Chimpanzee Populations Research Articles

Fossil hominin ulnae and the forelimb ofParanthropus

The discovery of Pan in the Middle Pleistocene deposits of the Kapthurin Formation of the Tugen Hills (McBrearty and Jablonski: Nature 437 (2005) 105-108) inspires new interest in the search for other chimpanzee fossils in the East African Rift Valley. Craniodental evidence of an eastward excursion of chimpanzee populations in the Plio-Pleistocene goes undetected in other hominin sites, but one enigmatic postcranial fossil, the Olduvai Hominid 36 ulna, has many chimp-like features. Analyses by Aiello et al. (Aiello et al.: Am J Phys Anthropol 109 (1999) 89-110) reveal that it is similar to extant Pan in some respects, but it also has unique traits not seen in other hominoid species. They refer it to Paranthropus boisei. In this study, we reassess the affinities of OH 36 using a different data set that includes more recently discovered hominin fossils including those attributed to Paranthropus. Despite its superficial resemblance to modern Pan, our results agree with those of Aiello et al. (Aiello et al.: Am J Phys Anthropol 109 (1999) 89-110) that OH 36 is distinctly different from modern chimpanzees. By default, it is reasonable to assign this specimen to P. boisei, but it is not at all similar to other ulnae referred to this genus. Ulnae attributed to Paranthropus from South Africa, Kenya, and Ethiopia are morphologically more heterogeneous than those within species of large-bodied Hominoidea. Although there are many apparent shared derived traits justifying a monophyletic Paranthropus clade, most if not all of these traits are related to a single functional complex (hypermastication) that may have evolved in parallel and thereby constituting a paraphyletic group of species.

New Streptococcus pneumoniae Clones in Deceased Wild Chimpanzees

In wild chimpanzees in the Taï National Park, Côte d'Ivoire, sudden deaths which were preceded by respiratory problems had been observed since 1999. Two new clones of Streptococcus pneumoniae were identified in deceased apes on the basis of multilocus sequence typing analysis and ply, lytA, and pbp2x sequences. The findings suggest that virulent S. pneumoniae occurs in populations of wild chimpanzees with the potential to cause infections similar to those observed in humans.

The origins of HIV and implications for the global epidemic

HIV type 1 (HIV-1) and type 2 (HIV-2) are the result of several cross-species transmissions from primates to humans. Recently, the ancestral strains of HIV-1 groups M and N were shown to still persist in today's wild chimpanzee populations (Pan troglodytes troglodytes) in south Cameroon. Lately, HIV-1 group O-related viruses have been identified in western gorillas (Gorilla gorilla), called SIVgor, but chimpanzees are most likely the original reservoir of this simian immunodeficiency virus (SIV) infection. HIV-2 is the result of at least eight distinct cross-species transmissions of SIV from sooty mangabeys (Cercocebus atys) in West Africa. Although the origin of HIV-1 and HIV-2 became clearer, some important questions concerning pathogenicity and epidemic spread of certain HIV/SIV variants need to be further elucidated. Because humans are still exposed to a plethora of primate lentiviruses through hunting and handling of primate bushmeat, the possibility of additional zoonotic transfers of primate lentiviruses from other primates must be considered.

The Contribution of Long‐Term Research at Gombe National Park to Chimpanzee Conservation

Long-term research projects can provide important conservation benefits, not only through research specifically focused on conservation problems, but also from various incidental benefits, such as increased intensity of monitoring and building support for the protection of an area. At Gombe National Park, Tanzania, long-term research has provided at least four distinct benefits to wildlife conservation. (1) Jane Goodall's groundbreaking discoveries of chimpanzee (Pan troglodytes) tool use, hunting, and complex social relationships in what was then a game reserve drew attention to the area and created support for upgrading Gombe to national park status in 1968. (2) The highly publicized findings have earned Gombe and Tanzania the attention of a worldwide public that includes tourists and donors that provide financial support for Gombe, other parks in Tanzania, and chimpanzee conservation in general. (3) Crucial information on social structure and habitat use has been gathered that is essential for effective conservation of chimpanzees at Gombe and elsewhere. (4) A clear picture of Gombe's chimpanzee population over the past 40 years has been determined, and this has helped identify the greatest threats to the viability of this population, namely disease and habitat loss outside the park. These threats are severe and because of the small size of the population it is extremely vulnerable. Research at Gombe has led to the establishment of conservation education and development projects around Gombe, which are needed to build local support for the park and its chimpanzees, but saving these famous chimpanzees will take a larger integrated effort on the part of park managers, researchers, and the local community with financial help from international donors.

