Community Of Wild Chimpanzees Research Articles

Strontium isotopes track female dispersal in Taï chimpanzees.

Chimpanzees (Pan troglodytes) are patrilocal, with males remaining in their natal community and females dispersing when they reach sexual maturity. However, the details of female chimpanzee dispersal, such as their possible origin, are difficult to assess, even in habituated communities. This study investigates the utility of 87Sr/86Sr analysis for (1) assessing Sr baseline differences between chimpanzee territories and (2) identifying the status (immigrant or natal) of females of unknown origin within the territories of five neighboring communities in Taï National Park (Côte d'Ivoire). To create a local Sr isoscape for the Taï Chimpanzee Project (TCP) study area, we sampled environmental samples from TCP-established territories (n = 35). To assess dispersal patterns, 34 tooth enamel samples (one per individual) were selected from the Taï chimpanzee skeletal collection. 87Sr/86Sr analysis was performed on all 69 samples at the W.M. Keck Lab. The theoretical density and overlap of chimpanzee communities as well as generalized linear mixed models (GLMMs) were used to test each question. 87Sr/86Sr ratios for natal male chimpanzees ranged from 0.71662 to 0.72187, which is well within the corresponding environmental baseline range of 0.70774-0.73460. The local Sr isoscapes fit was estimated with the root-mean-square error value, which was 0.0048 (22% of the whole 87Sr/86Sr data range). GLMMs identified significant differences in 87Sr/86Sr ratios between natal and unknown North community origin groups, suggesting that after 1980, females of unknown origin could be immigrants to North community (n = 7, z-ratio = -4.08, p = 0.0001, power = 0.94). This study indicates that 87Sr/86This study indicates that 87Sr/86Sr analysis can successfully identify immigrant females in skeletal collections obtained from wild chimpanzee communities, enabling the tracking of female dispersal patterns historically. There are, however, significant limitations within the scope of this study, such as (1) the absence of reliable maps for the TCP study area, (2) limited capacity for environmental sampling, (3) small sample sizes, and (4) tooth formation in wild chimpanzees.

Population-specific call order in chimpanzee greeting vocal sequences

SummaryPrimates rarely learn new vocalizations, but they can learn to use their vocalizations in different contexts. Such “vocal usage learning,” particularly in vocal sequences, is a hallmark of human language, but remains understudied in non-human primates. We assess usage learning in four wild chimpanzee communities of Taï and Budongo Forests by investigating population differences in call ordering of a greeting vocal sequence. Whilst in all groups, these sequences consisted of pant-hoots (long-distance contact call) and pant-grunts (short-distance submissive call), the order of the two calls differed across populations. Taï chimpanzees consistently commenced greetings with pant-hoots, whereas Budongo chimpanzees started with pant-grunts. We discuss different hypotheses to explain this pattern and conclude that higher intra-group aggression in Budongo may have led to a local pattern of individuals signaling submission first. This highlights how within-species variation in social dynamics may lead to flexibility in call order production, possibly acquired via usage learning.

Well-digging in a community of forest-living wild East African chimpanzees (Pan troglodytes schweinfurthii)

Access to resources shapes species’ physiology and behaviour. Water is not typically considered a limiting resource for rainforest-living chimpanzees; however, several savannah and savannah-woodland communities show behavioural adaptations to limited water. Here, we provide a first report of habitual well-digging in a rainforest-living group of East African chimpanzees (Pan troglodytes schweinfurthii) and suggest that it may have been imported into the community’s behavioural repertoire by an immigrant female. We describe the presence and frequency of well-digging and related behaviour, and suggest that its subsequent spread in the group may have involved some degree of social learning. We highlight that subsurface water is a concealed resource, and that the limited spread of well-digging in the group may highlight the cognitive, rather than physical, challenges it presents in a rainforest environment.

Gregariousness is associated with parasite species richness in a community of wild chimpanzees.

