5–9.99 years of age; however, females who experienced maternal loss between 10 and 14.99 years of age were no more likely to die than non-orphans. Females orphaned in this later age class also lived significantly longer beyond maternal loss than their male counterparts. As observed in other mammals, philopatric male chimpanzees may continue to benefit from their mother’s ecological knowledge, whereas maternal influence on female offspring likely fades as they prepare to emigrate. These results emphasize how maternal influence on offspring outcomes can extend well beyond weaning, particularly for the philopatric sex. Mammalian mothers are crucial to their infant’s survival and in species where offspring continue to live with their mothers after weaning, maternal influence may extend beyond dependence on mother’s milk. While in most group-living mammals females remain in their natal group, chimpanzees typically display the opposite pattern with males residing alongside their mothers into adulthood. Using over 50 years of data on wild chimpanzees, we investigated the consequences of maternal loss both before and after weaning. We found that both males and females orphaned up to 10 years of age were less likely to survive than non-orphans; however, only males orphaned between 10 and 15 years also faced lower survival. These results emphasize how chimpanzee mothers continue to matter for offspring beyond infancy and provide novel data on reduced maternal influence on survival for daughters compared to sons.

Forest fragments become farmland: Dietary Response of wild chimpanzees (Pan troglodytes) to fast-changing anthropogenic landscapes.

Behavioral flexibility, including an ability to modify feeding behavior, is a key trait enabling primates to survive in forest fragments. In human-dominated landscapes, unprotected forest fragments can become progressively degraded, and maybe cleared entirely, challenging the capacity of primates to adjust to the changes. We examined responses of wild chimpanzees (Pan troglodytes schweinfurthii) to major habitat change: that is, clearance of forest fragments for agriculture. Over 7 years, fragments in Bulindi, Uganda, were reduced in size by 80%. We compared the chimpanzees' diet at the start and end of this period of rapid deforestation, using data derived mainly from fecal analysis. Similar to other long-term study populations, chimpanzees in Bulindi have a diverse diet comprising over 169 plant foods. However, extensive deforestation seemed to impact their feeding ecology. Dietary changes after fragment clearance included reduced overall frugivory, reduced intake of figs (Ficus spp.; formerly a dietary "staple" for these chimpanzees), and reduced variety of fruits in fecal samples. Nevertheless, the magnitude of most changes was remarkably minor given the extent of forest loss. Agricultural fruits increased in dietary importance, with crops accounting for a greater proportion of fruits in fecal samples after deforestation. In particular, cultivated jackfruit (Artocarpus heterophyllus) became a "staple" food for the chimpanzees but was scarcely eaten before fragment clearance. Crops offer some nutritional benefits for primates, being high in carbohydrate energy and low in hard-to-digest fiber. Thus, crop feeding may have offset foraging costs associated with loss of wild foods and reduced overall frugivory for the chimpanzees. The adaptability of many primates offers hope for their conservation in fragmented, rural landscapes. However, long-term data are needed to establish whether potential benefits (i.e. energetic, reproductive) of foraging in agricultural matrix habitats outweigh fitness costs from anthropogenic mortality risk for chimpanzees and other adaptable primates.

Maternal effects on offspring growth indicate post-weaning juvenile dependence in chimpanzees (Pan troglodytes verus)

BackgroundIn animals with altricial offspring, most growth occurs after birth and may be optimized by post-natal maternal care. Maternal effects on growth may be influenced by individual characteristics of the mothers, such as social status, individual investment strategies and the length of association with offspring. The prolonged juvenile dependence seen in humans is a distinctive life history adaptation, which may have evolved to facilitate sustained somatic and brain growth.In chimpanzees, offspring are typically weaned at approximately 4 years old, yet immature individuals continue to associate with their mothers for up to 10 years beyond weaning. Whether this lengthy association or the individual characteristics of mothers influences growth patterns in this species is not clear.The relationship between urinary creatinine and specific gravity is an established non-invasive measure of muscle mass in humans and chimpanzees. We analysed the urinary creatinine and specific gravity of 1318 urine samples from 70 wild chimpanzees from the Taï Forest, Ivory Coast aged 4 to 15 years.ResultsWe showed a clear increase in urinary creatinine levels with age in both males and females, replicating established growth curves in this species and reaffirming this measure as a reliable proxy for lean body mass. Comparing those who experience maternal loss (orphans) with non-orphan chimpanzees, maternal presence beyond weaning age and into late juvenility positively influenced offspring muscle mass throughout ontogeny such that orphans had significantly less muscle mass than age-matched non-orphans. In age-matched offspring with mothers, those with high-ranking mothers had greater muscle mass. Accounting for variation in muscle mass attributable to maternal presence, we found no effect of maternal investment (length of inter birth interval, from own birth to birth of following sibling) on offspring muscle mass.ConclusionChimpanzee mothers have an extended and multi-faceted influence on offspring phenotypes. Our results suggest that maternal investment extends beyond lactation and into early adulthood and has clear benefits to offspring physical development. Therefore, prolonged juvenile dependence, although unique in its form in human societies, may be a trait with deeper evolutionary origins.