Effects of male group size, parity, and cycle stage on female chimpanzee copulation rates at Ngogo, Kibale National Park, Uganda

Chimpanzees have complex and variable mating strategies, but most copulations occur when females with full sexual swellings are in parties with multiple males and mate with most or all of those males. Daily copulation rates for fully swollen females vary at different times of a female's cycle, among females, and across communities and populations. Variation in female age, parity, and cycle stage underlie some of this variation, but possible demographic effects on copulation rates have not been systematically investigated. Demographic variation can affect many aspects of behavior and ecology, including the frequency and success of different mating tactics. Analysis of data from the unusually large chimpanzee community at Ngogo produces two results that are consistent with the hypothesis that demographic variation affects female copulation rates. Copulation rates were high compared with those reported from other research sites, where females had fewer potential mates available. Daily copulation rates of fully swollen females were also positively related to the number of males with whom they associated. Ngogo data also re-confirm results from other studies, of both wild and captive populations, showing that female copulation rates increase during periovulatory periods. This is consistent with the hypothesis that sexual swellings and extended receptivity and proceptivity help to protect females against infanticide by helping to ensure they mate with all potential sires. As at some other sites, parous females at Ngogo copulated at higher rates than nulliparous females. Possible effects of demography on sexual behavior should be considered in assessments of differences between chimpanzees and bonobos and of variation across chimpanzee populations.

Experimental studies of traditions and underlying transmission processes in chimpanzees

Multiple regional differences in tool use have been identified among wild chimpanzees, Pan troglodytes, but the hypothesis that these represent traditions, transmitted through social learning, is difficult to substantiate without experimentation. To test chimpanzees' capacity to sustain traditions, we seeded alternative tool use techniques in single individuals in different captive groups. One technique, ‘Lift’, spread in the group into which it was introduced and not in chimpanzees who saw no model or whose group was seeded with the alternative technique, ‘Poke’. Poke was also not discovered by control animals tested individually. However, Poke emerged spontaneously in the Lift group and became dominant in both groups, regardless of the founder's Lift or Poke technique. Accordingly, this study demonstrated a statistically significant, differential spread of alternative techniques through social learning, yet no clear separation of traditions, unlike an earlier study with a different population of chimpanzees. This difference may be attributable to prior experience with relevant tools. In further experiments we investigated the basis of the social learning evident in acquisition of the Lift technique, using ‘ghost’ conditions in which the task was operated automatically rather than by a chimpanzee. Differential movement of the feeding device either by itself or with the tool coupled to it was not sufficient for learning to occur. It appears necessary for a chimpanzee to observe another chimpanzee performing the Lift technique for transmission to ensue.

The Uncertain Future of Research Chimpanzees

The otherwise excellent News Focus article by Jon Cohen on the future of “The endangered lab chimp” (26 Jan., p. 450) does not emphasize one compelling reason why studies of captive chimpanzees should continue—the significant differences in their disease patterns, incidence, and severity from those of humans (1). As human and chimpanzee proteins are >99% identical (2), it should be possible to explain some of these surprising disease differences at the molecular level. Thus, more studies are needed not because chimpanzees are good models for human diseases, but rather because they are surprisingly bad models in many instances, for example, HIV infection progressing to AIDS and P. falciparum malaria. Such investigations could adopt approaches similar to those currently used for studying human diseases, and the results would benefit the care of both humans and chimpanzees. The NIH spent many dollars to sequence the chimpanzee genome (2). If the existing captive chimpanzee population is allowed to die out in sanctuaries without adequate funding or facilities for such research, some of the most biomedically valuable benefits of the chimpanzee genome sequencing will never be realized.

Fruit availability, chimpanzee diet, and grouping patterns on Rubondo Island, Tanzania

