Variation of thoracolumbar vertebral morphology in anthropoid primates

OBJECTIVES

Morphological variation among extant primates in the lumbar vertebral column is well studied. However, knowledge concerning the thoracic spine, an important region responsible for supporting and facilitating movement in the upper trunk, remains relatively scarce. Consequently, our comprehension of the functional differentiation exhibited throughout the thoracolumbar vertebral column among various primate species remains constrained. In this study, we examined patterns of morphological variation in the thoracolumbar vertebral column of extant hominoids, cercopithecoids, and Ateles.

MATERIALS AND METHODS

We collected external shape data on 606 thoracic and lumbar vertebrae from Homo sapiens, Pan troglodytes, Hylobates lar, Macaca fuscata, Chlorocebus aethiops, Colobus guereza, Ateles geoffroyi, and A. belzebuth. Forty-four landmarks were obtained on the three-dimensional surface. Geometric morphometrics was used to quantify the centroid size and variation of the shapes of thoracic and lumbar vertebrae.

RESULTS

Cercopithecoids exhibited greater variation in the size and shape of their thoracic and lumbar vertebrae compared to hominoids and Ateles. Although many vertebral features contributed to the observed variation throughout the thoracolumbar vertebral column within the taxon, the transverse and spinous processes exhibited relatively major contributions.

DISCUSSION

Our results suggest that quadrupedal locomotion requires the functional differentiation between thoracic and lumbar vertebrae, and for hominoids, functional adaptation to orthograde posture necessitates a relatively more uniform shape of thoracic and lumbar vertebrae.

Conserved patterns and locomotor-related evolutionary constraints in the hominoid vertebral column

The evolution of the hominoid lineage is characterized by pervasive homoplasy, notably in regions such as the vertebral column, which plays a central role in body support and locomotion. Few isolated and fewer associated vertebrae are known for most fossil hominoid taxa, but identified specimens indicate potentially high levels of convergence in terms of both form and number. Homoplasy thus complicates attempts to identify the anatomy of the last common ancestor of hominins and other taxa and stymies reconstructions of evolutionary scenarios. One way to clarify the role of homoplasy is by investigating constraints via phenotypic integration, which assesses covariation among traits, shapes evolutionary pathways, and itself evolves in response to selection. We assessed phenotypic integration and evolvability across the subaxial (cervical, thoracic, lumbar, sacral) vertebral column of macaques (n = 96), gibbons (n = 77), chimpanzees (n = 92), and modern humans (n = 151). We found a mid-cervical cluster that may have shifted cranially in hominoids, a persistent thoracic cluster that is most marked in chimpanzees, and an expanded lumbosacral cluster in hominoids that is most expanded in gibbons. Our results highlight the highly conserved nature of the vertebral column. Taxa appear to exploit existing patterns of integration and ontogenetic processes to shift, expand, or reduce cluster boundaries. Gibbons appear to be the most highly derived taxon in our sample, possibly in response to their highly specialized locomotion.

Water scooping: tool use by a wild bonobo (Pan paniscus) at LuiKotale, a case report

Tool use diversity is often considered to differentiate our two closest living relatives: the chimpanzee (Pan troglodytes) and the bonobo (P. paniscus). Chimpanzees appear to have the largest repertoire of tools amongst nonhuman primates, and in this species, many forms of tool use enhance food and water acquisition. In captivity, bonobos seem as adept as chimpanzees in tool use complexity, including in the foraging context. However, in the wild, bonobos have only been observed engaging in habitual tool use in the contexts of comfort, play, self-directed behaviour and communication, whilst no tool-assisted food acquisition has been reported. Whereas captive bonobos use tools for drinking, so far, the only report from the wild populations comes down to four observations of moss sponges used at Lomako. Here, we present the first report of tool use in the form of water scooping by a wild bonobo at LuiKotale. An adult female was observed and videotaped whilst using an emptied Cola chlamydantha pod to scoop and drink water from a stream. We discuss the conditions for such observations and the importance of looking out for rare behaviours and attempt to put the observation into the context of the opportunity versus necessity hypotheses. By adding novel information on tool use, our report contributes to the ongoing efforts to differentiate population-specific traits in the behavioural ecology of the bonobo.

Applying collocation and APRIORI analyses to chimpanzee diets: Methods for investigating nonrandom food combinations in primate self-medication

Identifying novel medicinal resources in chimpanzee diets has historically presented challenges, requiring extensive behavioral data collection and health monitoring, accompanied by expensive pharmacological analyses. When putative therapeutic self-medicative behaviors are observed, these events are often considered isolated occurrences, with little attention paid to other resources ingested in combination. For chimpanzees, medicinal resource combinations could play an important role in maintaining well-being by tackling different symptoms of an illness, chemically strengthening efficacy of a treatment, or providing prophylactic compounds that prevent future ailments. We call this concept the self-medicative resource combination hypothesis. However, a dearth of methodological approaches for holistically investigating primate feeding ecology has limited our ability to identify nonrandom resource combinations and explore potential synergistic relationships between medicinal resource candidates. Here we present two analytical tools that test such a hypothesis and demonstrate these approaches on feeding data from the Sonso chimpanzee community in Budongo Forest, Uganda. Using 4 months of data, we establish that both collocation and APRIORI analyses are effective exploratory tools for identifying binary combinations, and that APRIORI is effective for multi-item rule associations. We then compare outputs from both methods, finding up to 60% agreement, and propose APRIORI as more effective for studies requiring control over confidence intervals and those investigating nonrandom associations between more than two resources. These analytical tools, which can be extrapolated across the animal kingdom, can provide a cost-effective and efficient method for targeting resources for further pharmacological investigation, potentially aiding in the discovery of novel medicines.

Humans (Homo sapiens) but not baboons (Papio papio) demonstrate crossmodal pitch-luminance correspondence

Humans spontaneously and consistently map information coming from different sensory modalities. Surprisingly, the phylogenetic origin of such cross-modal correspondences has been under-investigated. A notable exception is the study of Ludwig et al. (Visuoauditory mappings between high luminance and high pitch are shared by chimpanzees [Pan troglodytes] and humans. Proceedings of the National Academy of Sciences, 108(51), 20661-20665) which reports that both humans and chimpanzees spontaneously map high-pitched sounds with bright objects and low-pitched sounds with dark objects. Our pre-registered study aimed to directly replicate this research on both humans and baboons (Papio papio), an old world monkey which is more phylogenetically distant from humans than chimpanzees. Following Ludwig et al. participants were presented with a visual classification task where they had to sort black and white square (low and high luminance), while background sounds (low or high-pitched tones) were playing. Whereas we replicated the finding that humans' performance on the visual task was affected by congruency between sound and luminance of the target, we did not find any of those effects on baboons' performance. These results question the presence of a shared cross-modal pitch-luminance mapping in other nonhuman primates.