Increased risk of pathogen transmission through proximity and contact is a well-documented cost of sociality. Affiliative social contact, however, is an integral part of primate group life and can benefit health. Despite its importance to the evolution and maintenance of sociality, the tradeoff between costs and benefits of social contact for group-living primate species remains poorly understood. To improve our understanding of this interplay, we used social network analysis to investigate whether contact via association in the same space and/or physical contact measured through grooming were associated with helminth parasite species richness in a community of wild chimpanzees (Pan troglodytes schweinfurthii). We identified parasite taxa in 381 fecal samples from 36 individuals from the Kasekela community of chimpanzees in Gombe National Park, Tanzania, from November 1, 2006 - October 31, 2012. Over the study period, eight environmentally transmitted helminth taxa were identified. We quantified three network metrics for association and grooming contact, including degree strength, betweenness, and closeness. Our findings suggest that more gregarious individuals - those who spent more time with more individuals in the same space - had higher parasite richness, while the connections in the grooming network were not related to parasite richness. The expected parasite richness in individuals increased by 1.13 taxa (CI: 1.04, 1.22; p = 0.02) per one standard deviation increase in degree strength of association contact. The results of this study add to the understanding of the role that different types of social contact plays in the parasite richness of group-living social primates.

The function of chimpanzee greeting calls is modulated by their acoustic variation

Signalling plays an important role in mediating social interactions in many animal species. For example, during approaches certain species produce ‘greetings’, which can take the form of vocal or visual signals, which reduce the probability of aggressive interactions and/or facilitate affiliation when approaching each other. However, in species where greetings comprise both vocal and visual signals, little is known about how the vocal component relates to the visual component or, in species with fission–fusion dynamics, to the time spent together by the dyad in the same subgroup prior to the approach. Similarly, in species with several acoustic variants of greeting calls, it is unclear whether different variants have different functions. We looked at the production of two acoustically distinct greeting call variants, low-fundamental frequency pant grunts and high-fundamental frequency pant barks, during approaches between two individuals in five communities of wild chimpanzees, Pan troglodytes, in Uganda and Ivory Coast. More specifically, we explored the relationship between greeting call production and (1) aggressive and submissive interactions during the approach and (2) preceding and subsequent proximity levels between the involved individuals. Calls were more likely to be produced during aggressive interactions and were associated with postures and gestures linked to submission; these patterns were stronger when the utterance contained a pant bark rather than a pant grunt alone. The production of greeting calls was more likely soon after party fusion and was negatively related to subsequent proximity levels between the caller and receiver. These results expand our knowledge of greeting calls and imply that these calls might be used to re-establish dominance relationships after a period of separation, and that the function of these calls can be modulated by their specific acoustic variants and by visual signals that often accompany them.

Social Network Predicts Exposure to Respiratory Infection in a Wild Chimpanzee Group.

Respiratory pathogens are expected to spread through social contacts, but outbreaks often occur quickly and unpredictably, making it challenging to simultaneously record social contact and disease incidence data, especially in wildlife. Thus, the role of social contacts in the spread of infectious disease is often treated as an assumption in disease simulation studies, and few studies have empirically demonstrated how pathogens spread through social networks. In July–August 2015, an outbreak of respiratory disease was observed in a wild chimpanzee community in Kibale National Park, Uganda, during an ongoing behavioral study of male chimpanzees, offering a rare opportunity to evaluate how social behavior affects individual exposure to socially transmissible diseases. From May to August 2015, we identified adult and adolescent male chimpanzees displaying coughs and rhinorrhea and recorded 5-m proximity data on males (N = 40). Using the network k-test, we found significant relationships between male network connectivity and the distribution of cases within the network, supporting the importance of short-distance contacts for the spread of the respiratory outbreak. Additionally, chimpanzees central to the network were more likely to display clinical signs than those with fewer connections. Although our analyses were limited to male chimpanzees, these findings underscore the value of social connectivity data in predicting disease outcomes and elucidate a potential evolutionary cost of being social.Supplementary informationThe online version of this article (10.1007/s10393-020-01507-7) contains supplementary material, which is available to authorized users.

The Kibale Chimpanzee Project: Over thirty years of research, conservation, and change

