Construction of playgrounds for chimpanzees in biomedical research

An outdoor 9,000 sq. ft. playground connected to the indoor-outdoor runs of the breeding facility at Southwest Foundation for Biomedical Research was constructed to simulate a near natural environment for chimpanzees in biomedical research. It is divided into three 75 X 40 ft. compounds to allow several groups of animals to utilize the area simultaneously. Environmental enrichment devices have been added to improve physical and psychological well-being.     

Electroejaculation in chimpanzees and gorillas and artificial insemination in chimpanzees

Electroejaculation was performed in 3 chimpanzees, 1 pygmy chimpanzee, and 2 gorillas with an instrument that delivers a modified sine wave current with a frequency of 24 Hz. The current stimuli were applied by a rectal probe with longitudinal electrodes. The electrical parameters varied from 6 to 12 V and from 30 to 40 mA for response of erection and lay between 8 and 18 V and between 40 and 145 mA during semen emission. Eleven chimpanzee semen samples showed the following data (x ± SD): total volume 1.9 ± 1.3 ml, volume of the liquid fraction 0.3 ± 0.2 ml, spermatozoa per ejaculate 743 ± 376 × 10⁶, sperm motility 52.7 ± 9.6%, morphologically abnormal spermatozoa 12.2 ± 7.5%. From an adult gorilla, three semen samples were collected, in each case without spermatozoa. The electrostimulation of a 6-year-old gorilla led to an erection, but not to semen emission. Three female chimpanzees were inseminated with fresh or frozen semen, each of them within three different estrous cycles. None of these inseminations led to a pregnancy.     

Innovation in chimpanzees

The study of innovation in non‐human animals (henceforth: animals) has recently gained momentum across fields including primatology, animal behaviour and cultural evolution. Examining the rate of innovations, and the cognitive mechanisms driving these innovations across species, can provide insights into the evolution of human culture. Especially relevant to the study of human culture is one of our closest living relatives, the chimpanzee (Pan troglodytes). Both wild and captive chimpanzees demonstrate an impressive ability to innovate solutions to novel problems, but also a striking level of conservatism in some contexts, creating a unique and at times puzzling, picture of animal innovation. Whilst the animal innovation field is rife with potential for expanding our knowledge of human and non‐human cognition and problem‐solving, it is undermined by a lack of consistency across studies. The field is yet to settle on a definition of the term ‘innovation’, leading to studies being incomparable across and even within the same species. Here, we fill two gaps in the literature. First, we discuss some of the most prevalent definitions of ‘innovation’ from different fields, highlighting similarities and differences between them. Secondly, we provide an up‐to‐date review of accounts of innovations in both wild and captive chimpanzees. We hope this review will provide a resource for researchers interested in the study of innovation in chimpanzees and other animals, as well as emphasising the need for consistency in the way in which innovations are reported.     

Inbreeding avoidance in chimpanzees

In a community of chimpanzees in Gombe National Park, females' associations with their previous closest male associates (usually maternal siblings) dropped abruptly when they commenced full oestrous cycles, in some cases because the females changed their range within their natal community. Sexual activity was very infrequent between maternal siblings and between mothers and sons. Whereas males remained in their natal community all their lives, most or all females transferred to other communities during adolescence either permanently or temporarily. Inter-community transfer by females apparently resulted from attraction to unfamiliar males. Thus inbreeding appears to be avoided in this species as a consequence of reduced sexual attraction between individuals who were familiar with each other in immaturity.     

Female competition in chimpanzees

Female chimpanzees exhibit exceptionally slow rates of reproduction and raise their offspring without direct paternal care. Therefore, their reproductive success depends critically on long-term access to high-quality food resources over a long lifespan. Chimpanzee communities contain multiple adult males, multiple adult females and their offspring. Because males are philopatric and jointly defend the community range while most females transfer to new communities before breeding, adult females are typically surrounded by unrelated competitors. Communities are fission–fusion societies in which individuals spend time alone or in fluid subgroups, whose size depends mostly on the abundance and distribution of food. To varying extents in different populations, females avoid direct competition by foraging alone or in small groups in distinct, but overlapping core areas within the community range to which they show high fidelity. Although rates of aggression are low, females compete for space and access to food. High rank correlates with high reproductive success, and high-ranking females win direct contests for food and gain preferential access to resource-rich sites. Females are aggressive to immigrant females and even kill the newborn infants of community members. The intensity of such aggression correlates with population density. These patterns are compared to those in other species, including humans.     

