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Extant great apes are characterized by a wide range of locomotor, postural and manipulative behaviours that each require the limbs to be used in different ways. In addition to external bone morphology, comparative investigation of trabecular bone, which (re‐)models to reflect loads incurred during life, can provide novel insights into bone functional adaptation. Here, we use canonical holistic morphometric analysis (cHMA) to analyse the trabecular morphology in the distal femoral epiphysis of Homo sapiens (n = 26), Gorilla gorilla (n = 14), Pan troglodytes (n = 15) and Pongo sp. (n = 9). We test two predictions: (1) that differing locomotor behaviours will be reflected in differing trabecular architecture of the distal femur across Homo, Pan, Gorilla and Pongo; (2) that trabecular architecture will significantly differ between male and female Gorilla due to their different levels of arboreality but not between male and female Pan or Homo based on previous studies of locomotor behaviours. Results indicate that trabecular architecture differs among extant great apes based on their locomotor repertoires. The relative bone volume and degree of anisotropy patterns found reflect habitual use of extended knee postures during bipedalism in Homo, and habitual use of flexed knee posture during terrestrial and arboreal locomotion in Pan and Gorilla. Trabecular architecture in Pongo is consistent with a highly mobile knee joint that may vary in posture from extension to full flexion. Within Gorilla, trabecular architecture suggests a different loading of knee in extension/flexion between females and males, but no sex differences were found in Pan or Homo, supporting our predictions. Inter‐ and intra‐specific variation in trabecular architecture of distal femur provides a comparative context to interpret knee postures and, in turn, locomotor behaviours in fossil hominins. [ABSTRACT FROM AUTHOR]

Strong, affiliative relationships are important across social mammals, and in many species, relationships between female kin form the basis of group life. Relationships are expected to be weaker in cases where females disperse or do not cooperatively defend resources. Mountain gorillas, Gorilla beringei beringei , seem to support this, as females can emigrate multiple times throughout their life and do not jointly defend the abundant vegetation they feed on. Unsurprisingly, mountain gorillas have been reported to form variable or weak relationships with other females and seemingly prioritize relationships with adult males. But prior studies may have misinterpreted relationships due to a focus on grooming and understandable limitations of small sample sizes and short study periods. Here, we examine proximity and grooming between 47 adult female mountain gorillas in five groups over 5–13 years. We analyse proximity data (2 m, 5 m) and grooming relationships between 366 individual dyads to determine (1) whether proximity and grooming relationships are preferential and (2) whether they endure across time. Most females formed at least one preferential 2 m and 5 m proximity relationship (43 of 47), which both lasted a mean of 2.1 years. Additionally, 3.6% of dyads (N = 13/366) formed enduring 2 m proximity preferences that exceeded 4 years, with the longest lasting at least 12 years. Maternal kin had the most enduring proximity and grooming relationships, although grooming was rare overall. The enduring proximity relationships between some female gorillas in our sample are similar in length to those of female yellow baboons, Papio cynocephalus , and male chimpanzees, Pan troglodytes , which are considered social bonds. Mountain gorillas provide a system in which factors influencing bonds can be better understood, and our study highlights a need to refine definitions of social bonds while potentially reassessing their evolutionary function. • We examined proximity (2 m, 5 m) and grooming in female mountain gorilla dyads. • Most females formed one long-term (2–12 years) preferential proximity relationship. • Proximity relationships were akin to social bonds in baboons and chimpanzees. • Maternal kin were more likely to have preferential 2 m proximity relationships. • Dispersal patterns may allow adult females to remain with maternal kin longer. [ABSTRACT FROM AUTHOR]

Objectives: Low‐energy vertebral fractures are a common health concern, especially in elderly people. Interestingly, African apes do not seem to experience as many vertebral fractures and the low‐energy ones are even rarer. One potential explanation for this difference is the lower bone density in humans. Yet, only limited research has been done on the vertebral bone density of the great apes and these have mainly included only single vertebrae. Hence the study aim is to expand our understanding of the vertebral microstructure of African apes in multiple spinal segments. Materials: Bone density in the vertebral body of C7, T12, and L3 was measured from 32 Pan troglodytes and 26 Gorilla gorilla using peripheral quantitative computed tomography (pQCT). Results: There was a clear difference between the three individual vertebrae and consequently the spinal segments in terms of trabecular density and cortical density and thickness. The variation of these bone parameters between the vertebrae differed between the apes but was also different from those reported for humans. The chimpanzees were observed to have overall higher trabecular density, but gorillas had higher cortical density and thickness. Cortical thickness had a relatively strong association with the vertebral size. Discussion: Despite the similarity in locomotion and posture, the results show slight differences in the bone parameters and their variation between spinal segments in African apes. This variation also differs from humans and appears to indicate a complex influence of locomotion, posture, and body size on the different spinal segments. [ABSTRACT FROM AUTHOR]

We identified five distinct full-length human mineralocorticoid receptor (MR) genes containing either 984 amino acids (MR-984) or 988 amino acids (MR-988), which can be distinguished by the presence or absence of Lys, Cys, Ser, and Trp (KCSW) in their DNA-binding domain (DBD) and mutations at codons 180 and 241 in their amino-terminal domain (NTD). Two human MR-KCSW genes contain either (Val-180, Val-241) or (Ile-180, Val-241) in their NTD, and three human MR-984 genes contain either (Ile-180, Ala-241), (Val-180, Val-241), or (Ile-180, Val-241). Human MR-KCSW with (Ile-180, Ala-241) has not been cloned. In contrast, chimpanzees contain four MRs: two MR-988s with KCSW in their DBD, or two MR-984s without KCSW in their DBD. Chimpanzee MRs only contain (Ile180, Val-241) in their NTD. A chimpanzee MR with either (Val-180, Val-241) or (Ile-180, Ala-241) in the NTD has not been cloned. Gorillas and orangutans each contain one MR-988 with KCSW in the DBD and one MR-984 without KCSW, and these MRs only contain (Ile-180, Val-241) in their NTD. A gorilla MR or orangutan MR with either (Val-180, Val-241) or (Ile-180, Ala-241) in the NTD has not been cloned. Together, these data suggest that human MRs with (Val-180, Val-241) or (Ile-180, Ala-241) in the NTD evolved after humans and chimpanzees diverged from their common ancestor. Considering the multiple functions in human development of the MR in kidney, brain, heart, skin, and lungs, as well as MR activity in interaction with the glucocorticoid receptor, we suggest that the evolution of human MRs that are absent in chimpanzees may have been important in the evolution of humans from chimpanzees. Investigation of the physiological responses to corticosteroids mediated by the MR in humans, chimpanzees, gorillas, and orangutans may provide insights into the evolution of humans and their closest relatives. [ABSTRACT FROM AUTHOR]

Imitation is a social learning mechanism in humans but its relevance in nonhuman primates is controversial. Studies have suggested that some ape species, such chimpanzees and orangutans, may be able to imitate. However, records of true imitation in gorillas are scarce. This study was designed to evaluate the imitation ability of two female western lowland gorillas (Gorilla gorilla gorilla) by using the "do as I do" method, after 15 months of training. For the final evaluation, we tested the gorillas with 52 novel actions classified in four categories (Gestures, Object, Object-Object, and Object-Subject). To assess the difficulty of the novel actions, the lead researcher and two independent observers scored the responses from 0 to 3 based on how well they were done. During the training period, the two gorillas obtained similar success rates for imitation. During the evaluation, they achieved true imitation in 46% of transparent actions and 58% of the opaque actions. We identified "Gestures" as the easiest actions for one gorilla and "Object-Subject" for the other. "Object-Object" were the most difficult actions for both gorillas. Our findings show that female western lowland gorillas can imitate after a training period. [ABSTRACT FROM AUTHOR]

This article discusses the process of habituation in moor macaques (Macaca maura) and how it is affected by changes in group composition. The researchers conducted a study on a wild group of moor macaques in Indonesia, observing their responses to human researchers during two habituation phases. They found that the macaques were less likely to show neutral responses and be tolerant of researcher proximity at the start of the second habituation phase compared to the first. However, the macaques in the second phase habituated more quickly overall, suggesting that previous experience of neutral exposure to researchers facilitated the habituation process. The researchers also noted the need for further study on social learning and individual differences in habituation, as well as the potential risks for habituated groups. [Extracted from the article]

