Publications

Submitted
Alexander Mielke and Liran Samuni. Submitted. “Accuracy and precision of social relationship indices”.
2022
Liran Samuni, Kevin Langergraber, and Martin Surbeck. 2022. “Characterization of Pan social systems reveals in-group/out-group distinction and out-group tolerance in bonobos.” PNAS.Abstract
Human between-group interactions are highly variable, ranging from violent to tolerant and affiliative. Tolerance between groups is linked to our unique capacity for large-scale cooperation and cumulative culture, but its evolutionary origins are understudied. In chimpanzees, one of our closest living relatives, predominantly hostile between-group interactions impede cooperation and information flow across groups. In contrast, in our other closest living relative, the bonobo, tolerant between-group associations are observed. However, as these associations can be frequent and prolonged and involve social interactions that mirror those within groups, it is unclear whether these bonobos really do belong to separate groups. Alternatively, the bonobo grouping patterns may be homologous to observations from the large Ngogo chimpanzee community, where individuals form within-group neighborhoods despite sharing the same membership in the larger group. To characterize bonobo grouping patterns, we compare the social structure of the Kokolopori bonobos with the chimpanzee group of Ngogo. Using cluster analysis, we find temporally stable clusters only in bonobos. Despite the large spatial overlap and frequent interactions between the bonobo clusters, we identified significant association preference within but not between clusters and a unique space use of each cluster. Although bonobo associations are flexible (i.e., fission–fusion dynamics), cluster membership predicted the bonobo fission compositions and the spatial cohesion of individuals during encounters. These findings suggest the presence of a social system that combines clear in-group/out-group distinction and out-group tolerance in bonobos, offering a unique referential model for the evolution of tolerant between-group interactions in humans.
Gal Badihi, Kelsey Bodden, Klaus Zuberbühler, Liran Samuni, and Catherine Hobaiter. 2022. “Flexibility in the social structure of male chimpanzees (Pan troglodytes schweinfurthii) in the Budongo Forest, Uganda.” Royal Society Open Science. Publisher's VersionAbstract
Individuals of social species experience competitive costs and social benefits of group living. Substantial flexibility in humans' social structure and the combination of different types of social structure with fission–fusion dynamics allow us to live in extremely large groups—overcoming some of the costs of group living while capitalizing on the benefits. Non-human species also show a range of social strategies to deal with this trade-off. Chimpanzees are an archetypical fission–fusion species, using dynamic changes in day-to-day association to moderate the costs of within-group competition. Using 4 years of association data from two neighbouring communities of East African chimpanzees (Pan troglodytes schweinfurthii), we describe an unexplored level of flexibility in chimpanzee social structure. We show that males from the larger Waibira community (N = 24–31) exhibited additional structural levels of semi-stable core–periphery society, while males from the smaller Sonso community (N = 10–13) did not. This novel core–periphery pattern adds to previous results describing alternative modular social structure in other large communities of chimpanzees. Our data support the hypothesis that chimpanzees can incorporate a range of strategies in addition to fission–fusion to overcome costs of social living, and that their social structures may be closer to that of modern humans than previously described.
Leveda Cheng, Liran Samuni, Stefano Lucchesi, Tobias Deschner, and Martin Surbeck. 2022. “Love thy neighbour: behavioural and endocrine correlates of male strategies during intergroup encounters in bonobos.” Animal Behaviour. Publisher's VersionAbstract
Across group-living taxa, males act aggressively towards outgroup males because they represent a threat to reproduction with ingroup females. This intergroup aggression can entail agonistic coalition formation between group members, is typically associated with higher testosterone levels and prevents extended associations between members of different groups. However, in a few species, including humans, groups can interact peacefully, allowing the exchange of resources and information. To better understand how social relationships are manifested between groups and the involvement of males in these relationships, we investigated behavioural and endocrine correlates of male strategies during intergroup encounters in bonobos, Pan paniscus. We found that, despite overt intergroup aggression, males rarely engaged in coalitionary attacks against outgroup individuals and their testosterone levels did not rise during intergroup encounters. Also, males sacrificed the time available to affiliate with ingroup individuals and actively affiliated with outgroup individuals, especially outgroup males. The paucity of cooperative group defence and high levels of intergroup affiliation suggest that male bonobos play a role in maintaining tolerant intergroup relationships. We discuss how our findings relate to the establishment of male–male social relationships beyond the group level in other species.