Handedness in wild chimpanzees

The debate over nonhuman primate precursors to human handedness is unsettled mainly due to lack of data, particularly on apes. Handedness in wild chimpanzees at the Taï National Park Côte d'Ivoire, has been monitored in four tasks. For the simple unimanual ones, reaching and grooming, adults use both hands equally (ambidextrous), while for the more complex unimanual wadge-dipping and the complex bimanual nut-cracking, adults are highly lateralized. These results support the hypothesis that lateralization increases with the complexity of the task. The lateralization is constant for years for each task but may vary in an individual with respect to different tasks. For nutcracking females are more lateralized than males. The ontogeny of handedness for nut-cracking shows many variations in the tendency to use one hand and in the side preferred, until at about 10 years of age, the individual achieves her adult handedness. No population bias toward one side exists in Taï chimpanzees. No heritability of handedness between mother and offspring was observed. Human and chimpanzees handedness are compared.     

Endowment effects in chimpanzees

Human behavior is not always consistent with standard rational choice predictions. Apparent deviations from rational choice predictions provide a promising arena for the merger of economics and biology [1-6]. Although little is known about the extent to which other species exhibit these seemingly irrational patterns [7-9], similarities across species would suggest a common evolutionary root to the phenomena. The present study investigated whether chimpanzees exhibit an endowment effect, a seemingly paradoxical behavior in which humans tend to value a good they have just come to possess more than they would have only a moment before [10-13]. We show the first evidence that chimpanzees do exhibit an endowment effect, by favoring items they just received more than their preferred items that could be acquired through exchange. Moreover, the effect is stronger for food than for less evolutionarily salient objects, perhaps because of historically greater risks associated with keeping a valuable item versus attempting to exchange it for another [14, 15]. These findings suggest that many seeming deviations from rational choice predictions may be common to humans and chimpanzees and that the evaluation of these through a lens of evolutionary relevance may yield further insights in humans and other species.     

Dialects in wild chimpanzees?

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. © 1992 Wiley-Liss, Inc.     

Behavioral seasonality in Mahale chimpanzees

To analyze how the chimpanzees in the Mahale Mountains National Park, Tanzania, change their grouping pattern, activity budget, travel speed, and travel distance within an annual cycle, I divided 1-year data into four periods. The Mahale chimpanzees have the behavioral flexibility to adapt to various climates and exhibited at least three behavioral seasons. In the early wet season, chimpanzees formed a few, large parties, and spent much time feeding on insects and animal meat. In the early and late dry seasons, chimpanzees maintained party sizes as large as in the early wet season, and traveled distances similar to the early wet season, but spent the most time feeding and traveling within the year. By contrast, in the late wet season chimpanzee parties broke up into more numerous, small groups, and traveled slowly over shorter distances. Although time spent feeding and traveling were the same as that in the early wet season, time spent feeding on terrestrial herbaceous vegetation (THV) was the highest in the year. The results suggest that chimpanzees travel longer, faster, and farther in seasons when they form large parties.     

Reactive erosive arthritis in chimpanzees

Diagnosis of diseases of bone, without benefit of soft tissue, in vivo observation, or blood component analysis requires the development of new criteria for diagnosis. Analyzing chimpanzee skeletal populations, applying such criteria (e.g., lesion character, distribution, radiologic appearance, and sex ratios), revealed a picture indistinguishable from human spondyloarthropathy. As Africa has been shown to manifest this condition in indigenous human, chimpanzee, and lowland gorilla populations, the possibility of a non-species specific etiology is suggested.     

Peer interaction in infant chimpanzees

The peer interactions of 6 infant chimpanzees (Pan troglodytes) ranging in age from 18 to 50 months were observed in a seminatural context. The infants and their mothers lived as members of a captive social group at the Yerkes Regional Primate Research Center. An analysis of contact initiations between infants indicated that the most preferred peer interactant was the youngest and the least preferred was the oldest infant. Infants also initiated more interactions with the offspring of adults that had the closest relationships with both themselves and their mothers. These results indicate that a number of factors may influence the peer affiliations of infant chimpanzees, including the age of the infant and the mother's social relationships.