A shared pattern of midfacial bone modelling in hominids suggests deep evolutionary roots for human facial morphogenesis

Midfacial morphology varies between hominoids, in particular between great apes and humans for which the face is small and retracted. The underlying developmental processes for these morphological differences are still largely unknown. Here, we investigate the cellular mechanism of maxillary development (bone modelling, BM), and how potential changes in this process may have shaped facial evolution. We analysed cross-sectional developmental series of gibbons, orangutans, gorillas, chimpanzees and present-day humans (n = 183). Individuals were organized into five age groups according to their dental development. To visualize each species's BM pattern and corresponding morphology during ontogeny, maps based on microscopic data were mapped onto species-specific age group average shapes obtained using geometric morphometrics. The amount of bone resorption was quantified and compared between species. Great apes share a highly similar BM pattern, whereas gibbons have a distinctive resorption pattern. This suggests a change in cellular activity on the hominid branch. Humans possess most of the great ape pattern, but bone resorption is high in the canine area from birth on, suggesting a key role of canine reduction in facial evolution. We also observed that humans have high levels of bone resorption during childhood, a feature not shared with other apes.

The work to swing limbs in humans versus chimpanzees and its relation to the metabolic cost of walking

Compared to their closest ape relatives, humans walk bipedally with lower metabolic cost (C) and less mechanical work to move their body center of mass (external mechanical work, WEXT). However, differences in WEXT are not large enough to explain the observed lower C: humans may also do less work to move limbs relative to their body center of mass (internal kinetic mechanical work, WINT,k). From published data, we estimated differences in WINT,k, total mechanical work (WTOT), and efficiency between humans and chimpanzees walking bipedally. Estimated WINT,k is ~ 60% lower in humans due to changes in limb mass distribution, lower stride frequency and duty factor. When summing WINT,k to WEXT, between-species differences in efficiency are smaller than those in C; variations in WTOT correlate with between-species, but not within-species, differences in C. These results partially support the hypothesis that the low cost of human walking is due to the concerted low WINT,k and WEXT.

How can I find what I want? Can children, chimpanzees and capuchin monkeys form abstract representations to guide their behavior in a sampling task?

concepts are a powerful tool for making wide-ranging predictions in new situations based on little experience. Whereas looking-time studies suggest an early emergence of this ability in human infancy, other paradigms like the relational match to sample task often fail to detect abstract concepts until late preschool years. Similarly, non-human animals show difficulties and often succeed only after long training regimes. Given the considerable influence of slight task modifications, the conclusiveness of these findings for the development and phylogenetic distribution of abstract reasoning is debated. Here, we tested the abilities of 3 to 5-year-old children, chimpanzees, and capuchin monkeys in a unified and more ecologically valid task design based on the concept of "overhypotheses" (Goodman, 1955). Participants sampled high- and low-valued items from containers that either each offered items of uniform value or a mix of high- and low-valued items. In a test situation, participants should switch away earlier from a container offering low-valued items when they learned that, in general, items within a container are of the same type, but should stay longer if they formed the overhypothesis that containers bear a mix of types. We compared each species' performance to the predictions of a probabilistic hierarchical Bayesian model forming overhypotheses at a first and second level of abstraction, adapted to each species' reward preferences. Children and, to a more limited extent, chimpanzees demonstrated their sensitivity to abstract patterns in the evidence. In contrast, capuchin monkeys did not exhibit conclusive evidence for the ability of abstract knowledge formation.

Flexible grouping patterns in a western and eastern chimpanzee community

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

Ecological variation in adult social play reveals a hidden cost of motherhood for wild chimpanzees

Though common among humans, social play by adults is an uncommon occurrence in most animals, even between parents and offspring.1,2,3 The most common explanation for why adult play is so rare is that its function and benefits are largely limited to development, so that social play has little value later in life.3,4,5,6 Here, we draw from 10 years of behavioral data collected by the Kibale Chimpanzee Project to consider an alternative hypothesis: that despite its benefits, adult play in non-humans is ecologically constrained by energy shortage or time limitations. We further hypothesized that, since they may be the only available partners for their young offspring, mother chimpanzees pay greater costs of play than other adults. Our analysis of nearly 4,000 adult play bouts revealed that adult chimpanzees played both among themselves and with immature partners. Social play was infrequent when diet quality was low but increased with the proportion of high-quality fruits in the diet. This suggests that adults engage in play facultatively when they have more energy and/or time to do so. However, when diet quality was low and most adult play fell to near zero, play persisted between mothers and offspring. Increased use of play by adult chimpanzees during periods of resource abundance suggests that play retains value as a social currency beyond development but that its costs constrain its use. At the same time, when ecological conditions constrain opportunities for young to play, play by mothers fills a critical role to promote healthy offspring development.

Macrophages derived from human induced pluripotent stem cells (iPSCs) serve as a high-fidelity cellular model for investigating HIV-1, dengue, and influenza viruses

Macrophages are important target cells for diverse viruses and thus represent a valuable system for studying virus biology. Isolation of primary human macrophages is done by culture of dissociated tissues or from differentiated blood monocytes, but these methods are both time consuming and result in low numbers of recovered macrophages. Here, we explore whether macrophages derived from human induced pluripotent stem cells (iPSCs)-which proliferate indefinitely and potentially provide unlimited starting material-could serve as a faithful model system for studying virus biology. Human iPSC-derived monocytes were differentiated into macrophages and then infected with HIV-1, dengue virus, or influenza virus as model human viruses. We show that iPSC-derived macrophages support the replication of these viruses with kinetics and phenotypes similar to human blood monocyte-derived macrophages. These iPSC-derived macrophages were virtually indistinguishable from human blood monocyte-derived macrophages based on surface marker expression (flow cytometry), transcriptomics (RNA sequencing), and chromatin accessibility profiling. iPSC lines were additionally generated from non-human primate (chimpanzee) fibroblasts. When challenged with dengue virus, human and chimpanzee iPSC-derived macrophages show differential susceptibility to infection, thus providing a valuable resource for studying the species-tropism of viruses. We also show that blood- and iPSC-derived macrophages both restrict influenza virus at a late stage of the virus lifecycle. Collectively, our results substantiate iPSC-derived macrophages as an alternative to blood monocyte-derived macrophages for the study of virus biology.

IMPORTANCE

Macrophages have complex relationships with viruses: while macrophages aid in the removal of pathogenic viruses from the body, macrophages are also manipulated by some viruses to serve as vessels for viral replication, dissemination, and long-term persistence. Here, we show that iPSC-derived macrophages are an excellent model that can be exploited in virology.

A chimp algorithm based on the foraging strategy of manta rays and its application

To address the issue of poor performance in the chimp optimization (ChOA) algorithm, a new algorithm called the manta ray-based chimpa optimization algorithm (MChOA) was developed. Introducing the Latin hypercube method to construct the initial population so that the individuals of the initial population are evenly distributed in the solution space, increasing the diversity of the initial population. Introducing nonlinear convergence factors based on positive cut functions to changing the convergence of algorithms, the early survey capabilities and later development capabilities of the algorithm are balanced. The manta ray foraging strategy is introduced at the position update to make up for the defect that the algorithm is prone to local optimization, which effectively improves the optimization performance of the algorithm. To evaluate the performance of the proposed algorithm, 27 well-known test reference functions were selected for experimentation, which showed significant advantages compared to other algorithms. Finally, in order to further verify the algorithm's applicability in actual production processes, it was applied to solve scheduling problems in three flexible workshop scenarios and an aviation engine job shop scheduling in an enterprise. This confirmed its efficacy in addressing complex real-world problems.