Vpu of a Simian Immunodeficiency Virus Isolated from Greater Spot-Nosed Monkey Antagonizes Human BST-2 via Two AxxxxxxxW Motifs.

BST-2/CD317/tetherin is a host transmembrane protein that potently inhibits human immunodeficiency virus type 1 (HIV-1) virion release by tethering the nascent virions to the plasma membrane. Viral protein U (Vpu) is an accessory protein encoded by HIV-1 as well as by some simian immunodeficiency viruses (SIVs) infecting wild chimpanzees, gorillas, or monkeys (SIVcpz, SIVgor, or SIVgsn/SIVmon/SIVmus, respectively). HIV-1 Vpu directly binds to and downregulates human BST-2. The antagonism is highly species specific because the amino acid sequences of BST-2 are different among animal species. Here, we show that Vpu proteins from several SIVcpz, SIVgsn, SIVmon, or SIVmus isolates fail to antagonize human BST-2. Only Vpu from an SIVgsn isolate (SIVgsn-99CM71 [SIVgsn71]) was able to antagonize human BST-2 as well as BST-2 of its natural host, greater spot-nosed monkey (GSN). This SIVgsn Vpu interacted with human BST-2, downregulated cell surface human BST-2 expression, and facilitated HIV-1 virion release in the presence of human BST-2. While the unique 14AxxxxxxxW22 motif in the transmembrane domain of HIV-1NL4-3Vpu was reported to be important for antagonizing human BST-2, we show here that two AxxxxxxxW motifs (A22W30 and A25W33) exist in SIVgsn71 Vpu. Only the A22W30 motif was needed for SIVgsn71 Vpu to antagonize GSN BST-2, suggesting that the mechanism of this antagonism resembles that of HIV-1NL4-3 Vpu against human BST-2. Interestingly, SIVgsn71 Vpu requires two AxxxxxxxW (A22W30 and A25W33) motifs to antagonize human BST-2, suggesting an as-yet-undefined way that SIVgsn71 Vpu works against human BST-2. These results imply an evolutionary impact of primate BST-2 on lentiviral Vpu.IMPORTANCE Genetic alterations conferring a selective advantage in protecting from life-threating pathogens are maintained during evolution. In fact, the amino acid sequences of BST-2 differ among primate animals and their susceptibility to viral proteins is species specific, suggesting that such genetic diversity has arisen through the evolutionarily controlled balance between the host and pathogens. The M (main) group of HIV-1 is thought to be derived from SIVcpz, which utilizes Nef, but not Vpu, to antagonize chimpanzee BST-2. SIVcpz Nef is, however, unable to antagonize human BST-2, and Vpu was consequently chosen again as an antagonist against human BST-2 in the context of HIV-1. Studies on how Vpu lost and acquired this ability, together with the distinct mechanisms by which SIVgsn71 Vpu binds to and downregulates human or GSN BST-2, may help to explain the evolution of this lentiviral protein as a result of host-pathogen interactions.

Between-Group Competition Impacts Reproductive Success in Wild Chimpanzees.

SummaryBetween-group competition in social animals appears to be a prominent selective pressure shaping the evolution of territoriality and cooperation [1, 2, 3, 4]. Evidence for an effect of between-group competition on fitness in territorial species, however, is mostly lacking because of difficulty in measuring between-group competition and its long-term impact [5]. Between-group competition corresponds to a complex set of interactions between neighboring groups, and its intensity seems to depend on the competitive abilities of each interacting group [6, 7]. We tested whether the competitive ability of groups and the pressure exerted by neighboring groups affected the reproductive success of wild female chimpanzees (Pan troglodytes verus). Using long-term data on four neighboring groups in the Taï National Park, Côte d’Ivoire, collected over the course of 54 observation years, we measured the competitive ability of habituated groups using the number of mature males and the pressure exerted by non-habituated neighbors with an index of neighbor pressure that combined the frequency of neighboring encounters and related spatial information. Importantly, we found that experiencing low neighbor pressure provides fitness benefits through increased offspring survival and shorter inter-birth intervals. Also, many males in a group are associated with shorter inter-birth intervals. We conclude that high between-group competition hampers fast reproduction and offspring survival when exposure is during the prenatal period. Our findings suggest that having many males in a group results in fitness benefits and that between-group competition should be considered as a potential selective pressure that shaped key social adaptations in the hominoid lineage.

