Wild West African Chimpanzees Research Articles

Reciprocity and trades in wild West African chimpanzees

Why do animals help other individuals and provide benefits to the recipient, sometimes at personal cost? In this study, we aim to determine if some of the helpful behaviors observed in a group of wild chimpanzees (Tai chimpanzee group, Cote d'Ivoire, West Africa) are exchanged among individuals resulting in a net benefit for both participants. We adopted an inclusive view of exchanges by considering that all commodities (i.e., social behaviors as grooming, sex, support, as well as resources, such as meat) can be exchanged. This would result in “market” type social interactions in which debts of one commodity can be met by giving the same or other commodities. We investigated whether both in-kind exchanges and trades of commodities occurred. The Tai chimpanzees reciprocated the amount of grooming they received and were more likely to give support in agonistic conflicts to those who also supported them. In addition, they traded support for meat and meat for sex. Both male and female chimpanzees exchanged many different commodities, which seemed to result in long-term balanced relationships. Our results suggest that wild chimpanzees rely on other group members to obtain many of the important commodities they need.

No evidence for transmission of SIVwrc from western red colobus monkeys (piliocolobus badius badius) to wild west african chimpanzees (pan troglodytes verus) despite high exposure through hunting

BackgroundSimian Immunodeficiency Viruses (SIVs) are the precursors of Human Immunodeficiency Viruses (HIVs) which have lead to the worldwide HIV/AIDS pandemic. By studying SIVs in wild primates we can better understand the circulation of these viruses in their natural hosts and habitat, and perhaps identify factors that influence susceptibility and transmission within and between various host species. We investigated the SIV status of wild West African chimpanzees (Pan troglodytes verus) which frequently hunt and consume the western red colobus monkey (Piliocolobus badius badius), a species known to be infected to a high percentage with its specific SIV strain (SIVwrc).ResultsBlood and plasma samples from 32 wild chimpanzees were tested with INNO-LIA HIV I/II Score kit to detect cross-reactive antibodies to HIV antigens. Twenty-three of the samples were also tested for antibodies to 43 specific SIV and HIV lineages, including SIVwrc. Tissue samples from all but two chimpanzees were tested for SIV by PCRs using generic SIV primers that detect all known primate lentiviruses as well as primers designed to specifically detect SIVwrc. Seventeen of the chimpanzees showed varying degrees of cross-reactivity to the HIV specific antigens in the INNO-LIA test; however no sample had antibodies to SIV or HIV strain - and lineage specific antigens in the Luminex test. No SIV DNA was found in any of the samples.ConclusionsWe could not detect any conclusive trace of SIV infection from the red colobus monkeys in the chimpanzees, despite high exposure to this virus through frequent hunting. The results of our study raise interesting questions regarding the host-parasite relationship of SIVwrc and wild chimpanzees in their natural habitat.

Wild chimpanzees are infected with homologous types of human malaria

BackgroundDespite ongoing - and in some regions escalating -morbidity and mortality associated with malaria para-sites, evolutionary epidemiology of Plasmodium is notwell characterized. Recent studies using molecularapproaches demonstrated that wild and captive gorillasand captive bonobos and chimpanzees are infected withP. falciparum and that these apes harbor parasitesbroadly related to P. falciparum[1]. Captive chimpanzeesand bonobos had malaria parasites related to humanP. ovale and P. malariae and various monkeys and onesemi-wild chimpanzee hadP. vivax[2]. It is not clearwhether these apes harbor naturally these parasites orwhether they are transmitted from humans. Most of theexamined animals had close contact with humans, com-parable studies in wild living apes are missing. We pro-vide the first survey ofPlasmodium diversity in wildchimpanzees living in an undisturbed tropical rainforestin Africa.MethodsWe examined tissue from 16 wild West African chim-panzees that lived in the Tai National Park, Ivory Coast,where human contact with animals is limited toresearchers who access the territory only during the day.Samples were collected from animals that died primarilyfrom anthrax or respiratory disease. Generic real timePCR assay was used to detect all knownPlasmodiumspecies.Results11/16 (68%) animals tested positive. Sequence analysesof cytB and 18S rRNA genes identifiedP. malariae,P. ovale, P. vivax, P. gaboni, P. reichenowi, P. billcollinsiand P. billbraii.DiscussionPrevious examination of the role of our closest phyloge-netic relatives, the great apes, in the evolution andpersistence of human malarias has been limited by a lackof data from wild ape populations. Interpretation ofpatterns of malaria infection in captive ape populationsmust consider ample opportunities for human to apetransmission, negating the opportunity to investigate theevolutionary origins and public health-related risks ofthese parasites. Our examination of malaria parasites inwild chimpanzees demonstrates that these apes are mostlikely naturally infected with Plasmodium species homolo-gous toP. malariae, P. vivaxand P. ovale as well asP. falciparum. Whether wild great apes are the origin ofthese malaria types requires further investigation but theymay act as reservoir of infection. These results haveimportant implications for global efforts underway to era-dicate malaria in humans including vaccine developmentbased on animal variants of human parasites.

