Plant foods consumed by Pan: Exploring the variation of nutritional ecology across Africa

It has been shown that differences in resource density and nutrient supply affect variation in ranging patterns, habitat use, and sociality. Among nonhuman primates, chimpanzees (Pan troglodytes) and bonobos (P. paniscus) have often been used as models for the link between social system and habitat ecology. Field reports suggest that resource density is higher in habitats occupied by bonobos (compared to chimpanzee habitats), and in the West (compared to the East) of the range of chimpanzees. In this study we compared diet quality at the level of species and populations using information from nutritional analyses of fruit and leaves consumed by chimpanzees (three) and bonobos (one population). Quality of plant foods was assessed on the basis of a) the concentration of macronutrients, fiber, and anti‐feedants, and b) associations of different nutrient components. Overall plant samples collected at each site differed in terms of macronutrient content. However, nutritious quality and gross energy content of food samples were similar suggesting that dietary quality reflects selectivity rather than habitat ecology. The quality of plant foods consumed by bonobos was within the range of chimpanzees and the quality of plant foods consumed by western chimpanzees was not higher than that of eastern chimpanzees. While the results showed significant variation across forests inhabited by Pan, they did not match with geographical patterns between and within Pan species as proposed in previous studies. This suggests that the nutritional quality of the habitat is not always a reliable predictor of the quality of the diet. Am J Phys Anthropol 2010. © 2009 Wiley‐Liss, Inc.     

The relationship between socio‐sexual behavior and salivary cortisol in bonobos: tests of the tension regulation hypothesis

Bonobos are known for their pacifistic behavior and their large repertoire of behaviors that are thought to serve conflict resolution. One is an unusual form of ventro‐ventral mounting that facilitates genital contacts (GC). Various hypotheses have been proposed to explain its function. In this study we tested predictions of the tension regulation hypothesis using salivary cortisol as a marker for social stress. The results indicate a temporal relationship between GC and cortisol levels. Compared with baseline data and matched samples of unrestricted food access, rates of GC increased when access to food sources was restricted. Cortisol levels were highest when access to food was constrained. However, because the behavioral and hormonal responses occurred when viewing the stimulus at a distance and preceded the physical presence of the stimulus, we conclude that the anticipation of a competitive situation was sufficient to induce social stress. Contrary to our prediction, targets of aggression did not have higher rates of GC nor did they solicit GC more often than others. Furthermore, higher GC rates did not correlate with a more pronounced decrease in cortisol levels. Not all results obtained in this study supported the predictions concerning the regulatory function of GC on social tension and further research is needed to explore this question. However, the results indicate that the anticipation of competition may be sufficient to induce a costly physiological response, and that high levels of resource competition may have lasting effects on physical stress and stress management. Am. J. Primatol. 71:223–232, 2009. © 2008 Wiley‐Liss, Inc.     

Population Dynamics of Wild Bonobos (Pan paniscus) at Wamba

We analyzed population dynamics and birth seasonality of wild bonobos at Wamba, Democratic Republic of the Congo, based on 20 years of observations (1976–1996). Wamba Bonobo infant mortality is much lower than that reported for chimpanzees. This seemes to be related to several socioecological characteristics of bonobos: the use of abundant fruit and herbaceous foods, larger food patch size, female feeding priority, and the absence of infanticide. The mean interval between live births of 4.8 years is shorter than those reported for chimpanzees, and some females simultaneously carried and nursed two successive offspring. Mother–offspring conflicts, such as refusal of suckling attempts and interference with mothers' copulation, which are common in chimpanzees, are rare in Wamba bonobos. A birth peak seems to occur during the light rainy season from March to May, just after the season with the least rainfall. This timing of births is similar to those reported for chimpanzee populations, and might benefit both mother and offspring by maximizing the amount of time before the next dry season.     