Aisha Bründl, Cédric Girard-Buttoz, Tatiana Bortolato, Liran Samuni, Mathilde Grampp, Therese Löhrich, Patrick Tkaczynski, Roman Wittig, and Catherine Crockford. 2022. “Maternal effects on the development of vocal communication in wild chimpanzees.” iScience.Abstract
Early-life experiences, such as maternal care received, influence adult social integration and survival. We examine what changes to social behavior through ontogeny lead to these lifelong effects, particularly whether early-life maternal environment impacts the development of social communication. Chimpanzees experience prolonged social communication development. Focusing on a central communicative trait, the “pant-hoot” contact call used to solicit social engagement, we collected cross-sectional data on wild chimpanzees (52 immatures and 36 mothers). We assessed early-life socioecological impacts on pant-hoot rates across development, specifically: mothers’ gregariousness, age, pant-hoot rates and dominance rank, maternal loss, and food availability, controlling for current maternal effects. We found that early-life maternal gregariousness correlated positively with offspring pant-hoot rates, while maternal loss led to reduced pant-hoot rates across development. Males had steeper developmental trajectories in pant-hoot rates than females. We demonstrate the impact of maternal effects on developmental trajectories of a rarely investigated social trait, vocal production.
Sven Grawunder, Natalie Uomini, Liran Samuni, Roman Wittig, and Catherine Crockford. 2022. “Chimpanzee modification of vowel-like sounds and voice quality suggest expansion through the hominoid lineage.” Philosophical Transactions of the Royal Society.Abstract
The origins of human speech are obscure; it is still unclear what aspects are unique to our species or shared with our evolutionary cousins, in part due to a lack of a common framework for comparison. We asked what chimpanzee and human vocal production acoustics have in common. We examined visible supra-laryngeal articulators of four major chimpanzee vocalizations (hoos, grunts, barks, screams) and their associated acoustic structures, using techniques from human phonetic and animal communication analysis. Data were collected from wild adult chimpanzees, Taï National Park, Ivory Coast. Both discriminant and principal component classification procedures revealed classification of call types. Discriminating acoustic features include voice quality and formant structure, mirroring phonetic features in human speech. Chimpanzee lip and jaw articulation variables also offered similar discrimination of call types. Formant maps distinguished call types with different vowel-like sounds. Comparing our results with published primate data, humans show less F1–F2 correlation and further expansion of the vowel space, particularly for [i] sounds. Unlike recent studies suggesting monkeys achieve human vowel space, we conclude from our results that supra-laryngeal articulatory capacities show moderate evolutionary change, with vowel space expansion continuing through hominoid evolution. Studies on more primate species will be required to substantiate this.
Sylvain Lemoine, Liran Samuni, Catherine Crockford, and Roman Wittig. 2022. “Parochial cooperation in wild chimpanzees: a model to explain the evolution of parochial altruism.” Philosophical Transactions of the Royal Society. Publisher's VersionAbstract
Parochial altruism, taking individual costs to benefit the in-group and harm the out-group, has been proposed as one of the mechanisms underlying the human ability of large-scale cooperation. How parochial altruism has evolved remains unclear. In this review paper, we formulate a parochial cooperation model in small-scale groups and examine the model in wild chimpanzees. As suggested for human parochial altruism, we review evidence that the oxytocinergic system and in-group cooperation and cohesion during out-group threat are integral parts of chimpanzee collective action during intergroup competition. We expand this model by suggesting that chimpanzee parochial cooperation is supported by the social structure of chimpanzee groups which enables repeated interaction history and established social ties between co-operators. We discuss in detail the role of the oxytocinergic system in supporting parochial cooperation, a pathway that appears integral already in chimpanzees. The reviewed evidence suggests that prerequisites of human parochial altruism were probably present in the last common ancestor between Pan and Homo.