Despite zoonotic potential, data are lacking on enteric infection diversity in wild apes. We employed a novel molecular diagnostic platform to detect enteric infections in wild chimpanzees and gorillas. Prevalent Cryptosporidium parvum, adenovirus, and diarrheagenic Escherichia coli across divergent sites and species demonstrates potential widespread circulation among apes in Africa. [ABSTRACT FROM AUTHOR]

Oral health is a crucial aspect of overall well‐being in both humans and nonhuman primates. Understanding the oral pathologies and dental conditions in apes can provide valuable insights into their evolutionary history, dietary habits, and overall health. The present study evaluates dental findings in wild great apes from museum specimens to gain insights into the influence of natural nutrition on dental health. Complete macerated skulls of wild, adult great apes from the collection of the Museum of Natural History, Berlin, Germany, were examined. We analyzed skulls of 53 gorillas (Gorilla gorilla), 63 chimpanzees (Pan troglodytes), and 41 orangutans (Pongo spp.). For each skull, we recorded wear of dental hard tissues (Lussi and Ganss index), carious lesions, and periodontal bone loss. Incisal and occlusal dental hard tissue defects were found in all skulls, as well as considerable external staining. In all species, incisors and canines showed the greatest loss of tissue, followed by molars. The wear of molars decreased from the first to the third molars, premolars showed the least pronounced defects. Some individuals had apical osteolytic defects along with severe dental hard tissue loss with pulp involvement or after dental trauma, respectively (n = 5). Our study did not observe any carious lesions among the examined great ape skulls. However, we did find evidence for localized or generalized periodontal bone loss in a subset of the specimens (n = 3 chimpanzees, n = 7 orangutans). The natural diet and foraging behavior of great apes induces abrasion and attrition of dental hard tissue but does not yield carious lesions. The occurrence of periodontitis in individual apes indicates that the natural circumstances can induce periodontal bone loss even in the wild, despite physiological nutrition. Research Highlights: The natural diet and foraging behavior of great apes induces wear of dental hard tissues but not carious lesions.The occurrence of periodontitis in individual apes indicates that the natural microbiome, in conjunction with the host's defense, can induce periodontal bone loss even in the wild. [ABSTRACT FROM AUTHOR]

We investigated children's and non-human great apes' ability to anticipate others' choices from their evident food preferences—regardless of whether these preferences deviate or align with one's own. We assessed children from three culturally-diverse societies (Namibia, Germany, and Samoa; N = 71; age range = 5–11) and four non-human great ape species (chimpanzees (Pan troglodytes), bonobos (Pan paniscus), gorillas (Gorilla gorilla), and orangutans (Pongo abelii); N = 25; age range = 7–29) regarding their choices in a dyadic food-retrieval task. Across conditions, participants' preferences were either aligned (same preference condition) or opposed (opposite preference condition) to those of their competitors. Children across societies altered their choices based on their competitor's preferences, indicating a cross-culturally recurrent capacity to anticipate others' choices relying on preferences-based inferences. In contrast to human children, all non-human great apes chose according to their own preferences but independent of those of their competitors. In sum, these results suggest that the tendency to anticipate others' choices based on their food preferences is cross-culturally robust and, among the great apes, most likely specific to humans. [ABSTRACT FROM AUTHOR]

Objectives: Modular architecture of traits in complex organisms can be important for morphological evolution at micro‐ and sometimes macroevolutionary scales as it may influence the tempo and direction of changes to groups of traits that are essential for particular functions, including food acquisition and processing. We tested several distinct hypotheses about craniofacial modularity in the hominine skull in relation to feeding biomechanics. Materials and Methods: First, we formulated hypothesized functional modules for craniofacial traits reflecting specific demands of feeding biomechanics (e.g., masseter leverage/gape or tooth crown mechanics) in Homo sapiens, Pan troglodytes, and Gorilla gorilla. Then, the pattern and strength of modular signal was quantified by the covariance ratio coefficient and compared across groups using covariance ratio effect size. Hierarchical clustering analysis was then conducted to examine whether a priori‐defined functional modules correspond to empirically recovered clusters. Results: There was statistical support for most a priori‐defined functional modules in the cranium and half of the functional modules in the mandible. Modularity signal was similar in the cranium and mandible, and across the three taxa. Despite a similar strength of modularity, the empirically recovered clusters do not map perfectly onto our priori functional modules, indicating that further work is needed to refine our hypothesized functional modules. Conclusion: The results suggest that modular structure of traits in association with feeding biomechanics were mostly shared with humans and the two African apes. Thus, conserved patterns of functional modularity may have facilitated evolutionary changes to the skull during human evolution. [ABSTRACT FROM AUTHOR]

Flexor digitorum superficialis (FDS) shows diverse muscle–tendon arrangements among primates. The intramuscular nerve distribution pattern is a criterion for discussing the homology of FDS. In this study, the muscle–tendon arrangement and intramuscular nerve distribution of FDS were examined in the siamang, western lowland gorilla, western chimpanzee, and Japanese macaques. The FDS had muscle bellies to digits II–V. FDS had proximal belly and intermediate tendon except for siamang. Distal belly to digit II (in the western lowland gorilla and western chimpanzees) or distal bellies to digits II and V (in Japanese macaque) originated from the intermediate tendon. In all specimens, nerve branches within digit III belly extended into digit IV belly, and nerve branch(es) within digit IV belly extended into digit V belly. This consistent pattern suggested that each muscle belly to digits III–V is interspecifically homologous. The digit II belly in the siamang and the distal belly to digit II in the western lowland gorilla, western chimpanzees, and Japanese macaques could be homologous based on their similar innervating patterns. The proximal belly was innervated by branches from the communicating nerve between median and ulnar nerves in the western lowland gorilla or branches from median and ulnar nerves in western chimpanzees. In the siamang and Japanese macaque, the whole FDS was innervated by median nerve. The proximal belly in the western lowland gorilla, western chimpanzees, and Japanese macaques could be classified into different groups from the other part of the FDS. [ABSTRACT FROM AUTHOR]

Objectives: Morphological intraspecific variation is due to the balance between skeletal plasticity and genetic constraint on the skeleton. Osteogenic responses to external stimuli, such as locomotion, have been well documented interspecifically across the primate order, but less so at the intraspecific level. Here, we examine the differences in cross‐sectional variability of the femur, humerus, radius, and tibia in Pan troglodytes troglodytes versus Gorilla gorilla gorilla. We investigate whether there are sex, species, bone, and trait differences in response to variable body size and locomotion. Materials and Methods: Adult male and female P. t. troglodytes and G. g. gorilla long bones from the Cleveland Museum of Natural History were scanned with a peripheral quantitative computer tomography system. Scans were taken at the midshaft of each bone according to functional bone length. Coefficients of variation were used to provide a size‐independent measure of variation. We applied a Bonferroni correction to account for the multiple pairwise tests. Results: There were limited significant differences between males and females, however, females tended to be more variable than males. Variation in Gorilla, when significant, was greater than in Pan, although significant differences were limited. There were no differences between bone variability in male and female Gorilla, and female Pan. Discussion: Increased female variability may be due to more variable locomotor behavior, particularly during periods of pregnancy, lactation, and caring for an offspring compared to consistent locomotion over the life course by males. Body size may be a contributing factor to variability; more work is needed to understand this relationship. [ABSTRACT FROM AUTHOR]

Since the first discovery of human fossils in the mid‐19th century, two subjects—our phylogenetic relationship to living and fossil apes and the ancestral locomotor behaviors preceding bipedalism—have driven the majority of discourse in the study of human origins. With few fossils and thus limited comparative evidence available to inform or constrain them, morphologists of the 19th and early mid‐20th centuries posited a range of scenarios for the evolution of bipedalism. In contrast, there exists a rich hominin fossil record and the acceptance of Pan (chimpanzees and bonobos) as our closest living relatives is nearly universal, yet consensus about the ancestral condition from which hominins evolved remains elusive. Notably, while the earliest known hominins are generally congruent with parsimonious inferences of an African ape‐like last common ancestor, our more distantly related Miocene ape cousins are frequently invoked as evidence in favor of more complex scenarios that require substantial homoplasy. Debate over these alternatives suggests that how we infer ancestral nodes and weigh evidence to test their relative likelihoods remains a stumbling block. Here we argue that a key contributor to this impasse includes the history of terminology associated with positional behavior, which has become confused over the last century. We aim to clarify positional behavior concepts and contextualize knuckle‐walking and other forms of posture and locomotion chimpanzees and gorillas engage in, while arguing that the presence of homoplasy in ape evolution does not alter the weight of evidence in favor of an African ape‐like evolutionary history of hominins. [ABSTRACT FROM AUTHOR]

