The Foraging Costs of Mating Effort in Male Chimpanzees (Pan troglodytes schweinfurthii)

Costs of mating effort can affect the reproductive strategies and lifetime fitness of male primates, but interspecific and interindividual variation in the magnitude and distribution of costs is poorly understood. Male costs have primarily been recognized in seasonally breeding species that experience concentrated periods of mating competition. Here, we examine foraging costs associated with male mating effort in chimpanzees (Pan troglodytes schweinfurthii), a polygynandrous species, in which mating opportunities occur intermittently throughout the year. To quantify male feeding, aggression, and mating, we conducted focal follows on 12 males in a wild community (Kanyawara, Kibale National Park, Uganda) for 11 mo. Males fed less on days when high-value mating opportunities (estrous parous females) were available than on days without any mating opportunities. Reductions in feeding time were related to increased rates of aggression and copulation, indicating that the proximate cause of changes in male foraging was mating effort. Surprisingly, however, there was no relationship between dominance rank and the extent to which feeding time was reduced. High costs of mating effort may reduce the degree of reproductive skew and limit the use of possessive tactics in chimpanzees. We suggest that male bonding in chimpanzees may be favored not only for its benefits but because intragroup competition is so costly. Our results complement the available data on mammals, and primates in particular, by showing that mating effort can have measurable foraging costs even in species, in which breeding is aseasonal and only moderately skewed.     

Gastrointestinal Parasites of Savanna Chimpanzees (Pan troglodytes schweinfurthii) in Ugalla,Tanzania

Understanding variability in patterns of parasite infections requires studies of multiple populations inhabiting a variety of habitats. Gastrointestinal parasites of chimpanzees (Pan troglodytes) have been studied extensively at several forested sites, but the parasite fauna of chimpanzees living in dry, open habitats is less well known. We studied the parasites of savanna chimpanzees (Pan troglodytes schweinfurthii) living in the Issa Valley, Ugalla (Tanzania). We examined 119 fresh fecal samples using standard coproscopical methods. We detected protozoans including Blastocystis sp., Entamoeba coli, E. histolytica/dispar, Iodamoeba buetschlii, Troglodytella abrassarti, and Troglocorys cava, but only two types of spirurid nematodes among the helminths. The parasites of the Ugalla chimpanzees differ from those of forest chimpanzees in the absence of Strongyloides sp. and strongylid nematodes and a high prevalence of spirurids. Strongylids and Strongyloides sp. have thin-shelled eggs and larvae, which develop in the external environment; thus they may not be able to survive for prolonged periods in the extreme environment of Ugalla. The Ugalla chimpanzees also live at a lower population density and exhibit a larger home range than forest chimpanzees, factors that may lead to lower exposure to infective nematode larvae. Spirurid eggs, however, have thick shells and a life cycle dependent on intermediary hosts, making their survival and transmission in such extreme conditions more feasible. These differences between parasite fauna of closed and open forest chimpanzees contribute to our understanding of the ecology of infectious disease, and have the potential to contribute to conservation policies and practices.     

Food Acceptance and Social Learning Opportunities in Semi‐Free Eastern Chimpanzees (Pan troglodytes schweinfurthii)

When confronted with novel foods, chimpanzees’ responses combine a mixture of curiosity and cautiousness. Once the item is in the mouth, the initial cautiousness is followed by an aversion to bitter taste that is mediated mainly by the TAS2R gene family. For instance, variations on the TAS2R38 locus which has been studied extensively in humans have been associated with different acceptance of bitter substances. Surprisingly, while cautiousness and bitter taste aversion were selected to prevent any risk of poisoning, very few studies on novel food acceptance have included the vegetative parts of plants. Moreover, the studies were usually carried out with captive apes faced to a very restricted variety of non‐toxic plants, hardly making the results representative. This study aims to replicate previous findings obtained in zoos while controlling for these limitations. We provided nine subgroups of eastern chimpanzees (Pan troglodytes schweinfurthii) living in the Ugandan sanctuary of Ngamba Island with novel plants known to be consumed by wild chimpanzees of the same subspecies, as well as domestic plants, wild sapota fruit and grey clay used by human local communities. We also genotyped their TAS2R38 gene. Our results confirm the very low genetic heterogeneity for TAS2R38 in this chimpanzee subspecies. Chimpanzees were particularly cautious towards the vegetative parts of novel plants, likely reflecting their behavioural strategy for avoiding toxic compounds. We also confirmed their higher propensity towards testing sapota and clay, reflecting their ability to expand their diet. In contrast with the results found in zoos, familiar and novel less‐palatable vegetative parts of plants did not elicit many interindividual observations. This may be explained by the items presented, which could have been so novel to be considered as enrichment in captive conditions, where the apes are rarely exposed to plants.     

