Sociality and social relationships are important to both human and non-human primates because they lead to fitness benefits, measured by infant survival, fertility and net reproductive rates. Lack of social support, on the other hand, has been shown to be associated with chronic stress in human and non-human primates. Chronic stress, by causing prolonged elevation of glucocorticoid hormones, can severely impact individual health and survival and can also adversely affect reproductive physiology. Thus it is important to understand the importance of social bonds to individual primates, and to understand both the beneficial effects of social bonds on fitness as well as the negative impacts of the lack of social support on stress physiology. Hamadryas baboons (Papio hamadryas hamadryas) provide an ideal system in which to study the effects of social bonds on proximate measures of fitness and the lack of bonds on stress physiology. Hamadryas live in a multi-level social system with the smallest level being a one-male unit (OMU). An OMU, in addition to a "leader" male, variably contains one or more females and their offspring, as well as secondary "follower" males. Hamadryas society is probably the most male-dominated society among primates and females receive a substantial amount of aggression from leader males, especially during and after takeovers. Even though females focus a sizeable proportion of their affiliative interactions on the leader male, they also form social relationships both with other females and even follower males. It is obvious, therefore, that depending on the type of OMU in which a female resides, she will form very different social bonds with consequent variable effects on her fitness. This study will examine variation in the behavior of hamadryas females across different types of OMUs in a population of hamadryas baboons at the Filoha outpost of the Awash National Park in Ethiopia. Using proximate measures of fitness, such as short-term reproductive parameters (conception rates and infant survival), and both physiological (glucocorticoid hormones) and behavioral (self-directed behavior such as self-grooming, scratching, self-touching and body-shaking) indicators of stress, this project aims to determine the effect on female fitness of the strength and quality of social bonds and whether females exercise strategies to cope with their specific social environment. This project will examine a female's relationships with each type of adult partner available to her in an OMU and answer questions addressing the effects of social bonds on fitness measures and stress levels. By examining female relationships with other females as well as with follower males, this project aims to elucidate whether social bonds with others benefit both mothers and infants in the form of alloparental help and extra protection received as well as lower stress levels due to better social integration. Female relationships with the leader male will also be studied to understand whether females benefit from more tolerant leader males who allow females to have relationships with other females or follower males, or whether females benefit from more aggressive males who are more protective towards their infants.
This study will contribute to the slowly growing body of knowledge about the effects of factors such as the availability of social support on the physiology, health and reproduction of animals. This research will improve knowledge of the adaptive value of social bonds and coping mechanisms in primates and the effects of both on stress physiology. By examining the effects on infants and female fitness of alloparenting by various members of the social unit, particularly by males, this study can contribute to our understanding of larger theoretical questions in evolutionary primatology, as alloparenting has been suggested to be important in the evolution of both human and non-human primates. The results of this study may also contribute to our understanding of the evolution of baboon social systems and the evolution of social behavior in primates as a whole. Lastly, their similarities with hominids make baboons, especially hamadryas baboons with their multi-level social system and strong long-term male-female bonds, very useful as models of hominid origins and this study may therefore contribute to our understanding of human social evolution.
