Urinary Cortisol, Aggression, Dominance and Competition in Wild, West African Male Chimpanzees

Anna Preis,Tobias Deschner,Catherine Crockford,Liran Samuni,Roman M Wittig

doi:10.3389/fevo.2019.00107

Abstract

High dominance status is associated with fitness benefits in many social mammals. Yet, attaining and maintaining a high social status often comes with elevated energetic costs. Dominance rank-related exposure to energetic and psychosocial stressors is predicted to vary depending on the type of breeding system, the means a high rank is acquired and maintained, and the stability of the dominance hierarchy. Using behavioral data and urinary cortisol levels, we investigated whether a high dominance rank is associated with elevated energetic costs in Tai male chimpanzees and whether the relationship between male dominance rank and cortisol levels varies between stable and unstable dominance periods. Additionally, we investigated potential sources of energetic and psychosocial stress linked to competition over dominance status and mating opportunities. We found that higher-ranking males gave more aggressions than lower ranking males in stable and unstable dominance periods, but that dominance rank and urinary cortisol levels were not associated in either period. Urinary cortisol levels were higher in all males in unstable compared to stable dominance periods, whereas aggression rates showed the reversed pattern, with higher rates in stable periods. Our results indicate that dominance maintenance is not associated with elevated physiological stress for dominant Tai male chimpanzees, and that social instability exposed all males to psychosocial stress, despite lower rates of aggressive interactions. Overall, these findings suggest that male chimpanzees adjust competitive behavior to context dependent conditions, possibly by means of predictability of outcomes of social interactions, and use conflict management strategies, such as avoidance of aggression potentially diminishing the risk of escalation.

Highlights

High dominance status is associated with fitness benefits for males and females in many animal societies (Clutton-Brock, 1988; Lloyd and Rasa, 1989; Cowlishaw and Dunbar, 1991; Pusey, 1997; van Noordwijk and van Schaik, 1999; King and Allainé, 2002; Boesch et al, 2006; Natoli et al, 2007; Rodriguez-Llanes et al, 2009; Majolo et al, 2012)
A focal male’s dominance rank was not significantly associated with urinary cortisol levels, nor aggression rates given or received
Our results indicate that dominance maintenance is not associated with elevated physiological stress for dominant males in our study groups, or alternatively that dominant males are able to counterbalance energetically demanding behavior with energy intake or other coping mechanisms

Summary

Introduction

High dominance status is associated with fitness benefits for males and females in many animal societies (Clutton-Brock, 1988; Lloyd and Rasa, 1989; Cowlishaw and Dunbar, 1991; Pusey, 1997; van Noordwijk and van Schaik, 1999; King and Allainé, 2002; Boesch et al, 2006; Natoli et al, 2007; Rodriguez-Llanes et al, 2009; Majolo et al, 2012). Dominance status predicted faster wound healing in male baboons (Archie et al, 2012), survival and stronger immune defenses in female spotted hyenas (Watts et al, 2009; Flies et al, 2016), and high socioeconomic status has been related to increased health and longevity in humans (Marmot, 2004). Inconsistent findings across different populations of the same species may relate to differences in the stability of the dominance hierarchy, availability of coping or avoidance strategies, as well as differences in analytical methods (Sapolsky, 1983; Creel, 2001; Ostner et al, 2008; Muehlenbein and Watts, 2010; Gesquiere et al, 2011a). Despite various studies examining rank related differences in stressor exposure, more comprehensive studies are needed to disentangle the relationship between social and energetic challenges associated with social status, as well as behavioral causes and consequences of dominance rank in social animals (Creel et al, 2013)

Objectives

Methods

Results

Discussion

Conclusion