The deep trabecular structure of first metacarpals in extant hominids

OBJECTIVES

Recent studies have associated subarticular trabecular bone distribution in the extant hominid first metacarpal (Mc1) with observed thumb use, to infer fossil hominin thumb use. Here, we analyze the entire Mc1 to test for interspecific differences in: (1) the absolute volume of trabecular volume fraction, (2) the distribution of the deeper trabecular network, and (3) the distribution of trabeculae in the medullary cavity, especially beneath the Mc1 disto-radial flange.

MATERIALS AND METHODS

Trabecular bone was imaged using micro-computed tomography in a sample of Homo sapiens (n = 11), Pan paniscus (n = 10), Pan troglodytes (n = 11), Gorilla gorilla (n = 10) and Pongo sp., (n = 7). Using Canonical Holistic Morphometric Analysis (cHMA), we tested for interspecific differences in the trabecular bone volume fraction (BV/TV) and its relative distribution (rBV/TV) throughout the Mc1, including within the head, medullary cavity, and base.

RESULTS

P. paniscus had the highest, and H. sapiens the lowest, BV/TV relative to other species. rBV/TV distribution statistically distinguished the radial concentrations and lack of medullary trabecular bone in the H. sapiens Mc1 from all other hominids. H. sapiens and, to a lesser extent, G. gorilla also had a significantly higher trabecular volume beneath the disto-radial flange relative to other hominids.

DISCUSSION

These results are consistent with differences in observed thumb use in these species and may also reflect systemic differences in bone volume fraction. The trabecular bone extension into the medullary cavity and concentrations beneath the disto-radial flange may represent crucial biomechanical signals that will aid in the inference of fossil hominin thumb use.

Sketches of chimpanzee (Pan troglodytes) hoo's: vowels by any other name?

In human speech, the close back rounded vowel /u/ (the vowel in "boot") is articulated with the tongue arched toward the dorsal boundary of the hard palate, with the pharyngeal cavity open. Acoustic and perceptual properties of chimpanzee (Pan troglodytes) hoo's are similar to those of the human vowel /u/. However, the vocal tract morphology of chimpanzees likely limits their phonetic capabilities, so that it is unlikely, or even impossible, that their articulation is comparable to that of a human. To determine how qualities of the vowel /u/ may be achieved given the chimpanzee vocal tract, we calculated transfer functions of the vocal tract area for tube models of vocal tract configurations in which vocal tract length, length and area of a laryngeal air sac simulacrum, length of lip protrusion, and area of lip opening were systematically varied. The method described is principally acoustic; we make no claim as to the actual shape of the chimpanzee vocal tract during call production. Nonetheless, we demonstrate that it may be possible to achieve the acoustic and perceptual qualities of back vowels without a reconfigured human vocal tract. The results, while tentative, suggest that the production of hoo's by chimpanzees, while achieving comparable vowel-like qualities to the human /u/, may involve articulatory gestures that are beyond the range of the human articulators. The purpose of this study was to (1) stimulate further simulation research on great ape articulation, and (2) show that apparently vowel-like phenomena in nature are not necessarily indicative of evolutionary continuity per se.

Potentially Zoonotic Enteric Infections in Gorillas and Chimpanzees, Cameroon and Tanzania

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.

New craniodental fossils of Paranthropus robustus from Kromdraai, South Africa (2014-2017 excavations)

Since the initial discovery of Paranthropus robustus at the site of Kromdraai in 1938, the hypodigm of this species has been expanded by subsequent work at the localities of Swartkrans and Drimolen, with a few fossils also known from Cooper's D, Gondolin and Sterkfontein Member 5. Beginning in 2014, systematic excavations at Kromdraai uncovered a large and previously unknown fossiliferous area, shedding light on Units O and P in the earliest part of the site's stratigraphic sequence. The aim of this paper is to provide detailed descriptions and illustrations of 30 P. robustus craniodental specimens recovered between 2014 and 2017 within the Unit P deposits at Kromdraai. This new sample predates all prior conspecific specimens found at this site (including the holotype of P. robustus from Kromdraai, TM 1517). Its basic dental morphology dimensions and cranial features are compared in a preliminary analysis with other P. robustus samples. The P. robustus sample from Kromdraai Unit P documents previously unknown portions of the P. robustus juvenile cranium. The new dental and cranial remains aid in the exploration of potential morphological distinctions between site-specific P. robustus samples and are compared favorably in size and morphology with the small P. robustus specimens from Drimolen (e.g., DNH 7). These findings do not support the hypothesis that the specimens from Drimolen belong to a different taxonomic group. Instead, they reinforce the presence of a significant degree of sexual dimorphism within P. robustus. The Kromdraai Unit P specimens also contribute to the biodemographic profile of P. robustus. The notable prevalence of infants (i.e., juvenile individuals before the emergence of their first permanent molars) mirrors the natural mortality profiles observed in wild chimpanzees. This suggests a closer resemblance in the processes of accumulation in Kromdraai Unit P and Drimolen than at Swartkrans.

Estimating the cardiac signals of chimpanzees using a digital camera: validation and application of a novel non-invasive method for primate research

Cardiac measures such as heart rate measurements are important indicators of both physiological and psychological states. However, despite their extraordinary potential, their use is restricted in comparative psychology because traditionally cardiac measures involved the attachment of sensors to the participant's body, which, in the case of undomesticated animals such as nonhuman primates, is usually only possible during anesthesia or after extensive training. Here, we validate and apply a camera-based system that enables contact-free detection of animals' heart rates. The system automatically detects and estimates the cardiac signals from cyclic change in the hue of the facial area of a chimpanzee. In Study 1, we recorded the heart rate of chimpanzees using the new technology, while simultaneously measuring heart rate using classic PPG (photoplethysmography) finger sensors. We found that both methods were in good agreement. In Study 2, we applied our new method to measure chimpanzees' heart rate in response to seeing different types of video scenes (groupmates in an agonistic interaction, conspecific strangers feeding, nature videos, etc.). Heart rates changed during video presentation, depending on the video content: Agonistic interactions and conspecific strangers feeding lead to accelerated heart rate relative to baseline, indicating increased emotional arousal. Nature videos lead to decelerated heart rate relative to baseline, indicating a relaxing effect or heightened attention caused by these stimuli. Our results show that the new contact-free technology can reliably assess the heart rate of unrestrained chimpanzees, and most likely other primates. Furthermore, our technique opens up new avenues of research within comparative psychology and facilitates the health management of captive individuals.