Long-term primate field research programs contribute to the protection of endangered primate species and their vanishing habitats by informing and fostering local and international conservation programs. The Kibale Chimpanzee Project (KCP) has studied the Kanyawara community of wild chimpanzees continuously since 1987, investigating a wide range of behavioral, ecological, and physiological questions. The study area includes the northwest boundary of Kibale National Park, Uganda, and has experienced habitat change driven by multiple causes, including forest regeneration, an increasingly warmer and wetter climate, and impacts from the neighboring human population. Here, we review the history of research on Kanyawara chimpanzees and examine how their demography, diet, and social behavior have changed over the last 30+ years. While Kanyawara chimpanzees were protected from the major threats of poaching and habitat loss, respiratory diseases of human origin were a major source of mortality. Many individuals were also injured by wire hunting snares. Nevertheless, the study community has grown modestly in size, individuals have become increasingly gregarious, and birth rates have increased. These results are likely attributable to improved habitat productivity that can be traced to decades-long efforts by wildlife authorities and the associated research and conservation programs in Kibale. Overall, research has contributed both to understanding interactions among nutritional ecology, social behavior, physiology, and health of an endangered species, and also to conservation activities in the Kibale community through direct interventions, positive economic impacts, and conservation education programs.

Environmental variability supports chimpanzee behavioural diversity

Large brains and behavioural innovation are positively correlated, species-specific traits, associated with the behavioural flexibility animals need for adapting to seasonal and unpredictable habitats. Similar ecological challenges would have been important drivers throughout human evolution. However, studies examining the influence of environmental variability on within-species behavioural diversity are lacking despite the critical assumption that population diversification precedes genetic divergence and speciation. Here, using a dataset of 144 wild chimpanzee (Pan troglodytes) communities, we show that chimpanzees exhibit greater behavioural diversity in environments with more variability — in both recent and historical timescales. Notably, distance from Pleistocene forest refugia is associated with the presence of a larger number of behavioural traits, including both tool and non-tool use behaviours. Since more than half of the behaviours investigated are also likely to be cultural, we suggest that environmental variability was a critical evolutionary force promoting the behavioural, as well as cultural diversification of great apes.

Maternal cannibalism in two populations of wild chimpanzees

Maternal cannibalism has been reported in several animal taxa, prompting speculations that the behavior may be part of an evolved strategy. In chimpanzees, however, maternal cannibalism has been conspicuously absent, despite high levels of infant mortality and reports of non-maternal cannibalism. The typical response of chimpanzee mothers is to abandon their deceased infant, sometimes after prolonged periods of carrying and grooming the corpse. Here, we report two anomalous observations of maternal cannibalism in communities of wild chimpanzees in Uganda and Ivory Coast and discuss the evolutionary implications. Both infants likely died under different circumstances; one apparently as a result of premature birth, the other possibly as a result of infanticide. In both cases, the mothers consumed parts of the corpse and participated in meat sharing with other group members. Neither female presented any apparent signs of ill health before or after the events. We concluded that, in both cases, cannibalizing the infant was unlikely due to health-related issues by the mothers. We discuss these observations against a background of chimpanzee mothers consistently refraining from maternal cannibalism, despite ample opportunities and nutritional advantages. We conclude that maternal cannibalism is extremely rare in this primate, likely due to early and strong mother–offspring bond formation, which may have been profoundly disrupted in the current cases.

Tropical rainforest flies carrying pathogens form stable associations with social nonhuman primates.

Living in groups provides benefits but also incurs costs such as attracting disease vectors. For example, synanthropic flies associate with human settlements, and higher fly densities increase pathogen transmission. We investigated whether such associations also exist in highly mobile nonhuman primate (NHP) Groups. We studied flies in a group of wild sooty mangabeys (Cercocebus atys atys) and three communities of wild chimpanzees (Pan troglodytes verus) in Taï National Park, Côte d'Ivoire. We observed markedly higher fly densities within both mangabey and chimpanzee groups. Using a mark-recapture experiment, we showed that flies stayed with the sooty mangabey group for up to 12days and for up to 1.3km. We also tested mangabey-associated flies for pathogens infecting mangabeys in this ecosystem, Bacillus cereus biovar anthracis (Bcbva), causing sylvatic anthrax, and Treponema pallidum pertenue, causing yaws. Flies contained treponemal (6/103) and Bcbva (7/103) DNA. We cultured Bcbva from all PCR-positive flies, confirming bacterial viability and suggesting that this bacterium might be transmitted and disseminated by flies. Whole genome sequences of Bcbva isolates revealed a diversity of Bcbva, probably derived from several sources. We conclude that flies actively track mangabeys and carry infectious bacterial pathogens; these associations represent an understudied cost of sociality and potentially expose many social animals to a diversity of pathogens.

Risk factors for respiratory illness in a community of wild chimpanzees (Pan troglodytes schweinfurthii).