Case study on the bone density pattern of subaxial vertebral column in African apes. Introduction: African apes have been noted to experience fewer back ailments than humans and to have higher vertebral bone density. Yet, research on the subject is quite limited and has usually included only one or few vertebrae. However, to understand vertebral column as whole and how posture and locomotion might have affected it, we need to know how bone density varies between adjacent vertebrae. Materials and Methods: Bone density in the vertebral body was measured for all subaxial vertebrae of five specimens including two Pan troglodytes (1 male and 1 female) and three Gorilla gorilla (2 males and 1 female) using peripheral quantitative computed tomography (pQCT). Results: The results tentatively indicated differences between species, especially in the trabecular density of the cervical segment and support the need for further studies on this subject. [ABSTRACT FROM AUTHOR]

Many animals will seek information when they do not know the answer to a problem, suggesting that they monitor their knowledge state. In the classic "tubes task," subjects are presented with a set of opaque tubes and either see (visible trials) or do not see (hidden trials) which tube holds a food reward on a given trial. Chimpanzees, bonobos, orangutans, and human children show information-seeking behavior on this task, looking into the tubes to find the reward more on hidden than on visible trials. However, evidence for information-seeking behavior in gorillas is limited. In Experiment 1, gorillas that were presented with a classic information-seeking tubes task showed performance patterns consistent with metacognitive behavior; they looked down tubes more on hidden than on visible trials, their accuracy on hidden trials on which they looked was higher than on hidden trials on which they did not look, and they primarily employed an appropriate search strategy when looking down the tubes. In Experiment 2, we decreased or increased the amount of effort required to look down the tubes by increasing or decreasing the height of the tubes, respectively. Gorillas were less likely to look in tubes on trials that required high effort, but continued to look more on hidden than on visible trials, indicating that their tendency to look was affected by both knowledge state and effort. Together these results provide strong evidence for logical, controlled information-seeking behavior by gorillas. [ABSTRACT FROM AUTHOR]

Cardiovascular disease is the leading cause of morbidity and mortality in zoologically managed adult great apes, accounting for 29%−77% of adult deaths in the North American population depending on the species. In an effort to better understand the underlying causes of heart disease, implantable loop recorders (ILRs) have been used in some cases to monitor great apes with suspected or known cases of arrhythmia. This is a 10‐year review of the Great Ape Heart Project's experience of implanting 21 ILRs in 7 gorillas (Gorilla gorilla gorilla; 9 total ILR devices), 5 chimpanzees (Pan troglodytes, 11 total ILR devices), and 1 orangutan (Pongo abelii, 1 ILR device) in an effort to develop effective methods for surgical implantation and remote collection of the data for analysis. Research Highlights: Cardiac health monitoring using implantable loop recorders contributes to the Great Ape Heart Project's research efforts to better understand cardiovascular disease in great apes and further enhance their care. The cardiac monitors, the same ones used to monitor humans, are used to track apes' heart activity for signs of irregular heartbeats, called arrhythmias, and upload the data to the Great Ape Heart Project. [ABSTRACT FROM AUTHOR]

Stressors over the lifespan can contribute to physiological dysregulation, or allostatic load. Allostatic load has been studied in humans using allostatic load indices (ALIs) for over 25 years, but the same methods are rarely applied to other species. We constructed an ALI for zoo-housed western lowland gorillas, chimpanzees, and bonobos and tested potential predictors of and health outcomes associated with allostatic load. Allostatic load scores ranged from 0–6 for gorillas and chimpanzees and 0–7 for bonobos. Age was significantly associated with allostatic load in gorillas and chimpanzees but not bonobos. Cumulative stressful events were positively associated with allostatic load in chimpanzees. Wild-caught gorillas had higher allostatic load than zoo-born conspecifics, but rearing differences between zoo-born animals were not significant for any species. Age may affect associations of allostatic load with stressful events and birthplace as results change when it is included as a covariate. Allostatic load was not retained in best-fit models for risk of all-cause morbidity, cardiac disease, or mortality risk. Some analyses herein were limited by the use of retrospective data, such as reason for sample collection and length of records provided for individual animals. Nevertheless, these data indicate additional research is needed to optimize ALIs for non-human primates. [ABSTRACT FROM AUTHOR]

Program of the Forty-Fourth Meeting of The American Society of Primatologists. [Extracted from the article]

Objectives: This study investigates patterns of bone functional adaptations in extant apes through comparing hindlimb to forelimb bone rigidity ratios in groups with varying levels of arboreality. Materials and Methods: Using CT scans, bone rigidity (J) was calculated at three regions of interest (ROI) along femoral and humeral diaphyses in Homo, Pongo, Pan, and Gorilla with further comparisons made between species and subspecies divisions within Pan and Gorilla. Results: Consistent with previous work on extant hominoids, species exhibited differences in midshaft femoral to humeral (F/H) rigidity ratios. Results of the present study confirm that these midshaft differences extend to 35% and 65% diaphyseal ROIs. Modern humans, exhibiting larger ratios, and orangutans, exhibiting smaller ratios, bracketed the intermediate African apes in comparisons. Within some African apes, limb rigidity ratios varied significantly between taxonomic groups. Eastern gorillas exhibited the highest mean ratios and chimpanzees the lowest at all three ROIs. In posthoc comparisons, chimpanzees and bonobos did not differ in relative limb rigidity ratios at any of the three ROIs. However, western gorillas were more similar to bonobos than eastern gorillas at 50% and 35% ROIs, but not at the 65% ROI. Conclusion: Species, and to a lesser extent subspecies, can be distinguished by F/H limb rigidity ratios according to broad positional behavior patterns at multiple regions of interest along the diaphyses. Similarity of bonobos and western gorillas is in line with behavioral data of bonobos being the most terrestrial of Pan species, and western gorillas the most arboreal of the Gorilla groups. [ABSTRACT FROM AUTHOR]

Background: While of predominant abundance across vertebrate genomes and significant biological implications, the relevance of short tandem repeats (STRs) (also known as microsatellites) to speciation remains largely elusive and attributed to random coincidence for the most part. Here we collected data on the whole-genome abundance of mono-, di-, and trinucleotide STRs in nine species, encompassing rodents and primates, including rat, mouse, olive baboon, gelada, macaque, gorilla, chimpanzee, bonobo, and human. The collected data were used to analyze hierarchical clustering of the STR abundances in the selected species. Results: We found massive differential STR abundances between the rodent and primate orders. In addition, while numerous STRs had random abundance across the nine selected species, the global abundance conformed to three consistent < clusters>, as follows: , , and , which coincided with the phylogenetic distances of the selected species (p < 4E-05). Exceptionally, in the trinucleotide STR compartment, human was significantly distant from all other species. Conclusion: Based on hierarchical clustering, we propose that the global abundance of STRs is non-random in rodents and primates, and probably had a determining impact on the speciation of the two orders. We also propose the STRs and STR lengths, which predominantly conformed to the phylogeny of the selected species, exemplified by (t)10, (ct)6, and (taa4). Phylogenetic and experimental platforms are warranted to further examine the observed patterns and the biological mechanisms associated with those STRs. [ABSTRACT FROM AUTHOR]

The adenoviruses (AdVs) isolated from humans are taxonomically grouped in seven different species in the Mastadenovirus genus (HAdV-A through G). AdVs isolated from apes are often included in one of the human AdV species. Here we describe the sequence analyses of ten new AdVs that are related to the HAdV-C species and that were isolated from healthy western lowland gorillas, bonobos, chimpanzees, and orangutans kept in Dutch zoos. We analyzed these viruses and compared their genome sequences to those of human- and ape-derived AdV sequences in the NCBI GenBank database. Our data demonstrated that the ape-derived viruses clustering to HAdV-C are markedly distinct from the human HAdV-C species in the size and nucleotide composition (%GC) of their genome, differ in the amino-acid sequence of AdV proteins, and have longer RGD-loops in their penton-base proteins. The viruses form three well-separated clades (the human, the gorilla, and the combined group of the bonobo and chimpanzee viruses), and we propose that these should each be given species-level ranks. The Ad-lumc005 AdV isolated from orangutans was found to be very similar to the gorilla AdVs, and bootstrap inference provided evidence of recombination between the orangutan AdV and the gorilla AdVs. This suggests that this virus may not be a genuine orangutan AdV but may have been transferred from a gorilla to an orangutan host. [ABSTRACT FROM AUTHOR]

