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Objectives: This study examines the sensitivity of the development of the dorsal metacarpal ridge (DMR) to the frequency of knuckle‐walking during ontogeny in chimpanzees, and compares the prevalence and prominence of the DMR in hominoids and baboons. Materials and Methods: We characterized the type and frequency of quadrupedalism of wild chimpanzees of different ages from the Ngogo community, Uganda. Using museum specimens, we quantified third metacarpal DMR angle and height in Pan individuals of different developmental stages, and in adult Gorilla, Pongo, Hylobates, and Papio. Results: When terrestrial, all quadrupedalism consisted of knuckle‐walking, although older individuals knuckle‐walked more than younger. The total amount of quadrupedalism engaged in by different age groups while arboreal was consistent; however, knuckle usage while arboreally quadrupedal increased with age. The DMR ridge did not emerge in Pan until older infancy, after the onset of knuckle‐walking, and reached prominence by the juvenile stage. The DMR angle increased significantly after juvenility but relative height did not. Adult Pan and Gorilla have more prevalent and prominent DMRs than Papio; the DMR was rare in Pongo and absent in Hylobates. Discussion: The timing of development of the DMR in chimpanzees supports it as a knuckle walking character, as does its occurrence in gorillas, and virtual absence in suspensory orangutans and gibbons. The DMR in baboons differs in appearance and frequency from DMRs in African apes, and so differentiates knuckle‐walking from digitigrady in catarrhines. The relationship between the DMR and loading of a vertical hand while terrestrial deserves further study. [ABSTRACT FROM AUTHOR]

Viral infection is a major cause of ill health in wild chimpanzees (Pan troglodytes), but most evidence to date has come from conspicuous disease outbreaks with high morbidity and mortality. To examine the relationship between viral infection and ill health during periods not associated with disease outbreaks, we conducted a longitudinal study of wild eastern chimpanzees (P. t. schweinfurthii) in the Kanyawara and Ngogo communities of Kibale National Park, Uganda. We collected standardized, observational health data for 4 years and then used metagenomics to characterize gastrointestinal viromes (i.e., all viruses recovered from fecal samples) in individual chimpanzees before and during episodes of clinical disease. We restricted our analyses to viruses thought to infect mammals or primarily associated with mammals, discarding viruses associated with nonmammalian hosts. We found 18 viruses (nine of which were previously identified in this population) from at least five viral families. Viral richness (number of viruses per sample) did not vary by health status. By contrast, total viral load (normalized proportion of sequences mapping to viruses) was significantly higher in ill individuals compared with healthy individuals. Furthermore, when ill, Kanyawara chimpanzees exhibited higher viral loads than Ngogo chimpanzees, and males, but not females, exhibited higher infection rates with certain viruses and higher total viral loads as they aged. Post‐hoc analyses, including the use of a machine‐learning classification method, indicated that one virus, salivirus (Picornaviridae), was the main contributor to health‐related and community‐level variation in viral loads. Another virus, chimpanzee stool‐associated virus (chisavirus; unclassified Picornavirales), was associated with ill health at Ngogo but not at Kanyawara. Chisavirus, chimpanzee adenovirus (Adenoviridae), and bufavirus (Parvoviridae) were also associated with increased age in males. Associations with sex and age are consistent with the hypothesis that nonlethal viral infections cumulatively reflect or contribute to senescence in long‐lived species such as chimpanzees. Research Highlights: Some viruses of wild primates are relatively benign but may be useful as biomarkers of physiology and health.We used metagenomic methods to characterize viral communities in feces of wild chimpanzees in two long‐term study communities (Kanyawara and Ngogo) in Kibale National Park, Uganda.Chimpanzees exhibited higher viral loads (normalized abundances of viral genetic sequences) when they were ill than when those same individuals were previously healthy.When ill, Kanyawara chimpanzees exhibited higher viral loads than Ngogo chimpanzees, and males, but not females, exhibited higher viral loads as they aged. [ABSTRACT FROM AUTHOR]

I have spent over 40 years studying the behavior of our closest living relatives, the apes. In this paper, I review my research on the spacing, mating, and vocal behavior of gibbons and orangutans (Pongo pygmaeus) and the vocal and social behavior of chimpanzees (Pan troglodytes). I devote special attention to results derived from a 25‐year‐long study of a remarkable and extraordinarily large group of chimpanzees that has recently fissioned at Ngogo in Kibale National Park, Uganda. I conclude with some advice for the next generation of field primatologists. Research Highlights: I review the results of my field research on gibbons, orangutans, and chimpanzees.My findings provide insights into the spacing, mating, and vocal behavior of gibbons and orangutans and the vocal and social behavior of chimpanzees. [ABSTRACT FROM AUTHOR]