Atherosclerosis as the Damocles' sword of human evolution: insights from nonhuman ape-like primates, ancient human remains, and isolated modern human populations

Atherosclerosis is the leading cause of death worldwide, and the predominant risk factors are advanced age and high-circulating low-density lipoprotein cholesterol (LDL-C). However, the findings of atherosclerosis in relatively young mummified remains and a lack of atherosclerosis in chimpanzees despite high LDL-C call into question the role of traditional cardiovascular risk factors. The inflammatory theory of atherosclerosis may explain the discrepancies between traditional risk factors and observed phenomena in current literature. Following the divergence from chimpanzees several millennia ago, loss of function mutations in immune regulatory genes and changes in gene expression have resulted in an overactive human immune system. The ubiquity of atherosclerosis in the modern era may reflect a selective pressure that enhanced the innate immune response at the cost of atherogenesis and other chronic disease states. Evidence provided from the fields of genetics, evolutionary biology, and paleoanthropology demonstrates a sort of circular dependency between inflammation, immune system functioning, and evolution at both a species and cellular level. More recently, the role of proinflammatory stimuli, somatic mutations, and the gene-environment effect appear to be underappreciated elements in the development and progression of atherosclerosis. Neurobiological stress, metabolic syndrome, and traditional cardiovascular risk factors may instead function as intermediary links between inflammation and atherosclerosis. Therefore, considering evolution as a mechanistic process and atherosclerosis as part of the inertia of evolution, greater insight into future preventative and therapeutic interventions for atherosclerosis can be gained by examining the past.

Mucosal vaccine-induced cross-reactive CD8+ T cells protect against SARS-CoV-2 XBB.1.5 respiratory tract infection

A nasally delivered chimpanzee adenoviral-vectored severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine (ChAd-SARS-CoV-2-S) is currently used in India (iNCOVACC). Here, we update this vaccine by creating ChAd-SARS-CoV-2-BA.5-S, which encodes a prefusion-stabilized BA.5 spike protein. Whereas serum neutralizing antibody responses induced by monovalent or bivalent adenoviral vaccines were poor against the antigenically distant XBB.1.5 strain and insufficient to protect in passive transfer experiments, mucosal antibody and cross-reactive memory T cell responses were robust, and protection was evident against WA1/2020 D614G and Omicron variants BQ.1.1 and XBB.1.5 in mice and hamsters. However, depletion of memory CD8+ T cells before XBB.1.5 challenge resulted in loss of protection against upper and lower respiratory tract infection. Thus, nasally delivered vaccines stimulate mucosal immunity against emerging SARS-CoV-2 strains, and cross-reactive memory CD8+ T cells mediate protection against lung infection by antigenically distant strains in the setting of low serum levels of cross-reactive neutralizing antibodies.

A three-dimensional musculoskeletal model of the pelvis and lower limb of Australopithecus afarensis

OBJECTIVES

Musculoskeletal modeling is a powerful approach for studying the biomechanics and energetics of locomotion. Australopithecus (A.) afarensis is among the best represented fossil hominins and provides critical information about the evolution of musculoskeletal design and locomotion in the hominin lineage. Here, we develop and evaluate a three-dimensional (3-D) musculoskeletal model of the pelvis and lower limb of A. afarensis for predicting muscle-tendon moment arms and moment-generating capacities across lower limb joint positions encompassing a range of locomotor behaviors.

MATERIALS AND METHODS

A 3-D musculoskeletal model of an adult A. afarensis pelvis and lower limb was developed based primarily on the A.L. 288-1 partial skeleton. The model includes geometric representations of bones, joints and 35 muscle-tendon units represented using 43 Hill-type muscle models. Two muscle parameter datasets were created from human and chimpanzee sources. 3-D muscle-tendon moment arms and isometric joint moments were predicted over a wide range of joint positions.

RESULTS

Predicted muscle-tendon moment arms generally agreed with skeletal metrics, and corresponded with human and chimpanzee models. Human and chimpanzee-based muscle parameterizations were similar, with some differences in maximum isometric force-producing capabilities. The model is amenable to size scaling from A.L. 288-1 to the larger KSD-VP-1/1, which subsumes a wide range of size variation in A. afarensis.

DISCUSSION

This model represents an important tool for studying the integrated function of the neuromusculoskeletal systems in A. afarensis. It is similar to current human and chimpanzee models in musculoskeletal detail, and will permit direct, comparative 3-D simulation studies.

Comparative ontogeny of functional aspects of human cervical vertebrae

OBJECTIVES

Differences between adult humans and great apes in cervical vertebral morphology are well documented, but the ontogeny of this variation is still largely unexplored. This study examines patterns of growth in functionally relevant features of C1, C2, C4, and C6 in extant humans and apes to understand the development of their disparate morphologies.

MATERIALS AND METHODS

Linear and angular measurements were taken from 530 cervical vertebrae representing 146 individual humans, chimpanzees, gorillas, and orangutans. Specimens were divided into three age-categories based on dental eruption: juvenile, adolescent, and adult. Inter- and intraspecific comparisons were evaluated using resampling methods.

RESULTS

Of the eighteen variables examined here, seven distinguish humans from apes at the adult stage. Human-ape differences in features related to atlantoaxial joint function tend to be established by the juvenile stage, whereas differences in features related to the nuchal musculature and movement of the subaxial elements do not fully emerge until adolescence or later. The orientation of the odontoid process-often cited as a feature that distinguishes humans from apes-is similar in adult humans and adult chimpanzees, but the developmental patterns are distinct, with human adultlike morphology being achieved much earlier.

DISCUSSION

The biomechanical consequences of the variation observed here is poorly understood. Whether the differences in growth patterns represent functional links to cranial development or postural changes, or both, requires additional investigation. Determining when humanlike ontogenetic patterns evolved in hominins may provide insight into the functional basis driving the morphological divergence between extant humans and apes.

Captive bonobos (Pan paniscus) apply precision grips when using flaked stone tools

OBJECTIVES

Current evidence suggests that flaked stone tool technologies did not emerge until ~3.3-2.6 million-years-ago (Ma). It is often hypothesized that early hominin (principally Ardipithecus and early Australopithecus) manual anatomy may have prevented an earlier emergence, as the forceful precision grips essential to flake tool-use may have been ineffectively performed by these species. Marzke, Marchant, McGrew, and Reece (2015) observed potentially forceful pad-to-side precision grips being recruited by wild chimpanzees (Pan troglodytes) during feeding behaviors, indicating that Pan-like manual anatomy, and therefore potentially early hominin anatomy, may be capable of effectively securing flake stone tools during their use.

MATERIALS AND METHODS

Here, we report on the grips recruited by four captive, human-trained, bonobos (Pan paniscus) during the use of stone and organic tools, including flake stone tools during cutting behaviors.

RESULTS

It is revealed that pad-to-side precision grips are frequently recruited by these bonobos when securing stone flakes during cutting actions. In some instances, high forces could have been resisted and applied by the thumb and fingers.