Objectives: Dietary diversity in primates is reflected in their dental morphology, with differences in size and shape of teeth. The objective of this study is to investigate the relationship between molar morphology and macrowear patterns in Pongo, Gorilla, and Pan to obtain dietary information. Methods: We have examined 68 second lower molars using the Occlusal Fingerprint Analysis method including 18 chimpanzees, 28 gorillas, and 22 orangutans. We selected only molars from wildshot specimens characterized by a moderate degree of wear. High‐resolution digital models of teeth were created using a white scanning light system with a resolution of 45 μm. Results: The macrowear patterns of Pan were significantly different from those of Gorilla and of Pongo, differences that are mostly due to shearing wear. Gorilla and Pongo macrowear patterns are dominated by phase II areas, followed by lingual phase I facets, while in Pan we observe a significant increase in buccal phase I facets. The latter group also displays the highest macrowear variation across the sample examined in this study. Conclusions: The molar macrowear patterns of the great apes analyzed in this study did not confirm our initial hypothesis of finding larger crushing and grinding areas in Pongo and more shearing wear in Gorilla. Pan shows the most variable macrowear, which is probably associated with their more flexible diet. The similarity between Pongo and Gorilla macrowear patterns may be due to a larger intake of mechanically challenging foods that could obfuscate dietary wear signals generated by softer foods. [ABSTRACT FROM AUTHOR]

Simple Summary: Zoo visitors can have a positive, negative, or neutral impact on animals. Primates are cognitively very advanced and their interactions with human visitors are complex. The COVID-19 pandemic led to a prolonged absence of visitors in zoos. This enabled an opportunity to compare how primates behaved when the zoo was open to visitors as opposed to when it was closed. We studied four primate species housed in the UK: bonobos, chimpanzees, and western lowland gorillas held at Twycross Zoo and olive baboons held at Knowsley Safari. Bonobos and gorillas spent less time alone when facilities were open to the public. Gorillas also spent less time resting when the facility was open to the public. Chimpanzees ate more and engaged more with enrichment when the zoo was open to the public. Olive baboons performed less sexual and dominance behaviour and approached visitor cars more frequently when the safari park was opened to the public than the ranger's vehicle during closure periods. The results suggest that the zoo closures had variable impacts on the primates and that the closure periods were neither "negative" or "positive" for all of the studied species. There are likely to be differences between individuals due to prior experiences. We recommend that future work seeks to understand the impact individual differences and animal environments have on animals' experiences with visitors. Primates are some of the most cognitively advanced species held in zoos, and their interactions with visitors are complex. The COVID-19 pandemic provided a unique opportunity to understand the impact of zoo visitors on animals, in comparison to "empty zoos". This study sought to understand the impact of facility closures and subsequent reopenings on behavioural and physiological parameters of welfare in four primate species housed in the UK: bonobos (Pan paniscus) (n = 8), chimpanzees (Pan troglodytes) (n = 11), and western lowland gorillas (Gorilla gorilla gorilla) (n = 6) held at Twycross Zoo (TZ); and olive baboons (Papio anubis) (n = 192) held at Knowsley Safari (KS). Behavioural data were collected from April–September 2020 (KS) and November 2020–January 2021 (TZ). Faecal samples were collected during morning checks from October–November (TZ) and July–November 2020 (KS). Faecal glucocorticoid metabolites (FGMs) were measured using ELISA kits. Statistical analysis for behavioural observations was undertaken using general linear models. Enclosure usage was assessed using t-tests and Mann–Whitney U-tests as appropriate. Bonobos and gorillas spent less time alone when facilities were open to the public (p = 0.004, p = 0.02 respectively). Gorillas spent less time resting when the facility was open to the public (p = 0.04), and chimpanzees engaged in more feeding (p = 0.02) and engagement with enrichment (p = 0.03) when the zoo was open to the public than when it was closed. Olive baboons performed less sexual and dominance behaviour and approached visitor cars more frequently when the safari park was opened to the public than they did the ranger's vehicle during closure periods. There were no significant changes in physiological parameters for any of the study species. The results suggest variable impacts of the zoo closures on zoo-housed primates. We recommend future work that seeks to understand the impact of individual-level differences on "visitor effects" and that differences between animal experiences in zoos and safari parks are further explored in a range of species. [ABSTRACT FROM AUTHOR]

Quantifying morphological variation is critical for conducting anatomical research. Three‐dimensional geometric morphometric (3D GM) landmark analyses quantify shape using homologous Cartesian coordinates (landmarks). Setting up a high‐density landmark set and placing it on all specimens, however, can be a time‐consuming task. Weighted spherical harmonics (SPHARM) provides an alternative method for analyzing the shape of such objects. Here we compare sliding semilandmark and SPHARM analyses of the calcaneus of Gorilla gorilla gorilla (n = 20), Pan troglodytes troglodytes (n = 20), and Homo sapiens (n = 20) to determine whether the SPHARM and sliding semilandmark analyses capture comparable levels of shape variation. We also compare both the sliding semilandmark and SPHARM analyses to a novel combination of the two methods, here termed SPHARM–sliding. In SPHARM–sliding, the vertices of the surface models produced from the SPHARM analysis (that are the same in number and relative location) are used as the starting landmark positions for a sliding semilandmark analysis. Calcaneal shape variation quantified by all three analyses was summarized using separate principal components analyses. Results were compared using the root mean square (RMS) and maximum distance between surface models of species averages scaled (up) to centroid size created from each analysis. The average RMS was 0.23 mm between sliding semilandmark and SPHARM average surface models, 0.19 mm between SPHARM and SPHARM sliding average surface models, and 0.22 mm between sliding semilandmark and SPHARM sliding average surface models. Although results indicate that all three analyses are comparable methods for 3D shape analysis, there are advantages and disadvantages to each. While the SPHARM analysis is less time‐intensive, it is unable to capture the same level of detail around the sharp edges of articular facets on average surface models as the sliding semilandmark analysis. The SPHARM analysis also does not allow for individual articular facets to be analyzed in isolation. SPHARM–sliding, however, captures the same level of detail as the sliding semilandmark analysis, and (as in the sliding semilandmark analysis) allows for the evaluation of individual portions of bone. SPHARM is a comparable method to a 3D GM analysis for small, irregularly shaped bones, such as the calcaneus, and SPHARM–sliding allows for an expedited set up process for a sliding semilandmark analysis. [ABSTRACT FROM AUTHOR]

In the last decade, two hypotheses, one on the evolution of animal vocal communication in general and the other on the origins of human language, have gained ground. The first hypothesis argues that the complexity of communication co‐evolved with the complexity of sociality. Species forming larger groups with complex social networks have more elaborate vocal repertoires. The second hypothesis posits that the core of communication is represented not only by what can be expressed by an isolated caller, but also by the way that vocal interactions are structured, language being above all a social act. Primitive forms of conversational rules based on a vocal turn‐taking principle are thought to exist in primates. To support and bring together these hypotheses, more comparative studies of socially diverse species at different levels of the primate phylogeny are needed. However, the majority of available studies focus on monkeys, primates that are distant from the human lineage. Great apes represent excellent candidates for such comparative studies because of their phylogenetic proximity to humans and their varied social lives. We propose that studying vocal turn‐taking in apes could address several major gaps regarding the social relevance of vocal turn‐taking and the evolutionary trajectory of this behaviour among anthropoids. Indeed, how the social structure of a species may influence the vocal interaction patterns observed among group members remains an open question. We gathered data from the literature as well as original unpublished data (where absent in the literature) on four great ape species: chimpanzees Pan troglodytes, bonobos Pan paniscus, western lowland gorillas Gorilla gorilla gorilla and Bornean orang‐utans Pongo pygmaeus. We found no clear‐cut relationship between classical social complexity metrics (e.g. number of group members, interaction rates) and vocal complexity parameters (e.g. repertoire size, call rates). Nevertheless, the nature of the society (i.e. group composition, diversity and valence of social bonds) and the type of vocal interaction patterns (isolated calling, call overlap, turn‐taking‐based vocal exchanges) do appear to be related. Isolated calling is the main vocal pattern found in the species with the smallest social networks (orang‐utan), while the other species show vocal interactions that are structured according to temporal rules. A high proportion of overlapping vocalisations is found in the most competitive species (chimpanzee), while vocal turn‐taking predominates in more tolerant bonobos and gorillas. Also, preferentially interacting individuals and call types used to interact are not randomly distributed. Vocal overlap ('chorusing') and vocal exchange ('conversing') appear as possible social strategies used to advertise/strengthen social bonds. Our analyses highlight that: (i) vocal turn‐taking is also observed in non‐human great apes, revealing universal rules for conversing that may be deeply rooted in the primate lineage; (ii) vocal interaction patterns match the species' social lifestyle; (iii) although limited to four species here, adopting a targeted comparative approach could help to identify the multiple and subtle factors underlying social and vocal complexity. We believe that vocal interaction patterns form the basis of a promising field of investigation that may ultimately improve our understanding of the socially driven evolution of communication. [ABSTRACT FROM AUTHOR]