Controversy exists regarding the nature of primate social relationships. While individual primates are frequently hypothesized to form enduring social bonds with conspecifics, recent studies suggest that relationships are labile, with animals interacting only over short periods to satisfy their immediate needs. Here I use data collected over 10 years on a community of chimpanzees, Pan troglodytes, at Ngogo, Kibale National Park, Uganda, to investigate whether male chimpanzees establish long-term social relationships and to determine the factors that affect variation in relationship quality and the stability of social bonds. Kinship and dominance rank influenced the quality of relationships. Maternal brothers and males of the same dominance rank class groomed each other more equitably than did unrelated males and males that were dissimilar in rank. In addition, males that formed strong social bonds groomed more equitably than did males that displayed weaker bonds. Social bonds were stable over time, with relationships in one year predicting those in subsequent years. Kinship and the quality of social relationships affected bond stability. Maternal half siblings and males that groomed each other equitably maintained longer-lasting bonds than did nonkin and males that groomed each other unevenly. Virtually all of the males established at least one enduring relationship with another individual. The most enduring bonds formed between a few pairs of maternal brothers and dyads that maintained balanced grooming interactions. These results indicate that male chimpanzees maintain long-lasting and equitable social bonds whose formation is affected by maternal kinship and the quality of social relationships. [Copyright &y& Elsevier]

The complex cooperative behavior exhibited by wild chimpanzees generates considerable theoretical and empirical interest, yet we know very little about the mechanisms responsible for its evolution. Here, we investigate the influence of kinship on the cooperative behavior of male chimpanzees living in an unusually large community at Ngogo in Kibale National Park, Uganda. Using long-term field observations and molecular genetic techniques to identify kin relations between individuals, we show that male chimpanzees clearly prefer to affiliate and cooperate with their maternal brothers in several behavioral contexts. Despite these results, additional analyses reveal that the impact of kinship is limited; paternal brothers do not selectively affiliate and cooperate, probably because they cannot be reliably recognized, and the majority of highly affiliative and cooperative dyads are actually unrelated or distantly related. These findings add to a growing body of research that indicates that animals cooperate with each other to obtain both direct and indirect fitness benefits and that complex cooperation can occur between kin and nonkin alike. [ABSTRACT FROM AUTHOR]

Territorial boundary patrols are a distinctive and unique aspect of wild chimpanzee, Pan troglodytes, behaviour. Although patrolling has been frequently observed in nature and several proposed functional explanations for it exist, scant information is available regarding the proximate factors that affect this activity. We found that there is considerable temporal variation in the frequency of patrolling by chimpanzees at Ngogo, Kibale National Park, Uganda. We examined several ecological and social factors that potentially influence this variation. Results of logistic regression analyses revealed that male party size was the single best predictor of the tendency to patrol. Lethal intergroup aggression occurs in chimpanzees, and patrols are likely to be dangerous and costly. Our findings are consistent with the hypothesis that chimpanzees at Ngogo reduce these costs by patrolling together in large parties. [Copyright &y& Elsevier]

Strong social bonds typically develop between dyadic pairs of male chimpanzees. These bonds are manifest in several contexts, including association, grooming, and proximity. Here we demonstrate that social bonds exist at a higher level of organization among males living in an extremely large community at Ngogo, Kibale National Park, Uganda. An analysis of over 2,500 hours of observation of 35 individuals revealed two distinct subgroups of male chimpanzees. Males that composed each subgroup can be identified on the basis of their tendency to associate in temporary parties. Matrix permutation tests indicated that subgroup members tended to maintain spatial proximity to each other and participate together in territorial boundary patrols. Subgroups formed along the lines of age and rank; members of a small subgroup were younger and lower ranking than individuals in a larger subgroup. Despite this social clustering of males, community integrity remained intact with low levels of aggression between individuals of different subgroups. After controlling for the effect of association, significantly more aggression occurred within compared to between subgroups. In addition, males of the different subgroups displayed significant overlap in their use of the community territory and thus showed no tendency to divide spatially. We compare our findings with those from other animal species and chimpanzee populations and discuss them in the context of the unusual demography of the Ngogo community. [ABSTRACT FROM AUTHOR]

Male chimpanzees, Pan troglodytes, are well known for affiliating and cooperating in a variety of behavioural contexts. Prior field research indicates that maternal kinship does not affect patterns of affiliation and cooperation by males in the same social group. Two questions remain unclear from this finding. First, why do male chimpanzees not bias their behaviour towards maternal kin? Second, what factors account for who affiliates and cooperates with whom? We conducted behavioural observations of an unusually large community of chimpanzees at Ngogo, Kibale National Park, Uganda, to test the hypothesis that demographic constraints limit the number of maternal kin with whom male chimpanzees can cooperate, and thereby lead them to form selective bonds with nonkin of similar age and status. Results indicated that male age and rank are significantly associated with four measures of social behaviour. Members of the same age class and individuals close in rank were more likely to affiliate and cooperate than males that belonged to different age and rank classes. Additional analyses replicate earlier findings and show that males who affiliated and cooperated were not closely related through the maternal line, as assayed by mtDNA haplotype sharing. These results add to our growing understanding of the important role demographic and social constraints play in animal behaviour. [Copyright &y& Elsevier]