The Legacy of Jane Goodall: Using Children's Literature to Teach about an Iconic Scientist

The Legacy of Jane Goodall:Using Children's Literature to Teach about an Iconic Scientist David Campos (bio) When I was a boy in the 1970s, I watched a National Geographic documentary about a young woman scientist who traveled from her native United Kingdom to live in the forests of Tanzania to learn about chimpanzees in their natural habitat. The documentary, Miss Goodall and the Wild Chimpanzees (1965), left me inspired by her unbridled enthusiasm. Indeed, Jane Goodall's lifelong passion for observing animals compelled her to leave the comforts of her home to live in the remote forest and study as much as she could about chimpanzees. For years throughout my schooling, I would think about Jane Goodall and wonder what had become of her. Without the aid and benefit of the Internet at that time, I was left speculating whether her adventurous quest proved valuable. Two decades later, I was teaching second grade. By happenstance, I found a videocassette of that documentary that had piqued my curiosity for the dedicated woman who had a penchant for observing and socially connecting with chimpanzees. I decided to show my students the documentary with the aim of introducing the living scientist and recognizing her contributions to primatology, while stimulating their inquisitive nature to pursue their own study of animals. At the time, children's books about Jane Goodall were not readily available, so I used encyclopedic entries that my students and I read together to learn more about her life work. Click for larger view View full resolution Indeed, the children's literature on Jane Good-all while I was growing up and available to me as a young public-school teacher was scarce. At the time it seemed nonexistent. Today, however, there is a wide range of children's books that teachers, librarians, and parents can use to offer insight into Goodall's legacy, such as the 2012 Caldecott Honor book Me…Jane (McDonnell; 2011). My goal in this article is to share how you can use these children's books as instructional tools to help students develop historical [End Page 79] knowledge about Jane Goodall and recognize her contributions to science. Through their reading endeavors, I expect that students can become inspired to pursue their own research or take action against injustice to animals or humans alike. Exploring the Lived Experiences of Jane Goodall through Children's Books There are many contemporary children's books on Jane Goodall. Plenty of them share the same elements of her inspiring story through salient pictures and photographs and powerful messages, leaving young readers with lasting impressions. The principal advantage of having a spread of books that recount these aspects of Goodall's life is that you can use the inherent text variations to scaffold instruction and support all learners. You can choose from these books to meet the unique needs of individual children predicated on different features. Reading levels: A range of publications exist, from a board book to picture and chapter books and a graphic novel. You can present the books first, allow the students to browse the content and text features, and then help them select ones that align with their reading level: not terribly hard or easy, but challenging enough. Preferences: Of course, students should be given the opportunity to select their own books. However, you may want to demonstrate how the presentation of content differs among them. You can compare the books composed of hand-painted pictures with those that display vivid photographs and those that offer differing mediums. The students can then select the books they favor based on the graphic representations they find appealing. Click for larger view View full resolution Reading purposes and interests: You can remind students that readers often have a purpose when they select books: to be entertained, to strengthen their understanding of a topic, or to learn a new skill, among others, not to mention a blend of these intentions. Moreover, you can emphasize that knowing their purpose enhances the reading experience. As all teachers and librarians can attest, when presenting books to children, certain factors certainly matter: the literary merit; the authenticity of the content; the unification of text, illustrations...

