My work focuses on the measurement of steroid hormone metabolites from non-invasively collected feces of wild and captive primates. In orangutans this method is applied to investigate reproductive strategies in the wild and will also lead to a better understanding of the physiological responses to changes in the environment of this species. The hormone project complements the conservation aspects of genetic studies carried out at the institute and will provide important information to identify priority populations for which conservation efforts need to be intensified and to improve housing conditions of captive orangutans.
Endocrinology is also prominently featured in a wild chacma baboon project. Together with behavioral and genetic data this study aims to improve our understanding of the role of sexual conflict as a selection pressure. Infanticide by males has been observed in many primate species and case studies indicate that males killing dependent offspring that are not their own gain a fitness benefit. Infanticide can be regarded as the most severe form of sexual conflict between males and females, and it is likely that it has acted as an important selection pressure shaping reproductive physiology of females as well as protective responses from fathers. One important female counter strategy against infanticide is to find the optimal balance between paternity confusion and paternity concentration. To prevent attacks against their prospective infant, females may confuse paternity by mating with many males during the receptive period of a cycle and by passing through multiple cycles before conceiving. But a female should also ensure that the dominant male has a high enough perceived paternity probability that he will protect the infant in conflicts. The research project focuses on this female dilemma in chacma baboons, where infanticide occurs more often than in other baboon species. We are examining how effective females can implement countermeasures against male infanticide (e.g., long follicular phase, exaggerated sexual swellings, copulations calls), and how well males can estimate paternity probabilities based on their previous mating history. Besides collecting behavioral data, we are monitoring size and shape of sexual swellings. We are also collecting fecal samples to assess timing of ovulation relative to swelling size and to conduct paternity analysis. The findings of this project will improve our understanding of how counterstrategies to infanticide have shaped sociality and sexuality in primates.