Chimpanzees (Pan troglodytes ) prey on a variety of vertebrates, mostly on red colobus (Procolobus spp. ) where the two species are sympatric. Variation across population occurs in hunting frequency and success, in whether hunting is cooperative, i.e., payoffs to individual hunters increase with group size, and in the extent to which hunters coordinate their actions in space and time, and in the impact of hunting on red colobus populations. Also, hunting frequency varies over time within populations, for reasons that are unclear. We present new data on hunting by chimpanzees at Ngogo, Kibale National Park, Uganda, and combine them with earlier data (Mitani and Watts, 1999, Am. J. Phys. Anthropol. 109: 439–454) to examine hunting frequency and success, seasonality, and cooperation. The Ngogo community is the largest and has the most males of any known community. Chimpanzees there mostly hunt red colobus and are much more successful and make many more kills per hunt than at other sites; they kill 6–12% of the red colobus population annually. The number of kills and the offtake of meat per hunt increase with the number of hunters, but per capita meat intake is independent of hunting party size; this suggests that cheating occurs in large parties. Some behavioral cooperation occurs. Hunting success and estimated meat intake vary greatly among males, partly due to dominance rank effects. The high overall success rate leads to relatively high average per capita meat intake despite the large number of consumers. The frequency of hunts and of hunting patrols varies positively with the availability of ripe fruit; this is the first quantitative demonstration of a relationship between hunting frequency and the availability of other food, and implies that the chimpanzees hunt most when they can easily meet energy needs from other sources. We provide the first quantitative support for the argument that variation in canopy structure influences decisions to hunt red colobus because hunts are easier where the canopy is broken. [ABSTRACT FROM AUTHOR]

Investigates the factors that influence chimpanzee hunting decisions and meat sharing. Compensation for seasonal shortages in food availability; Use of meat as a social tool to develop and maintain alliances with other males; Use of meat in exchange for matings; Frequency of hunting.

Chimpanzees are among the few mammals that engage in lethal coalitionary aggression between groups. Most attacks on neighbors occur when parties made up mostly of adult males patrol boundaries of their community's range. Patrols have time, energy, and opportunity costs, and entail some risks despite the tendency of males to attack only when they greatly outnumber their targets. These factors may lead to a collective action problem. Potential benefits include protection of community members, particularly infants; range expansion and increases in the amount and quality of food available; and incorporation of more females into the community. Males may not share these equally; for example, those able to obtain large shares of matings may stand to gain most by participating in patrols and to lose most by refraining. Despite the attention that boundary patrolling has attracted, few relevant quantitative data are available. Here, we present detailed data on boundary patrolling and intergroup aggression in a chimpanzee community at Ngogo, Kibale National Park, Uganda, that is unusually large and has more males than any other known community. Males there patrolled much more often, and patrol parties were much larger on average, than at two other sites for which comparative data exist. Our findings support the argument that male participation varies along with variation in potential gains, in willingness to take risks, and in skill at handling these risks. Both the overall frequency with which individual males patrolled and their willingness to join patrols as others set off on them were positively associated with variation in mating success, in participation in hunts of red colobus monkeys, and in hunting success. Males patrolled relatively often with others with whom they associated often in general, with whom they often groomed, and with whom they formed coalitions in withincommunity agonism. This indicates that they were most willing to take risks associated with patrolling when with others they trusted to take the same risks. [ABSTRACT FROM AUTHOR]

Few data exist regarding long-term changes in primate populations in old-growth, tropical forests. In the absence of this information, it is unclear how to assess population trends efficiently and economically. We addressed these problems by conducting line-transect censuses 23.5 years apart at the Ngogo study area in Kibale National Park, Uganda. We conducted additional censuses over short time intervals to determine the degree to which the temporal distribution of censuses affected estimates of primate numbers. Results indicate that two species, blue monkeys and red colobus, may have experienced significant reductions over the past 23.5 years at Ngogo. In contrast, five other species, baboons, black-and-white colobus, chimpanzees, mangabeys, and red-tailed guenons, have not changed in relative abundance. Additional findings indicate that different observers may vary significantly in their estimates of sighting distances of animals during censuses, thus rendering the use of measures of absolute densities problematic. Moreover, censuses conducted over short periods produce biased estimates of primate numbers. These results provide guidelines for the use of line-transect censuses and underscore the importance of protecting large blocks of forests for primate conservation. [ABSTRACT FROM AUTHOR]

Tests the hypothesis that matrilineal genetic relatedness affects patterns of male social affiliation and cooperation in an unusually large community of chimpanzees at the Ngogo study site at the Kibale National Park in Uganda. Behavioral observations; Neighbor-joining trees of affiliation between adult male chimpanzees.