We examined seasonal patterns of fruit availability, dietary quality, and group size in the descendants of an introduced chimpanzee population on Rubondo Island, Tanzania. The site has supported a free-ranging population without provisioning for 40 years. Our goals were to determine whether Rubondo chimpanzees experience periods of fruit shortage, and whether they respond to changes in fruit availability similarly to chimpanzees at endemic sites. We indexed the fruit availability of tree and liana species on transects stratified across three chimpanzee ranging areas. We used fecal analyses to evaluate seasonal changes in diet, and used data on party size and nesting group size to examine seasonal patterns of grouping. Tree fruit availability was positively correlated with rainfall, with a period of relative tree fruit scarcity corresponding with the long dry season. Liana fruit availability was not related to rainfall, and lianas exhibited less variable fruiting patterns across seasons. Fruits made up the majority of the chimpanzee diet, with lianas accounting for 35% of dietary fruit species. Fruits of the liana Saba comorensis were available during all months of phenological monitoring, but they were consumed more when tree fruit was scarce, suggesting that Saba comorensis fruits may be a fallback food for Rubondo chimpanzees. There were no increases in consumption of lower-quality plant parts between seasons, and there were no changes in group size between seasons. These results contrast with evidence from several endemic chimpanzee study sites, and indicate that Rubondo chimpanzees may have access to abundant and high-quality foods year round.

Bonobos

Bonobos

New Case of Intragroup Infanticide in the Chimpanzees of Gombe National Park

Researchers have reported a total of 31 infanticides in 4 different chimpanzee (Pan troglodytes) populations. Though infanticide is infrequent, low reproductive rates of females likely make it a strong selective pressure in the species. We report a new incident of intragroup infanticide in Gombe National Park, Tanzania, in which a community male attacked a 3.5-yr-old male. We then consider the infanticide in terms of adaptive and nonadaptive explanations for infanticide including the social pathology, by-product of male aggression, nutritive benefits, resource competition, and sexual selection hypotheses. The incident reported here is not well explained by any of them. While the infanticide is puzzling in terms of ultimate explanations for infanticide, it provides a good context in which to consider proximate mechanisms for offspring recognition. The incident provides some evidence that males may use their mating history with the mother to assess paternity likelihood.

Introduction. Social intelligence: from brain to culture

Humans are perhaps the most social animals. Although some eusocial insects, herd mammals and seabirds live in colonies comprising millions of individuals, no other species lives in such a variety of social groups as Homo sapiens . We live in many different sized societies, from small, nomadic hunter

What makes us human (Homo sapiens)? The challenge of cognitive cross-species comparison.

Two major theoretical approaches have dominated the quest for uniquely human cognitive abilities: a developmentalist approach stressing the importance of environmental and social conditions, and a predominant approach in experimental and comparative psychology, the deterministic approach suggesting the effect of environmental and social conditions to be minimal. As a consequence, most claims of human cognitive uniqueness are based on comparisons of White middle class Westerner humans (Homo sapiens) with captive chimpanzees (Pan troglodytes). However, humans are much more than only White middle class Westerners, and chimpanzees are much more than only captives. A review of some data available on different populations of humans and chimpanzees reveals that only the predictions of the developmentalist approach are supported. In addition, systematic biases are too often introduced in experiment protocols when comparing humans with apes that further cast doubts on cross-species comparisons. The author argues that only with consideration of within-species population differences in the cognitive domains and the use of well-matched cross-species experimental procedures will an objective understanding of the different cognitive abilities between species emerge. This will require a shift in the theoretical approach adopted by many in experimental and comparative psychology.

Fission–fusion social systems as a strategy for coping with ecological constraints: a primate case

Fission–fusion social systems, in which members of a social community form frequently changing subgroups, occur in a number of mammalian taxa. Such systems are assumed to be a response to the costs of grouping, but evidence to support this hypothesis is limited. We use a linear programming approach to build a time budget model that predicts the upper bound on group size in order to test the hypothesis that fission–fusion social systems are the outcome of time constraints. Comparative data from 14 wild chimpanzee (Pan spp.) populations are used to derive a set of equations defining the relationship between climatic variables and time budget components, which are then used to calculate the upper limits on group size that can be maintained in different habitats. We validate the model by showing that it correctly predicts the presence/absence of chimpanzees across sub-Saharan Africa and the group sizes observed in natural populations. The model suggests that the costs of travel are limiting for chimpanzees. Chimpanzees can reduce these costs dramatically by fissioning their bonded communities into small foraging parties. If they did not, they would be unable to live in any habitats where they currently occur.

