Studies Of Wild Chimpanzees Research Articles

Common cold viruses circulating in children threaten wild chimpanzees through asymptomatic adult carriers

Reverse zoonotic respiratory diseases threaten great apes across Sub-Saharan Africa. Studies of wild chimpanzees have identified the causative agents of most respiratory disease outbreaks as “common cold” paediatric human pathogens, but reverse zoonotic transmission pathways have remained unclear. Between May 2019 and August 2021, we conducted a prospective cohort study of 234 children aged 3–11 years in communities bordering Kibale National Park, Uganda, and 30 adults who were forest workers and regularly entered the park. We collected 2047 respiratory symptoms surveys to quantify clinical severity and simultaneously collected 1989 nasopharyngeal swabs approximately monthly for multiplex viral diagnostics. Throughout the course of the study, we also collected 445 faecal samples from 55 wild chimpanzees living nearby in Kibale in social groups that have experienced repeated, and sometimes lethal, epidemics of human-origin respiratory viral disease. We characterized respiratory pathogens in each cohort and examined statistical associations between PCR positivity for detected pathogens and potential risk factors. Children exhibited high incidence rates of respiratory infections, whereas incidence rates in adults were far lower. COVID-19 lockdown in 2020–2021 significantly decreased respiratory disease incidence in both people and chimpanzees. Human respiratory infections peaked in June and September, corresponding to when children returned to school. Rhinovirus, which caused a 2013 outbreak that killed 10% of chimpanzees in a Kibale community, was the most prevalent human pathogen throughout the study and the only pathogen present at each monthly sampling, even during COVID-19 lockdown. Rhinovirus was also most likely to be carried asymptomatically by adults. Although we did not detect human respiratory pathogens in the chimpanzees during the cohort study, we detected human metapneumovirus in two chimpanzees from a February 2023 outbreak that were genetically similar to viruses detected in study participants in 2019. Our data suggest that respiratory pathogens circulate in children and that adults become asymptomatically infected during high-transmission times of year. These asymptomatic adults may then unknowingly carry the pathogens into forest and infect chimpanzees. This conclusion, in turn, implies that intervention strategies based on respiratory symptoms in adults are unlikely to be effective for reducing reverse zoonotic transmission of respiratory viruses to chimpanzees.

Collective intentionality: A basic and early component of moral evolution

ABSTRACTMichael Tomasello’s account of moral evolution includes both a synthesis of extensive experimental work done on humans and chimpanzees on their potential for perspective-taking and helpful, altruistic generosity and a major emphasis on “collective intentionality” as an important component of morality in humans. Both will be very useful to the evolutionary study of this subject. However, his disavowal of collective intentions on the parts of chimpanzees would appear to be empirically incorrect, owing to reliance on experimental captive research focused only on dyadic interactions. Here, evidence to the contrary is provided from studies of wild chimpanzees as they naturally cooperate in sizable groups. Collective intentions are inferable when they go on patrol, when they mob predators, when they go hunting, and when large coalitions gang-attack disliked members of the same community. This last behavior has particularly significant pre-adaptive implications for the evolution of moralistic social control, and it suggests that moral evolution has deep roots, going back to the Last Common Ancestor of humans, bonobos, and chimpanzees.

Chimpanzee food-associated calls display low referential potential in a wild population

Studies of non-human primate vocal communication commonly focus on “functionally referential signals,” which are thought to function like human words, informing receivers about stimuli in the external environment. Captive studies of the food-associated “rough-grunt” of chimpanzees (Pan troglodytes) report that their acoustic structure varies according to food quality and even type, suggesting the existence of functionally referential communication in humans' evolutionary cousins. Nevertheless, studies of wild chimpanzees have produced mixed evidence that rough-grunts function referentially in natural contexts. The current study builds upon these findings by conducting an acoustic analysis of rough-grunts produced by wild chimpanzees at Gombe National Park, Tanzania, examining acoustic variation in call duration and peak frequency both within and between feeding bouts. We found that peak frequency, but not duration, displayed a bimodal distribution, supporting the view that rough-grunts include at least tw...

Genetic and ‘cultural’ similarity in wild chimpanzees

The question of whether animals possess 'cultures' or 'traditions' continues to generate widespread theoretical and empirical interest. Studies of wild chimpanzees have featured prominently in this discussion, as the dominant approach used to identify culture in wild animals was first applied to them. This procedure, the 'method of exclusion,' begins by documenting behavioural differences between groups and then infers the existence of culture by eliminating ecological explanations for their occurrence. The validity of this approach has been questioned because genetic differences between groups have not explicitly been ruled out as a factor contributing to between-group differences in behaviour. Here we investigate this issue directly by analysing genetic and behavioural data from nine groups of wild chimpanzees. We find that the overall levels of genetic and behavioural dissimilarity between groups are highly and statistically significantly correlated. Additional analyses show that only a very small number of behaviours vary between genetically similar groups, and that there is no obvious pattern as to which classes of behaviours (e.g. tool-use versus communicative) have a distribution that matches patterns of between-group genetic dissimilarity. These results indicate that genetic dissimilarity cannot be eliminated as playing a major role in generating group differences in chimpanzee behaviour.

