Innovation in wild chimpanzees (Pan troglodytes)

Innovations of behavior have major implications for the concept of culture in animals. Innovation has rarefy been documented in wild animal populations. The chimpanzees of the Taï National Park, Côte d’Ivoire, spontaneously included new patterns of behavior in their repertoire during our study. Some innovations were incorporated into a minority of the group members’ repertoire, whereas others, such as building day nests in trees and on the ground more frequently, became general behaviors. Similarly, new contexts for use of leaf- clipping behavior and novel ways of feeding on some leaves appeared and rapidly became part of the behavior of most group members. The environmental parameters were too stable to explain these new forms of behavior, as most of them took place within 1 month during the same dry season. In a similar way, leaf- grooming acquired a new function in Gombe chimpanzees. A process similar to social conventions could explain the emergence of these new functions for an existing behavior in a way rather similar to human “fashion. ” Three major characteristics of human culture — the absence of individual variations in the performance of the behavior, the general use of the behavior by group members, and the ability to modify the function of a behavior — characterize leaf-clipping in Taï chimpanzees and leaf- grooming in Gombe chimpanzees.     

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.     

Elemental variation in the termite fishing of wild chimpanzees (Pan troglodytes)

Chimpanzee tool behaviours vary dramatically in their complexity and extent of geographical distribution. The use of tool sets with specific design features to gather termites extends across a large portion of central Africa. Detailed examination of the composition and uniformity of such complex tool tasks has the potential to advance our understanding of the cognitive capabilities of tool users and processes underlying the maintenance of technological skills. In this study, we examined variation in chimpanzee tool use in termite gathering from video-recorded sequences that were scored to the level of functionally distinct behavioural elements. Overall, we found a high degree of similarity in tool-using techniques exhibited by individuals in this population. The number of elements in each individual's repertoire often exceeded that necessary to accomplish the task, with consistent differences in repertoire sizes between age classes. Adults and subadults had the largest repertoires and more consistently exhibited element strings than younger individuals. Larger repertoires were typically associated with incorporation of rare variants, some of which indicate flexibility and intelligence. These tool using apes aid us in understanding the evolution of technology, including that of our human ancestors, which showed a high degree of uniformity over large spatial scales.     

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.     

Primate archaeology reveals cultural transmission in wild chimpanzees (Pan troglodytes verus)

Recovering evidence of past human activities enables us to recreate behaviour where direct observations are missing. Here, we apply archaeological methods to further investigate cultural transmission processes in percussive tool use among neighbouring chimpanzee communities in the Taï National Park, Côte d''Ivoire, West Africa. Differences in the selection of nut-cracking tools between neighbouring groups are maintained over time, despite frequent female transfer, which leads to persistent cultural diversity between chimpanzee groups. Through the recovery of used tools in the suggested natal territory of immigrants, we have been able to reconstruct the tool material selection of females prior to migration. In combination with direct observations of tool selection of local residents and immigrants after migration, we uncovered temporal changes in tool selection for immigrating females. After controlling for ecological differences between territories of immigrants and residents our data suggest that immigrants abandoned their previous tool preference and adopted the pattern of their new community, despite previous personal proficiency of the same foraging task. Our study adds to the growing body of knowledge on the importance of conformist tendencies in animals.     

Skeletal differences between pygmy (Pan paniscus) and common chimpanzees (Pan troglodytes)

Skeletal dimensions of pygmy (Pan paniscus) and common (Pan troglodytes) chimpanzees were compared. Significant differences were found in the clavicles, scapulae, pelvises, and in the humerus/femur and femur head/length ratios. No significant differences were observed in long bone lengths or talar breadths. There is extensive overlap in body weights, so that the observed differences cannot be accounted for by body size alone. We conclude that pygmy and common chimpanzees are morphologically distinct. Implications for hominoid evolution are discussed.     

Imaginary Play in chimpanzees (Pan troglodytes)

Imaginary Play was studied in a group of five signing chimpanzees and it was found that chimpanzees engage in imaginary play similar to that found in human children. Fifteen hours of remote videotapes were analyzed for instances of imaginary play. Behaviors were defined as imaginary play by meeting a predetermined criteria which allowed them to be classified into one of six different categories of imaginary play. Six instances of imaginary play were found and these were classified into the two categories of Animation and Substitution. Observations of imaginary play in other research with chimpanzees were discussed.     