DISCUSSION

While our analyzes are preliminary and limited to captive individuals, and Pan is not suggested to secure flakes with the same efficacy as Homo or Australopithecus, it points to early hominins potentially being able to perform the precision grips required to use flake stone tools. In turn, the ability to gain tangible benefits from the effective use of flake tools (i.e., gain energetic returns from processing food resources) may have been - at least anatomically - possible in early Australopithecus and other pre-Early Stone Age hominin species. In turn, hominin manual anatomy may not be a leading restriction on the emergence of the earliest stone tool technologies.

Endodontic Treatment of a Maxillary Incisor Tooth in a Chimpanzee (Pan troglodytes)

Chimpanzees (Pan troglodytes) with teeth severely damaged by dental caries and/or periodontal disease are often managed with medication and/or tooth extraction. A common endodontic treatment for severely decayed teeth in a 26-year-old female chimpanzee is reported. The left maxillary central incisor tooth had lost its crown, probably due to trauma that was not recent, and it had a fistula most likely due to chronic apical periodontitis. The diagnosis was confirmed radiographically before treatment. To treat the infected root canal, endodontic treatment used in humans was adapted for a chimpanzee. After the treatment, the tooth was sealed using an adhesive resin composite. At 11-years post-treatment, there were no signs of recurrence of the lesion or of failure of the tooth seal. The results of this case report suggest that common endodontic treatments used in humans are also effective in chimpanzees.

Two-step evolution of HIV-1 budding system leading to pandemic in the human population

The pandemic HIV-1, HIV-1 group M, emerged from a single spillover event of its ancestral lentivirus from a chimpanzee. During human-to-human spread worldwide, HIV-1 diversified into multiple subtypes. Here, our interdisciplinary investigation mainly sheds light on the evolutionary scenario of the viral budding system of HIV-1 subtype C (HIV-1C), a most successfully spread subtype. Of the two amino acid motifs for HIV-1 budding, the P(T/S)AP and YPxL motifs, HIV-1C loses the YPxL motif. Our data imply that HIV-1C might lose this motif to evade immune pressure. Additionally, the P(T/S)AP motif is duplicated dependently of the level of HIV-1 spread in the human population, and >20% of HIV-1C harbored the duplicated P(T/S)AP motif. We further show that the duplication of the P(T/S)AP motif is caused by the expansion of the CTG triplet repeat. Altogether, our results suggest that HIV-1 has experienced a two-step evolution of the viral budding process during human-to-human spread worldwide.

Cell-type-specific cis-regulatory divergence in gene expression and chromatin accessibility revealed by human-chimpanzee hybrid cells

Although gene expression divergence has long been postulated to be the primary driver of human evolution, identifying the genes and genetic variants underlying uniquely human traits has proven to be quite challenging. Theory suggests that cell-type-specific cis-regulatory variants may fuel evolutionary adaptation due to the specificity of their effects. These variants can precisely tune the expression of a single gene in a single cell-type, avoiding the potentially deleterious consequences of trans-acting changes and non-cell type-specific changes that can impact many genes and cell types, respectively. It has recently become possible to quantify human-specific cis-acting regulatory divergence by measuring allele-specific expression in human-chimpanzee hybrid cells-the product of fusing induced pluripotent stem (iPS) cells of each species in vitro. However, these cis-regulatory changes have only been explored in a limited number of cell types. Here, we quantify human-chimpanzee cis-regulatory divergence in gene expression and chromatin accessibility across six cell types, enabling the identification of highly cell-type-specific cis-regulatory changes. We find that cell-type-specific genes and regulatory elements evolve faster than those shared across cell types, suggesting an important role for genes with cell-type-specific expression in human evolution. Furthermore, we identify several instances of lineage-specific natural selection that may have played key roles in specific cell types, such as coordinated changes in the cis-regulation of dozens of genes involved in neuronal firing in motor neurons. Finally, using novel metrics and a machine learning model, we identify genetic variants that likely alter chromatin accessibility and transcription factor binding, leading to neuron-specific changes in the expression of the neurodevelopmentally important genes FABP7 and GAD1. Overall, our results demonstrate that integrative analysis of cis-regulatory divergence in chromatin accessibility and gene expression across cell types is a promising approach to identify the specific genes and genetic variants that make us human.

Chimpanzees engage in competitive altruism in a triadic ultimatum game

Partner choice promotes competition among individuals to be selected as a cooperative partner, a phenomenon referred to as competitive altruism. We explored whether chimpanzees engage in competitive altruism in a triadic Ultimatum Game where two proposers can send offers simultaneously or consecutively to a responder who can only accept one of the two competing offers. In a dyadic control condition only one proposer at a time could send an offer to the responder. Chimpanzees increased their offers across trials in the competitive triadic, but not in the dyadic control condition. Chimpanzees also increased their offers after being rejected in previous triadic trials. Furthermore, we found that chimpanzees, under specific conditions, outcompete first proposers in triadic consecutive trials before the responder could choose which offer to accept by offering more than what is expected if they acted randomly or simply offered the smallest possible amount. These results suggest that competitive altruism in chimpanzees did not emerge just as a by-product of them trying to increase over previous losses. Chimpanzees might consider how others' interactions affect their outcomes and engage in strategies to maximize their chances of being selected as cooperative partners.

Habitual ground nesting in the Bugoma Forest chimpanzees (Pan troglodytes schweinfurthii), Uganda

We report the presence of habitual ground nesting in a newly studied East African chimpanzee (Pan troglodytes schweinfurthii) population in the Bugoma Central Forest Reserve, Uganda. Across a 2-year period, we encountered 891 night nests, 189 of which were classified as ground nests, a rate of ~21%. We find no preliminary evidence of socio-ecological factors that would promote its use and highlight local factors, such as high incidence of forest disturbance due to poaching and logging, which appear to make its use disadvantageous. While further study is required to establish whether this behavior meets the strict criteria for nonhuman animal culture, we support the argument that the wider use of population and group-specific behavioral repertoires in flagship species, such as chimpanzees, offers a tool to promote the urgent conservation action needed to protect threatened ecosystems, including the Bugoma forest.

A reanalysis of strontium isotope ratios as indicators of dispersal in South African hominins

Dispersal patterns in primates have major implications for behavior and sociality but are difficult to reconstruct for fossil species. This study applies novel strontium isotope methodologies that have reliably predicted philopatry and dispersal patterns in chimpanzees and other modern primates to previously published strontium isotope ratios (87Sr/86Sr) of two South African hominins, Australopithecus africanus and Australopithecus robustus. In this study, the difference or 'offset' was calculated between the 87Sr/86Sr of each fossil tooth compared to local bioavailable 87Sr/86Sr as defined by cluster analysis of modern plant isotope ratios. Large teeth (presumably belonging to males) have low offsets from local 87Sr/86Sr proxies, while small teeth (presumably from females) have greater offsets from local 87Sr/86Sr proxies. This supports previous conclusions of male philopatry and female dispersal in both A. africanus and A. robustus. Furthermore, A. robustus shows more extreme differences between presumed males and females compared to A. africanus. This is analogous to differences seen in modern olive baboons compared to chimpanzees and suggests that A. africanus may have had a larger home range than A. robustus. Neither hominin species has 87Sr/86Sr consistent with riparian habitat preferences despite the demonstrated presence of riparian habitats in South Africa at the time.