Respiratory illnesses have caused significant mortality in African great ape populations. While much effort has been given to identifying the responsible pathogens, little is known about the factors that influence disease transmission or individual susceptibility. In the Kanyawara community of wild chimpanzees, respiratory illness has been the leading cause of mortality over 31 years, contributing to 27% of deaths. Deaths were common in all age groups except juveniles. Over 22 years of health observations, respiratory signs were rare among infants and most common among older adults of both sexes. Respiratory signs were also common among males during the transition to adulthood (ages 10–20 years), particularly among those of low rank. Respiratory signs peaked conspicuously in March, a pattern that we could not explain after modelling climatic factors, group sizes, diet or exposure to humans. Furthermore, rates of respiratory illness in the chimpanzees did not track seasonal rates of illness in the nearby village. Our data indicate that the epidemiology of chimpanzee respiratory illness warrants more investigation but clearly differs in important ways from humans. Findings on individual susceptibility patterns suggest that respiratory signs are a robust indicator for investigating immunocompetence in wild chimpanzees.

Evidence for Human Streptococcus pneumoniae in wild and captive chimpanzees: A potential threat to wild populations

Habituation of wild great apes for tourism and research has had a significant positive effect on the conservation of these species. However, risks associated with such activities have been identified, specifically the transmission of human respiratory viruses to wild great apes, causing high morbidity and, occasionally, mortality. Here, we investigate the source of bacterial-viral co-infections in wild and captive chimpanzee communities in the course of several respiratory disease outbreaks. Molecular analyses showed that human respiratory syncytial viruses (HRSV) and human metapneumoviruses (HMPV) were involved in the etiology of the disease. In addition our analysis provide evidence for coinfection with Streptococcus (S.) pneumoniae. Characterisation of isolates from wild chimpanzees point towards a human origin of these bacteria. Transmission of these bacteria is of concern because – in contrast to HRSV and HMPV - S. pneumoniae can become part of the nasopharyngeal flora, contributing to the severity of respiratory disease progression. Furthermore these bacteria have the potential to spread to other individuals in the community and ultimately into the population. Targeted vaccination programs could be used to vaccinate habituated great apes but also human populations around great ape habitats, bringing health benefits to both humans and wild great apes.

Travel fosters tool use in wild chimpanzees.

Ecological variation influences the appearance and maintenance of tool use in animals, either due to necessity or opportunity, but little is known about the relative importance of these two factors. Here, we combined long-term behavioural data on feeding and travelling with six years of field experiments in a wild chimpanzee community. In the experiments, subjects engaged with natural logs, which contained energetically valuable honey that was only accessible through tool use. Engagement with the experiment was highest after periods of low fruit availability involving more travel between food patches, while instances of actual tool-using were significantly influenced by prior travel effort only. Additionally, combining data from the main chimpanzee study communities across Africa supported this result, insofar as groups with larger travel efforts had larger tool repertoires. Travel thus appears to foster tool use in wild chimpanzees and may also have been a driving force in early hominin technological evolution.

Socioecological correlates of clinical signs in two communities of wild chimpanzees (Pan troglodytes) at Gombe National Park, Tanzania.

Disease and other health hazards pose serious threats to the persistence of wild ape populations. The total chimpanzee population at Gombe National Park, Tanzania, has declined from an estimated 120 to 150 individuals in the 1960's to around 100 individuals by the end of 2013, with death associated with observable signs of disease as the leading cause of mortality. In 2004, we began a non-invasive health-monitoring program in the two habituated communities in the park (Kasekela and Mitumba) with the aim of understanding the prevalence of health issues in the population, and identifying the presence and impacts of various pathogens. Here we present prospectively collected data on clinical signs (observable changes in health) in the chimpanzees of the Kasekela (n = 81) and Mitumba (n = 32) communities over an 8-year period (2005-2012). First, we take a population approach and analyze prevalence of clinical signs in five different categories: gastrointestinal system (diarrhea), body condition (estimated weight loss), respiratory system (coughing, sneezing etc.), wounds/lameness, and dermatologic issues by year, month, and community membership. Mean monthly prevalence of each clinical sign per community varied, but typically affected <10% of observed individuals. Secondly, we analyze the presence of clinical signs in these categories as they relate to individual demographic and social factors (age, sex, and dominance rank) and simian immunodeficiency virus (SIVcpz) infection status. Adults have higher odds of being observed with diarrhea, loss of body condition, and wounds or lameness when compared to immatures, while males have a higher probability of being observed with wounds or lameness than females. In contrast, signs of respiratory illness appear not to be related to chimpanzee-specific factors and skin abnormalities are very rare. For a subset of known-rank individuals, dominance rank predicts the probability of wounding/lameness in adult males, but does not predict any adverse clinical signs in adult females. Instead, adult females with SIVcpz infection are more likely to be observed with diarrhea, a finding that warrants further investigation. Comparable data are needed from other sites to determine whether the prevalence of clinical signs we observe are relatively high or low, as well as to more fully understand the factors influencing health of wild apes at both the population and individual level. Am. J. Primatol. 80:e22562, 2018. © 2016 Wiley Periodicals, Inc.