Twinning and heteropaternity in chimpanzees (Pan troglodytes)

Unlike monozygotic (MZ) twins, dizygotic (DZ) twins develop from separate ova. The resulting twins can have different sires if the fertilizing sperm comes from different males. Routine paternity testing of a pair of same-sexed chimpanzee twins born to a female housed with two males indicated that the twins were sired by two different males. DNA typing of 22 short-tandem repeat (STR) loci demonstrated that these twins were not MZ twins but heteropaternal DZ twins. Reproductive data from 1926-2002 at five domestic chimpanzee colonies, including 52 twins and two triplets in 1,865 maternities, were used to estimate total twinning rates and the MZ and DZ components. The average chimpanzee MZ twinning rate (0.43%) equaled the average human MZ rate (0.48%). However, the chimpanzee DZ twinning rate (2.36%) was over twice the human average, and higher than all but the fertility-enhanced human populations of Nigeria. Similarly high twinning rates among African chimpanzees indicated that these estimates were not artifacts of captivity. Log-linear analyses of maternal and paternal effects on recurrent twinning indicated that females who twinned previously had recurrence risks five times greater than average, while evidence for a paternal twinning effect was weak. Chimpanzee twinning rates appear to be elevated relative to corresponding estimated human rates, making twinning and possibly heteropaternity more important features of chimpanzee reproductive biology than previously recognized.     

Measurement of eye-gaze in chimpanzees (Pan troglodytes)

Gaze cues are used as an index of social cognition in primates, yet the sensitivity to different forms of gaze, and consequently the cues required to test gaze-following abilities remain understudied. Whereas the eye is attributed special signal value in humans, the camouflaged ocular morphology of non-human primates has led to the consensus that head orientation may be a more salient cue. This study presents the first documentation of the surface eye movements of the chimpanzee, Pan troglodytes, in order to determine the behavioral forms of eye-gaze and their saliency as signals, document their functional variation, and address the signal value of the eyes distinct from head orientation. Movements of the eye were identified as Scan (continuous movement), Glance (a single movement <1 sec), or Fixate (no movement). Scans, glances, and fixations were reliably detected by humans during live observation and from video (Cohen's kappa over 0.70) and, therefore, are likely also to be detected by conspecifics. Eye-gaze comprised a nonunitary measure of visual attention, reflecting the attentional task demands of different activities. Specifically, chimpanzees spent significantly more time scanning while feeding and resting, than grooming, F(2,28) = 10.23, P<0.001, and spent significantly more time fixating while grooming, than feeding or resting, F(2,28) = 7.52, P<0.01. Further, eye-gaze was often incongruent with head movement, varying significantly with the form of eye-gaze: incongruence was found during 12-21% of fixations, during 42-49% of scans, and during 70-100% of glances, F(2,16) = 30.17, P<0.001. These findings provide the basis for discrimination of the adaptive significance of gaze-processing abilities with emphasis on sensitivity to eye-gaze distinct from head orientation. If we are to continue exploring gaze-processing abilities in primates, then we need greater consideration of the precise nature of the signals themselves. Here we present evidence for special consideration of the eyes as a salient signal in P. troglodytes.     

Molar development in common chimpanzees (Pan troglodytes)

Numerous studies have reported on enamel and dentine development in hominoid molars, although little is known about intraspecific incremental feature variation. Furthermore, a recent histological study suggested that there is little or no time between age at chimpanzee crown completion and age at molar eruption, which is unlikely given that root growth is necessary for tooth eruption. The study presented here redefines growth standards for chimpanzee molar teeth and examines variation in incremental features. The periodicity of Retzius lines in a relatively large sample was found to be 6 or 7 days. The number of Retzius lines and cuspal enamel thickness both vary within a cusp type, among cusps, and among molars, resulting in marked variation in formation time. Daily secretion rate is consistent within analogous cuspal zones (inner, middle, and outer enamel) within and among cusp types and among molar types. Significantly increasing trends are found from inner to outer cuspal enamel (3 to 5 microns/day). Cuspal initiation and completion sequences also vary, although sequences for mandibular molar cusps are more consistent. Cusp-specific formation time ranges from approximately 2 to 3 years, increasing from M1 to M2, and often decreasing from M2 to M3. These times are intermediate between radiographic studies and a previous histological study, although both formation time within cusps and overlap between molars vary considerably. Cusp-specific (coronal) extension rates range from approximately 4 to 9 microns/day, and root extension rates in the first 5 mm of roots range from 3 to 9 microns/day. These rates are greater in M1 than in M2 or M3, and they are greater in mandibular molars than in respective maxillary molars. This significant enlargement of comparative data on nonhuman primate incremental development demonstrates that developmental variation among cusp and molar types should be considered during interpretations and comparisons of small samples of fossil hominins and hominoids.     