Vocal communication as a function of differential rearing experiences inPan paniscus: A preliminary report

There is little evidence of vocal learning in nonhuman primates despite the well-documented abilities found in avian species. We describe the vocal repertoire of five bonobos (Pan paniscus), four of which live in a seminatural environment. The fifth subject, Kanzi, has been reared with humans during the course of language training. The data indicated that the four bonobos living in a seminatural environment exhibit a variety of species-typical vocalizations. In addition to producing all the species-typical vocalization, Kanzi produced four structurally unique vocalizations that were not heard among the other subjects. These data suggest that Kanzi has learned vocalizations that are novel due to his unique rearing experience. Discussion is focused on the flexibility of vocal communication and vocal comprehension inPan paniscus.     

Female feeding priority in bonobos, Pan paniscus, and the question of female dominance

The question of whether bonobos show feeding priority and female dominance has been proposed and examined, both in the wild and in captive studies, with differing results. The relationship between female dominance and female feeding priority has been best studied in prosimian primates. These studies use established criteria of females consistently evoking submissive behavior from males in dyadic encounters for determining female dominance. Although the relationship is complex, female dominance in prosimians is associated with preferential access to food. Data from studies of wild habituated bonobos in the Lomako Forest, Democratic Republic of the Congo, are examined for evidence of both female feeding priority and female social dominance using similar criteria as used for prosimians. Bonobos showed evidence of female feeding priority in small, but not in large, food patches. Male-male competition for mating opportunities at the start of the food bout was related to some, but not all, differences in time spent feeding between the sexes. Female dominance similar to that seen in prosimians was not observed in these bonobos. Males were consistently dominant in dyadic interactions. Female feeding priority with male dyadic social dominance implies that male deference during feeding cannot be excluded as one explanation of interpretations of female dominance in bonobos. Additionally, dominance of male bonobos by females appears to require the presence of female coalition partners. As in other primates with female feeding priority, bonobo females express this trait where food is economically defendable. Unlike prosimians, however, bonobo female feeding priority may result from male deference and the importance of female coalitions in nondyadic interactions.     

Vocal Production by a Language-Competent Pan paniscus

Human spoken language and nonhuman primate vocalization systems have traditionally been regarded as qualitatively different from one another with respect to their semanticity and the way in which individuals acquire and utilize these signals. However, recent studies of the vocal behaviors of both captive and free-ranging monkeys and apes suggest that this dichotomy may not be unequivocal. We examined the vocalizations produced by a linguistically-competent adult male bonobo (Pan paniscus) named Kanzi. We analyzed his vocalizations during communicative interactions with humans in order to determine whether they vary systematically according to the semantic context in which they are produced. We determined semantic contexts based upon a vocalization's co-occurrence with predefined behavioral correlates. Spectrographic and statistical analyses revealed that acoustic structure is similar among the vocalizations that occurred within a specific semantic context and structural differences are evident between the vocalizations produced in different contexts. The results provide evidence that, during communicative interactions with humans, Kanzi modulates his vocal output on both the temporal and spectral levels.     

Pan paniscus 1973 to 1996: Twenty-three years of field research

Although the pygmy chimpanzee is not smaller than a chimpanzee, it has long intrigued anthropologists with its more gracile build and greater arboreality. The social organization of the pygmy chimpanzee is unique among primates in showing female-bonding among nonrelatives, little male bonding despite male residence, and relative inability of males to outrank females. The crucial ecological basis for this difference from the male-bonded system of chimpanzees is that pygmy chimpanzees do not go through an extended season of low food availability during which party sizes fall to low levels.     

Bipedality in chimpanzee (Pan troglodytes) and bonobo (Pan paniscus): testing hypotheses on the evolution of bipedalism

A host of ecological, anatomical, and physiological selective pressures are hypothesized to have played a role in the evolution of hominid bipedalism. A referential model, based on the chimpanzee (Pan troglodytes) and bonobo (Pan paniscus), was used to test through experimental manipulation four hypotheses on the evolution of hominid bipedalism. The introduction of food piles (Carry hypothesis) increased locomotor bipedality in both species. Neither the introduction of branches (Display hypothesis) nor the construction of visual barriers (Vigilance hypothesis) altered bipedality in either species. Introduction of raised foraging structures (Forage hypothesis) increased postural bipedality in chimpanzees. These experimental manipulations provided support for carrying of portable objects and foraging on elevated food-items as plausible mechanisms that shaped bipedalism in hominids.