The purpose of this project is to understand the proximate mechanisms, form, and evolutionary function(s) of social relationships between adult male and immature mountain gorillas (Gorilla beringei beringei). The project will address four primary questions: 1) are male and immature gorillas capable of distinguishing paternal kin from non-kin? 2) are such relationships hormonally mediated, specifically through testosterone and prolactin? 3) how do male-immature relationships change over time as immatures grow? and 4) is there evidence to support alternative hypotheses about the function of these relationships? Behavioral observations will be conducted on at least four groups of habituated gorillas living in Parc des Volcans, Rwanda, and monitored by the Karisoke Research Center. Adult males and immatures will be followed four days per week, and all relevant behaviors recorded. Hormonal data will be collected using non-invasive methods, specifically collection of urine samples from adult males and collection of fecal samples from males, mothers, and immatures. Hormones will be extracted from the samples in Rwanda before being shipped to the Lincoln Park Zoo in Chicago, Illinois for analysis.

The role of fathers is variable across non-human primate species, but to date little research has been conducted on non-monogamous species and great apes. Mountain gorillas are an interesting study species because of their highly flexible social structure, which includes both multi and single-male groups, and therefore bears similarities to variability in human mating systems. This project will give us insight into the origins of paternal behavior in different mating systems and the implications it has for offspring, in both the short and long term. This award will provide support to enable a promising student to establish a strong independent research career.

Project Report

This project investigated the "why" and "how" of relationships between wild adult male gorillas and the young animals living in their social groups. All work was conducted at the Karisoke Research Center in Rwanda, on the gorillas living in Volcanoes National Park. We used a combination of behavioral, hormonal, and paternity (genetic) data to test different hypotheses about the reasons these close relationships exist, and what the mechanisms are that regulate them. Although the project encompasses many questions about the origins of paternal care, several important ones are, "Can gorillas recognize paternity?" "Do mothers faciliate the development of relationships between males and their offspring?" and "What hormones might be responsible for variation in male attention to young animals?" Gorillas are a close human ancestor, sharing nearly 98% of our DNA. Investigating such questions in great apes helps us understand the origins of male parenting in humans. In most mammal species, males are completely uninvolved in child care; for humans and many other primate species, this is not the case. Full results from our project will not be available for another 1-2 years, as data summary and analysis from the enormous dataset acquired are ongoing. We collected more than 1,000 hours of behavioral data, 6,000 fecal samples for testosterone and cortisol analysis, and 600 urine samples for prolactin analysis. Preliminary analyses show that there are indicators that gorillas may be distinguishing between possible fathers and unlikely fathers based on age differences between males and maturing animals. Work on this project not only contributes to our understanding of an important and under-studied topic in the evolution of human behavior. It also promotes the conservation of an endangered species, supports the mission of a scientifically and economically valuable research station in a poor and politically volatile region, and contribes greatly to the training and careers of multiple people. Mountain gorillas are one of the world's most endangered primates, with less than 800 remaining. However, they are also the only great ape whose population is currently increasing. This is because of the funding and interest that research on the population brings. Understanding their social behavior also helps park staff and researchers make appropriate management decisions for the gorillas. The research station where this work was conducted employees nearly 130 people, generating a source of income for a very poor community who would otherwise be reliant on poaching and other illegal activities instead of contributing to conservation. Finally, this project trained an American scientist who is now applying for faculty and postdoctoral positions, and provided extensive scientific training for two Rwandans in laboratory techniques, data collection and processing, and scientific writing.

National Science Foundation (NSF)
Division of Behavioral and Cognitive Sciences (BCS)
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Elizabeth Tran
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University of California Los Angeles
Los Angeles
United States
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