Liran Samuni, David Lemieux, Alicia Lamb, Daiane Galdino, and Martin Surbeck. 2022. “Tool use behavior in three wild bonobo communities at Kokolopori.” American Journal of Primatology, e23342. Publisher's VersionAbstract
Comparative studies on tool technologies in extant primates, especially in our closest living relatives, offer a window into the evolutionary foundations of tool use in hominins. Whereas chimpanzee tool technology is well studied across populations, the scarcity of described tool technology in wild populations of our other closest living relative, the bonobo, is a mystery. Here we provide a first report of the tool use repertoire of the Kokolopori bonobos and describe in detail the use of leaf-umbrellas during rainfall, with the aim to improve our knowledge of bonobo tool use capacity in the wild. The tool use repertoire of the Kokolopori bonobos was most similar to that of the nearby population of Wamba and comprised eight behaviors, none in a foraging context. Further, over a 6-month period we documented 44 instances of leaf-umbrella use by 22 individuals from three communities, suggesting that this behavior is habitual. Most leaf-umbrella tool users were adult females, and we observed a nonadult using a leaf-umbrella on only a single occasion. While the study and theory of tool technologies is often based on the use of tools in foraging tasks, tool use in bonobos typically occurs in nonforaging contexts across populations. Therefore, incorporating both foraging and nonforaging contexts into our theoretical framework is essential if we wish to advance our understanding of the evolutionary trajectories of tool technology in humans.
2021
Maureen McCarthy, Colleen Stephens, Paula Dieguez, Liran Samuni, Marie‐Lyne Després‐Einspenner, Briana Harder, Anja Landsman, Laura Lynn, Nuria Maldonado, Zuzana Ročkaiová, Jane Widness, Roman M. Wittig, Christophe Boesch, Hjalmar Kühl, and Mimi Arandjelovic. 2021. “Chimpanzee identification and social network construction through an online citizen science platform.” Ecology and Evolution, 4, Pp. 1598-1608. Publisher's VersionAbstract
Citizen science has grown rapidly in popularity in recent years due to its potential to educate and engage the public while providing a means to address a myriad of scientific questions. However, the rise in popularity of citizen science has also been accompanied by concerns about the quality of data emerging from citizen science research projects. We assessed data quality in the online citizen scientist platform Chimp&See, which hosts camera trap videos of chimpanzees (Pan troglodytes) and other species across Equatorial Africa. In particular, we compared detection and identification of individual chimpanzees by citizen scientists with that of experts with years of experience studying those chimpanzees. We found that citizen scientists typically detected the same number of individual chimpanzees as experts, but assigned far fewer identifications (IDs) to those individuals. Those IDs assigned, however, were nearly always in agreement with the IDs provided by experts. We applied the data sets of citizen scientists and experts by constructing social networks from each. We found that both social networks were relatively robust and shared a similar structure, as well as having positively correlated individual network positions. Our findings demonstrate that, although citizen scientists produced a smaller data set based on fewer confirmed IDs, the data strongly reflect expert classifications and can be used for meaningful assessments of group structure and dynamics. This approach expands opportunities for social research and conservation monitoring in great apes and many other individually identifiable species.