A longitudinal study of urinary dipstick parameters in wild chimpanzees (Pan troglodytes verus) in Côte d'Ivoire

We performed 796 dip-stick tests on urine from 100 wild West African chimpanzees (Pan troglodytes verus) from 4 habituated groups in the tropical rain forest of Taï National Park, Cote d'Ivoire, to establish reference values for health monitoring. Specific gravity was also measured on 359 urine samples from 62 chimpanzees. The effect of age, sex, group, month, estrus, pregnancy, meat consumption, and acute respiratory disease on pH, leucocytes, protein, blood, hemoglobin, and glucose was examined using ordinal logistic regression. The presence of nitrite, ketones, bilirubin, and urobilinogen in urine was also recorded. Outbreak of acute respiratory disease did not influence any of the urinary parameters. Thirty-seven percent of the samples had a pH <7 and the whole range of pH was found through the year, in all age groups, and in both sexes. Meat consumption lowered the urinary pH. Our results show that all pH levels must be considered normal for the West African chimpanzee subspecies P. troglodytes verus living in the rainforest. We also found a cluster of glucose-positive samples at a specific point in time which was not attributed to diabetes mellitus. These findings highlight that there are differences in normal physiological parameters among wild chimpanzees living in different habitats.

Long-term reciprocation of grooming in wild West African chimpanzees

Humans are well known for their ability to keep track of social debts over extended periods of time, and for their tendency to preferentially cooperate with closely bonded partners. Non-human primates have been shown to cooperate with kin and non-kin, and reciprocate helpful acts. However, there is ongoing debate over whether they keep track of previous interactions and, if so, whether they can do it over extended periods of time, or are constrained to finalize exchanges within a single encounter. In this study, we used 3000 hours of all-day focal follows of wild chimpanzees (Pan troglodytes verus) to investigate whether both females and males reciprocate grooming within a single interaction, throughout the day, or over longer periods of time. We found that grooming was reciprocated more symmetrically when measured on a long-term, rather than on an immediate or short-term basis. Random giving, general allocation of grooming efforts, similarities among individuals and kinship do not appear to explain these highly reciprocal exchanges. Previously collected consecutive focal follows of single individuals revealed that dyads groomed an average of once every 7 days. Our findings strongly suggest that chimpanzees, similar to humans, are able to keep track of past social interactions, at least for a one-week period, and balance services over repeated encounters.

Reproductive endocrinology of wild female Chimpanzees (Pan troglodytes schweinfurthii): methodological considerations and the role of hormones in sex and conception

Fecal and urine samples were collected from 81 female East African chimpanzees (Pan troglodytes schweinfurthii) in three major study populations in Gombe National Park, Tanzania, and Budongo Forest Reserve and Kibale National Park, Uganda. In this study I evaluated issues related to sample storage and assay reliability, and used these methods to investigate the significance of ovarian hormone levels in terms of conception success and sexual behavior. Drying of feces proved to be an effective technique and resulted in hormonal concentrations that were significantly correlated with concentrations in frozen feces. Estimates of ovarian steroid production based on urine and fecal sampling were significantly correlated with each other. The ovarian cycle profiles obtained, which were aligned relative to sexual swelling detumescence, corroborate previous findings in wild west African chimpanzees [Deschner et al., Animal Behaviour 66:551-560, 2003] in suggesting that the fertile period is limited to the last week of tumescence, but that ovulatory timing is not as precise as previously thought. A comparison across cycles confirmed the hypothesis that higher ovarian steroid levels are associated with an increased probability of conception. Females that did conceive with relatively low hormone levels had poor reproductive outcomes. Sexual behavior was tied to the probability of conception both within and across cycles. Copulatory activity within cycles closely followed the estrogen profile and was timed to coincide, on average, with the peak fertile period of females. Further, rates of copulation were significantly higher during the fertile periods of cycles that led to conception than those that did not.