Dominance and Immunity in Chimpanzees (Pan troglodytes)

The study reported here examined the effect of dominance status on serum immunoglobulin (IgG and IgM) levels in chimpanzees living in five captive colonies. Blood samples were collected from each individual twice, and agonistic and grooming interactions were observed. After initial group observations, members of four of the five groups were caged singly. Thereafter blood samples were again taken. Both IgG and IgM levels of the animals living in groups were significantly negatively correlated with their dominance status in all five groups. The higher-ranked chimpanzees were likely to show lower levels of IgG and IgM. No such consistent correlation was found between individual Ig levels and frequency of aggressive behaviour or grooming. On transfer to isolated conditions, Ig levels of the chimpanzees did not correlate with their previous dominance status in the groups. Being of high rank is a biological cost for colony-living chimpanzees with regard to immunity levels.     

Testosterone and energetics in wild chimpanzees (Pan troglodytes schweinfurthii)

Ovarian function in female hominoids is sensitive to both energy flux and energy balance, resulting in a reduced probability of conception during periods when a successful reproductive outcome is less likely. However, the extent to which energetic factors constrain gonadal function in male hominoids is not clear. We examined the effects of both acute and chronic variation in energy availability on urinary testosterone (T) levels in adult male chimpanzees. Acute changes in energy availability, which were assayed by means of observational data on feeding behavior, did not result in decreased T production for 11 individuals at Kibale National Park, Uganda. Chronic energy shortages, on the other hand, may be associated with lower T levels in this population. Adult males in Kibale (n=11), who maintain suboptimal access to energy, exhibit significantly lower urinary T levels than males in captivity (n=11), who are more sedentary and better fed. These results suggest that data on hormonal function in captive chimpanzees should be interpreted with caution because individuals may produce T at levels well above those that are typical in the wild. They also suggest that short-term variations in T levels in male hominoids are more likely to be explained by social factors than by energetic ones.     

Chronic diseases in captive geriatric female Chimpanzees (Pan troglodytes)

The current aging population of captive chimpanzees is expected to develop age-related diseases and present new challenges to providing their veterinary care. Spontaneous heart disease and sudden cardiac death are the main causes of death in chimpanzees (especially of male animals), but little is known about the relative frequency of other chronic diseases. Furthermore, female chimpanzees appear to outlive the males and scant literature addresses clinical conditions that affect female chimpanzees. Here we characterize the types and prevalence of chronic disease seen in geriatric (older than 35 y) female chimpanzees in the colony at Alamogordo Primate Facility. Of the 16 female chimpanzees that fit the age category, 87.5% had some form of chronic age-related disease. Cardiovascular-related disease was the most common (81.25%) followed by metabolic syndrome (43.75%) and renal disease (31.25%). These data show the incidence of disease in geriatric female chimpanzees and predict likely medical management challenges associated with maintaining an aging chimpanzee population.     

Task Design Influences Prosociality in Captive Chimpanzees (Pan troglodytes)