Presents information on a study which investigated the demographic effects on the hunting behavior of a community of wild chimpanzees at Ngogo in the Kibale National Park, Uganda. Methods; Results; Discussion and comparisons with other studies.

Wild chimpanzees form temporary parties that vary in size and composition. Previous studies have revealed considerable intraspecific variation in party compositions. We examined patterns of association among age, sex, and reproductive classes of chimpanzees at Ngogo in the Kibale National Park, Uganda. We employed a class-based association index and a randomization procedure to control for confounding factors and to test for differences between classes. Results indicate that males associated with other males significantly more than expected if all classes behaved equivalently, while females generally associated with individuals of the same sex less than expected. To interpret these patterns we used two additional indices that separate associations into two components: general gregariousness and preference for particular classes of associates. Males and estrous females were more gregarious than other classes, while anestrous females were less so. After controlling for general gregariousness, adult males as a class showed no specific preference for associating with each other. Anestrous females preferred each other as party members, and estrous females avoided each other. These results are consistent with previous findings that adult males are more gregarious than females. They diverge from the standard picture of chimpanzee society, however, by suggesting a mutual affinity among anestrous females, but not among adult males as a class. [ABSTRACT FROM AUTHOR]

Primate social groups frequently contain multiple males. Male group size has been hypothesized to result from male mating competition, but the selective factors responsible for the evolution of multimale groups are unclear. Short breeding seasons create situations that are not conducive for single males to monopolize mating access to females, and may therefore favor the formation of large male groups. Alternately, since the costs of mate defense increase with the spatial clumping of females, female group size may be a primary determinant of the number of males in a primate group. We used comparative methods designed to control for the potentially confounding effects of hidden third variables associated with phylogeny to test the breeding season and female group size hypotheses for the evolution of multimale groups. Our results revealed no association between breeding season duration and the number of males in groups. In contrast, we provide support for the female group size hypothesis by demonstrating a strong pattern of correlated evolution between female and male group size. [ABSTRACT FROM AUTHOR]

Chimpanzees emit a loud, species-typical long distance call known as the pant hoot. Geographic variation between the pant hoots of chimpanzees living in two neighboring populations, the Mahale Mountains and Gombe Stream National Parks, Tanzania, was examined. Analysis of six acoustic features revealed subtle differences in the way chimpanzees from the two populations called. Individuals from the Mahale study site uttered one section of their pant hoots at a faster rate and with shorter elements than animals from Gombe Stream. In addition, individuals at Mahale delivered broader-band, higher pitched "climax" elements than males from Gombe. While genetic factors, anatomical differences, variations in the use of calls at the two sites, and changes in calling over time may account for the variability between populations, we suggest the additional possibility that differences in pant hooting may be due to learning. [ABSTRACT FROM AUTHOR]

Acoustic analyses and field playback experiments were conducted to investigate interspecific song differences and discrimination in male gibbons. Songs were recorded and analyzed from males of three populations: agile gibbons (Hylobates agilis) in West Kalimantan and South Sumatra and Müller's gibbons (Hylobates muelleri) in East Kalimantan. Male songs from each of the three populations were played back to West Kalimantan agile gibbons. Acoustic analyses indicated that the songs of the two Species differed in spectral features and in the temporal patterning of syllables. Agile gibbon songs from the West Kalimantan and South Sumatran populations varied in song durations and in the maximum frequencies of one song element. Field playbacks showed that West Katimantan agile gibbons respond in a similar manner to local songs and to conspecific songs from South Sumatra. In contrast, the animals responded differentially to conspecific and heterospecific Müller's gibbon songs. These results indicate that gibbons discriminate specific differences in songs, and support the division of agile and Müller's gibbons into distinct species. [ABSTRACT FROM AUTHOR]

Investigates the factors that facilitate the evolution of individual vocal signatures of wild chimpanzees by examining two components of call repertoire--the pant hoot and the pant grunt. Within-individual acoustic variation; Between individual acoustic variation.

Examines screams of chimpanzees and bonobos to investigate variability in call structure. Differences between and within species; Spectral characteristics; Acoustic differences; Factors for variations.

Examines the contexts in which calls by male chimpanzees were produced and the effects several social factors had on pan-hoot production. Maintenance of spatial contact theory supported; Necessity of investigating chimpanzees' response to pan-hoots.