Alexander Mielke, Anna Preis, Liran Samuni, Jan Gogarten, Jack Lester, Catherine Crockford, and Roman Wittig. 2021. “Consistency of social interactions in sooty mangabeys and chimpanzees.” Frontiers in Ecology and Evolution. Publisher's VersionAbstract
Predictability of social interactions can be an important measure for the social complexity of an animal group. Predictability is partially dependent on how consistent interaction patterns are over time: does the behavior on 1 day explain the behavior on another? We developed a consistency measure that serves two functions: detecting which interaction types in a dataset are so inconsistent that including them in further analyses risks introducing unexplained error; and comparatively quantifying differences in consistency within and between animal groups. We applied the consistency measure to simulated data and field data for one group of sooty mangabeys (Cercocebus atys atys) and to groups of Western chimpanzees (Pan troglodytes verus) in the Taï National Park, Côte d'Ivoire, to test its properties and compare consistency across groups. The consistency measures successfully identified interaction types whose low internal consistency would likely create analytical problems. Species-level differences in consistency were less pronounced than differences within groups: in all groups, aggression and dominance interactions were the most consistent, followed by grooming; spatial proximity at different levels was much less consistent than directed interactions. Our consistency measure can facilitate decision making of researchers wondering whether to include interaction types in their analyses or social networks and allows us to compare interaction types within and between species regarding their predictability.
Cédric Girard-Buttoz, Patrick Tkaczynski, Liran Samuni, Pawel Fedurek, Cristina Gomes, Therese Loehrich, Virgile Manin, Anna Preis, Prince Valé, Tobias Deschner, Roman M. Wittig, and Catherine Crockford. 2021. “Early maternal loss affects diurnal cortisol slopes in immature but not mature wild chimpanzees.” eLife. Publisher's VersionAbstract
The biological embedding model (BEM) suggests that fitness costs of maternal loss arise when early-life experience embeds long-term alterations to hypothalamic-pituitary-adrenal (HPA) axis activity. Alternatively, the adaptive calibration model (ACM) regards physiological changes during ontogeny as short-term adaptations. Both models have been tested in humans but rarely in wild, long-lived animals. We assessed whether, as in humans, maternal loss had short- and long-term impacts on orphan wild chimpanzee urinary cortisol levels and diurnal urinary cortisol slopes, both indicative of HPA axis functioning. Immature chimpanzees recently orphaned and/or orphaned early in life had diurnal cortisol slopes reflecting heightened activation of the HPA axis. However, these effects appeared short-term, with no consistent differences between orphan and non-orphan cortisol profiles in mature males, suggesting stronger support for the ACM than the BEM in wild chimpanzees. Compensatory mechanisms, such as adoption, may buffer against certain physiological effects of maternal loss in this species.
Liran Samuni, Catherine Crockford, and Roman Wittig. 2021. “Group-level cooperation in chimpanzees is shaped by strong social ties.” Nature Communications, 12, 1, Pp. 1-10. Publisher's Version
Leveda Cheng, Stefano Lucchesi, Roger Mundry, Liran Samuni, Tobias Deschner, and Martin Surbeck. 2021. “Variation in aggression rates and urinary cortisol levels indicates intergroup competition in wild bonobos.” Hormones & Behavior, 128, 104914. Publisher's VersionAbstract
Intergroup competition is a widespread phenomenon across taxa and groups typically compete over access to limited resources, such as food and mates. Such competition may be quantified by changes in individuals' behavioral and physiological status in response to intergroup encounters (IGEs). Bonobos, one of our closest living relatives, are often regarded as xenophilic and exhibit high tolerance towards out-group individuals. This tolerance between groups may still be accompanied by intergroup competition over resources. We hereby compared variation in aggression rates and urinary cortisol levels of bonobos during and outside contexts of IGEs in the Kokolopori Bonobo Reserve and investigated whether food and mate availability influenced males' and females' aggression and cortisol levels, when controlling for dominance rank and the number of individuals present. We found that although females had higher aggression rates and urinary cortisol levels during than outside contexts of IGEs, these increases were not related to food availability or changes in between-group dynamics when maximally tumescent females were present, rather than absent. Furthermore, males showed higher aggression rates and urinary cortisol levels during than outside contexts of IGEs. However, males' responses during IGEs were not related to the presence of maximally tumescent females and food availability. Taken together, while competition intensified during seemingly tolerant IGEs in bonobos, such competition was unrelated to short-term changes in food and mate availability. Despite physical and physiological costs of aggression, bonobos associate with out-group individuals frequently and for extended periods. This suggests potential benefits of bonobo intergroup associations.