Chimpanzees confer benefits on group members, both in the wild and in captive populations. Experimental studies of how animals allocate resources can provide useful insights about the motivations underlying prosocial behavior, and understanding the relationship between task design and prosocial behavior provides an important foundation for future research exploring these animals'' social preferences. A number of studies have been designed to assess chimpanzees'' preferences for outcomes that benefit others (prosocial preferences), but these studies vary greatly in both the results obtained and the methods used, and in most cases employ procedures that reduce critical features of naturalistic social interactions, such as partner choice. The focus of the current study is on understanding the link between experimental methodology and prosocial behavior in captive chimpanzees, rather than on describing these animals'' social motivations themselves. We introduce a task design that avoids isolating subjects and allows them to freely decide whether to participate in the experiment. We explore key elements of the methods utilized in previous experiments in an effort to evaluate two possibilities that have been offered to explain why different experimental designs produce different results: (a) chimpanzees are less likely to deliver food to others when they obtain food for themselves, and (b) evidence of prosociality may be obscured by more “complex” experimental apparatuses (e.g., those including more components or alternative choices). Our results suggest that the complexity of laboratory tasks may generate observed variation in prosocial behavior in laboratory experiments, and highlights the need for more naturalistic research designs while also providing one example of such a paradigm.     

The Relationship Between Tool Use and Prey Availability in Chimpanzees (Pan troglodytes schweinfurthii) of Northern Democratic Republic of Congo

International Journal of Primatology - A key feature of human behavioral diversity is that it can be constrained by cultural preference (“cultural override”); that is,...     

Alpha status and agonistic alliance in wild chimpanzees (Pan troglodytes schweinfurthii)

Intermale competition was studied in a habituated group of wild chimpanzees (Pan troglodytes schweinfurthii) in the Mahale Mountains of Tanzania. The group of 27 individuals included 3 adult males and 12 adult females. The beta-ranked male was observed to attack the alpha male and usurp his status. The beta male was supported by an ally, the gamma male. Earlier in the competition the gamma male had supported the alpha male. When the alpha male was displaced, he completely lost what had been an exclusive copulatory right. It was clear that alliance with the most subordinate male was a critically effective strategy for the major competitors. The alliance strategy of the gamma male invested him with important power. The strategy of changing alliance is referred to as “allegiance fickleness.” It is suggested that allegiance fickleness could provide a basis for individual selection of social intelligence.     

Hyperprogesteronemia in response to Vitex fischeri consumption in wild chimpanzees (Pan troglodytes schweinfurthii)

Chimpanzees in Gombe National Park consume fruits of Vitex fischeri during a short annual fruiting season. This fruit species is a member of a genus widely studied for phytoestrogen composition and varied physiological effects. One particularly well-studied species, V. agnus-castus, is noted for its documented effects on female reproductive function, evidenced in increased progesterone levels and consequent regulation of luteal function. We examined reproductive hormone levels in both male and female chimpanzees during a 6-week period of intense V. fischeri consumption. V. fischeri consumption was associated with an abrupt and dramatic increase in urinary progesterone levels of female chimpanzees to levels far exceeding the normal range of variation. Female estrogen levels were not significantly impacted, nor were male testosterone levels. These are some of the first data indicating that phytochemicals in the natural diet of a primate can have significant impacts on the endocrine system, though the fluctuating nature of chimpanzee diet and reproductive function does not allow us to determine whether the effects observed during this short period had a broader positive or negative impact on female fertility. Given the widespread use of various Vitex species by African primates and the as-yet-undescribed phytochemical properties of these species, we predict that our observations may be indicative of a broader phenomenon.     

Correction to: The Relationship Between Tool Use and Prey Availability in Chimpanzees (Pan troglodytes schweinfurthii) of Northern Democratic Republic of Congo

International Journal of Primatology - The original version of this article unfortunately contained mistakes in the Discussion and Acknowledgments sections. The changes are shown below:     

Genetic Sampling of Unhabituated Chimpanzees (Pan troglodytes schweinfurthii) in Gishwati Forest Reserve, an Isolated Forest Fragment in Western Rwanda

Many primate populations currently live in forest fragments. These populations are often unhabituated, elusive, and contain few individuals, making them difficult to study through direct observation. Noninvasive genetic methods are useful for surveying these unhabituated populations to infer the number and sex of individuals and the genetic diversity of the population. We conducted genetic analysis on 70 fecal samples from eastern chimpanzees (Pan troglodytes schweinfurthii) in Gishwati Forest Reserve, a forest fragment in western Rwanda. We genotyped all but two of these samples using 12 autosomal and 13 Y-chromosome microsatellite markers previously used in analyses of other chimpanzee populations. The genetic data show that these samples represent a minimum of 19 individuals (7 females, 12 males). However, because we may not have sampled all individuals in the population, we also performed mark-recapture analysis with the genetic data and found that the entire population likely numbers between 19 and 29 individuals. These results are consistent with opportunistic observations of at least 19 individual chimpanzees. Levels of variation at the Y-chromosome microsatellites were similar to those observed in other chimpanzee communities, suggesting that the chimpanzees in this forest are members of a single community. These results provide a baseline count of the number of male and female chimpanzees in the Gishwati Forest Reserve, and the data provide the potential for follow-up studies aimed at tracking individuals over time, thus aiding conservation management of this unhabituated population.     