Female sexual swelling size, timing of ovulation, and male behavior in wild West African chimpanzees

Conspicuous swellings of the perineal skin can be observed in females of many catharrine primate species particularly during the middle stages of the ovarian cycle. The functional significance of this trait remains poorly understood. Recently, two hypotheses, the “reliable indicator” hypothesis and the “graded signal” hypothesis that take into account not only the pattern but also the exaggerated size of sexual swellings, have gained attention. Here we test several predictions made by these hypotheses by combining (i) direct size measures (from video captures) of female sexual swellings with (ii) urinary hormone data to indicate timing of ovulation through enzyme immunoassay measurements of estrone conjugates and pregnanediol glucuronide (PdG) and (iii) behavioral observations of male mating efforts throughout 36 ovulatory cycles in 12 wild chimpanzees. We are able to show that (i) even within the traditionally defined maximum swelling period, further slight increases in swelling size indicate approaching ovulation, and (ii) that male mating interest changes according to the changes in swelling size. Furthermore, absolute swelling size during the periovulatory period increases and the alpha male associates more with females as the number of cycles to conception decreases. Finally, when having the choice between several “maximally” tumescent females, the alpha male prefers the female that is in the fertile phase of her cycle rather than that with the biggest swelling at that time. Thus, most of our findings are in line with the predictions of the graded signal hypothesis while none of them would support the reliable indicator hypothesis.

Social influences on ranging patterns among chimpanzees (Pan troglodytes verus) in the Tai National Park, Cote d'Ivoire

Group size is expected to be an important factor to predict home-range (HR) size in social animals. In chimpanzees adult males play an important role in defending the HR against neighbors, and therefore it has been suggested that HR size depends on the number of adult males. In this long-term study on wild West African chimpanzees, we analyzed the relative importance of community size and composition on ranging patterns over a 10-year period, using multivariate statistics. Because community size decreased from 51 individuals with 6 adult males in 1992 to 22 individuals with only 1 adult male in 2001, we expected a decrease in HR size, which should be better predicted by the number of males than by community size. We further investigated the effect of fruit availability on monthly HRs over a 4-year period. As predicted, HR size decreased during the first 7 years of our study but increased during the last 3 years. Overall, the number of adult males was the best predictor of HR size, whereas fruit availability did not correlate with HR size. HR use remained stable over the entire study period, with a constant proportion of about 35% of the HR used as core area. High HR and core-area overlap values between different years indicated strong site-fidelity. Although the number of males within the community explained the decrease in HR size, the recent increase in size remains unexplained. This finding suggests that other factors such as relative fighting power of males affect HR size. Copyright 2003.

Timing and probability of ovulation in relation to sex skin swelling in wild West African chimpanzees, Pan troglodytes verus

Females of many catharrine primates show a periodic and often pronounced swelling of the perineum, the functional significance of which is unclear. Several hypotheses that exist to explain the function of this conspicuous trait are based on assumptions about the temporal relation between the period of maximum swelling and ovulation, and remain largely untested. We examined this relation in free-living chimpanzees of the Taı National Park, Côte d'Ivoire, and assessed the reliability of perineal swelling as an indicator of ovulation in this species. We used noninvasive urinary progestogen analysis of female reproductive status, together with observational data on swelling characteristics, to determine the variability of timing of ovulation within the maximum swelling phase in 36 cycles from 12 females. The period of maximum swelling was highly variable, lasting from 6 to 18 days. Although ovulation was virtually restricted to the second half of the period of maximum tumescence, its timing varied considerably in relation to both the onset and the end of the maximum tumescence phase. Probability of ovulation, however, was not random, but peaked on day 7 after the onset of the maximum swelling phase, and was almost 60% between days 7 and 9. Thus, in wild chimpanzees perineal swelling indicates the probability of ovulation, but does not provide sufficient information to deduce its exact timing. Given the temporal variability of ovulation relative to the last day of maximum tumescence, field workers should try to include hormonal analysis if information on timing of ovulation is required for interpretation of observational data. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.

Female reproductive strategies, paternity and community structure in wild West African chimpanzees

Although the variability and complexity of chimpanzee behaviour frustrates generalization, it is widely believed that social evolution in this species occurs in the context of the recognizable social group or community. We used a combination of field observations and noninvasive genotyping to study the genetic structure of a habituated community of 55 wild chimpanzees,Pan troglodytes verus, in the Taı̈ Forest, Côte d’Ivoire. Pedigree relationships in that community show that female mate choice strategies are more variable than previously supposed and that the observed social groups are not the exclusive reproductive units. Genetic evidence based on nuclear microsatellite markers and behavioural obser-vations reveal that females in the Taı̈ forest actively seek mating partners outside their social unit; noncommunity males accounted for half the paternities over 5 years. This female mating strategy increases male gene flow between communities despite male philopatry, and negates the predicted higher relatedness among community males. Kin selection seems unlikely to explain the frequent cooperation and sharing observed among group males in this population. Similarly, inbreeding avoidance is probably not the sole cause of permanent adolescent female dispersal as a combination of extragroup mating and avoidance of incest with home group males would allow females to avoid inbreeding without the hazards associated with immigration into a new community. Extragroup mating as part of chimpanzee females’ reproductive strategy may allow them to choose from a wider variety and number of males, without losing the resources and support provided by their male social group partners.