Assessing the motivational value of infant video clips on chimpanzees through discrimination learning task

The motivational value of visual infant stimuli in humans is considered to encourage parental behavior. To explore the evolutionary roots of this preference for infants, we examined the reward value of conspecific infant videos compared to adult ones in nine chimpanzees. We employed a novel approach, a simultaneous discrimination task with differential sensory reinforcement. In Experiments 1 and 2, we tested if watching conspecific infant videos is more rewarding than watching adult ones. Participants were required to discriminate between two visual stimuli by a touch panel task. In video reward trials, a video clip featuring a chimpanzee infant followed a correct choice, while one featuring an adult followed an incorrect choice. However, the percentage of correct choices did not significantly differ from chance except in one chimpanzee, indicating that chimpanzees did not exhibit a preference for watching infant videos over those of adult. In Experiment 3, we tested if chimpanzees prefer conspecific videos over a blank screen; however, we did not find evidence either at a group level. These results suggest that the incentive salience of infant stimuli may not be universally compelling across species. Additionally, we discuss the limitations of the task using sensory reinforcement.

Replicative fitness and pathogenicity of primate lentiviruses in lymphoid tissue, primary human and chimpanzee cells: relation to possible jumps to humans

BACKGROUND

Simian immunodeficiency viruses (SIV) have been jumping between non-human primates in West/Central Africa for thousands of years and yet, the HIV-1 epidemic only originated from a primate lentivirus over 100 years ago.

METHODS

This study examined the replicative fitness, transmission, restriction, and cytopathogenicity of 22 primate lentiviruses in primary human lymphoid tissue and both primary human and chimpanzee peripheral blood mononuclear cells.

FINDINGS

Pairwise competitions revealed that SIV from chimpanzees (cpz) had the highest replicative fitness in human or chimpanzee peripheral blood mononuclear cells, even higher fitness than HIV-1 group M strains responsible for worldwide epidemic. The SIV strains belonging to the "HIV-2 lineage" (including SIVsmm, SIVmac, SIVagm) had the lowest replicative fitness. SIVcpz strains were less inhibited by human restriction factors than the "HIV-2 lineage" strains. SIVcpz efficiently replicated in human tonsillar tissue but did not deplete CD4+ T-cells, consistent with the slow or nonpathogenic disease observed in most chimpanzees. In contrast, HIV-1 isolates and SIV of the HIV-2 lineage were pathogenic to the human tonsillar tissue, almost independent of the level of virus replication.

INTERPRETATION

Of all primate lentiviruses, SIV from chimpanzees appears most capable of infecting and replicating in humans, establishing HIV-1. SIV from other Old World monkeys, e.g. the progenitor of HIV-2, replicate slowly in humans due in part to restriction factors. Nonetheless, many of these SIV strains were more pathogenic than SIVcpz. Either SIVcpz evolved into a more pathogenic virus while in humans or a rare SIVcpz, possibly extinct in chimpanzees, was pathogenic immediately following the jump into human.

FUNDING

Support for this study to E.J.A. was provided by the NIH/NIAID R01 AI49170 and CIHR project grant 385787. Infrastructure support was provided by the NIH CFAR AI36219 and Canadian CFI/Ontario ORF 36287. Efforts of J.A.B. and N.J.H. was provided by NIH AI099473 and for D.H.C., by VA and NIH AI AI080313.

Camera traps unveil demography, social structure, and home range of six unhabituated Western chimpanzee groups in the Moyen Bafing National Park, Guinea

Precise estimates of population dynamics and social grouping patterns are required for effective conservation of wild animal populations. It is difficult to obtain such information on non-human great apes as they have slow reproductive rates. To gain a better understanding of demography in these populations, previous research has typically involved habituation\, a process that requires years. Here, we collected data continuously over year-long periods to monitor an unhabituated population of critically endangered Western chimpanzees (Pan troglodytes verus) in the Moyen Bafing National Park, Guinea. We used two arrays of 100 camera traps that were placed opportunistically in two distinct 100 km2 sites, named Bakoun and Koukoutamba. We identified 227 individuals in Bakoun and 207 in Koukoutamba through their unique facial features. Our camera trap data make clear that these individuals belong to six and seven closed groups, respectively. Six of those groups were near-completely sampled with an average minimum size of 46.8 individuals (range: 37-58), and a mean adult sex ratio of 1.32 (range: 0.93-2.10). We described the demographic composition of these groups and use Bayesian social network analysis to understand population structure. The network analyses suggested that the social bonds within the two populations were structured by sex homophily, with male chimpanzees being more or equally likely to be observed together than other adult associations. Through estimation of minimum convex polygons, we described the minimum home range for those groups. Compared to other chimpanzee groups living in a similar environment (mosaic savanna-forest), the Moyen Bafing region seems to host a high-density of chimpanzees with small home ranges for their group size. Our research highlights the potential of camera traps for studying the demographic composition of chimpanzee populations with high resolution and obtaining crucial information on several groups in a time-efficient and cost-effective way.

Vulvar squamous cell carcinoma in a captive female chimpanzee: A case report

A necropsy was performed on a 43-year-old female zoo chimpanzee, with cancer in the vulvar and perivulvar region. She was diagnosed with squamous cell carcinoma, the presence of this tumor in domestic animals and non-human primates is very rare in the vulvar region and there were no previous reports found on it in chimpanzee, due to which this report contributes to the knowledge on chimpanzee pathologies.

Dental findings in wild great apes from macerated skull analysis

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.

The relative size of the calcaneal tuber reflects heel strike plantigrady in African apes and humans

OBJECTIVES

The positional repertoire of the human-chimpanzee last common ancestor is critical for reconstructing the evolution of bipedalism. African apes and humans share a heel strike plantigrade foot posture associated with terrestriality. Previous research has established that modern humans have a relatively large and intrinsically robust calcaneal tuber equipped to withstand heel strike forces associated with bipedal walking and running. However, it is unclear whether African apes have a relatively larger calcaneal tuber than non-heel-striking primates, and how this trait might have evolved among anthropoids. Here, I test the hypothesis that heel-striking primates have a relatively larger calcaneal tuber than non-heel-striking primates.

METHODS

The comparative sample includes 331 individuals and 53 taxa representing hominoids, cercopithecoids, and platyrrhines. Evolutionary modeling was used to test for the effect of foot posture on the relative size of the calcaneal tuber in a phylogenetic framework that accounts for adaptation and inertia. Bayesian evolutionary modeling was used to identify selective regime shifts in the relative size of the calcaneal tuber among anthropoids.

RESULTS

The best fitting evolutionary model was a Brownian motion model with regime-dependent trends characterized by relatively large calcaneal tubers among African apes and humans. Evolutionary modeling provided support for an evolutionary shift toward a larger calcaneal tuber at the base of the African ape and human clade.