Hand Preferences for a Haptic Task in Chimpanzees (Pan troglodytes)

We tested the hand preferences of 20 chimpanzees (Pan troglodytes) for a haptic task requiring individuals to search for grapes in an opaque bucket filled with water. We compared these data to the hand preferences displayed by the same chimpanzees during reaching and bimanual feeding tasks. The chimpanzees displayed no significant hand preference for the reaching or bimanual feeding tasks, but exhibited a right-hand preference while performing the haptic task. In contrast, New and Old World monkeys display left-hand preferences for similar tasks. We discuss the relevance of these findings for the evolution of handedness in primates.     

Hypertension Increases With Aging and Obesity in Chimpanzees (Pan troglodytes)

Cardiovascular disease is a primary cause of morbidity and mortality in captive chimpanzees. Four years of blood pressure (BP) data were analyzed from a captive former laboratory population of 201 healthy adult chimpanzees with assessment of age and obesity on elevated BP. Five different measures of obesity were compared: abdominal girth, basal metabolic rate, body‐mass index (BMI), body weight, and surface area. Systolic BP varied by sex. Obesity did not influence male BP. For females, obesity was a significant determinant of BP. The best measure of female obesity was basal metabolic rate and the worst was BMI. Median systolic BP of healthy weight females (<54.5 kg) was significantly lower (128 mmHg) than overweight or obese females (140 mmHg), but both were lower than all males (147 mmHg). For diastolic BP, neither sex nor any of the five obesity measures was significant. But age was highly significant, with geriatric chimpanzees (>30 years) having higher median diastolic BP (74 mmHg) than young adults of 10–29 years of age (65 mmHg). By these criteria, 80% of this population is normotensive, 7% prehypertensive, and 13% hypertensive. In summary, systolic BP intervals required adjustment for obesity among females but not males. Diastolic BP required adjustment for advanced age (≥30 years). Use of these reference intervals can facilitate timely clinical care of captive chimpanzees. Zoo Biol. 32:79‐87, 2013. © 2012 Wiley Periodicals, Inc.     

How to Repair Relationships – Reconciliation in Wild Chimpanzees (Pan troglodytes)

Reconciliation appears to repair the relationships of former opponents after being disturbed by aggressive interactions. Despite a consensus about the benefit of reconciliation, how former opponents achieve this benefit remains unclear. Variation within reconciliation is evident in many species, but understanding what causes the variation has been mostly neglected until now. We collected 178 events of reconciliation of both sexes in a community of wild chimpanzees (Pan troglodytes) in the Taï National Park, Côte d'Ivoire. Our data provide evidence for the relationship‐repair function of reconciliation, as aggression disturbed tolerance levels among former opponents and reconciliation restored tolerance to normal levels again. Partners with highly beneficial relationships reconciled more often compared with partners of low mutual benefit. Latency and duration of reconciliation varied in combination, such that short reconciliations were initiated soon after the conflict, while long reconciliations were initiated later. Latency increased with the risk of further aggression, while duration decreased when costs were incurred from interruption of beneficial activities. In contrast, the complexity of reconciliation varied according to the intensity of the preceding conflict, such that reconciliation was more complex after more intense conflicts. Our results suggest that relationships between opponents are increasingly disturbed with increasing conflict intensity and reconciliation repairs all relationships independent of their relationship value. We propose that the function of reconciliation is to reduce the disturbance created by aggression, but the more frequent the reconciliation, the more beneficial it is for former opponents.     

Intergroup Encounters of Chimpanzees (Pan troglodytes) from the Female Perspective

International Journal of Primatology -