By identifying homogeneity in bone and soft tissue covariation patterns in living hominids, it is possible to produce facial approximation methods with interspecies compatibility. These methods may be useful for producing facial approximations of fossil hominids that are more realistic than currently possible. In this study, we conducted an interspecific comparison of the nasomaxillary region in chimpanzees and modern humans with the aim of producing a method for predicting the positions of the nasal tips of Plio-Pleistocene hominids. We addressed this aim by first collecting and performing regression analyses of linear and angular measurements of nasal cavity length and inclination in modern humans (Homo sapiens; n = 72) and chimpanzees (Pan troglodytes; n = 19), and then performing a set of out-of-group tests. The first test was performed on four subjects that belonged to the same genus as the training sample, i.e., Homo (n = 2) and Pan (n = 2), and the second test, which functioned as an interspecies compatibility test, was performed on Pan paniscus (n = 1), Gorilla gorilla (n = 3), Pongo pygmaeus (n = 1), Pongo abelli (n = 1), Symphalangus syndactylus (n = 3), and Papio hamadryas (n = 3). We identified statistically significant correlations in both humans and chimpanzees with slopes that displayed homogeneity of covariation. Prediction formulae combining these data were found to be compatible with humans and chimpanzees as well as all other African great apes, i.e., bonobos and gorillas. The main conclusion that can be drawn from this study is that our set of regression models for approximating the position of the nasal tip are homogenous among humans and African apes, and can thus be reasonably extended to ancestors leading to these clades. [ABSTRACT FROM AUTHOR]

Central chimpanzee (Pan troglodytes troglodytes) and western lowland gorilla (Gorilla gorilla gorilla) populations are rapidly declining due to habitat loss, poaching, and disease epidemics. We estimate the abundance and distribution of both species in the 5,260-km² Dja Faunal Reserve, a World Heritage Site in Cameroon. We compare with previous site estimates and with other great ape population estimates from the region. We also document illegal activities in the reserve. A total of 298.2 km of line transects (283) were completed using the standing-crop nest counts method, with a further 1,681.4 km of recces recording human signs. We estimated a chimpanzee nest mean decay rate of 95.4 days (SE = 4.45) and a combined great ape nest mean decay rate of 96.6 days (SE = 2.87). Gorilla population estimates of 0.38 (95% CI = 0.28-0.53) individuals/km² and 2,004 (95% CI = 1,447-2,774) individuals confirmed a significant decline since the 1995 survey in the north-central part of the reserve (a 57% decline for the area) and the reserve-wide survey in 2015 (a 70% decline). The population was also much lower than in most other protected areas in the region. The chimpanzee population with an estimated 0.53 (95% CI = 0.38-0.73) individuals/km² and 2,785 (95% CI = 2,020-3,839) individuals also revealed a marked decline of 34% and 23% compared to the 1995 and 2015 surveys, respectively. Human activity occurred throughout, with the highest levels encountered in the northwest of the reserve. Occupancy estimates from four 40 camera-trap grid surveys showed great apes persisting mainly in the north-eastern part of the reserve where Cameroon's Ministry of Forestry and Wildlife (MINFOF) is considering a community support partnership agreement on sustainable access to forest resources, along with community surveillance networks. The reserve management is also increasing law-enforcement patrols across the reserve. Our findings also inform conservation strategies for great apes across the TRIDOM landscape across Cameroon, Gabon and the Republic of Congo. [ABSTRACT FROM AUTHOR]

Dental caries has been reported in a variety of primates, although it is still considered rare in wild populations. In this study, 11 catarrhine primate taxa (n = 339 individuals; 7946 teeth) were studied for the presence of caries. A differential diagnosis of lesions in interproximal regions of anterior teeth was undertaken, since they had been previously described as both carious and non‐carious in origin. Each permanent tooth was examined macroscopically, with severity and position of lesions recorded. Two specimens were examined further, using micro‐CT scans to assess demineralization. Differential diagnosis confirmed the cariogenic nature of interproximal cavities on anterior teeth (ICATs). Overall results show 3.3% of all teeth (i.e., anterior and posterior teeth combined) were carious (n = 262), with prevalence varying among species from 0% to >7% of teeth affected. Those with the highest prevalence of ICATs include Pan troglodytes verus (9.8% of anterior teeth), Gorilla gorilla gorilla (2.6%), Cercopithecus denti (22.4%), Presbytis femoralis (19.5%), and Cercopithecus mitis (18.3%). ICATs make up 87.9% of carious lesions on anterior teeth. These results likely reflect dietary and food processing differences among species, but also between the sexes (e.g., 9.3% of all female P. troglodytes verus teeth were carious vs. 1.8% in males). Processing cariogenic fruits and seeds with the anterior dentition (e.g., wadging) likely contributes to ICAT formation. Further research is needed in living primate populations to ascertain behavioral/dietary influences on caries occurrence. Given the presence of ICATs in frugivorous primates, their diagnosis in archaeological and paleontological specimens may shed light on diet and food processing behaviors in fossil primates. Research Highlights: Substantial variance in caries prevalence was evident among primate species studied, ranging from 0% to 7.4% of teeth with lesions.Several species display moderate to high caries levels on anterior teeth (2.6%–22.4%).The results reflect dietary and food processing differences among species, including processing cariogenic fruits and seeds with the anterior dentition. [ABSTRACT FROM AUTHOR]

Background and Aim: Gastrointestinal parasites identified in the wild can negatively affect host fitness, lower performance, and growth. On the other side, sympatric mammals that share habitat and resources may also cross-transmit parasites, which are often zoonotic and can contribute to morbidity and mortality. This study aimed to characterize the diversity of gastrointestinal parasites circulating in mammalian hosts in Moukalaba-Doudou National Park. Materials and Methods: We screened a total of 25 fecal samples collected from nine wild mammalian species, namely, western gorilla (Gorilla gorilla gorilla), chimpanzee (Pan troglodytes), putty-nosed monkey (Cercopithecus nictitans), African forest elephant (Loxodonta cyclotis), African buffalo (Syncerus caffer), blue duiker (Philantomba monticola), bay duiker (Cephalophus dorsalis), and red river hog (Potamochoerus porcus) as well as people working as trackers (Homo sapiens) using direct microscopic observations following a sedimentation technique to concentrate the fecal material. Results: Of the total 25 fecal samples screened, 15 (60%) were positive for parasitic gastrointestinal infection. Based on the morphology of parasite eggs and cysts, we identified a rich diversity of nematodes, protozoans, trematodes, and cestodes, including unidentified strongyles (73%), Oesophagostomum spp. (53%), Ancylostoma spp. (27%), Trichuris spp. (13%), Ascaris spp. (13%), Mammomonogamus spp. (13%), Strongyloides spp. (47%), Balantidium coli (20%), Entamoeba coli (20%), Endolimax nana (6%), Fasciola hepatica (6%), Paramphistomum spp. (13%), and Taenia spp. (6%). Conclusion: All parasites were found at least once in one of the hosts, and most were potentially zoonotic and responsible for several diseases of public health concern. Because of the small sample size, our findings should not be considered conclusive. Nevertheless, they highlight the diversity of gastrointestinal parasites in this area. [ABSTRACT FROM AUTHOR]