Chimpanzee non-avoidance of hyper-proximity to humans

A species, especially when it is endangered and surrounded by anthropogenic elements, can be threatened by habitat fragmentation. Food resource availability in the species’ usual or surrogate habitats may reinforce or decrease its use of certain areas. Our objective was to to determine the influence of natural and anthropogenic variables on spatial distribution of eastern chimpanzees (Pan troglodytes schweinfurthii). We first determined the home range of a wild chimpanzee community (hereafter Sebitoli Chimpanzee Community [SCC]) based on global positioning system (GPS) point locations (n¼2,586 direct observations and feces locations) collected between 2009 and 2013 in Sebitoli, Kibale National Park, Uganda. We described SCC home range using grid cells (2,959 cells of 100m100m) referencing environmental, spatial, and topographical variables (n¼15). We then determined diet and food species abundance within their territory (n¼63 vegetation plots and 18 months phenological survey) and predicted distribution of the 10 most foraged fruit species within SCC home range, using environmental, spatial, and topographical variables (n¼10) by applying a maximum entropy model (maxent). We then predicted chimpanzee presence as a function of environmental, spatial, and topographical variables (n¼15) using the maxent model and assessed its truthfulness with the kernel model, based only on GPS point locations. Chimpanzees in Sebitoli were mostly observed in a core area of 5.42 km2 within the 25-km2 home range. They did not avoid forest edges in contact with human populations, especially males who used larger core areas than females. Factors with the greatest positive impact on the chimpanzee distribution model (maxent area under the curve [AUC]¼0.907) were related to 3 different food resources: 1) proximity to forest edges considered as attractive because of presence of crops cultivated by local farmers; 2) proximity to a tarmac road that crosses the SCC home range with shoulders covered by attractive terrestrial herbaceous vegetation; and 3) presence of wild forest fruiting resources. The results obtained with the maxent predictive model, applied on a fine scale, were consistent with the kernel model, based on real observations. Therefore, such an approach may be recommended for surveys or action plans interested in sustainable management of wildlife in an anthropogenic environment and may be a useful tool to better understand parameters of a prefered zone for an endangered species.

Should I stay or should I go? Initiation of joint travel in mother-infant dyads of two chimpanzee communities in the wild.

It is well established that great apes communicate via intentionally produced, elaborate and flexible gestural means. Yet relatively little is known about the most fundamental steps into this communicative endeavour—communicative exchanges of mother–infant dyads and gestural acquisition; perhaps because the majority of studies concerned captive groups and single communities in the wild only. Here, we report the first systematic, quantitative comparison of communicative interactions of mother–infant dyads in two communities of wild chimpanzees by focusing on a single communicative function: initiation of carries for joint travel. Over 156 days of observation, we recorded 442 actions, 599 cases of intentional gesture production, 51 multi-modal combinations and 80 vocalisations in the Kanyawara community, Kibale National Park, Uganda, and the Taï South community, Taï National Park, Côte d’Ivoire. Our results showed that (1) mothers and infants differed concerning the signal frequency and modality employed to initiate joint travel, (2) concordance rates of mothers’ gestural production were relatively low within but also between communities, (3) infant communicative development is characterised by a shift from mainly vocal to gestural means, and (4) chimpanzee mothers adjusted their signals to the communicative level of their infants. Since neither genetic channelling nor ontogenetic ritualization explains our results satisfactorily, we propose a revised theory of gestural acquisition, social negotiation, in which gestures are the output of social shaping, shared understanding and mutual construction in real time by both interactants.Electronic supplementary materialThe online version of this article (doi:10.1007/s10071-015-0948-z) contains supplementary material, which is available to authorized users.

