The Price of Play: Self-Organized Infant Mortality Cycles in Chimpanzees

Chimpanzees have been used extensively as a model system for laboratory research on infectious diseases. Ironically, we know next to nothing about disease dynamics in wild chimpanzee populations. Here, we analyze long-term demographic and behavioral data from two habituated chimpanzee communities in Taï National Park, Côte d'Ivoire, where previous work has shown respiratory pathogens to be an important source of infant mortality. In this paper we trace the effect of social connectivity on infant mortality dynamics. We focus on social play which, as the primary context of contact between young chimpanzees, may serve as a key venue for pathogen transmission. Infant abundance and mortality rates at Taï cycled regularly and in a way that was not well explained in terms of environmental forcing. Rather, infant mortality cycles appeared to self-organize in response to the ontogeny of social play. Each cycle started when the death of multiple infants in an outbreak synchronized the reproductive cycles of their mothers. A pulse of births predictably arrived about twelve months later, with social connectivity increasing over the following two years as the large birth cohort approached the peak of social play. The high social connectivity at this play peak then appeared to facilitate further outbreaks. Our results provide the first evidence that social play has a strong role in determining chimpanzee disease transmission risk and the first record of chimpanzee disease cycles similar to those seen in human children. They also lend more support to the view that infectious diseases are a major threat to the survival of remaining chimpanzee populations

Chimpanzee accumulative stone throwing

The study of the archaeological remains of fossil hominins must rely on reconstructions to elucidate the behaviour that may have resulted in particular stone tools and their accumulation. Comparatively, stone tool use among living primates has illuminated behaviours that are also amenable to archaeological examination, permitting direct observations of the behaviour leading to artefacts and their assemblages to be incorporated. Here, we describe newly discovered stone tool-use behaviour and stone accumulation sites in wild chimpanzees reminiscent of human cairns. In addition to data from 17 mid- to long-term chimpanzee research sites, we sampled a further 34 Pan troglodytes communities. We found four populations in West Africa where chimpanzees habitually bang and throw rocks against trees, or toss them into tree cavities, resulting in conspicuous stone accumulations at these sites. This represents the first record of repeated observations of individual chimpanzees exhibiting stone tool use for a purpose other than extractive foraging at what appear to be targeted trees. The ritualized behavioural display and collection of artefacts at particular locations observed in chimpanzee accumulative stone throwing may have implications for the inferences that can be drawn from archaeological stone assemblages and the origins of ritual sites

The nature of culture: Technological variation in chimpanzee predation on army ants revisited

Chimpanzee (Pan troglodytes) predation on army ants (Dorylus, subgenus Anomma) is an impressive example of skillful use of elementary technology, and it has been suggested to reflect cultural differences among chimpanzee communities. Alternatively, the observed geographic diversity in army-ant-eating may represent local behavioral responses of the chimpanzees to the anti-predator traits of the army ant species present at the different sites. We examined assemblages of available prey species, their behavior and morphology, consumption by chimpanzees, techniques employed, and tool lengths at 14 sites in eastern, central, and western Africa. Where army ants are eaten, tool length and concomitant technique are a function of prey type. Epigaeically foraging species with aggressive workers that inflict painful bites are harvested with longer tools and usually by the "pull-through" technique; species foraging in leaf-litter with less aggressive workers that inflict less painful bites are harvested with short tools and by the "direct-mouthing" technique. However, prey species characteristics do not explain several differences in army-ant-eating between Bossou (Guinea) and Tai (Ivory Coast), where the same suite of prey species is available and is consumed. Moreover, the absence of army-ant-eating at five sites cannot be explained by the identity of available prey species, as all the species found at these sites are eaten elsewhere. We conclude that some of the observed variation in the predator-prey relationship of chimpanzees and army ants reflects environmental influences driven by the prey, while other variation is not linked to prey characteristics and may be solely sociocultural

Cultural differences in army ant predation by West African chimpanzees? A comparative study of microecological variables

Behavioural diversity in the predation pattern of army ants (Dorylus spp.) by different populations of wild chimpanzees, Pan troglodytes, has been proposed to reflect different cultural traditions. Chimpanzees use either stick tools (known as ant dipping) or simply their hands to prey on two groups of army ants (epigaeic and intermediate species). A recent analysis has shown that, contrary to the cultural hypothesis, the tool length and associated harvesting technique used by chimpanzees in different populations is to a large extent influenced by characteristics of the ants themselves. However, in line with the cultural hypothesis, chimpanzees at two long-term study sites in West Africa (Bossou, Guinea, and Tai National Park, Cote d'Ivoire) prey on the same five army ant species but adopt different strategies to do so. We conducted controlled human simulations of ant dipping and an ant survey at these two sites to evaluate alternative ecological explanations related to ant behaviour and ecology that could account for the observed differences in chimpanzee predation behaviour. Ant speed explained differences in tool length within Bossou but not between Bossou and Taï. Our results do not support an ecological basis underlying the lack of dipping at ant trails in Taï chimpanzees. Finally, neither ant aggressiveness (measured as speed and persistence) nor yield when using tools could explain why, unlike Bossou chimpanzees, Taï chimpanzees do not use tools to harvest epigaeic species. We conclude that an interaction of cultural and ecological factors shapes the differences in army ant predation between Tai and Bossou chimpanzees

Intergroup conflicts among chimpanzees in Tai National Park: Lethal violence and the female perspective

Intercommunity aggression in chimpanzees and primitive warfare in humans possess striking similarities, such as the common occurrence of large male coalitions, systematic control of territory boundaries, and lethal attacks on isolated individuals from neighboring groups. However, an important apparent contrast is the absence of recurrent peaceful interactions between neighboring groups of chimpanzees. We observed a remarkable range of behavior in intergroup encounters among three habituated communities of chimpanzees in Tai National Park, Cote d'voire. Lethal attacks are documented in these study groups for the first time, as well as year-long exchanges of parous adult females and peaceful intergroup visits of mothers with infants. Demographic factors, including group size and number of adult males, are shown to affect the nature of intergroup interactions in ways not considered previously. A reconsideration of the difference in intergroup interactions between eastern and western chimpanzees is proposed including a more important consideration of the female's perspective. The inclusion of the new complexities in intergroup interactions in chimpanzees allows new parallels to be drawn with the evolution of primitive warfare in humans.</p

Chimpanzee accumulative stone throwing

The study of the archaeological remains of fossil hominins must rely on reconstructions to elucidate the behaviour that may have resulted in particular stone tools and their accumulation. Comparatively, stone tool use among living primates has illuminated behaviours that are also amenable to archaeological examination, permitting direct observations of the behaviour leading to artefacts and their assemblages to be incorporated. Here, we describe newly discovered stone tool-use behaviour and stone accumulation sites in wild chimpanzees reminiscent of human cairns. In addition to data from 17 mid- to long-term chimpanzee research sites, we sampled a further 34 Pan troglodytes communities. We found four populations in West Africa where chimpanzees habitually bang and throw rocks against trees, or toss them into tree cavities, resulting in conspicuous stone accumulations at these sites. This represents the first record of repeated observations of individual chimpanzees exhibiting stone tool use for a purpose other than extractive foraging at what appear to be targeted trees. The ritualized behavioural display and collection of artefacts at particular locations observed in chimpanzee accumulative stone throwing may have implications for the inferences that can be drawn from archaeological stone assemblages and the origins of ritual sites.This is an article from Scientific Reports 6 (2016): 22219, doi:10.1038/srep22219. Posted with permission.</p