Teaching varies with task complexity in wild chimpanzees

Cumulative culture is a transformative force in human evolution, but the social underpinnings of this capacity are debated. Identifying social influences on how chimpanzees acquire tool tasks of differing complexity may help illuminate the evolutionary origins of technology in our own lineage. Humans routinely transfer tools to novices to scaffold their skill development. While tool transfers occur in wild chimpanzees and fulfill criteria for teaching, it is unknown whether this form of helping varies between populations and across tasks. Applying standardized methods, we compared tool transfers during termite gathering by chimpanzees in the Goualougo Triangle, Republic of Congo, and in Gombe, Tanzania. At Goualougo, chimpanzees use multiple, different tool types sequentially, choose specific raw materials, and perform modifications that improve tool efficiency, which could make it challenging for novices to manufacture suitable tools. Termite gathering at Gombe involves a single tool type, fishing probes, which can be manufactured from various materials. Multiple measures indicated population differences in tool-transfer behavior. The rate of transfers and probability of transfer upon request were significantly higher at Goualougo, while resistance to transfers was significantly higher at Gombe. Active transfers of tools in which possessors moved to facilitate possession change upon request occurred only at Goualougo, where they were the most common transfer type. At Gombe, tool requests were typically refused. We suggest that these population differences in tool-transfer behavior may relate to task complexity and that active helping plays an enhanced role in the cultural transmission of complex technology in wild apes.

Dominance rank and the presence of sexually receptive females predict feces-measured body temperature in male chimpanzees.

Quantifying the costs of mating is key for understanding life-history trade-offs. As a reflection of metabolic rate, body temperature is one metric for assaying these costs. However, conventional methods for measuring body temperature are invasive and unsuitable for the study of free-living populations of endangered species, including great apes. A promising proxy for body temperature is fecal temperature, the internal temperature of fecal deposits shortly following defecation. We validated this method with humans, finding that maximum fecal temperature is a reliable proxy for rectal temperature. We then applied this method to wild chimpanzees (Pan troglodytes schweinfurthii) at Ngogo, Kibale National Park, Uganda. We collected and analyzed 101 fecal temperature measurements from 43 adult chimpanzees (male: N = 28; female: N = 15). Chimpanzee fecal temperature ranged from 33.4 to 38.9 °C, with a mean of 35.8 °C. Although fecal temperature was not predicted by sex, age, or ambient temperature, male fecal temperature was 1.1 °C higher on days when sexually receptive females were present and was positively correlated with male dominance rank. Post hoc analyses showed that overall copulation rates, but not aggression rates, were positively correlated with fecal temperature, suggesting that sexual physiology and behavior best explain mating-related temperature variation. Together, these results indicate fecal temperature is a reliable proxy for core body temperature in large-bodied mammals, captures metabolic costs associated with male mating behavior, and represents a valuable noninvasive tool for biological field research.

Sources of variation in weaned age among wild chimpanzees in Gombe National Park, Tanzania.

A key feature of human life history evolution is that modern humans wean their infants 2-4 years earlier on average than African apes. However, our understanding of weaning variation in apes remains limited. Here we provide the first such report in chimpanzees by examining weaned age variation using long-term data from Gombe National Park, Tanzania. We analyzed 41 years of observational behavioral data from 65 offspring of 29 mothers to examine the relationships between weaned age (defined as cessation of suckling) in wild chimpanzees and maternal age, dominance rank and parity, and offspring sex. We used Cox proportional hazards regression with mixed effects to model time to weaning and to examine potential sources of variation in offspring weaned age. We found that male offspring were less likely than female offspring to wean by a given age and that weaned age of males varied more than weaned age of females. In addition, maternal dominance rank interacted with offspring age, such that low-ranking mothers were less likely to wean offspring early, but this effect decreased with offspring age. We found that male offspring and offspring of low-ranking females were less likely to wean early, but did not find evidence for variable weaning according to maternal age or parity. As more data accumulate, we will be better able to disentangle the effects of maternal dominance rank, age and parity. Such studies will not only provide a richer understanding of living ape life history characteristics, but will also provide an important framework for understanding the evolution of early weaning in humans.

Chimpanzees use tree species with a resonant timbre for accumulative stone throwing.

Animals use tools for communication relatively rarely compared to tool use for extractive foraging. We investigated the tool-use behaviour accumulative stone throwing (AST) in wild chimpanzees, who regularly throw rocks at trees, producing impact sounds and resulting in the aggregations of rocks. The function of AST remains unknown but appears to be communication-related. We conducted field experiments to test whether impact sounds produced by throwing rocks at trees varied according to the tree's properties. Specifically, we compared impact sounds of AST and non-AST tree species. We measured three acoustic descriptors related to intrinsic timbre quality, and found that AST tree species produced impact sounds that were less damped, with spectral energy concentrated at lower frequencies compared to non-AST tree species. Buttress roots in particular produced timbres with low-frequency energy (low spectral centroid) and slower signal onset (longer attack time). In summary, chimpanzees use tree species capable of producing more resonant sounds for AST compared to other tree species available.