Chimpanzee tool technology in the Goualougo Triangle, Republic of Congo

With the exception of humans, chimpanzees show the most diverse and complex tool-using repertoires of all extant species. Specific tool repertoires differ between wild chimpanzee populations, but no apparent genetic or environmental factors have emerged as definitive forces shaping variation between populations. However, identification of such patterns has likely been hindered by a lack of information from chimpanzee taxa residing in central Africa. We report our observations of the technological system of chimpanzees in the Goualougo Triangle, located in the Republic of Congo, which is the first study to compile a complete tool repertoire from the Lower Guinean subspecies of chimpanzee ( Pan troglodytes troglodytes). Between 1999 and 2006, we documented the tool use of chimpanzees by direct observations, remote video monitoring, and collections of tool assemblages. We observed 22 different types of tool behavior, almost half of which were habitual (shown repeatedly by several individuals) or customary (shown by most members of at least one age-sex class). Several behaviors considered universals among chimpanzees were confirmed in this population, but we also report the first observations of known individuals using tools to perforate termite nests, puncture termite nests, pound for honey, and use leafy twigs for rain cover. Tool behavior in this chimpanzee population ranged from simple tasks to hierarchical sequences. We report three different tool sets and a high degree of tool-material selectivity for particular tasks, which are otherwise rare in wild chimpanzees. Chimpanzees in the Goualougo Triangle are shown to have one of the largest and most complex tool repertoires reported in wild chimpanzee populations. We highlight new insights from this chimpanzee population to our understanding of ape technological systems and evolutionary models of tool-using behavior.

Female Coalitions Against Male Aggression in Wild Chimpanzees of the Budongo Forest

In the wild, female chimpanzees (Pan troglodytes) are subject to male aggression that at times can be prolonged or particularly violent. There are no reports of cooperative retaliation to such aggression, a strategy observed in the congeneric Pan paniscus, from the wild despite >4 decades of detailed behavioral study across a number of populations and its occurrence among captive female chimpanzees. If the reports from captivity represent an inherent capacity, then the absence of similar reports from wild populations suggests that females may be able to form coalitions only under appropriate ecological and demographic conditions. During a study of male and female aggressive interactions among chimpanzees of the Budongo Forest, Uganda, wild adult female chimpanzees sometimes formed coalitions with one another to retaliate against male aggression. This may be possible because these females tend to be more gregarious than in other populations of East African chimpanzees, as other studies of the same population have suggested; the extent and variation of female chimpanzee social strategies may, therefore, need reconsideration. Further, my observations strengthen the argument that at least some of the differences between chimpanzees and bonobos may be more of degree than of kind.

New Genetic Evidence on the Evolution of Chimpanzee Populations and Implications for Taxonomy

Primatologists widely recognize chimpanzees as belonging to a single species, Pan troglodytes, which they traditionally have further divided into 3 subspecies: west African P. t. verus, central African P. t. troglodytes, and east African P. t. schweinfurthii. Previously, we suggested that the phylogeographic history of chimpanzees may be different from that implied by the widely used taxonomy of the species. We based the suggestion on only a limited sample of haplotypes from the first hypervariable region (HVRI) of mitochondrial (mt)DNA from chimpanzees in Nigeria. We have now compiled a more geographically comprehensive genetic database for chimpanzees, including samples obtained near the Niger and Sanaga Rivers. Our database is composed of 254 HVRI haplotypes from chimpanzees of known geographic origin, including 79 unique HVRI haplotypes from chimpanzees living in Nigeria and Cameroon. The genetic data provide clear evidence that a major phylogeographic break between chimpanzee lineages occurs near the Sanaga River in central Cameroon and suggest the need for a reclassification of chimpanzees.

Using retrospective health data from the Gombe chimpanzee study to inform future monitoring efforts

Disease outbreaks, either in isolation or in concert with other risk factors, can pose serious threats to the long-term persistence of mammal populations, and these risks become elevated as population size decreases and/or population isolation increases. Many chimpanzee study sites are increasingly isolated by loss of habitat due to human encroachment, and managers of parks that contain chimpanzees perceive that disease outbreaks have been and continue to be significant causes of mortality for chimpanzees. Major epidemics at Gombe National Park include suspected polio in 1966; respiratory diseases in 1968, 1987, 1996, 2000, and 2002; and sarcoptic mange in 1997. These outbreaks have led park managers and researchers working in Gombe to conclude that disease poses a substantial risk to the long-term survival of Gombe's chimpanzee population. We surveyed behavioral data records spanning 44 years for health-related data and found a combination of standardized and nonstandardized data for the entire period. Here we present the types of data found during the survey, discuss the usefulness of these data in the context of risk assessment, and describe how our current monitoring effort at Gombe was designed based on our findings.