Innovative social behavior in chimpanzees (Pan troglodytes)

We present evidence of agonistic buffering in captive chimpanzees, recorded from 1993 until 2005, mainly from ad libitum sampling in over 2000 hr of observation. A total of 33 agonistic buffering episodes were analyzed for context and effects of this complex social behavior. Agonistic buffering was directed at the whole chimpanzee colony as they supported an individual who initially received aggression from the alpha male, independently of the victim's age, sex or social rank. Chimpanzee agonistic buffering behavior is compared with that in other nonhuman primate species, and we describe some particularities of chimpanzee agonistic buffering: the status of the buffers used-socially important offspring such as those from the alpha female-and the social rank of the adult male responsible for the buffering episode-alpha male. Possible functions for this behavior in chimpanzees are suggested as appeasement of group members in a particularly crowded captive setting, and/or as a "forced reconciliation" mechanism. Chimpanzees exhibit behavioral flexibility by adapting themselves to new social and physical situations and use novel behavior to achieve social benefits.     

Electrocardiogram abnormalities in captive chimpanzees (Pan troglodytes)

Although cardiovascular disease is the leading cause of death in the captive chimpanzee population, little is known about the prevalence and etiology of heart disease in this species. We reviewed the physical exam records of 265 common chimpanzees (Pan troglodytes) for electrocardiogram abnormalities. During the 24-mo period reviewed (August 2003 through August 2005), 34 animals were diagnosed with cardiac arrhythmias consisting of ventricular arrhythmias, supraventricular arrhythmias, conduction disturbances, mixed arrhythmias, and bradycardia. The incidence of cardiac arrhythmia was significantly higher in male animals, chimpanzees 20 to 39 y old, and those with structural heart disease. Incidence of cardiac arrhythmia was not significantly higher in animals with hypertension, hyperlipidemia, or chronic viral infections. During the retrospective period, 7 animals with cardiac arrhythmias died or were euthanized. Mortality was significantly higher in animals with ventricular arrhythmias compared with those without ventricular arrhythmias. We conclude that in the common chimpanzee, age, male gender, and structural heart disease are risk factors for developing cardiac arrhythmias and that ventricular arrhythmias are risk factors for mortality.     

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.     

Videotapes as enrichment for captive chimpanzees (Pan troglodytes)

The effectiveness of showing videotapes to captive chimpanzees as an environmental enrichment was quantitatively tested. The responses of 10 subjects (3 adult males and 7 adult females) to videotapes of chimpanzees engaging in a variety of behaviors, to videotapes of other animals and humans, and to television programs were compared. Data collection consisted of 20-minute, continuous sampling tests while various videotapes were shown. A total of 400 tests were conducted. Multivariate analysis of variance was applied to measure differences in the duration of eight categories of behavior across videotapes of varying content. No general behavioral differences in response to the tapes based on sex or housing were revealed. However, with the behavior of monitor-watching analyzed alone, we found that individually housed subjects watched the videotapes more than socially housed subjects. When viewing time was averaged across all videotapes, the chimpanzees watched the monitor a mean of 38.4% of the time available. The chimpanzees' behavior varied significantly only when they were watching the videotapes of various human and chimpanzee activities and not when watching a blank screen. A Pearson's correlation indicated that subjects habituated to repeated presentations of the videotapes, although the effect was small numerically. Although this type of enrichment did not extensively alter behavior, it did occupy a significant portion of the subjects' activity budget; thus, the amount of time spent watching the video stimuli indicated that videotapes may be a useful enrichment for captive chimpanzees. Zoo Biol 19:541-551, 2000. Copyright 2000 Wiley-Liss, Inc.     

Evidence for social referencing in young chimpanzees (Pan troglodytes)

A captive chimpanzee group was observed in order to determine the extent to which the social interactions of the infants and juveniles (18-50 months) were affected by their mothers' relationships with other adult group members. It was found that the young chimpanzees initiated more interactions with adults who interacted more with their mothers. A vast majority of those interactions occurred at significant distances from the mother. It is argued that these data imply a social-cognitive ability in young chimpanzees closely related to the human infant's ability to use its mother in 'social referencing'.