CONCLUSIONS

The results of this study support the view that African apes and humans share derived traits related to heel strike plantigrady, which implies that humans evolved from a semi-terrestrial quadrupedal ancestor.

Caveats of chimpanzee ChAdOx1 adenovirus-vectored vaccines to boost anti-SARS-CoV-2 protective immunity in mice

Several COVID-19 vaccines use adenovirus vectors to deliver the SARS-CoV-2 spike (S) protein. Immunization with these vaccines promotes immunity against the S protein, but against also the adenovirus itself. This could interfere with the entry of the vaccine into the cell, reducing its efficacy. Herein, we evaluate the efficiency of an adenovirus-vectored vaccine (chimpanzee ChAdOx1 adenovirus, AZD1222) in boosting the specific immunity compared to that induced by a recombinant receptor-binding domain (RBD)-based vaccine without viral vector. Mice immunized with the AZD1222 human vaccine were given a booster 6 months later, with either the homologous vaccine or a recombinant vaccine based on RBD of the delta variant, which was prevalent at the start of this study. A significant increase in anti-RBD antibody levels was observed in rRBD-boosted mice (31-61%) compared to those receiving two doses of AZD1222 (0%). Significantly higher rates of PepMix™- or RBD-elicited proliferation were also observed in IFNγ-producing CD4 and CD8 cells from mice boosted with one or two doses of RBD, respectively. The lower efficiency of the ChAdOx1-S vaccine in boosting specific immunity could be the result of a pre-existing anti-vector immunity, induced by increased levels of anti-adenovirus antibodies found both in mice and humans. Taken together, these results point to the importance of avoiding the recurrent use of the same adenovirus vector in individuals with immunity and memory against them. It also illustrates the disadvantages of ChAdOx1 adenovirus-vectored vaccine with respect to recombinant protein vaccines, which can be used without restriction in vaccine-booster programs. KEY POINTS: • ChAdOx1 adenovirus vaccine (AZD1222) may not be effective in boosting anti-SARS-CoV-2 immunity • A recombinant RBD protein vaccine is effective in boosting anti-SARS-CoV-2 immunity in mice • Antibodies elicited by the rRBD-delta vaccine persisted for up to 3 months in mice.

Apes able to recognise faces after quarter of a century

Recent research has provided evidence for the longest-lasting non-human social memory ever documented - in bonobos and chimpanzees. Arabella Gray finds out more about the study.

Functional host-specific adaptation of the intestinal microbiome in hominids

Fine-scale knowledge of the changes in composition and function of the human gut microbiome compared that of our closest relatives is critical for understanding the evolutionary processes underlying its developmental trajectory. To infer taxonomic and functional changes in the gut microbiome across hominids at different timescales, we perform high-resolution metagenomic-based analyzes of the fecal microbiome from over two hundred samples including diverse human populations, as well as wild-living chimpanzees, bonobos, and gorillas. We find human-associated taxa depleted within non-human apes and patterns of host-specific gut microbiota, suggesting the widespread acquisition of novel microbial clades along the evolutionary divergence of hosts. In contrast, we reveal multiple lines of evidence for a pervasive loss of diversity in human populations in correlation with a high Human Development Index, including evolutionarily conserved clades. Similarly, patterns of co-phylogeny between microbes and hosts are found to be disrupted in humans. Together with identifying individual microbial taxa and functional adaptations that correlate to host phylogeny, these findings offer insights into specific candidates playing a role in the diverging trajectories of the gut microbiome of hominids. We find that repeated horizontal gene transfer and gene loss, as well as the adaptation to transient microaerobic conditions appear to have played a role in the evolution of the human gut microbiome.

Evaluating modularity in the hominine skull related to feeding biomechanics

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.

Biomechanical and taxonomic diversity in the Early Pleistocene in East Africa: Structural analysis of a recently discovered femur shaft from Olduvai Gorge (bed I)

Recent Plio-Pleistocene hominin findings have revealed the complexity of human evolutionary history and the difficulties involved in its interpretation. Moreover, the study of hominin long bone remains is particularly problematic, since it commonly depends on the analysis of fragmentary skeletal elements that in many cases are merely represented by small diaphyseal portions and appear in an isolated fashion in the fossil record. Nevertheless, the study of the postcranial skeleton is particularly important to ascertain locomotor patterns. Here we report on the discovery of a robust hominin femoral fragment (OH 84) at the site of Amin Mturi Korongo dated to 1.84 Ma (Olduvai Bed I). External anatomy and internal bone structure of OH 84 were analyzed and compared with previously published data for modern humans and chimpanzees, as well as for Australopithecus, Paranthropus and Homo specimens ranging from the Late Pliocene to Late Pleistocene. Biomechanical analyses based on transverse cross-sections and the comparison of OH 84 with another robust Olduvai specimen (OH 80) suggest that OH 84 might be tentatively allocated to Paranthropus boisei. More importantly, the identification of a unique combination of traits in OH 84 could indicate both terrestrial bipedalism and an arboreal component in the locomotor repertoire of this individual. If interpreted correctly, OH 84 could thus add to the already mounting evidence of substantial locomotor diversity among Early Pleistocene hominins. Likewise, our results also highlight the difficulties in accurately interpreting the link between form and function in the human fossil record based on fragmentary remains, and ultimately in distinguishing between coeval hominin groups due to the heterogeneous pattern of inter- and intraspecific morphological variability detected among fossil femora.

MULTISPECIES SHIGELLA FLEXNERI OUTBREAK IN A ZOOLOGICAL COLLECTION COINCIDING WITH A CLUSTER IN THE LOCAL HUMAN POPULATION

Shigella flexneri is a nonmotile gram-negative bacillus that affects humans and nonhuman primates. In August 2021, 15 primates at the ABQ BioPark demonstrated clinical signs of Shigella infection: 3 out of 4 Sumatran and hybrid orangutans (Pongo abelii), 6 out of 8 gorillas (Gorilla gorilla), 2 out of 9 chimpanzees (Pan troglodytes), and 4 out of 4 siamangs (Hylobates syndactylus). Three siamangs and one gorilla succumbed to complications of shigellosis during the initial outbreak and a chimpanzee died 10 mon later. Although it is well documented that Shigella may cause morbidity and mortality in nonhuman primates, the rapid and devastating nature of the outbreak, the difference from previous reports in zoological collections (enzootic vs outbreak), and the chronological overlap with the increase in human cases in the region makes discussion of this Shigella outbreak of significance. The cases presented here are significantly different than previous reports, because these were part of an outbreak that arose and subsided, versus other reports where the authors describe an enzootic disease with persistently infected animals. Close communication with the New Mexico Department of Health allowed for the investigation into possible sources of the outbreak, recommendations regarding biosecurity protocols, and staff education.

