Department of Primatology
Max Planck Institute for Evolutionary Anthropology
Deutscher Platz 6
phone: +49 (341) 3550 - 200
fax: +49 (341) 3550 - 299
The majority of information from wild bonobos is obtained by systematic behavioral observations of focal individuals. In many cases, observations are combined with physiological and molecular data to explore causes and consequences of social behavior. Using material such as urine, feces, and hair that can be collected non-invasively from wild apes, we are able to measure hormones, stable isotopes and other physiological markers. The work on wild bonobos at LuiKotale is complemented by studies on captive bonobos. This approach takes advantage of having control of social and environmental parameters and permits validation of physiological markers and assessment of topics such as digestive kinetics, digestive efficiency, and hormonal responses to social and environmental stimuli.
Our Research Approaches
Nutrition and energy status
Diet composition is often regarded to constitute a species specific trait with certain food types being dominant over others. In the context of human evolution, the change from a plant based diet (herbivory) to a mixed diet combining several types of food (omnivory) is regarded a prime mover paving the way for other developments such as cooperation, food sharing, and technologies of food processing. Evolutionary models associate the emergence of these traits with relatively dry habitats, pronounced seasonality, and shortage of fruit bearing trees which implies that these traits would not have evolved in high productivity forest habitats. Some traits of bonobo feeding behaviour, namely the absence of tool use, the relatively low investment in food processing, and the lower frequency of meat eating seem to support such models. This work is combined this with data on the nutritional status and energy supply, using stable isotopes and other nutritional markers that can be extracted from non-invasive samples such as urine and faeces. In conjunction with this work experimental studies are conducted to explore the efficiency of digestion of certain macronutrients such as fat, starch, and structural carbohydrates to evaluate the capacity of bonobos and other Great apes to utilize macronutrients under changing environmental conditions.
This work is conducted in collaboration with Sylvia Ortmann, Leibnitz Institute for Zoo and Wildlife Research, Berlin.
Resource competition among females
by Niina Nurmi
Socio-ecology provides models that link characteristics of food resources to different modes of competition within and between groups. In addition the model predicts differential net energy gain to characteristics of dominance hierarchies and social relationships. In short, food resources that are defendable and worth defending lead to direct (or contest) competition that will take place within and/or between groups depending on patch size. On the other hand, indirect (or scramble) competition occurs over resources that are limited but indefensible. Different modes of competition lead to specific combinations of negative or positive individual net energy gain when associated with group size and dominance rank. This will select for behavioral kin biases, cooperation, and matrilineal hierarchies in some cases and egalitarian societies or social tolerance in others. The aim of this project is to evaluate socio-ecological models that link characteristics of the main food resources that females compete over with differential net energy gain.
Female mate choice and mating strategies in wild bonobos
by Pamela Heidi Douglas
The main objective of this study is to elucidate the role of females in the mating system of wild bonobos. Long-standing questions pertaining to female sexuality are being addressed in the free-ranging community of bonobos at Luikotale, using an integrated approach combining information on behaviour, sexual morphology, and reproductive physiology. Female mate choice is an important evolutionary process that imposes sexual selection on males, yet for nearly a century after it was proposed in Darwin’s seminal work (1871); females were considered to be less sexually strategic than males. Only in recent decades have female mate choice and mating strategies received considerable theoretical and empirical attention, and evidence that females actively pursue their own mating and reproductive strategies is continually increasing.
To address this question, I am conducting focal observations and collecting non-invasive hormone samples of female bonobos to obtain data on mating behaviour and reproductive endocrinology. More specifically, I will relate female mating behaviour to reproductive state and conception likelihood by considering visual signs of oestrus and timing of ovulation as assessed by urinary concentrations of sex steroids.
The data collected in this study are expected to answer the following questions:
- What mating strategies do female bonobos employ?
- How does female reproductive state influence female mating strategies and choice of mating partners?
- Is there evidence of female mate choice in bonobos, and if so, what is the function of female choice within the mating system of wild bonobos?
Cooperation without genetic ties: a behavioral endocrine model in bonobos
Humans are distinguished from other species by their high levels of sociality and cooperation with a diverse range of social partners, including relatives and also unrelated individuals. In non-human primates as well, individuals form selective social bonds that confer a range of fitness benefits. Most research on primate social bonds has focused on relationships among the philopatric sex, involving kin or same-sex peers who have grown up together. As a result, we currently know very little about the extent to which nonhuman primates have adaptations to maintain flexible social bonds outside of kinship, and we do not understand the function of differentiated social relationships for primates.
This research project will explore the causes and consequences of individual variation in affiliation and cooperation among unrelated female bonobos. Bonobos deviate from predictions of socio-ecological models in that the closest bonds involve females, the dispersing sex, while the weakest associations occur between the philopatric males. Unrelated females exhibit diverse affiliative behaviours and also cooperate in a range of contexts, including sharing preferred, monopolizable foods and providing coalitionary support, often against males.
The goals of this project are to:
- Characterize the quality and diversity of social relationships among female bonobos using multiple behavioural measures of affiliation,
- Identify factors that influence the exchange of cooperative acts between unrelated females and
- Identify physiological correlates of social relationships by non-invasively measuring peripheral levels of the neuropeptide hormone oxytocin and the steroid hormone cortisol under varied social contexts.
