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A large body of research has demonstrated that variation in competitive behavior across species and individuals is linked to variation in physiology. In particular, rapid changes in testosterone and cortisol during competition differ according to an individual's or species' psychological and behavioral responses to competition. This suggests that among pairs of species in which there are behavioral differences in competition, there should also be differences in the endocrine shifts surrounding competition. We tested this hypothesis by presenting humans' closest living relatives, chimpanzees (Pan troglodytes) and bonobos (Pan paniscus), with a dyadic food competition and measuring their salivary testosterone and cortisol levels. Given that chimpanzees and bonobos differ markedly in their food-sharing behavior, we predicted that they would differ in their rapid endocrine shifts. We found that in both species, males showed an anticipatory decrease (relative to baseline) in steroids when placed with a partner in a situation in which the two individuals shared food, and an anticipatory increase when placed with a partner in a situation in which the dominant individual obtained more food. The species differed, however, in terms of which hormone was affected; in bonobo males the shifts occurred in cortisol, whereas in chimpanzee males the shifts occurred in testosterone. Thus, in anticipation of an identical competition, bonobo and chimpanzee males showed differential endocrine shifts, perhaps due to differences in perception of the situation, that is, viewing the event either as a stressor or a dominance contest. In turn, common selection pressures in human evolution may have acted on the psychology and the endocrinology of our competitive behavior. doi/10.1073/pnas.1007411107

Intestinal entodiniomorphid ciliates are commonly diagnosed in the feces of wild apes of the genera Pan and Gorilla. Although some authors previously considered entodiniomorphid ciliates as possible pathogens, a symbiotic function within the intestinal ecosystem and their participation in fiber fermentation has been proposed. Previous studies have suggested that these ciliates gradually disappear under captive conditions. We studied entodiniomorphid ciliates in 23 captive groups of chimpanzees, three groups of captive bonobos and six populations of wild chimpanzees. Fecal samples were examined using Sheather's flotation and Merthiolate-Iodine-Formaldehyde Concentration (MIFC) methods. We quantified the number of ciliates per gram of feces. The MIFC method was more sensitive for ciliate detection than the flotation method. Ciliates of genus Troglodytella were detected in 13 groups of captive chimpanzees, two groups of bonobos and in all wild chimpanzee populations studied. The absence of entodiniomorphids in some captive groups might be because of the extensive administration of chemotherapeutics in the past or a side-effect of the causative or prophylactic administration of antiparasitic or antibiotic drugs. The infection intensities of ciliates in captive chimpanzees were higher than in wild ones. We suppose that the over-supply of starch, typical in captive primate diets, might induce an increase in the number of ciliates. In vitro studies on metabolism and biochemical activities of entodiniomorphids are needed to clarify their role in ape digestion. DOI 10.1002/ajpa.21191 KEY WORDS Troglodytella abrassarti; entodiniomorphids; Pan troglodytes: Pan paniscus: captivity

This study compares adult play behavior in the two Pan species in order to test the effects of phylogenetic closeness and the nature of social systems on play distribution. The social play (both with fertile and immature subjects) performed by adults did not differ between the two species. In contrast, in bonobos, play levels among fertile subjects were higher than in chimpanzees. Findings regarding levels of undecided conflicts (more frequent in bonobos) and formal submission displays (lacking in bonobos) confirm, in the two colonies under study, that bonobos exhibit 'egalitarianism' more than chimpanzees. Some authors emphasized the importance of play-fighting for social assessment when relationships among individuals are not codified and structured according to rank-rules. Indeed, adult bonobos played more roughly than chimpanzees. Moreover, adult bonobos displayed the full play-face at a high frequency especially during rough play sessions, whereas in chimpanzees, the frequency of play signals was not affected by roughness of play. The frequency of social play among bonobo females was higher than in any other sex combinations, whereas no difference was found for chimpanzees. As a matter of fact, social play can be viewed as a balance between cooperation and competition. Among bonobo females, characterized by social competence and affiliation, social play might enhance their behavioral flexibility and increase their socially symmetrical relationships which, after all, are the basis for their egalitarian society. KEY WORDS adult play; play signals; socials assessment; phylogenetic closeness; egalitarian societies

We collected high-resolution plantar pressure distributions of seven bonobos during terrestrial bipedal and quadrupedal locomotion (N = 146). Functional foot length, degree of hallux abduction, and total contact time were determined, and plots, showing pressure as a function of time for six different foot regions, were generated. We also studied five adult humans for comparison (N = 13). Both locomotion types of the bonobo show a large variation in plantar pressure distributions, which could be due to the interference of instantaneous behavior with locomotion and differences in walking speed and body dimensions. The heel and the lateral midfoot typically touch down simultaneously at initial ground contact in bipedal and quadrupedal walking of bonobos, in contrast with the typical heel-strike of human bipedalism. The center of pressure follows a curved course during quadrupedalism, as a consequence of the medial weight transfer during mid-stance. Bipedal locomotion of bonobos is characterized by a more plantar positioning of the feet and by a shorter contact time than during quadrupedal walking, according to a smaller stride and step length at a higher frequency. We observed a varus position of the foot with an abducted hallux, which likely possesses an important sustaining and stabilizing function during terrestrial locomotion. Am J Phys Anthropol 120:373-383, 2003. KEY WORDS foot function; bipedal/quadrupedal walking; primate locomotion; pedobarography