2020
Sylvain Lemoine, Anna Preis, Liran Samuni, Christophe Boesch, Catherine Crockford, and Roman Wittig. 2020. “Between-Group Competition Impacts Reproductive Success in Wild Chimpanzees.” Current Biology, 30, 2, Pp. 312-318. Publisher's VersionAbstract
Between-group competition in social animals appears to be a prominent selective pressure shaping the evolution of territoriality and cooperation [1234]. Evidence for an effect of between-group competition on fitness in territorial species, however, is mostly lacking because of difficulty in measuring between-group competition and its long-term impact [5]. Between-group competition corresponds to a complex set of interactions between neighboring groups, and its intensity seems to depend on the competitive abilities of each interacting group [67]. We tested whether the competitive ability of groups and the pressure exerted by neighboring groups affected the reproductive success of wild female chimpanzees (Pan troglodytes verus). Using long-term data on four neighboring groups in the Taï National Park, Côte d’Ivoire, collected over the course of 54 observation years, we measured the competitive ability of habituated groups using the number of mature males and the pressure exerted by non-habituated neighbors with an index of neighbor pressure that combined the frequency of neighboring encounters and related spatial information. Importantly, we found that experiencing low neighbor pressure provides fitness benefits through increased offspring survival and shorter inter-birth intervals. Also, many males in a group are associated with shorter inter-birth intervals. We conclude that high between-group competition hampers fast reproduction and offspring survival when exposure is during the prenatal period. Our findings suggest that having many males in a group results in fitness benefits and that between-group competition should be considered as a potential selective pressure that shaped key social adaptations in the hominoid lineage.
Sylvain Lemoine, Christophe Boesch, Anna Preis, Liran Samuni, Catherine Crockford, and Liran Samuni. 2020. “Group dominance increases territory size and reduces neighbor pressure in wild chimpanzees.” Royal Society Open Science, 7200577 . Publisher's VersionAbstract
Territorial social species, including humans, compete between groups over key resources. This between-group competition has evolutionary implications on adaptations like in-group cooperation even with non-kin. An emergent property of between-group competition is group dominance. Mechanisms of group dominance in wild animal populations are difficult to study, as they require long-term data on several groups within a population. Here, using long-term data on four neighbouring groups of wild western chimpanzees, we test the hypothesis that group dominance impacts the costs and benefits of between-group competition, measured by territory size and the pressure exerted by neighbouring groups. Larger groups had larger territories and suffered less neighbour pressure compared with smaller groups. Within-group increase in the number of males led to territory increase, suggesting the role of males in territory acquisition. However, variation in territory sizes and neighbour pressure was better explained by group size. This suggests that the bisexually-bonded social system of western chimpanzees, where females participate in territorial behaviour, confers a competitive advantage to larger groups and that group dominance acts through group size in this population. Considering variation in social systems offers new insights on how group dominance acts in territorial species and its evolutionary implications on within-group cooperation.
Cornelius Eichner, Michael Paquette, Toralf Mildner, Torsten Schlumm, Kamilla Pléh, Liran Samuni, Catherine Crockford, Roman Wittig, Carsten Jäger, Harald Möller, Angela Friederici, and Alfred Anwander. 2020. “Increased sensitivity and signal-to-noise ratio in diffusion-weighted MRI using multi-echo acquisitions.” Neuroimage, 117172. Publisher's VersionAbstract
Post-mortem diffusion MRI (dMRI) enables acquisitions of structural imaging data with otherwise unreachable resolutions - at the expense of longer scanning times. These data are typically acquired using highly segmented image acquisition strategies, thereby resulting in an incomplete signal decay before the MRI encoding continues. Especially in dMRI, with low signal intensities and lengthy contrast encoding, such temporal inefficiency translates into reduced image quality and longer scanning times. This study introduces Multi Echo (ME) acquisitions to dMRI on a human MRI system - a time-efficient approach, which increases SNR (Signal-to-Noise Ratio) and reduces noise bias for dMRI images. The benefit of the introduced ME-dMRI method was validated using numerical Monte Carlo simulations and showcased on a post-mortem brain of a wild chimpanzee. The proposed Maximum Likelihood Estimation echo combination results in an optimal SNR without detectable signal bias. The combined strategy comes at a small price in scanning time (here 30% additional) and leads to a substantial SNR increase (here white matter: ~ 1.6x, equivalent to 2.6 averages, grey matter: ~ 1.9x, equivalent to 3.6 averages) and a general reduction of the noise bias.