Background: Numerous Ebola virus outbreaks have occurred in Equatorial Africa over the past decades. Besides human fatalities, gorillas and chimpanzees have also succumbed to the fatal virus. The 2004 outbreak at the Odzala-Kokoua National Park (Republic of Congo) alone caused a severe decline in the resident western lowland gorilla (Gorilla gorilla gorilla) population, with a 95% mortality rate. Here, we explore the immediate genetic impact of the Ebola outbreak in the western lowland gorilla population. Results: Associations with survivorship were evaluated by utilizing DNA obtained from fecal samples from 16 gorilla individuals declared missing after the outbreak (non-survivors) and 15 individuals observed before and after the epidemic (survivors). We used a target enrichment approach to capture the sequences of 123 genes previously associated with immunology and Ebola virus resistance and additionally analyzed the gut microbiome which could influence the survival after an infection. Our results indicate no changes in the population genetic diversity before and after the Ebola outbreak, and no significant differences in microbial community composition between survivors and non-survivors. However, and despite the low power for an association analysis, we do detect six nominally significant missense mutations in four genes that might be candidate variants associated with an increased chance of survival. Conclusion: This study offers the first insight to the genetics of a wild great ape population before and after an Ebola outbreak using target capture experiments from fecal samples, and presents a list of candidate loci that may have facilitated their survival. [ABSTRACT FROM AUTHOR]

The native subcellular location (also referred to as localization or cellular compartment) of a protein is the one in which it acts most frequently; it is one aspect of protein function. Do ten eukaryotic model organisms differ in their location spectrum, i.e., the fraction of its proteome in each of seven major cellular compartments? As experimental annotations of locations remain biased and incomplete, we need prediction methods to answer this question. After systematic bias corrections, the complete but faulty prediction methods appeared to be more appropriate to compare location spectra between species than the incomplete more accurate experimental data. This work compared the location spectra for ten eukaryotes: Homo sapiens (human), Gorilla gorilla (gorilla), Pan troglodytes (chimpanzee), Mus musculus (mouse), Rattus norvegicus (rat), Drosophila melanogaster (fruit/vinegar fly), Anopheles gambiae (African malaria mosquito), Caenorhabitis elegans (nematode), Saccharomyces cerevisiae (baker's yeast), and Schizosaccharomyces pombe (fission yeast). The two largest classes were predicted to be the nucleus and the cytoplasm together accounting for 47–62% of all proteins, while 7–21% of the proteins were predicted in the plasma membrane and 4–15% to be secreted. Overall, the predicted location spectra were largely similar. However, in detail, the differences sufficed to plot trees (UPGMA) and 2D (PCA) maps relating the ten organisms using a simple Euclidean distance in seven states (location classes). The relations based on the simple predicted location spectra captured aspects of cross-species comparisons usually revealed only by much more detailed evolutionary comparisons. Most interestingly, known phylogenetic relations were reproduced better by paralog-only than by ortholog-only trees. [ABSTRACT FROM AUTHOR]

Small-scale comparisons help us to understand how habitat features and food availability impact primate abundance. This is particularly useful at sites without human impacts, as it allows for the investigation of the natural factors influencing nesting patterns and great ape abundance. We provide a small-scale study of sympatric great ape nests in an unlogged old-growth forest without poaching activities. We conducted a line transect survey (52 km total effort) around Mbeli Bai, a forest clearing in Nouabalé–Ndoki National Park, Congo, applying on-site nest decay rates and assigning nest builder using logistic regression. We found a high occurrence of monodominant Gilbertiodendron dewevrei at Mbeli Bai (34%) that correlates with low great ape densities at Mbeli Bai. Chimpanzees (Pan troglodytes troglodytes) showed a preference for nesting in trees in closed canopy monodominant forest. We found a low percentage of gorilla (Gorilla gorilla gorilla) nests in mixed species forest (35%) and a higher percentage in trees (64%) compared to other study sites. However, generalized additive models found higher gorilla nest encounter rates in mixed species forest with dense understory than in monodominant forest and open understory. We found no indication of higher gorilla densities close to Mbeli Bai than elsewhere, and line transect estimates were lower than the number of gorillas revealed from direct observations. There were substantial differences between our findings and those for nearby sites, demonstrating the utility of small-scale comparisons to further understand the factors determining chimpanzee and gorilla densities within and between sites and the limitations of nest surveys. [ABSTRACT FROM AUTHOR]

Intraspecies violence, including lethal interactions, is a relatively common phenomenon in mammals. Contrarily, interspecies violence has mainly been investigated in the context of predation and received most research attention in carnivores. Here, we provide the first information of two lethal coalitionary attacks of chimpanzees (Pan troglodytes troglodytes) on another hominid species, western lowland gorillas (Gorilla gorilla gorilla), that occur sympatrically in the Loango National Park in Gabon. In both events, the chimpanzees significantly outnumbered the gorillas and victims were infant gorillas. We discuss these observations in light of the two most widely accepted theoretical explanations for interspecific lethal violence, predation and competition, and combinations of the two-intraguild predation and interspecific killing. Given these events meet conditions proposed to trigger coalitional killing of neighbours in chimpanzees, we also discuss them in light of chimpanzees' intraspecific interactions and territorial nature. Our findings may spur further research into the complexity of interspecies interactions. In addition, they may aid in combining field data from extant models with the Pliocene hominid fossil record to better understand behavioural adaptations and interspecific killing in the hominin lineage. [ABSTRACT FROM AUTHOR]

Grauer's gorillas (Gorilla beringei graueri) have declined drastically across their range in eastern Democratic Republic of Congo (DRC). Survey data analysed in 2016 estimated a 77% decline in numbers between the mid‐ 1990s and 2016 and predicted that Kahuzi‐Biega National Park (KBNP), and the contiguous Oku Community Reserve (OCR) held much of the global population. An estimate of 3800 Grauer's gorillas was made across its range at that time. Here, we publish the most extensive survey of Grauer's gorilla numbers to date, using nest counts from 230 line transects across KBNP and OCR to derive more accurate estimates of both gorilla and chimpanzee numbers. Gorilla numbers were estimated from line transects at 1,571 (95% confidence interval [CI]: 824–2,993) within KBNP and at 2,244 (95% CI: 1,471–3,422) in OCR. Eastern chimpanzee (Pan troglodytes schweinfurthii) numbers were estimated at 2,500 (95% CI: 1,804–3,462) in KBNP and 687 (95% CI: 472–999) in OCR. Estimates of total numbers for the survey area were 5,252 (95% CI: 3,687–7,481) Grauer's gorillas and 4,275 (95% CI: 3,322–5,502) eastern chimpanzees. Chimpanzee numbers were not significantly different from the estimates in the mid‐1990s but the gorillas had significantly declined, mostly in KBNP. Modeled densities of these apes indicated that distances to mines, villages, or roads significantly explained part of the distribution of these apes, with higher densities also found in more rugged and remote sites. Other primates have all declined in this region, likely due to bushmeat hunting, especially the Endangered Ulindi River Red Colobus Piliocolobus lulindicus. These results confirm the negative impact of insecurity on Grauer's gorilla but indicate that the population declines may not be as great as previously feared. Using our revised gorilla density estimate we revise the original estimate of global numbers from 3,800 to 6,800 individuals. Highlights: Grauer's gorilla number an estimated 5,252 (95% confidence interval [CI]: 3,687–7,481) and eastern chimpanzees number 4,926 (95% CI: 3,656–6,634) in the Kahuzi‐Biega National Park (KBNP) and adjacent Oku Community Reserve (OCR).Grauer's gorilla is estimated to have declined by 80% in KBNP since the mid‐1990s but chimpanzees are estimated to have remained stable. The numbers of gorillas in OCR have remained stable and chimpanzees have increased.Most other primate species are estimated to have declined significantly because of hunting for bushmeat. [ABSTRACT FROM AUTHOR]

