Associations between glucocorticoids and sociality across a continuum of vertebrate social behavior.

Aura Raulo,Ben Dantzer

doi:10.1002/ece3.4059

Abstract

The causes and consequences of individual differences in animal behavior and stress physiology are increasingly studied in wild animals, yet the possibility that stress physiology underlies individual variation in social behavior has received less attention. In this review, we bring together these study areas and focus on understanding how the activity of the vertebrate neuroendocrine stress axis (HPA‐axis) may underlie individual differences in social behavior in wild animals. We first describe a continuum of vertebrate social behaviors spanning from initial social tendencies (proactive behavior) to social behavior occurring in reproductive contexts (parental care, sexual pair‐bonding) and lastly to social behavior occurring in nonreproductive contexts (nonsexual bonding, group‐level cooperation). We then perform a qualitative review of existing literature to address the correlative and causal association between measures of HPA‐axis activity (glucocorticoid levels or GCs) and each of these types of social behavior. As expected, elevated HPA‐axis activity can inhibit social behavior associated with initial social tendencies (approaching conspecifics) and reproduction. However, elevated HPA‐axis activity may also enhance more elaborate social behavior outside of reproductive contexts, such as alloparental care behavior. In addition, the effect of GCs on social behavior can depend upon the sociality of the stressor (cause of increase in GCs) and the severity of stress (extent of increase in GCs). Our review shows that the while the associations between stress responses and sociality are diverse, the role of HPA‐axis activity behind social behavior may shift toward more facilitating and less inhibiting in more social species, providing insight into how stress physiology and social systems may co‐evolve.

Highlights

Studies of individual differences in behavior have a long history in animal behavior and comparative psychology (e.g., Hall, 1934; Hall & Klein, 1942; Hinde, Bowell, & Spencer-Booth, 1964)
Empirical studies of the proximate causes of animal personality and behavioral syndromes are increasing in frequency (Carere, Caramaschi, & Fawcett, 2010; Hau, Casagrande, Ouyang, & Baugh, 2016; Sih, 2011) and several excellent reviews highlight that the neuroendocrine stress response and animal personality or coping syndromes may co-vary in laboratory animals (Carere et al, 2010; Koolhaas, de Boer, Coppens, & Buwalda, 2010; Koolhaas et al, 1999; Sih, 2011)
This is best illustrated by Engh et al (2006) who showed that female chacma baboons (Papio ursinus) that had higher integrated glucocorticoid levels (GCs) due to a death of close relative increased their rate of grooming others and the more they groomed the lower integrated GCs they had a month after the stressful incident

Summary

| INTRODUCTION

Studies of individual differences in behavior have a long history in animal behavior and comparative psychology (e.g., Hall, 1934; Hall & Klein, 1942; Hinde, Bowell, & Spencer-Booth, 1964). Fecal, and excreta GCs (Sheriff, Dantzer, Delehanty, Palme, & Boonstra, 2011) as well as feather/ hair GCs (Bortolotti, Marchant, Blas, & German, 2008; Lattin, Reed, DesRochers, & Romero, 2011) are thought to reflect a mixture of both baseline and stress-induced GC levels over a species-specific period of time and are here called “integrated GCs” In addition to these observational methods to measure glucocorticoids, experimental studies use different ways (e.g., hormone implants) to manipulate individual GCs (Sopinka et al., 2015). In nonsocial or territorial species, such as eastern chipmunks (Tamias striatus: Montiglio, Garant, Pelletier, & Réale, 2012), individuals with elevated GCs (baseline, stress- induced, or integrated) were less proactive in 50% of cases studies while 21% of studies found a positive correlation between GCs and proactivity (Figure 3)

| Discussion and future directions

Findings

| CONCLUSIONS