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. KEY WORDS bipedal; chimpanzee; bonobo; human evolution; referential model

The effect of posture on hand preferences was examined in an experiment with 5 bonobos (Pan paniscus). To obtain a food reward, the animals had to adopt 1 out of 7 different postures. These postures represented an increasing problem to the maintenance of body equilibrium. It was expected that an increasing demand for equilibrium maintenance would elicit individual preferences and a population-level bias. All animals showed an increasing trend toward left-handedness while shifting to a bipedal posture from a seated posture by way of a quadrupedal posture. The importance of bipedalism in the evolution of left- and right-handedness is discussed briefly.

Results from a 10 month study of adult male and female bonobos (Pan paniscus) in the Lomako Forest, Zaire, and those from a 7 month study of adult male and female chimpanzees in the Tai Forest, Ivory Coast (Pan troglodytes verus), were compared in order to determine whether there are species differences in locomotor behavior and substrate use and, if so, whether these differences support predictions made on the basis of interspecific morphological differences. Results indicate that bonobos are more arboreal than chimpanzees and that male bonobos are more suspensory than their chimpanzee counterpart. This would be predicted on the basis of male bonobo's longer and more narrow scapula. This particular finding is contrary to the prediction that the bonobo is a 'scaled reduced version of a chimpanzee' with little or no positional behavior difference as had been suggested. This study provides the behavioral data necessary to untangle contradictory interpretations of the morphological differences between chimpanzees and bonobos, and raises a previously discussed (Fleagle: Size and Scaling in Primate Biology, pp. 1-19, 1985) but frequently overlooked point - that isometry in allometric studies does not necessarily equate with behavioral equivalence. Several researchers have demonstrated that bonobos and chimpanzees follow the same scaling trends for many features, and are in some sense functionally equivalent, since they manage to feed and reproduce. However, as reflected in their morphologies, they do so through different types and frequencies of locomotor behaviors.

Enamel hypoplasia (EH). is a dental enamel defect that is often used as an indicator of non-specific systemic stress during the early stages of development. There are few reports of this enamel defect in non-human primates and little is known about the prevalence of this defect in the bonobo, Pan paniscus. The frequency and distribution of EH within the bonobo are investigated using skeletal specimens from the Royal Museum for Central Africa in Tervuren, Belgium. All permanent teeth were examined with a 5-20X pocket hand lens in oblique incandescent and natural light. Linear defects were scored as mild, moderate, or severe and defect distances from the cemento-enamel junction were measured with digital calipers. Pit-type hypoplasias were counted and recorded as present or absent. At the level of the individual (N=82), the vast majority of bonobos in this skeletal sample (98.8%) are affected to some degree with linear enamel hypoplasia (LEH) and there is no significant difference in the expression of LEH between the sexes. Pitting is observed in 13.4% of these individuals with no significant difference between the sexes. The anterior teeth are more affected with hypoplasias than the posterior teeth although maxillary and mandibular differences are noted. The incisors express the greatest frequency of enamel hypoplasias, closely followed by the canines. In contrast to previous studies, the mandibular canine does not demonstrate a marked difference in the expression of LEH when compared with the maxillary canine. Comparisons with the common chimpanzee are made and it appears that the bonobo is more developmentally stressed. Etiological factors such as locality and seasonal stress are examined. This macroscopic inventory of EH provides the necessary insight into the prevalence of this defect within the bonobo and serves as a foundation for the current micro-incremental analysis of EH within this endangered species. Research funded by Natural Sciences and Engineering Research Council of Canada (OGP0171168).

Selection against aggression seems to have occurred naturally in some animals and to have led to traits similar to those seen in domesticated animals. The bonobo (Pan paniscus) is less [...]

Enamel hypoplasia (EH) is a sensitive but non-specific marker of physiological or metabolic stress. There are numerous studies involving the prevalence of EH in human and non-human primates, however, the timing of these defects has only recently been examined. Although previous studies do show prevalence approaching 100% little is known about the timing of EH for bonobos. The timing and periodicity of repetitive linear enamel hypoplasia (rLEH) in the bonobo are determined through relative caliper measures of LEH location standardized against crown heights (n=490 teeth, 68 individuals) and perikymata counts (n=23 teeth, 17 individuals). Where possible, timings are ascertained from imbricational enamel formation estimates for the bonobo generated from SEM montages showing perikymata ranging from the occlusal to the cervical margins. These estimates are 3 and 5 years for the incisors (n=3) and canines (n=l), respectively. The bonobo specimens are from the Musee Royal de l'Afrique Centrale collection (Tervuren, Belgium). From caliper measures for the incisors and canines respectively, the onset of LEH ranges from 1.5-3 years, the stress is recorded for another 1-3 years, and the interval between rLEH is around 6-8 months although imbricational chronologies yield ah interval closer to 6 months. The 6-month periodicity is also observed with perikymata counts on incisors and canines. The duration of the hypoplastic event, including period of enamel recovery, ranges from 6-8 weeks based on the number of perikymata counted within an hypoplastic groove. This 6-month periodicity of rLEH in the bonobo is believed to be influenced by moisture cycles. Research funded by Natural Sciences and Engineering Research Council of Canada (OGP0171168)

