Assaying the Blood of the Sacred Baboon: Oxytocin, Arginine Vasopressin, and the Behavior of the Baboon Subspecies Open Access

Coppeto, Daniel (Fall 2020)

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Anthropologists have always been interested in the mechanisms, both proximate and ultimate, that create the enormous variety of primate social and mating relationships. Even among primates, baboon societies are incredibly diverse in their sociality, from the tightly-bound mating relationships within the harems of the hamadryas baboon (Papio hamadryas hamadryas), to the more promiscuous, yet highly affiliative friendships of anubis baboons (Papio hamadryas anubis). Likewise, within these societies, there are also broad individual differences in social behavior, with some individuals having more affiliative and gregarious personalities, while others can be more aggressive and domineering in their relationships. However, it is still unknown which proximate physiological mechanisms are responsible for generating this behavioral diversity both between and within the subspecies. Converging evidence from neurobiological research has identified the neurohormones oxytocin and arginine vasopressin as essential mediators of social behavior, particularly affiliative and bonding relationships. However, our knowledge of their social functions in primates is still limited and lacks a strong comparative model that has been so successful in other non-primate species. This dissertation sought to combine these lines of inquiry by investigating how oxytocin and arginine vasopressin may influence baboon behavioral diversity. Furthermore, as studies in wild primate populations often have to rely on peripheral sources of the neurohormones (such as in the urine), this study also collected samples from different central and peripheral sources in order to better understand their independent and correlated effects on behavior. Biosamples and behavioral data were collected from captive hamadryas and anubis populations and were assayed using ELISA. Results showed that neurohormone concentrations were surprisingly identical between the baboon subspecies. Nevertheless, the neurohormones were not only found to be associated with numerous demographic variables, but more importantly also with measures of individual social temperament and personality. Furthermore, many of these associations were found in the blood concentrations, rather than the cerebrospinal fluid where they were expected. While these findings are useful contributions to the field, the question remains as to what physiological factors are moderating baboon behavioral diversity. Ultimately, these proximate mechanisms are likely to be related to the distribution of receptors in the baboon brain.

Table of Contents

Chapter 1: Introduction 1

           Baboon Sociality  2

                       The Anubis Baboon 3

                       The Hamadryas Baboon 4

                       Mechanisms of Baboon Behavioral Diversity 5

           Oxytocin and Arginine Vasopressin: A Primer 8

                       Evolution 9

                       Structure  9

                       Central and Peripheral Levels 11

                       Receptors 14

           Social Functions of OT and AVP 15

                       OT in Primates 15

                       AVP in Primates 18

           Dissertation Objectives 19

           References 20

Chapter 2: Between-Species Comparison 40

           Abstract 40

           Introduction 40

           Methods 44

           Results 49

           Discussion 50

           References 64

Chapter 3: Between-Individuals Comparisons 75

           Abstract 75

           Introduction 75

           Methods 79

           Results 82

           Discussion 85

           References 97

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