Primates frequently form affiliative relationships that have important fitness consequences. Affiliative relationships between unrelated males and females are ubiquitous in humans but are not widely reported in humans' closest living relatives, chimpanzees (Pan troglodytes). Instead, adult male chimpanzees are extremely aggressive to females, using the aggression to coerce females to mate with them. Adolescent male chimpanzees are physically and socially immature and unable to use aggression toward females in the same way as adult males. Instead, adolescent males might build affiliative relationships with females as an alternative tactic to increase their chances of mating and reproducing. To investigate this possibility, we recorded social interactions between 20 adolescent and 10 young adult males and 78 adult female chimpanzees over 2 years at Ngogo in Kibale National Park, Uganda. Analyses using grooming and proximity as assays revealed that adolescent and young adult males formed differentiated, affiliative relationships with females. These relationships were as strong as the bonds young males formed with maternal kin and unrelated males and increased in strength and number as males aged and started to dominate females. Male-female relationships extended outside the immediate context of mating. Although males affiliated slightly more often with females when they were cycling, they also did so when females were pregnant and nursing young infants. Males and females who formed bonds reassured each other, looked back and waited for each other while traveling, and groomed more equitably than other male-female pairs, even after the time they spent together in association and the female's reproductive state were taken into account. Despite the affiliative nature of these relationships, adolescent and young adult males selectively targeted their female partners for aggression. These findings provide new insights into the evolution of social bonds between human females and males, which can involve both affiliation and coercive violence. • Adolescent and young adult male chimpanzees form affiliative relationships with females similar to, yet different from, bonds adult male chimpanzees form with other males and maternal kin. • As males enter adulthood, they form stronger relationships with more females than males do during adolescence. • Adolescent and young adult males direct aggression selectively to females with whom they form affiliative social bonds. [ABSTRACT FROM AUTHOR]

Demographic data on wild chimpanzees are crucial for understanding the evolution of chimpanzee and hominin life histories, but most data come from populations affected by disease outbreaks and anthropogenic disturbance. We present survivorship data from a relatively undisturbed and exceptionally large community of eastern chimpanzees ( Pan troglodytes schweinfurthii ) at Ngogo, Kibale National Park, Uganda. We monitored births, deaths, immigrations, and emigrations in the community between 1995 and 2016. Using known and estimated ages, we calculated survivorship curves for the whole community, for males and females separately, and for individuals ≤2 years old when identified. We used a novel method to address age estimation error by calculating stochastic survivorship curves. We compared Ngogo life expectancy, survivorship, and mortality rates to those from other chimpanzee communities and human hunter-gatherers. Life expectancy at birth for both sexes combined was 32.8 years, far exceeding estimates of chimpanzee life expectancy in other communities, and falling within the range of human hunter-gatherers (i.e., 27–37 years). Overall, the pattern of survivorship at Ngogo was more similar to that of human hunter-gatherers than to other chimpanzee communities. Maximum lifespan for the Ngogo chimpanzees, however, was similar to that reported at other chimpanzee research sites and was less than that of human-hunter gatherers. The absence of predation by large carnivores may contribute to some of the higher survivorship at Ngogo, but this cannot explain the much higher survivorship at Ngogo than at Kanyawara, another chimpanzee community in the same forest, which also lacks large carnivores. Higher survivorship at Ngogo appears to be an adaptive response to a food supply that is more abundant and varies less than that of Kanyawara. Future analyses of hominin life history evolution should take these results into account. [ABSTRACT FROM AUTHOR]

Summary: Chimpanzees make lethal coalitionary attacks on members of other groups . This behavior generates considerable attention because it resembles lethal intergroup raiding in humans . Similarities are nevertheless difficult to evaluate because the function of lethal intergroup aggression by chimpanzees remains unclear. One prominent hypothesis suggests that chimpanzees attack neighbors to expand their territories and to gain access to more food . Two cases apparently support this hypothesis, but neither furnishes definitive evidence. Chimpanzees in the Kasekela community at Gombe National Park took over the territory of the neighboring Kahama community after a series of lethal attacks . Understanding these events is complicated because the Kahama community had recently formed by fissioning from the Kasekela group and members of both communities had been provisioned with food. In a second example from the Mahale Mountains, the M group chimpanzees acquired part of the territory of the adjacent K group after all of the adult males in the latter disappeared . Although fatal attacks were suspected from observations of intergroup aggression, they were not witnessed, and as a consequence, this case also fails to furnish conclusive evidence. Here we present data collected over 10 years from an unusually large chimpanzee community at Ngogo, Kibale National Park, Uganda. During this time, we observed the Ngogo chimpanzees kill or fatally wound 18 individuals from other groups; we inferred three additional cases of lethal intergroup aggression based on circumstantial evidence (see ). Most victims were caught in the same region and likely belonged to the same neighboring group. A causal link between lethal intergroup aggression and territorial expansion can be made now that the Ngogo chimpanzees use the area once occupied by some of their victims. [Copyright &y& Elsevier]

Summary: During times of crisis, humans often seek the comforts of home. New observations indicate that, during periods of food shortage, male chimpanzees behave in similar fashion by returning to the areas they occupied with their mothers in youth. [Copyright &y& Elsevier]