Behavioural and endocrinological correlates of male mate competition and reproduction in bonobos
The bonobo society is characterized by high dominance status of adult females, co-dominance between the sexes, and cooperation and alliance formation between females. This is perhaps one of the reasons why previous research on bonobo has been biased towards social behaviour of females and the lack of information on males. However, in the light of the prominent function of female sexuality, is reasonable to assume that mating behaviour of males shows adaptations that enhance both mating success and reproductive success. Male bonobos have the reputation of being unusually peaceful and although agonistic encounters may be as frequent as in other primate species, the intensity of aggression appears to be low. Male aggression is usually related to the intensity of mate competition. When access to females can be monopolized, male contest is likely to lead to reproductive skew which can drive selection towards fighting ability and aggressiveness. This changes when males can not monopolise access to mates and under such circumstances, the need to invest in contest power and aggression will be reduced.
This project investigates mechanisms of male mate competition and its implications for the social relations among males and between the sexes. The aim of this study is to elucidate the role of male bonobos in the context of mate competition, mating, and reproduction. Behavioural observations and corresponding endocrinological data are used to investigate mate competition and alternative mating strategies in relation to social parameters such as age, dominance status, and kinship.
Specifically the research focuses on:
- elucidating basic patterns of male social relations including male dominance relations, patterns of spatial associations and affiliative behaviour,
- investigating social parameters affecting male mating success and,
- relating male behaviour to changes in the steroid hormones testosterone and cortisol in order to understand mechanisms of male mate competition and costs associated with dominance ranks and mating strategies.
Life history patterns of bonobos and chimpanzees and their relation to modern humans
Hominoid primates and humans share a suit of life history traits such as slow maturation, a delay in reproductive activity, and long life expectancy. Maturation until adulthood may account for one third of total life span and there is often a considerable gap between the emergence of reproductive competence and the onset of reproduction. While many components of the life history of modern humans reflect cultural and economic achievements of postindustrial societies, basic trends of developmental changes display phylogenetic heritage. The project aims to collect information on the physiological; development of bonobos and chimpanzees, two hominoid species that are equally closely related to humans. In this context we will explore physiological markers that have not been the subject of primate studies but that are known to be indicative of critical stages in the life history of humans. In order to establish the bench mark for comparative analyses, the project compiles a data set from modern humans that allows direct comparisons with the data from hominoid primates. The proximate goal of the project is a cross-sectional study that uses samples from a relatively large number of bonobos, chimpanzees, and modern humans to identify temporal patterns of fluctuation of physiological markers. The ultimate goal is to initiate a long-term project to monitor ontogenetic changes in physiology, physical development and behavior of individual bonobos and chimpanzees from birth to adulthood.
Gestural communication between mothers and infants
This project investigates the development of gestural communication in wild bonobos. Gestural abilities have received a great amount of research attention in recent years, due to the hypothesis that gesture played a major role in language evolution. In addition, studies on captive bonobos and other great ape species provided evidence that this channel of communication shows the highest degree of similarity to human language. However, virtually nothing is known about gestural communication in bonobos in their natural environments.
The study aims to fill this gap by analyzing videotaped interactions of bonobo mothers and infants in selected behavioral contexts. The main focus lies in the following cognitive domains:
- referentiality and
- acquisition of gestures.
As bonobos, together with chimpanzees, are the closest living relatives of humans, knowing the role gestures play under active selection pressures is essential for understanding the phylogeny of cognitive building blocks required for human language.
* The project is part of a program by the Humboldt Research Group Comparative Gestural Signalling at the Max Planck Institute for Ornithology, Seewiesen.
Consumption, dispersal and germination of seeds: the role of bonobos in the ecosystem of the Congo basin
by David Beaune
Bonobos are the largest primate in the Congo basin south of the Congo River and one of the largest consumers of fruit. Unlike many other primate species, bonobos tend to ingest the seeds of fruit and previous studies have shown that large amounts of seeds that have passed the digestive tract are intact. Therefore, bonobos are likely to have an important impact on seed dispersal and may serve an important function in the ecosystem of the lowland forest of the Congo basin. While the nutritional properties of the fruit consumed by bonobos have been studied, nothing is known about the trade offs that plants may derive from the dispersal by large frugivores. This study collects quantitative data on the ingestion and excretion of seeds by bonobos. Specifically, the following questions are addressed:
- What is the extend of seed ingestion by consumers and what proportion of seeds is excreted without physical damage?
- Does seed ingestion affect post-dispersal survival and germination?
- What is the dispersal pattern of ingested seeds?
The data obtained in this study will facilitate assessments of the ecological importance of bonobos in the ecosystem on plant community diversity and the abundance and dispersal of important food trees.
Positional Behavior in Pan paniscus
by Gilbert Ramos (Indiana University, Bloomington, Dept. Anthropology)
Detailed descriptions of fossil hominids encourages study of extant primates as potential models for understanding pre-hominid positional behaviours that may anticipate later hominid postural and locomotor adaptations. Historically, various hypotheses have been advanced to explain the unique body plan of the bonobo. Compared to chimpanzees, bonobos are more specialized for greater arboreal agility, quadrupedal terrestrial locomotion, and more frequent bipedalism. In addition bonobos are an allometrically scaled down version of the chimpanzee and their positional behaviour is expected to resemble that of immature chimpanzees. Positional adaptations among bonobos are poorly understood in part because studies to date have been limited to arboreal behaviour, and were conducted on incompletely habituated bonobos. Using a new data set from fully habituated bonobos at LuiKotale, this study explores a number of existing hypotheses concerning the positional behaviour and substrate use. The data collected in this project represent promising insights for our understanding of bonobo positional behaviour, its anatomical correlates, influences of forest topography and the changing seasons. Furthermore, this data will permit comparisons with other long-term ape positional behaviour studies on other hominoids.