Recombinant chimpanzee adenovirus expressing spike protein protects chickens against infectious bronchitis virus

Infectious bronchitis (IB) is an acute and highly contagious disease caused by avian infectious bronchitis virus (IBV), resulting in significant economic losses in the global poultry industry. In this study, we utilized a replication-incompetent adenovirus vector derived from chimpanzees for the first time to express the S gene of IBV. The adenovirus was successfully rescued and demonstrated convenient production, good growth performance, and stability on HEK293 A cells. Morphologically, the recombinant adenovirus (named PAD-S) appeared normal under transmission electron microscopy, and efficient expression of the exogenous gene was confirmed through immunofluorescence analysis and immunoblotting. Administration of PAD-S via ocular and nasal routes induced a strong immune response in the chicken population, as evidenced by specific antibody and cytokine measurements. PAD-S was unable to replicate within chickens and showed low pre-existing immunity, demonstrating high safety and environmental friendliness. The robust immune response triggered by PAD-S immunization effectively suppressed viral replication in various tissues, alleviating clinical symptoms and tissue damage, thus providing complete protection against viral challenges in the chicken population. In conclusion, this study successfully developed an IBV candidate vaccine strain that possesses biosafety, high protective efficacy, and ease of production.

A case of suspected chimpanzee scavenging in the Issa Valley, Tanzania

Like humans, chimpanzees (Pan troglodytes) are well known for their vertebrate and invertebrate hunting, but they rarely scavenge. In contrast, while hunting and meat consumption became increasingly important during the evolution of the genus Homo, scavenging meat and marrow from carcasses of large mammals was also likely to be an important component of their subsistence strategies. Here, we describe a confrontational scavenging interaction between an adult male chimpanzee from the Issa Valley and a crowned eagle (Stephanoaetus coronatus), which resulted in the chimpanzee capturing and consuming the carcass of a juvenile bushbuck (Tragelaphus scriptus). We describe the interaction and contextualize this with previous scavenging observations from chimpanzees.

Bonobos and chimpanzees remember familiar conspecifics for decades

Recognition and memory of familiar conspecifics provides the foundation for complex sociality and is vital to navigating an unpredictable social world [Tibbetts and Dale, Trends Ecol. Evol. 22, 529-537 (2007)]. Human social memory incorporates content about interactions and relationships and can last for decades [Sherry and Schacter, Psychol. Rev. 94, 439-454 (1987)]. Long-term social memory likely played a key role throughout human evolution, as our ancestors increasingly built relationships that operated across distant space and time [Malone et al., Int. J. Primatol. 33, 1251-1277 (2012)]. Although individual recognition is widespread among animals and sometimes lasts for years, little is known about social memory in nonhuman apes and the shared evolutionary foundations of human social memory. In a preferential-looking eye-tracking task, we presented chimpanzees and bonobos (N = 26) with side-by-side images of a previous groupmate and a conspecific stranger of the same sex. Apes' attention was biased toward former groupmates, indicating long-term memory for past social partners. The strength of biases toward former groupmates was not impacted by the duration apart, and our results suggest that recognition may persist for at least 26 y beyond separation. We also found significant but weak evidence that, like humans, apes may remember the quality or content of these past relationships: apes' looking biases were stronger for individuals with whom they had more positive histories of social interaction. Long-lasting social memory likely provided key foundations for the evolution of human culture and sociality as they extended across time, space, and group boundaries.

Naïve, adult, captive chimpanzees do not socially learn how to make and use sharp stone tools

Although once regarded as a unique human feature, tool-use is widespread in the animal kingdom. Some of the most proficient tool-users are our closest living relatives, chimpanzees. These repertoires however consist primarily of tool use, rather than tool manufacture (for later use). Furthermore, most populations of chimpanzees use organic materials, such as sticks and leaves, rather than stones as tools. This distinction may be partly ecological, but it is also important as chimpanzees are often used as models for the evolution of human material culture, the oldest traces of which consist of manufactured sharp stone tools (so-called "flakes"). Thus, examining the conditions (if any) under which chimpanzees may develop flake manufacture and use can provide insight into the drivers of these behaviours in our own lineage. Previous studies on non-human apes' ability to make and use flakes focused on enculturated apes, giving them full demonstrations of the behaviour immediately, without providing social information on the task in a stepwise manner. Here we tested naïve, captive chimpanzees (N = 4; three potentially enculturated and one unenculturated subject) in a social learning experimental paradigm to investigate whether enculturated and/or unenculturated chimpanzees would develop flake making and use after social information of various degrees (including a human demonstration) was provided in a scaffolded manner. Even though social learning opportunities were provided, neither the unenculturated subject nor any of the potentially enculturated subjects made or used flakes, in stark contrast to previous studies with enculturated apes. These data suggest that flake manufacture and use is outside of our tested group of captive chimpanzees' individual and social learning repertoires. It also suggests that high levels of enculturation alongside human demonstrations (and/or training) may be required before captive chimpanzees can develop this behaviour.

OpenApePose, a database of annotated ape photographs for pose estimation

Because of their close relationship with humans, non-human apes (chimpanzees, bonobos, gorillas, orangutans, and gibbons, including siamangs) are of great scientific interest. The goal of understanding their complex behavior would be greatly advanced by the ability to perform video-based pose tracking. Tracking, however, requires high-quality annotated datasets of ape photographs. Here we present OpenApePose, a new public dataset of 71,868 photographs, annotated with 16 body landmarks of six ape species in naturalistic contexts. We show that a standard deep net (HRNet-W48) trained on ape photos can reliably track out-of-sample ape photos better than networks trained on monkeys (specifically, the OpenMonkeyPose dataset) and on humans (COCO) can. This trained network can track apes almost as well as the other networks can track their respective taxa, and models trained without one of the six ape species can track the held-out species better than the monkey and human models can. Ultimately, the results of our analyses highlight the importance of large, specialized databases for animal tracking systems and confirm the utility of our new ape database.

State-transition-free reinforcement learning in chimpanzees (Pan troglodytes)

The outcome of an action often occurs after a delay. One solution for learning appropriate actions from delayed outcomes is to rely on a chain of state transitions. Another solution, which does not rest on state transitions, is to use an eligibility trace (ET) that directly bridges a current outcome and multiple past actions via transient memories. Previous studies revealed that humans (Homo sapiens) learned appropriate actions in a behavioral task in which solutions based on the ET were effective but transition-based solutions were ineffective. This suggests that ET may be used in human learning systems. However, no studies have examined nonhuman animals with an equivalent behavioral task. We designed a task for nonhuman animals following a previous human study. In each trial, participants chose one of two stimuli that were randomly selected from three stimulus types: a stimulus associated with a food reward delivered immediately, a stimulus associated with a reward delivered after a few trials, and a stimulus associated with no reward. The presented stimuli did not vary according to the participants' choices. To maximize the total reward, participants had to learn the value of the stimulus associated with a delayed reward. Five chimpanzees (Pan troglodytes) performed the task using a touchscreen. Two chimpanzees were able to learn successfully, indicating that learning mechanisms that do not depend on state transitions were involved in the learning processes. The current study extends previous ET research by proposing a behavioral task and providing empirical data from chimpanzees.