For energetically limited organisms, life‐history theory predicts trade‐offs between reproductive effort and somatic maintenance. This is especially true of female mammals, for whom reproduction presents multifarious energetic and physiological demands.Here, we examine longitudinal changes in the gut virome (viral community) with respect to reproductive status in wild mature female chimpanzees Pan troglodytes schweinfurthii from two communities, Kanyawara and Ngogo, in Kibale National Park, Uganda.We used metagenomic methods to characterize viromes of individual chimpanzees while they were cycling, pregnant and lactating.Females from Kanyawara, whose territory abuts the park's boundary, had higher viral richness and loads (relative quantity of viral sequences) than females from Ngogo, whose territory is more energetically rich and located farther from large human settlements. Viral richness (total number of distinct viruses per sample) was higher when females were lactating than when cycling or pregnant. In pregnant females, viral richness increased with estimated day of gestation. Richness did not vary with age, in contrast to prior research showing increased viral abundance in older males from these same communities.Our results provide evidence of short‐term physiological trade‐offs between reproduction and infection, which are often hypothesized to constrain health in long‐lived species. [ABSTRACT FROM AUTHOR]

ABSTRACT Objectives Recent studies indicate that the locomotor behavior of wild chimpanzees changes during development. Before transitioning to quadrupedal knuckle-walking in adulthood, young chimpanzees engage in a significant amount of upper limb loading suspensory behavior. We investigated whether these dramatic changes in locomotion influence the strength and shape of chimpanzee long bones. Materials and Methods We examined changes in chimpanzee arboreal locomotion over the course of development using behavioral data collected on wild chimpanzees. We measured the midshaft geometric properties of femora and humeri of wild-caught individuals housed in museum collections using micro computed tomographic scans. Results Chimpanzees spent less time moving arboreally as they aged. Femoral/humeral strength ratios also increased with age, as predicted by the changing loading environment during development. Additional analyses revealed that femoral shape, but not humeral shape, varied across chimpanzee age classes. Adult femora were more elliptical compared with those of infants. This change in adult femora is consistent with the observation that adult chimpanzees spend most of their time moving terrestrially and consequently experience a less variable loading environment than do infants. Discussion Taken together, these findings contribute to our understanding of how ontogenetic changes in function affect form. As similar changes may have characterized the behavioral and skeletal ontogeny of extinct hominoids including hominins, these findings furnish a potential means to make inferences about the behavior of fossil taxa based on the structural properties of their bones. Am J Phys Anthropol 160:16-29, 2016. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Phylogenetic comparative methods have become standard for investigating evolutionary hypotheses, including in studies of human evolution. While these methods account for the non-independence of trait data due to phylogeny, they often fail to consider intraspecific variation, which may lead to biased or erroneous results. We assessed the degree to which intraspecific variation impacts the results of comparative analyses by investigating the “social brain” hypothesis, which has provided a framework for explaining complex cognition and large brains in humans. This hypothesis suggests that group life imposes a cognitive challenge, with species living in larger social groups having comparably larger neocortex ratios than those living in smaller groups. Primates, however, vary considerably in group size within species, a fact that has been ignored in previous analyses. When within-species variation in group size is high, the common practice of using a mean value to represent the species may be inappropriate. We conducted regression and resampling analyses to ascertain whether the relationship between neocortex ratio and group size across primate species persists after controlling for within-species variation in group size. We found that in a sample of 23 primates, 70% of the variation in group size was due to between-species variation. Controlling for within-species variation in group size did not affect the results of phylogenetic analyses, which continued to show a positive relationship between neocortex ratio and group size. Analyses restricted to non-monogamous primates revealed considerable intraspecific variation in group size, but the positive association between neocortex ratio and group size remained even after controlling for within-species variation in group size. Our findings suggest that the relationship between neocortex size and group size in primates is robust. In addition, our methods and associated computer code provide a way to assess and account for intraspecific variation in other comparative analyses of primate evolution. [ABSTRACT FROM AUTHOR]

Observations of chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) provide valuable comparative data for understanding the significance of conspecific killing. Two kinds of hypothesis have been proposed. Lethal violence is sometimes concluded to be the result of adaptive strategies, such that killers ultimately gain fitness benefits by increasing their access to resources such as food or mates. Alternatively, it could be a non-adaptive result of human impacts, such as habitat change or food provisioning. To discriminate between these hypotheses we compiled information from 18 chimpanzee communities and 4 bonobo communities studied over five decades. Our data include 152 killings (n = 58 observed, 41 inferred, and 53 suspected killings) by chimpanzees in 15 communities and one suspected killing by bonobos. We found that males were the most frequent attackers (92% of participants) and victims (73%); most killings (66%) involved intercommunity attacks; and attackers greatly outnumbered their victims (median 8:1 ratio). Variation in killing rates was unrelated to measures of human impacts. Our results are compatible with previously proposed adaptive explanations for killing by chimpanzees, whereas the human impact hypothesis is not supported. [ABSTRACT FROM AUTHOR]