Cédric Girard-Buttoz, Martin Surbeck, Liran Samuni, Patrick Tkaczynski, Christophe Boesch, Barbara Fruth, Roman M. Wittig, Gottfried Hohmann, and Catherine Crockford. 2020. “Information transfer efficiency differs in wild chimpanzees and bonobos, but not social cognition.” Proceedings of the Royal Society of London B: Biological Sciences, 287: 20200523. Publisher's VersionAbstract
Several theories have been generated to understand the socio-cognitive mechanisms underlying the unique cooperative abilities of humans. The ‘interdependence hypothesis' posits first, that the cognitive dimension of human cooperation evolved in contexts when several individuals needed to act together to achieve a common goal, like when hunting large prey. Second, the more interdependent individuals are, the more likely they are to provide services to conspecifics in other contexts. Alternatively, the ‘social tolerance hypothesis' proposes that higher social tolerance allows conspecifics to cooperate more efficiently and with a wider range of partners. We conducted the first field experimental evaluation of both hypotheses in our closest living relatives by contrasting chimpanzees to the less interdependent but more tolerant bonobos. We compared each species' performance during a cooperative task: informing conspecifics about a danger. We presented Gaboon viper models to 82 individuals from five wild communities. Chimpanzees arriving late at the snake were significantly more likely to have heard a call and less likely to startle, indicating that chimpanzees were better informed about the presence of the threat than bonobos. This stems from clear species differences in how individuals adjusted their calling decisions to the level of information already available. Chimpanzees were more likely to call and produced more alarm calls when they had not yet heard a call, whereas bonobos did so when they already heard a call. Our results confirm the link between interdependence and cooperation performance. These species differences were most likely driven by differences in motivation rather than in cognitive capacities because both species tended to consider audience knowledge in their decision to call. Our results inform theories on the evolution of human cooperation by linking inter-group competition pressure and in-group cooperative motivation and/or capability.
Patrick Tkaczynski, Alexander Mielke, Liran Samuni, Anna Preis, Roman M. Wittig, and Catherine Crockford. 2020. “Long-term repeatability in social behaviour suggests stable social phenotypes in wild chimpanzees.” Royal Society Open Science, 7: 200454. Publisher's VersionAbstract
Consistent individual differences in social phenotypes have been observed in many animal species. Changes in demographics, dominance hierarchies or ecological factors, such as food availability or disease prevalence, are expected to influence decision-making processes regarding social interactions. Therefore, it should be expected that individuals show flexibility rather than stability in social behaviour over time to maximize the fitness benefits of social living. Understanding the processes that create and maintain social phenotypes requires data encompassing a range of socioecological settings and variation in intrinsic state or life-history stage or strategy. Using observational data spanning up to 19 years for some individuals, we demonstrate that multiple types of social behaviour are repeatable over the long term in wild chimpanzees, a long-lived species with complex fission–fusion societies. We controlled for temporal, ecological and demographic changes, limiting pseudo-repeatability. We conclude that chimpanzees living in natural ecological settings have relatively stable long-term social phenotypes over years that may be independent of life-history or reproductive strategies. Our results add to the growing body of the literature suggesting consistent individual differences in social tendencies are more likely the rule rather than the exception in group-living animals.