Two major groups of theories exist on the precursor of habitual bipedalism in hominids, both primarily based on paleontological findings. On the one hand, the 'terrestrial theories' postulate that bipedalism evolved from terrestrial quadrupedalism. On the other hand, the 'arboreal theories' state that bipedalism originated from climbing, the latter being an exaptation for (eventually habitual) bipedalism. In order to help evaluate current theories, we have recently started a project on the kinesiology of arboreal locomotion versus terrestrial locomotion in bonobos (Pan paniscus). Like all apes, bonobos are habitually arboreal, but they are also adept terrestrial walkers, both quadrupedally and bipedally. Together with chimpanzees (Pan troglodytes), they are the closest known relatives to hominids, but bonobes likely resemble the common ancestor better from a morphometrical point of view. For walking and climbing, two separate set-ups were used, both allowing for synchronous recording of kinematics (50 Hz video) and of substrate reaction forces. These were measured by force platforms for terrestrial walking, and by a 4-m long, straight pole (12 cm diameter), partially instrumented with two 3D force transducers for incline walking and climbing. During terrestrial quadrupedalism, weight is generally well distributed between the front and hind limbs, although this is variable and typically oblique to the walking direction. When the slope increases, the load shifts towards the feet. At a slope of 30[degrees] locomotor behavior resembles terrestrial walking, although less oblique, including knuckle-walking and bipedalism. At 60[degrees], bipedalism occasionally occurs, but locomotion is typically quadrupedal with grasping hands.

We collected a total of 96 traditional landmarks and semilandmarks on the face and cranial base of 268 adult and sub-adult crania for a geometric morphometric analysis of five different hominoid species--Homo sapiens, Pan paniscus, Pan troglodytes, Gorilla gorilla and Pongo pygmaeus. The standard relative warp (RW) morphospace was sheared so that pooled within-group size allometry, the axis assumed to express the 'common' ontogenetic shape change, lies horizontally. In the resulting analysis there are differences in size-adjusted mean forms--these appear in sheared RW's 2,3 ...--and there are also differences in the within-taxon ontogenetic trajectories (which appear as within-group correlations of RW's that must, per definition, be uncorrelated in the pool). When visualized, both correspond to regionalized shape differences. The shape differences associated with the second sheared RW, which separates Homo from Pongo and the African apes, are already manifest in the youngest forms we have. These ape ontogenies seem parallel, but the vector for H. sapiens is different (P=0.002). Shape features of the third component, which distinguishes among the African apes, develop during postnatal ontogeny, and thus express actual divergence of ontogenies. Assuming that Hominoidea is monophyletic, the average growth trajectory is a reasonable estimate of the ancestral ontogeny. This trajectory is closest to those observed in our two samples of chimps, particularly to that for bonobo. In the second and third dimensions, furthermore, the bonobos lie nearly at the grand mean. We suggest therefore that bonobo is a particularly good model species for speculations about hominoid ancestral ontogeny. Research supported by the Austrian Science Foundation Project P14738 and a Ph.D. grant of the University of Vienna.

Bipedal and quadrupedal walking are classified as symmetrical gaits because the footfalls of both body sides are evenly spaced in time. However, even in humans, subtle left-right differences or asymmetries are described in several respects. In apes, some literature data point to quantitative asymmetries with respect to ground-reaction forces and to the amplitude of arm muscle electomyograms. Most likely, these asymmetries are also reflected in kinematics and in locomotor anatomy, and may be related to behavioral laterality and handedness. Bonobos ate good facultative bipedal walkers with a 'bent-hip, bent-knee' gait. For morphometrical and paleo-ecological reasons, they may be a particularly good study species to contribute to our understanding of early hominid locomotion. We studied eight bonobos, walking on an instrumented walkway allowing for synchronous recording of kinematics (two 50 Hz cameras), ground-reaction forces (three AMTI force platforms), and plantar pressures (three Footscan pressure plates). Although bonobo walking is very variable, asymmetries are observed in terms of kinematics, ground reaction forces and plantar pressures. During quadrupedal locomotion, bonobos typically take long strides (compared to bipedal walking) and overstride, placing one foot inside, and the other foot outside the position of the hands. During bipedalism, bonobos also walk obliquely to the walking direction, with the preferred 'leading' and 'trailing' sides being individual characteristics. Kinetic and pedobarographic data are consistent with the asymmetries observed kinematically, and suggest that both body sides may be, to some extent, functionally different during locomotion. This study is supported by the FWO-Vlaanderen and by the CRC.