Metagenomic analysis of dental calculus in ancient Egyptian baboons

Dental calculus, or mineralized plaque, represents a record of ancient biomolecules and food residues. Recently, ancient metagenomics made it possible to unlock the wealth of microbial and dietary information of dental calculus to reconstruct oral microbiomes and lifestyle of humans from the past. Although most studies have so far focused on ancient humans, dental calculus is known to form in a wide range of animals, potentially informing on how human-animal interactions changed the animals’ oral ecology. Here, we characterise the oral microbiome of six ancient Egyptian baboons held in captivity during the late Pharaonic era (9th–6th centuries BC) and of two historical baboons from a zoo via shotgun metagenomics. We demonstrate that these captive baboons possessed a distinctive oral microbiome when compared to ancient and modern humans, Neanderthals and a wild chimpanzee. These results may reflect the omnivorous dietary behaviour of baboons, even though health, food provisioning and other factors associated with human management, may have changed the baboons’ oral microbiome. We anticipate our study to be a starting point for more extensive studies on ancient animal oral microbiomes to examine the extent to which domestication and human management in the past affected the diet, health and lifestyle of target animals.

Chimpanzee (Pan troglodytes schweinfurthii) Group Sleep and Pathogen-Vector Avoidance: Experimental Support for the Encounter-Dilution Effect

Sleep is essential for survival, yet it represents a time of extreme vulnerability, including through exposure to parasites and pathogens transmitted by biting insects. To reduce the risks of exposure to vector-borne disease, the encounter-dilution hypothesis proposes that the formation of groups at sleep sites is influenced by a “selfish herd” behavior, where individuals dilute risk by sleeping with other group members. To investigate this hypothesis in the context of chimpanzee (Pan troglodytes schweinfurthii) sleep site selection, we employed four light traps that we also baited with nontoxic chemical attractants to capture insects throughout the night. Across 74 nights with 294 traps set, we collected 66,545 individual insects. Consistent with the encounter-dilution hypothesis, we found that insect exposure, inferred by absolute numbers of insects caught in nighttime traps, was strongly influenced by the grouping of traps. Specifically, single traps caught more insects—including vector transmitting female mosquitoes—than grouped traps, and the number of insects caught increased with increasing distance between grouped traps. Moreover, ground sleep sites caught fewer insects than arboreal sleep sites. In addition, traps associated with Cynometra alexandri trees resulted in significantly lower catch rates than Pseudospondias microcarpa–associated traps. Our results suggest wild chimpanzees use group sleep as a strategy to avoid biting insects that serve as hosts for vector-borne diseases.

Oral microbiome diversity in chimpanzees from Gombe National Park

Historic calcified dental plaque (dental calculus) can provide a unique perspective into the health status of past human populations but currently no studies have focused on the oral microbial ecosystem of other primates, including our closest relatives, within the hominids. Here we use ancient DNA extraction methods, shotgun library preparation, and next generation Illumina sequencing to examine oral microbiota from 19 dental calculus samples recovered from wild chimpanzees (Pan troglodytes schweinfurthii) who died in Gombe National Park, Tanzania. The resulting sequences were trimmed for quality, analyzed using MALT, MEGAN, and alignment scripts, and integrated with previously published dental calculus microbiome data. We report significant differences in oral microbiome phyla between chimpanzees and anatomically modern humans (AMH), with chimpanzees possessing a greater abundance of Bacteroidetes and Fusobacteria, and AMH showing higher Firmicutes and Proteobacteria. Our results suggest that by using an enterotype clustering method, results cluster largely based on host species. These clusters are driven by Porphyromonas and Fusobacterium genera in chimpanzees and Haemophilus and Streptococcus in AMH. Additionally, we compare a nearly complete Porphyromonas gingivalis genome to previously published genomes recovered from human gingiva to gain perspective on evolutionary relationships across host species. Finally, using shotgun sequence data we assessed indicators of diet from DNA in calculus and suggest exercising caution when making assertions related to host lifestyle. These results showcase core differences between host species and stress the importance of continued sequencing of nonhuman primate microbiomes in order to fully understand the complexity of their oral ecologies.