Primate feeding behavior varies over long (e.g., weekly, seasonally, yearly) and short (e.g., hourly) scales of time due to changes in resource availability and the nutritional composition of foods. While the factors that affect long-term changes in feeding behavior have received considerable attention, few data exist regarding what drives variability in feeding behavior over the course of a single day. To address this problem, we investigated diurnal variation in chimpanzee feeding on the leaves of two species of saplings, Pterygota mildbraedii and Celtis africana, at Ngogo, Kibale National Park, Uganda. Specifically, we related short-term changes in chimpanzee feeding behavior on these leaves to diurnal variation in their nutritional composition. Results showed that chimpanzees fed on the leaves of both saplings more in the evening than they did in the morning. The nutritional quality of leaves also improved over the course of the day. Concentrations of cellulose and lignin were lower and total nonstructural carbohydrates (including sugars and starch) were higher in the evening for P. mildbraedii, and sugars were higher in the evening for C. africana. These data suggest that chimpanzees consume these resources when their quality is highest, and consequently, may track the nutrient composition of their foods over very short periods that span only a few hours. In the future, foods collected for analyses must control for time of sampling to ensure biologically meaningful assays of nutrient composition. Am. J. Primatol. 75:342-349, 2013. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Although testosterone (T) has well known organizational and activational effects on aggression, the relationship between the two is not always clear. The challenge hypothesis addresses this problem by proposing that T will affect aggression only in fitness-enhancing situations. One way to test the challenge hypothesis is to examine the relationship between T and different types of aggression. Chimpanzees, Pan troglodytes, show aggressive behaviours in several contexts and provide an opportunity for such a test. Here we show that urinary T influences a form of male chimpanzee reproductive aggression, territorial boundary patrols. In contrast, T does not affect predatory behaviour, a form of aggression that has no immediate link to male reproduction. While these results are consistent with the challenge hypothesis, our results indicate that male chimpanzees experience a significant drop in urinary T during hunts. Additional analyses reveal that males who share meat with others display this decrease. The reason for this decrement is unclear, but we hypothesize that the relative lack of aggression that results from voluntary sharing episodes and the tolerance engendered by such acts may be contributory factors. [Copyright &y& Elsevier]

Reconstructing diets from stable carbon isotopic signals in enamel bioapatite requires the application of a δ13C enamel-diet enrichment factor, or the isotopic offset between diet and enamel, which has not been empirically determined for any primate. In this study, an enamel-diet enrichment factor (ε∗ enamel-diet) of 11.8 ± 0.3‰ is calculated for chimpanzees (Pan troglodytes) at Ngogo in Kibale National Park, Uganda, based on a comprehensive isotopic assessment of previously analyzed dietary plant data and new isotopic analyses of enamel apatite. Different enamel sampling methods are evaluated to determine the potential influence of weaning on isotopic enamel values and dietary interpretations. The new chimpanzee enrichment factor and a sampling strategy that excludes teeth that formed before weaning completion are applied to all known chimpanzee δ13C enamel data, either previously published or newly derived in this study, resulting in a dietary range of almost 6‰ across all chimpanzees sampled. This new chimpanzee enamel-diet enrichment factor is then used to reassess dietary reconstructions of 12 fossil hominin species whose isotopic enamel signatures have been determined. Results reveal hominin diets that are isotopically more positive than previously reconstructed, highlighting the widespread contribution of 13C-enriched C 4 /crassulacean acid metabolism (CAM) resources in fossil hominin diets and emphasizing the broad use of these resources during human evolution. These findings stress the importance of ascertaining and employing an appropriate enrichment factor for dietary reconstructions of specific taxa as well as standardizing the sampling protocol for tooth enamel in isotopic paleodietary reconstructions. [ABSTRACT FROM AUTHOR]

This study provides a taphonomic analysis of prey accumulations of crowned hawk-eagles (Stephanoaetus coronatus) from Ngogo, Kibale National Park, Uganda, collected over 37 months from below nests of two eagle pairs. Crowned hawk-eagles are powerful predators capable of killing animals much larger than themselves, and are significant predators of cercopithecoid monkeys in forest habitats throughout sub-Saharan Africa. At Ngogo, 81% of the individuals in the kill sample are monkeys. Redtail monkeys (Cercopithecus ascanius) are particularly well represented in the sample, making up 66% of monkeys identified to species. Despite an impressive killing apparatus, crowned hawk-eagles are fastidious eaters that inflict far less damage to bone than mammalian predators. Examination of skeletal material from the Ngogo kill sample reveals that crania, hindlimb elements, and scapulae survive predation better than do other bones. Crania of adults are typically complete and accompanied by mandibles, while crania of young individuals are usually dissociated from mandibles and lack basicrania and faces. Long bones are often whole or show minimal damage. Thin bones, such as crania and innominates, are marked by numerous nicks, punctures, and “can-opener” perforations. Scapular blades are heavily raked and shattered. Along with the strong preference for cercopithecoids, these distinct patterns of bone survival and damage indicate the feasibility of recognizing specific taphonomic signatures of large raptors in fossil assemblages.Berger and Clarke (1995) hypothesized that crowned hawk-eagles or similar large raptors were principally responsible for the accumulation of the late Pliocene fossil fauna from Taung, South Africa, including the type infant skull of Australopithecus africanus. The results of our study suggest that the faunal composition and type of damage to the hominid skull and other bone from Taung are consistent with the predatory activities of large raptors. More rigorous assessment of their hypothesis will require sorting the Taung fauna by locality and further detailed analysis of species composition and bone damage and survivability patterns. [Copyright &y& Elsevier]