Liran Samuni, Patrick Tkaczynski, Therese Löhrrich, Tobias Deschner, Roman M. Wittig, and Catherine Crockford. 2020. “Maternal effects on offspring growth indicate post-weaning juvenile dependence in chimpanzees (Pan troglodytes verus).” Frontiers in Zoology. Publisher's VersionAbstract

Background

In animals with altricial offspring, most growth occurs after birth and may be optimized by post-natal maternal care. Maternal effects on growth may be influenced by individual characteristics of the mothers, such as social status, individual investment strategies and the length of association with offspring. The prolonged juvenile dependence seen in humans is a distinctive life history adaptation, which may have evolved to facilitate sustained somatic and brain growth.

In chimpanzees, offspring are typically weaned at approximately 4 years old, yet immature individuals continue to associate with their mothers for up to 10 years beyond weaning. Whether this lengthy association or the individual characteristics of mothers influences growth patterns in this species is not clear.

The relationship between urinary creatinine and specific gravity is an established non-invasive measure of muscle mass in humans and chimpanzees. We analysed the urinary creatinine and specific gravity of 1318 urine samples from 70 wild chimpanzees from the Taï Forest, Ivory Coast aged 4 to 15 years.

Results

We showed a clear increase in urinary creatinine levels with age in both males and females, replicating established growth curves in this species and reaffirming this measure as a reliable proxy for lean body mass. Comparing those who experience maternal loss (orphans) with non-orphan chimpanzees, maternal presence beyond weaning age and into late juvenility positively influenced offspring muscle mass throughout ontogeny such that orphans had significantly less muscle mass than age-matched non-orphans. In age-matched offspring with mothers, those with high-ranking mothers had greater muscle mass. Accounting for variation in muscle mass attributable to maternal presence, we found no effect of maternal investment (length of inter birth interval, from own birth to birth of following sibling) on offspring muscle mass.

Conclusion

Chimpanzee mothers have an extended and multi-faceted influence on offspring phenotypes. Our results suggest that maternal investment extends beyond lactation and into early adulthood and has clear benefits to offspring physical development. Therefore, prolonged juvenile dependence, although unique in its form in human societies, may be a trait with deeper evolutionary origins.

Livia V Patrono, Kamilla Pléh, Liran Samuni, Markus Ulrich, Caroline Röthemeier, Andreas Sachse, Silvia Muschter, Andreas Nitsche, Emmanuel Couacy-Hymann, Christophe Boesch, Roman M. Wittig, Sébastien Calvignac-Spencer, and Fabian H. Leendertz. 2020. “Monkeypox virus emergence in wild chimpanzees reveals distinct clinical outcomes and viral diversity.” Nature Microbiology, 5, Pp. 955–965. Publisher's VersionAbstract

Monkeypox is a viral zoonotic disease on the rise across endemic habitats. Despite the growing importance of monkeypox virus, our knowledge on its host spectrum and sylvatic maintenance is limited. Here, we describe the recent repeated emergence of monkeypox virus in a wild, human-habituated western chimpanzee (Pan troglodytes verus, hereafter chimpanzee) population from Taï National Park, Ivory Coast. Through daily monitoring, we show that further to causing its typical exanthematous syndrome, monkeypox can present itself as a severe respiratory disease without a diffuse rash. By analysing 949 non-invasively collected samples, we identify the circulation of at least two distinct monkeypox virus lineages and document the shedding of infectious particles in faeces and flies, suggesting that they could mediate indirect transmission. We also show that the carnivorous component of the Taï chimpanzees’ diet, mainly consisting of the sympatric monkeys they regularly hunt, did not change nor shift towards rodent consumption (the presumed reservoir) before the outbreaks, suggesting that the sudden emergence of monkeypox virus in this population is probably due to changes in the ecology of the virus itself. Using long-term mortality surveillance data from Taï National Park, we provide evidence of little to no prior viral activity over at least two decades. We conclude that great ape sentinel systems devoted to the longitudinal collection of behavioural and health data can help clarify the epidemiology and clinical presentation of zoonotic pathogens.

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