'Impact hunters' catalyse cooperative hunting in two wild chimpanzee communities.

Even when hunting in groups is mutually beneficial, it is unclear how communal hunts are initiated. If it is costly to be the only hunter, individuals should be reluctant to hunt unless others already are. We used 70 years of data from three communities to examine how male chimpanzees 'solve' this apparent collective action problem. The 'impact hunter' hypothesis proposes that group hunts are sometimes catalysed by certain individuals that hunt more readily than others. In two communities (Kasekela and Kanyawara), we identified a total of five males that exhibited high hunt participation rates for their age, and whose presence at an encounter with red colobus monkeys increased group hunting probability. Critically, these impact hunters were observed to hunt first more often than expected by chance. We argue that by hunting first, these males dilute prey defences and create opportunities for previously reluctant participants. This by-product mutualism can explain variation in group hunting rates within and between social groups. Hunting rates declined after the death of impact hunter FG in Kasekela and after impact hunter MS stopped hunting frequently in Kanyawara. There were no impact hunters in the third, smaller community (Mitumba), where, unlike the others, hunting probability increased with the number of females present at an encounter with prey.

A cautionary note on fecal sampling and molecular epidemiology in predatory wild great apes.

Fecal samples are an important source of information on parasites (viruses, prokaryotes, or eukaryotes) infecting wild great apes. Molecular analysis of fecal samples has already been used for deciphering the origins of major human pathogens such as HIV-1 or Plasmodium falciparum. However, for apes that hunt (chimpanzees and bonobos), detection of parasite nucleic acids may reflect either true infection of the host of interest or ingestion of an infected prey, for example, another non-human primate. To determine the potential magnitude of this issue, we estimated the prevalence of prey DNA in fecal samples obtained from two wild chimpanzee communities. We observed values >15%, which are higher than or close to the fecal detection rates of many great ape parasites. Contamination of fecal samples with parasite DNA from dietary origin may therefore occasionally impact non-invasive epidemiological studies. This problem can be addressed (at least partially) by monitoring the presence of prey DNA.

Chimps, Humans, and the Hominid Struggle against Viruses.

Chimps, Humans, and the Hominid Struggle against Viruses.

Signature Patterns of MHC Diversity in Three Gombe Communities of Wild Chimpanzees Reflect Fitness in Reproduction and Immune Defense against SIVcpz.

Major histocompatibility complex (MHC) class I molecules determine immune responses to viral infections. These polymorphic cell-surface glycoproteins bind peptide antigens, forming ligands for cytotoxic T and natural killer cell receptors. Under pressure from rapidly evolving viruses, hominoid MHC class I molecules also evolve rapidly, becoming diverse and species-specific. Little is known of the impact of infectious disease epidemics on MHC class I variant distributions in human populations, a context in which the chimpanzee is the superior animal model. Population dynamics of the chimpanzees inhabiting Gombe National Park, Tanzania have been studied for over 50 years. This population is infected with SIVcpz, the precursor of human HIV-1. Because HLA-B is the most polymorphic human MHC class I molecule and correlates strongly with HIV-1 progression, we determined sequences for its ortholog, Patr-B, in 125 Gombe chimpanzees. Eleven Patr-B variants were defined, as were their frequencies in Gombe’s three communities, changes in frequency with time, and effect of SIVcpz infection. The growing populations of the northern and central communities, where SIVcpz is less prevalent, have stable distributions comprising a majority of low-frequency Patr-B variants and a few high-frequency variants. Driving the latter to high frequency has been the fecundity of immigrants to the northern community, whereas in the central community, it has been the fecundity of socially dominant individuals. In the declining population of the southern community, where greater SIVcpz prevalence is associated with mortality and emigration, Patr-B variant distributions have been changing. Enriched in this community are Patr-B variants that engage with natural killer cell receptors. Elevated among SIVcpz-infected chimpanzees, the Patr-B*06:03 variant has striking structural and functional similarities to HLA-B*57, the human allotype most strongly associated with delayed HIV-1 progression. Like HLA-B*57, Patr-B*06:03 correlates with reduced viral load, as assessed by detection of SIVcpz RNA in feces.