Tool-use for drinking water by immature chimpanzees of Mahale: prevalence of an unessential behavior

Use of leaves or sticks for drinking water has only rarely been observed during long-term study of wild chimpanzees (Pan troglodytes schweinfurthii) at Mahale. Recently, however, we observed 42 episodes of tool-use for drinking water (73 tools and two cases of using "tool-sets") between 1999 and 2004. Interestingly, all of the performers were immature chimpanzees aged from 2 to 10 years. Immature chimpanzees sometimes observed the tool-using performance of others and subsequently reproduced the behavior, while adults usually paid no attention to the performance. This tool-use did not seem to occur out of necessity: (1) chimpanzees often used tools along streams where they could drink water without tools, (2) they used tools for drinking water from tree holes during the wet season when they could easily obtain water from many streams, and (3) the tool-using performance sometimes contained playful aspects. Between-site comparisons revealed that chimpanzees at drier habitats used tools for drinking water more frequently and in a more "conventional" manner. However, some variations could not be explained by ecological conditions. Such variations and the increase in this tool-use in recent years at Mahale strongly suggest that social learning plays an important role in the process of acquiring the behavior. We should note here that such behaviors that lack obvious benefits or necessity can be prevalent in a group.

Laterality of hand function in naturalistically housed chimpanzees (Pan troglodytes)

Studies of laterality of hand function in chimpanzees (Pan troglodytes) have the potential to tell us about the origins of handedness in Homo sapiens. However, the data are confusing, with discrepancies present between studies done in the field and the laboratory: the former show wild chimpanzees to be unlateralised at the population level, while the latter show captive chimpanzees as lateralised at the population level. This study of 26 semi-free ranging chimpanzees of Chester Zoo, UK, aimed to investigate a situation between the wild and captivity and provided ethological data for 43 categories of spontaneous manual use and 14 categories of tool use. Other variables recorded were subordinate hand activity, whether the subject was arboreal or terrestrial, and the identity of the subject. Using switching focal subject sampling, 23,978 bouts of hand use and 1,090 bouts of tool use were recorded. No population-level handedness was present for manual non-tool use activities in the naturalistically housed chimpanzees of Chester Zoo in a similar way to studies of wild chimpanzees. However, about half of the individuals were lateralised to one side or the other for the foraging behaviours of pick up, eat, and pluck. Using a modified version of McGrew and Marchant's (1997) Laterality Framework, these results are comparable to some wild and captive populations for similar foraging tasks. Bimanuality was rare and thus prevented comparison with captive experimental studies that have reported population right handedness. Behaviour involving contact with water elicited stronger lateralisation. Chester chimpanzees were more likely to exhibit hand preferences for manual tasks with increasing age but there were no effects of sex or rearing history on hand specialisations in adult individuals. Lateralisation was biased in tool use, which evoked significant left hand preferences in half the individuals, with no effect of age. Results are discussed comparatively with reference to methodological and developmental issues. Longitudinal studies of hand use are needed to increase our understanding of laterality of hand use in chimpanzees.

ESSAYS ON SCIENCE AND SOCIETY: Learning from the Chimpanzees: A Message Humans Can Understand

ESSAYS ON SCIENCE AND SOCIETY: Learning from the Chimpanzees: A Message Humans Can Understand

Studies of wild chimpanzees by DNA typing in prospect

Analysis of DNA polymorphisms was viewed as a new means of individual discrimination in studies of wild chimpanzees. DNA typing methodology was summarized for field primatologists, who often lack required knowledge of molecular biology, and expected impact of DNA typing on studies of wild chimpanzees was discussed. In particular, behavioral and social aspects were dealt with. A guide to noninvasive collection of samples in the field was appended.

Water-contact behavior of chimpanzees.

Chimpanzees are apparently unable to swim, a fact which may be accounted for by a low ratio of fat to muscle and a low specific gravity. A survey of field studies of wild chimpanzees indicates that they have very little contact with water. In contrast, chimpanzees in captivity frequently drink standing water, possibly because their diet is low in water content. Two of the semi-free-ranging chimpanzees observed in this study would immerse themselves to waist-level in moat water, replacing former behavior patterns of water avoidance.