Patterns of Diversity and Distribution of Arboreal Social Bees’ Beehives within Chimpanzees’ Home Range in a Forest-Savanna Mosaic (Comoé National Park, Côte d’Ivoire)

The goal of this study was to explain the patterns of diversity and distribution of arboreal social bees nesting in forest habitats of the Comoé National park, within the home-ranges of wild chimpanzees that consume their honey. Investigations were done using a total sixteen plots, one hectare each, established in three habitat types (mature forest island, secondary forest island and gallery forest). The diversity and distribution of arboreal social bees was estimated with visuals searches. The exploitation of the beehives of these bee by the chimpanzees was also evaluated using chimpanzees’ honey dipping tools as indicators. Results revealed five bees’ species belonging to two tribes; Meliponini (Meliponula ferruginea, Meliponula togoensis, Meliponula bocandei, Hypotrigona gribodoi) and Apini (Apis mellifera). Frequent exploitation of the honey of stingless bees by the chimpanzees was observed, except for H. gribodoi. Meliponula ferruginea was the most exploited species by chimpanzees. A total of 114 beehives were found in the overall established plots leading to an estimated density of 2.4 beehives/ha in the study area. Among the surveyed habitats, mature forest island was found to harbor the highest beehive density (4.2 beehives/ha), followed respectively by secondary-forest island (1.9 beehives/ha) and gallery forest (1.1 beehives/ha). Finally, all bee species were found nesting in cavities of trees with a DBH ranging from 15 to 87.3 cm, with a special preference for Dialium guinneense. However, the DBH of nesting trees and beehives’ height, measured from the ground level, did not significantly influence the honey exploitation by chimpanzees. In sum bee species diversity and distribution might be important in the survival of chimpanzees of a forest savanna landscape.

Human-like adrenal development in wild chimpanzees: A longitudinal study of urinary dehydroepiandrosterone-sulfate and cortisol.

The development of theadrenalcortex varies considerably across primates, being most conspicuous in humans, where a functional zona reticularis-the site of dehydroepiandrosterone-sulfate (DHEA/S) production-does not develop until middle childhood (5-8 years). Prior reports suggest that a human-like adrenarche, associated with a sharp prepubertal increase in DHEA/S, may only occur in the genus Pan. However, the timing and variability in adrenarche in chimpanzees remain poorly described, owing to the lack of longitudinal data, or data from wild populations. Here, we use urine samples from East African chimpanzees (Pan troglodytes schweinfurthii) collected over 20 years at Kanyawara in Kibale National Park, Uganda, to trace the developmental trajectories of DHEAS (n = 1,385 samples, 53 individuals) and cortisol (n = 12,726 samples, 68 individuals). We used generalized additive models (GAM) to investigate the relationship between age, sex, and hormone levels. Adrenarche began earlier in chimpanzees (~2-3 years) compared with what has been reported in humans (6-8 years) and, unlike humans, male and female chimpanzees did not differ significantly in the timing of adrenarche nor in DHEAS concentrations overall. Similar to what has been reported in humans, cortisol production decreased through early life, reaching a nadir around puberty (8-11 years), and a sex difference emerged with males exhibiting higher urinary cortisol levels compared with females by early adulthood (15-16 years). Our study establishes that wild chimpanzees exhibit a human-like pattern of cortisol production during development and corroborates prior reports from captive chimpanzees of a human-like adrenarche, accompanied by significant developmental increases in DHEAS. While the role of these developmental hormone shifts are as yet unclear, they have been implicated in stages of rapid behavioral development once thought unique to humans, especially in regard to explaining the divergence of female and male social behavior before pubertal increases in gonadal hormones.

Differences in MHC-B diversity and KIR epitopes in two populations of wild chimpanzees

The major histocompatibility complex (MHC) class I genes play a critical role within the immune system, both by the presentation of antigens from intracellular pathogens to immunocompetent cells and by the interaction with killer cell immunoglobulin-like receptors (KIR) on natural killer cells (NK cells). Genes of the MHC are highly diverse, and MHC variation can have effects on the immune functionality of individuals; hence, comparisons of MHC diversity among closely related phylogenetic taxa may give insight into the factors responsible for the shaping of its diversity. The four geographically separated chimpanzee subspecies differ in their overall genetic diversity, have different population histories, and are confronted with different pathogens in their natural habitat, all of which may affect MHC class I DNA sequence diversity. Here, we compare the MHC-B exon two DNA sequence diversity from 24 wild western and 46 wild eastern chimpanzees using necropsy and noninvasively collected fecal samples, respectively. We found a higher MHC-B exon two nucleotide diversity, in our western than eastern chimpanzees. The inclusion of previously published MHC-B exon two data from other western and eastern chimpanzees supported this finding. In addition, our results confirm and extend the finding of a very low C1 epitope frequency at eastern chimpanzee MHC-B molecules, which likely affects the ability of these molecules to interact with NK cells. While the understanding of the differing pathogen environments encountered by disparate populations of a species is a challenging endeavor, these findings highlight the potential for these pathogens to selectively shape immune system variation.