Army ant prey availability and consumption by chimpanzees (Pan troglodytes vellerosus) at Gashaka (Nigeria)

AbstractArmy ant predation by chimpanzees has been studied as an intriguing example of tool use and a possible case of cultural variation. However, the importance of army ant prey in chimpanzee diet and feeding ecology is still only poorly understood. We studied the availability and consumption of army ants in a population of the chimpanzee subspecies Pan troglodytes vellerosus in Nigeria. Army ants were collected from nests and trails (workers) and near artificial light sources (males). Three potential prey species were found: Dorylus rufescens, Dorylus gerstaeckeri and Dorylus kohli. Dorylus rufescens was by far more abundant than the other two species. Only remains from D. rufescens were present in chimpanzee faeces. This is the first report of consumption of this ant species by chimpanzees. However, because of the low availability of the other two species, it is unclear whether this pattern reflects a preference for D. rufescens. Although D. rufescens' availability varied with weather conditions, the occurrence as well as the absolute and relative numbers of Dorylus fragments in faeces did not. This finding, together with the considerable difficulties encountered by human observers in their efforts to locate nests by following trails, suggests that the chimpanzees in this population do not harvest army ants from trails and do not use trails to locate nests. The overall occurrence of army ant fragments in 42.3% of all faecal samples is the highest ever recorded in any chimpanzee population. This indicates that in this chimpanzee population, army ant prey is not a fallback during periods of sparse availability of plant food, but quantitatively important throughout the year. Future studies will be needed to clarify which cues and strategies chimpanzees use to locate army ant nests and to assess the role of myrmecophagy with respect to macro‐ or micronutrient demands.

Chimpanzees in the Ntakata and Kakungu Areas, Tanzania

Surveys were carried out for chimpanzees, Pan troglodytes schweinfurthii, in the areas of Ntakata (300 km2 between the Mkamba River and the Lubalisi River, 05°45′–06°15′S, 30°00′–30°15′E), and Kakungu (200 km2 between the Lubalisi River and the sources of the Rubufu River, 05°55′–06°15′S, 30°00′–30°15′E), Tanzania, during the dry seasons of 2001 and 2003. The predominant vegetation was savanna woodland with forest patches (mainly along watercourses and hillsides). Population information was obtained by sightings and sleeping-nest counts. In the Ntakata area, chimpanzees occur in Ntakata, Mlofwezi, Kapalagulu (05°52′S, 30°02′E), and Mpulumuka (5°58′S, 30°11 ′E) and in the Ntakata-Kapalagulu Hills (Fig. 1). No evidence was forthcoming for their existence in Ikubulu, Lunfampa, Kakundu, Kabufisa, and Kamafiga, nor the plains of north of Kapalagulu Hill and the entire Lugufu basin. In the Kakungu area, they occur at Kakungu itself (05°58′S, 30°03′E) and Kalobwa in the Kakungu-Kalobwa Hills. With evidently large home ranges, densities were found to be low in the 500-km2 area between the Ntakata-Kapalagulu Hills and Kakungu-Kalobwa Hills — everywhere less than 0.05(0.048) individuals/km2. Hunting (by immigrant farmers and refugees), besides habitat loss (logging, firewood, and clearing for agriculture) are believed be causing a steady decline of chimpanzee populations in the region.

Detailed characterization of the peptide binding specificity of five common Patr class I MHC molecules

The chimpanzee (Pan troglodytes) is an important model for studying the immune response to several human pathogens, but the study of correlates of immunity has been hindered by the fact that little is known about the epitope-binding specificity of chimpanzee (Patr) class I MHC. In the present study we have characterized the peptide binding specificity of several common Patr class I molecules. Using single amino acid substitution analogs and large peptide libraries, quantitative peptide binding motifs have been derived for Patr A*0101, A*0701, A*0901, B*0101, and B*2401. Each molecule was found to bind peptides using position 2 and the C terminus as main anchor contacts. On the other hand, each Patr molecule is associated with a unique binding specificity, and the range of specificities is similar to that seen amongst HLA alleles. A high degree of cross-reactivity was noted between Patr A*0701 and Patr A*0901, suggesting the existence of a Patr-specific supertype. Consistent with previous studies suggesting that some cross-reactivity may exist between HLA and Patr alleles, Patr A*0901 was found to have an appreciable degree of cross-reactivity with molecules of the HLA A24-supertype. Finally, utilizing motif scans and peptide binding and intracellular cytokine staining assays, 77 hepatitis B virus (HBV)-derived epitopes were identified in five chimpanzees that were recently convalescent from acute HBV infection. Because the Patr alleles studied herein were found to be very common in two different chimpanzee populations, the present data should facilitate the use of chimpanzees for immunological studies.