Despite large investments of funding into great ape conservation in Africa, wild populations of gorillas (Gorilla ssp), chimpanzees (Pan troglodytes ssp) and bonobos (Pan paniscus) continue to decline. Causes for this decline fall into three broad categories: habitat loss, illegal hunting, and disease. Contributing factors to all of these causes are linked to pressure from the expanding human population competing for forest resources. We have moved beyond the time of debating the pros and cons of including human engagement activities in conservation. If humans are part of the problem, they must also be part of the solution. To move our understanding of which human engagement activities are effective, what methodologies are being used and best practices for setting up a successful framework, we interviewed practitioners representing 53 projects working in great ape habitat in Africa. The interviewees represented almost 900 years of experience with African great ape conservation. We found that all practitioners agreed that for conservation to succeed, projects must engage with humans utilizing resources from great ape habitats. However, evaluation of such work was elusive. Projects that employed at least one person designated as an educator were more likely to have structured programs, regular engagement activities, and to evaluate their work. To date, little information on the success or failure of the activities has been published, thus perpetuating the problem of relying on personal experience rather than evidence when developing new engagement programs. Additionally, linking human engagement activities to biological impact remains a challenge. The results presented in this paper demonstrate the importance placed on human engagement activities to effectively conserve great apes in Africa while at the same time identifies gaps in our understanding on the link between such activities and project success. [ABSTRACT FROM AUTHOR]

Objectives: The ability to use visual signals to identify individuals is an important feature of primate social groups, including humans. Sheehan and Nachman (2014) showed that loci linked to facial morphology had elevated levels of diversity and interpreted this as evidence that the human face is under frequency‐dependent selection to enhance individual recognition (Nature Communications 5). In our study, we tested whether this pattern is found in non‐human ape species, to help understand whether individual recognition might also play a role in species other than humans. Materials and methods: We examined levels of genetic diversity in an available population genomic dataset of humans, chimpanzees, bonobos, gorillas, and orangutans for three sets of loci, (1) loci linked to facial morphology, (2) loci linked to height, and (3) neutrally evolving regions. We tested whether loci linked to facial morphology were more variable than loci linked to height or neutrally evolving loci in each of these species. Results: We found significantly elevated diversity in loci linked to facial morphology in chimpanzees, gorillas, and Sumatran and Bornean orangutans. Discussion: Our findings closely parallel those of Sheehan and Nachman and are consistent with the idea that selection for facial diversity and individual recognition has not only shaped the evolution of the human face, but it has similarly shaped the evolution of most of our closest primate relatives. We also discuss alternative hypotheses for this pattern. [ABSTRACT FROM AUTHOR]

Objectives: The Giles hypothesis posits that differences in the cranial morphology of Pan troglodytes and Gorilla gorilla are largely the result of allometric scaling. However, previous support for the Giles hypothesis was based on bivariate plots of linear measurements. This investigation uses geometric morphometric methods to retest this hypothesis and its prediction that extending the ontogenetic trajectory of a chimpanzee would produce an adult gorilla‐like cranial morphology. Materials and Methods: Forty‐three 3D cranial landmarks were collected from an ontogenetic series of 76 Pan troglodytes and 58 Gorilla gorilla specimens. Ontogenetic trajectories of cranial shape change were computed via multivariate regression of Procrustes aligned coordinates against LnCS (size vector) and molar eruption stage (developmental vector). These two vectors were then used in developmental simulations to extend the ontogenetic trajectories of adult chimpanzees. Allometric trajectories of chimpanzees and gorillas were also directly compared using Procrustes ANOVA. Results: Pan and Gorilla significantly differ in their allometric trajectories, and none of the Pan developmental simulations resembled actual adult gorillas. Additionally, the more the Pan developmental vector was extended, the more morphologically distinct the simulations became from actual adult gorillas. Discussion: Taken together, these results do not support the Giles hypothesis that allometric scaling is primarily responsible for observed morphological differences between chimpanzee and gorilla crania. This investigation demonstrates that neither "growing" a chimpanzee to the size of a gorilla, nor extending a chimpanzee's developmental shape trajectory will result in an adult gorilla‐like cranial morphology as they differ in their patterns of allometry. [ABSTRACT FROM AUTHOR]

Decision outcomes in unpredictable environments may not have exact known probabilities. Yet the predictability level of outcomes matters in decisions, and animals, including humans, generally avoid ambiguous options. Managing ambiguity may be more challenging and requires stronger cognitive skills than decision-making under risk, where decisions involve known probabilities. Here we compare decision-making in capuchins, macaques, orangutans, gorillas, chimpanzees and bonobos in risky and ambiguous contexts. Subjects were shown lotteries (a tray of potential rewards, some large, some small) and could gamble a medium-sized food item to obtain one of the displayed rewards. The odds of winning and losing varied and were accessible in the risky context (all rewards were visible) or partially available in the ambiguous context (some rewards were covered). In the latter case, the level of information varied from fully ambiguous (individuals could not guess what was under the covers) to predictable (individuals could guess). None of the species avoided gambling in ambiguous lotteries and gambling rates were high if at least two large rewards were visible. Capuchins and bonobos ignored the covered items and gorillas and macaques took the presence of potential rewards into account, but only chimpanzees and orangutans could consistently build correct expectations about the size of the covered rewards. Chimpanzees and orangutans combined decision rules according to the number of large visible rewards and the level of predictability, a process resembling conditional probabilities assessment in humans. Despite a low sample size, this is the first evidence in non-human primates that a combination of several rules can underlie choices made in an unpredictable environment. Our finding that non-human primates can deal with the uncertainty of an outcome when exchanging one food item for another is a key element to the understanding of the evolutionary origins of economic behaviour. [ABSTRACT FROM AUTHOR]

Parietal external surface disruption routinely referred to as porotic hyperostosis, and orbital alterations (cribra orbitalia), have been attributed to anemia‐related bone marrow hyperplasia in humans. A recent study in humans identified that they were actually vascular in nature. Skeletons were examined and epi‐illumination surface microscopy was performed on the parietal region and orbit of 156 Hominidae and 123 Hylobotidae to assess if these phenomena were trans‐phylogenetic. Trans‐cortical channels were recognized on the basis of visualized ectocranial surface defects penetrating the parietal; cribra orbitalia, by alteration of the normally smooth orbital roof appearance. Trans‐cortical parietal channels, ranging in size from 20 to 100 µm, are rare in Gorilla and Pan troglodytes and absent in Pan paniscus. They are universally present in adult Pongo abeli and in Hylobatidae, independent of species. Cribra orbitalia was common in Hylobotidae, Pongo pygmaeus and P. abelii, less prevalent in adult P. troglodytes, and not recognized in any Gorilla gorilla or P. paniscus examined. The proliferative form predominated, with the exception of Hylobates concolor and muelleri, in which uncalcified vascular grooves predominated. No correlation was observed between the presence of either trans‐cortical channels or cribra orbitalia and fractures, osteoarthritis, or inflammatory arthritis. Parietal alterations observed in apes are trans‐cortical channels, analogous to those observed in humans, and do not represent porosity. Similarly, cribra orbitalia in apes is confirmed as vascular in nature. The proliferative form apparently represents calcification of blood vessel walls, indistinguishable from observations in humans. Predominant presence in adults rather than in juveniles suggests that both forms are acquired rather than developmental in derivation. Sex and bone alteration/disease‐independence suggests that mechanical, endocrine, and inflammatory phenomena do not contribute to the development of either. Further, independent occurrence of trans‐cortical channels and cribra orbitalia suggests that they do not have a shared etiology. Research Highlights: Trans‐cortical channels and cribra orbitalia do not have a shared etiology.They are unrelated to mechanical, endocrine, or inflammatory processes or marrow hyperplasia.Apes and humans share an expression of trans‐cortical channels and cribra orbitalia. [ABSTRACT FROM AUTHOR]