Camera traps provide a robust alternative to direct observations for constructing social networks of wild chimpanzees

Social network analysis provides valuable opportunities to quantify the nature of social relationships in animal societies including aspects of group structure, dynamics and behaviour transmission. Remote monitoring approaches such as camera trapping offer rich data sets from groups and species that are difficult to observe, yet the robustness of these data for constructing social networks remains unexplored. Here we compared networks of party association based on camera traps with those based on direct observations over the same 9-month sampling period in a group of habituated western chimpanzees, Pan troglodytes verus. Networks based on camera traps and direct observations were both stable with sufficient sampling, and had very similar structures, patterns of sex assortment and individual network positions. However, camera trap data led to lower estimates of group density and dyadic association strengths, and slightly higher modularity, illustrating the limitations raised by differences in data collection methods for network comparisons. We then constructed a social network using camera trap data from unhabituated eastern chimpanzees, P.t. schweinfurthii, demonstrating the feasibility of this approach in the absence of extensive prior knowledge of the study subjects. Further, differences between the eastern and western chimpanzee social networks followed expected patterns based on recognized social differences, illustrating the promise of this approach for detecting within-species social variation. Although long-term behavioural observations will continue to provide rich data for many species, camera traps offer a powerful alternative to gain information on social group dynamics in elusive or unhabituated animals, as well as to conduct systematic multisite comparative studies.

Sympatric western lowland gorillas, central chimpanzees and humans are infected with different trichomonads.

We investigated intestinal trichomonads in western lowland gorillas, central chimpanzees and humans cohabiting the forest ecosystem of Dzanga-Sangha Protected Area in Central African Republic, using the internal transcribed spacer (ITS) region and SSU rRNA gene sequences. Trichomonads belonging to the genus Tetratrichomonas were detected in 23% of the faecal samples and in all host species. Different hosts were infected with different genotypes of Tetratrichomonas. In chimpanzees, we detected tetratrichomonads from 'novel lineage 2', which was previously reported mostly in captive and wild chimpanzees. In gorillas, we found two different genotypes of Tetratrichomonas. The ITS region sequences of the more frequent genotype were identical to the sequence found in a faecal sample of a wild western lowland gorilla from Cameroon. Sequences of the second genotype from gorillas were almost identical to sequences previously obtained from an anorexic French woman. We provide the first report of the presence of intestinal tetratrichomonads in asymptomatic, apparently healthy humans. Human tetratrichomonads belonged to the lineage 7, which was previously reported in domestic and wild pigs and a domestic horse. Our findings suggest that the ecology and spatial overlap among hominids in the tropical forest ecosystem has not resulted in exchange of intestinal trichomonads among these hosts.

Maternal cannibalism in two populations of wild chimpanzees

Maternal cannibalism has been reported in several animal taxa, prompting speculations that the behavior may be part of an evolved strategy. In chimpanzees, however, maternal cannibalism has been conspicuously absent, despite high levels of infant mortality and reports of non-maternal cannibalism. The typical response of chimpanzee mothers is to abandon their deceased infant, sometimes after prolonged periods of carrying and grooming the corpse. Here, we report two anomalous observations of maternal cannibalism in communities of wild chimpanzees in Uganda and Ivory Coast and discuss the evolutionary implications. Both infants likely died under different circumstances; one apparently as a result of premature birth, the other possibly as a result of infanticide. In both cases, the mothers consumed parts of the corpse and participated in meat sharing with other group members. Neither female presented any apparent signs of ill health before or after the events. We concluded that, in both cases, cannibalizing the infant was unlikely due to health-related issues by the mothers. We discuss these observations against a background of chimpanzee mothers consistently refraining from maternal cannibalism, despite ample opportunities and nutritional advantages. We conclude that maternal cannibalism is extremely rare in this primate, likely due to early and strong mother–offspring bond formation, which may have been profoundly disrupted in the current cases.