Like many animals, adult male chimpanzees often compete for a limited number of mates. They fight other males as they strive for status that confers reproductive benefits and use aggression to coerce females to mate with them. Nevertheless, small-bodied, socially immature adolescent male chimpanzees, who cannot compete with older males for status nor intimidate females, father offspring. We investigated how they do so through a study of adolescent and young adult males at Ngogo in Kibale National Park, Uganda. Adolescent males mated with nulliparous females and reproduced primarily with these first-time mothers, who are not preferred as mating partners by older males. Two other factors, affiliation and aggression, also influenced mating success. Specifically, the strength of affiliative bonds that males formed with females and the amount of aggression males directed toward females predicted male mating success. The effect of male aggression toward females on mating success increased as males aged, especially when they directed it toward females with whom they shared affiliative bonds. These results mirror sexual coercion in humans, which occurs most often between males and females involved in close, affiliative relationships. [ABSTRACT FROM AUTHOR]

In humans, senescence increases susceptibility to viral infection. However, comparative data on viral infection in free-living non-human primates—even in our closest living relatives, chimpanzees and bonobos (Pan troglodytes and P. paniscus)—are relatively scarce, thereby constraining an evolutionary understanding of age-related patterns of viral infection. We investigated a population of wild eastern chimpanzees (P. t. schweinfurthii), using metagenomics to characterize viromes (full viral communities) in the faeces of 42 sexually mature chimpanzees (22 males, 20 females) from the Kanyawara and Ngogo communities of Kibale National Park, Uganda. We identified 12 viruses from at least four viral families possessing genomes of both single-stranded RNA and single-stranded DNA. Faecal viromes of both sexes varied with chimpanzee age, but viral richness increased with age only in males. This effect was largely due to three viruses, salivirus, porprismacovirus and chimpanzee stool-associated RNA virus (chisavirus), which occurred most frequently in samples from older males. This finding is consistent with the hypothesis that selection on males for early-life reproduction compromises investment in somatic maintenance, which has delayed consequences for health later in life, in this case reflected in viral infection and/or shedding. Faecal viromes are therefore useful for studying processes related to the divergent reproductive strategies of males and females, ageing, and sex differences in longevity. This article is part of the theme issue 'Evolution of the primate ageing process'. [ABSTRACT FROM AUTHOR]

Social relationships play an important role in animal behavior. Bonds with kin provide indirect fitness benefits, and those with nonkin may furnish direct benefits. Adult male chimpanzees (Pan troglodytes) exhibit social bonds with maternal brothers as well as unrelated adult males, facilitating cooperative behavior, but it is unclear when these bonds develop. Prior studies suggest that social bonds emerge during adolescence. Alternatively, bonds may develop during adulthood when male chimpanzees can gain fitness benefits through alliances used to compete for dominance status. To investigate these possibilities and to determine who formed bonds, we studied the social relationships of adolescent and young adult male chimpanzees (N = 18) at Ngogo in Kibale National Park, Uganda. Adolescent male chimpanzees displayed social bonds with other males, and they did so as often as did young adult males. Adolescent and young adult males frequently joined subgroups with old males. They spent time in proximity to and grooming with old males, although they also did so with their age peers. Controlling for age and age difference, males formed strong association and proximity relationships with their maternal brothers and grooming relationships with their fathers. Grooming bonds between chimpanzee fathers and their adolescent and young adult sons have not been documented before and are unexpected because female chimpanzees mate with multiple males. How fathers recognize their sons and vice versa remains unclear but may be due to familiarity created by relationships earlier in development. Research Highlights: Adolescent male chimpanzees form social bonds with other males.Bonds were common between unrelated males, but frequent with maternal brothers, peers, old males, and fathers.Fathers may be important for male chimpanzees transitioning to adulthood. [ABSTRACT FROM AUTHOR]

The article focuses on the phenomenon of menopause in wild chimpanzees, particularly in the Ngogo community of wild chimpanzees in Kibale National Park, Uganda. The researchers combined demographic and hormonal data to investigate post-reproductive life spans and the underlying physiological mechanisms in chimpanzees. They found that, similar to humans, fertility declined after the age of 30, and no births were observed after the age of 50.