As a result of extensive data collection efforts over the last 20–30 years, there is quite a good understanding of the large‐scale geographic distribution and range limits of African great apes. However, as human activities increasingly fragment great ape spatial distribution, a better understanding of what constitutes suitable great ape habitat is needed to inform conservation and resource extraction management. Chimpanzees (Pan troglodytes troglodytes) and gorillas (Gorilla gorilla gorilla) inhabit the Lobéké National Park and its surrounding forest management units (FMUs) in South‐East Cameroon. Both park and neighboring forestry concessions require reliable evidence on key factors driving great ape distribution for their management plans, yet this information is largely missing and incomplete. This study aimed at mapping great ape habitat suitability in the area and at identifying the most influential predictors among three predictor categories, including landscape predictors (dense forest, swampy forest, distance to water bodies, and topography), human disturbance predictors (hunting, deforestation, distance to roads, and population density), and bioclimatic predictor (annual precipitation). We found that about 63% of highly to moderately suitable chimpanzee habitat occurred within the Lobéké National Park, while only 8.4% of similar habitat conditions occurred within FMUs. For gorillas, highly and moderately suitable habitats occurred within the Lobéké National Park and its surrounding FMUs (82.6% and 65.5%, respectively). Key determinants of suitable chimpanzee habitat were hunting pressure and dense forest, with species occurrence probability optimal at relatively lower hunting rates and at relatively high‐dense forest areas. Key determinants of suitable gorilla habitat were hunting pressure, dense forests, swampy forests, and slope, with species occurrence probability optimal at relatively high‐dense and swampy forest areas and at areas with mild slopes. Our findings show differential response of the two ape species to forestry activities in the study area, thus aligning with previous studies. [ABSTRACT FROM AUTHOR]

Objectives: The primary aim of this study was to describe the insertion sites of the ligaments holding the flexor digitorum profundus and superficialis muscles (flexor ridges) in proximal phalanges 2–5 of African apes and modern humans. To interpret differences in flexor ridge size based on general behavioral differences among taxa. Materials and methods: We analyzed 3D models of manual proximal phalanges 2–5 from 29 gorillas (Gorilla beringei and Gorilla gorilla), 30 chimpanzees (Pan troglodytes) and 36 recent modern humans. Flexor ridges (mm2) were compared within and across genera. Results: Gorillas and chimpanzees had larger flexor ridges for phalanges 2–4 than humans and this difference subsists when controlling for body size. Each genus had a unique insertion size pattern across the digits, with the most heterogeneous pattern found in chimpanzees, followed by humans, and lastly gorillas. These patterns corresponded strongly to the differences in the size of the phalanges within each genus, except for phalanx 5 in humans, which had a larger flexor ridge than expected. Discussion When comparing these genera, the flexor ridges signal differences between taxa that use their hands for manipulation and locomotion (gorillas and chimpanzees) and taxa that use them exclusively for manipulation (humans). This functional signal was also apparent in the PP5 of humans, whose larger FR may be indicating the high recruitment of this digit during forceful precision grip characteristic of humans. [ABSTRACT FROM AUTHOR]

Objectives: Because trabecular bone volume fraction (BV/TV) is influenced by variations in physical activity recent declines in BV/TV in humans are often attributed to modern sedentary lifestyles. This study tests the hypothesis that presumed variations in mechanical loading between groups can predict the observed BV/TV patterns in humans, chimpanzees and gorillas in two bones: the calcaneus which experiences high and well characterized impact forces, and the C2 vertebrae which experiences reduced locomotor forces. Materials and methods: BV/TV and other structural variables were quantified from high‐resolution microCT scans in gorillas, chimpanzees, and four Homo sapiens populations: Pleistocene, semi‐sedentary Natufians; Holocene hunter‐gatherers from Point Hope, Alaska; Holocene nomadic pastoralists from medieval Europe; and modern, sedentary Americans. Results: In the calcaneal tuberosity, Natufian BV/TV was 36, 46, and 46% greater than Alaskans (p =.02), Europeans (p =.005) and modern Americans (p =.002), respectively, but not significantly different from apes. BV/TV was not significantly different between modern Americans and Alaskans or Europeans. In the C2, Natufian BV/TV was 53 and 25% greater than in the Alaskan (p =.0001) and European (p =.048) populations. Discussion These results suggest that phenomena other than or in addition to variations in physical activity are needed to explain BV/TV patterns observed in H. sapiens, and point to a systemic decline in H. sapiens BV/TV after the Pleistocene. [ABSTRACT FROM AUTHOR]

The temporal association cortex is considered a primate specialization and is involved in complex behaviors, with some, such as language, particularly characteristic of humans. The emergence of these behaviors has been linked to major differences in temporal lobe white matter in humans compared with monkeys. It is unknown, however, how the organization of the temporal lobe differs across several anthropoid primates. Therefore, we systematically compared the organization of the major temporal lobe white matter tracts in the human, gorilla, and chimpanzee great apes and in the macaque monkey. We show that humans and great apes, in particular the chimpanzee, exhibit an expanded and more complex occipital–temporal white matter system; additionally, in humans, the invasion of dorsal tracts into the temporal lobe provides a further specialization. We demonstrate the reorganization of different tracts along the primate evolutionary tree, including distinctive connectivity of human temporal gray matter. A comparison of the organization of connections in the temporal association cortex sheds light on specializations underlying the unique behavioral abilities of monkeys, chimpanzee, gorillas and humans. [ABSTRACT FROM AUTHOR]

Photogrammetry is becoming increasingly popular in morphological research and teaching due to its portability, ability to reliably render 3D models, and quality-to-price relationship relative to some popular surface scanners. Compared to surface scanners, however, the learning process in photogrammetry can be very time consuming. Here we describe common mistakes of photo capture in close-range photogrammetry that greatly affect 3D output and tips to improve them. Problems were identified after the 3D model construction of 780 hand bones of chimpanzees and gorillas from museum collections. Their hands are composed of 27 bones which vary in length and complexity. We show how lighting, object position and orientation, camera angle, and background affect the 3D output. By taking these factors into account, time and error rates for beginners can be greatly reduced and 3D model quality can be considerably improved. [ABSTRACT FROM AUTHOR]

The evolutionary origins of how modern humans share and use space are often modelled on the territorial-based violence of chimpanzees, with limited comparison to other apes. Gorillas are widely assumed to be non-territorial due to their large home ranges, extensive range overlap, and limited inter-group aggression. Using large-scale camera trapping, we monitored western gorillas in Republic of Congo across 60 km2. Avoidance patterns between groups were consistent with an understanding of the "ownership" of specific regions, with greater avoidance of their neighbours the closer they were to their neighbours' home range centres. Groups also avoided larger groups' home ranges to a greater extent, consistent with stronger defensive responses from more dominant groups. Our results suggest that groups may show territoriality, defending core regions of their home ranges against neighbours, and mirror patterns common across human evolution, with core areas of resident dominance and larger zones of mutual tolerance. This implies western gorillas may be a key system for understanding how humans have evolved the capacity for extreme territorial-based violence and warfare, whilst also engaging in the strong affiliative inter-group relationships necessary for large-scale cooperation. [ABSTRACT FROM AUTHOR]

Language does not fossilize but this does not mean that the language's evolutionary timeline is lost forever. Great apes provide a window back in time on our last prelinguistic ancestor's communication and cognition. Phylogeny and cladistics implicitly conjure Pan (chimpanzees, bonobos) as a superior (often the only) model for language evolution compared with earlier diverging lineages, Gorilla and Pongo (orangutans). Here, in reviewing the literature, it is shown that Pan do not surpass other great apes along genetic, cognitive, ecologic, or vocal traits that are putatively paramount for language onset and evolution. Instead, revived herein is the idea that only by abandoning single‐species models and learning about the variation among great apes, there might be a chance to retrieve lost fragments of the evolutionary timeline of language. [ABSTRACT FROM AUTHOR]

Understanding captive animals' preferences is important for their care and management. However, pairwise testing for preference can be time consuming, open to bias, and typically restricted to stimuli that can be presented manually. We tested the efficacy of using touchscreens to test zoo-housed primates' food preferences and evaluated the primates' understanding and interpretation of photographic stimuli. We showed 18 subjects (six gorillas, five chimpanzees, and seven Japanese macaques) four food stimuli (digital photographs of familiar foods presented via touchscreens) to test their preferences in a forced-choice paradigm. We presented preliminary single-food training trials before paired forced-choice test trials, which revealed subjects' relative preferences for the four foods. To distinguish whether the primates' responses represented conditioned associations between the stimuli and rewards, or a true understanding of the food photographs, we ran a follow-up study with novel stimuli (novel photographs of familiar foods). We combined the two novel stimuli with the four stimuli presented in the first experiment in pairwise forced-choice trials (importantly, without training trials). Subjects did not preferentially select or avoid the novel stimuli, suggesting they spontaneously interpreted the stimuli without training. While there was interindividual variation in preferences, subject choices were consistent across studies, even with the addition of novel stimuli. These results suggest that preferences for a variety of stimuli could be tested quickly, efficiently, and accurately using touchscreens. [ABSTRACT FROM AUTHOR]