Prenatal Androgen Effects as a Proximate Mechanism Underpinning Variation in Social Behavior Among Female Nonhuman Primates

Caroline Howlett,Brandon C Wheeler

doi:10.1007/s10764-021-00204-8

Caroline Howlett, Brandon C Wheeler

Open Access

https://doi.org/10.1007/s10764-021-00204-8

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Abstract

While the role of ecological factors in shaping primate social systems has been a central focus for decades, less attention has been given to phylogenetic relationships and the potential role of underlying proximate mechanisms. This study aimed to investigate the relationship between one such proximate mechanism, prenatal androgen effects (PAEs), and aspects of social behavior in female nonhuman primates using the 2D:4D ratio as a proxy for PAEs and phylogenetically controlled methods. In general, female 2D:4D ratios were highest in monogamous species (low inferred PAEs) and lowest in polygynandrous and polygynous species (high inferred PAEs). 2D:4D ratios also varied with the form of polygyny/polygynandry, potentially with regard to the need for competitive over cooperative behaviors and the intensity of female reproductive competition. Species characterized by female dominance had lower 2D:4D ratios than species characterized by male dominance or codominance. There were no significant relationships between 2D:4D ratio and either degree of frugivory or group size. Relationships between 2D:4D ratios and the directional consistency index and 2D:4D ratios and rates of female–female agonism were also nonsignificant although sample sizes for both of these variables were small. Female social relationships are a manifestation of complex competitive and cooperative behaviors and the results suggest that PAEs may act as a proximate mechanism underlying the expression of certain aspects of behavior in female primates in ways that are adaptive to their social system.

Highlights

A basic assumption of socioecological theory is that females compete for access to nutritional resources and males compete for access to females (Kappeler and van Schaik 2002)
There were no significant associations between the percentage fruit in diet or group size and any of the 2D:4D ratio measures (Table VI)
There were no significant associations between either DCI (Fig. 2) or rate of agonism and any of the 2D:4D ratio measures (Table VII)

Summary

Introduction

A basic assumption of socioecological theory is that females compete for access to nutritional resources and males compete for access to females (Kappeler and van Schaik 2002). Relationships among females are thought to be influenced by the type and strength of the feeding competition they face within and between their social groups, and this is affected by the distribution of resources (Chapman et al 1995; Isbell 1991; Koenig 2002; Sterck et al 1997). When resources are clumped and monopolizable direct (contest) competition is expected to occur (Janson and van Schaik 1988) This type of competition is likely to result in agonistic interactions between females and the formation of hierarchical social relationships (Sterck et al 1997). Females with despotic relationships have established dominance relations with one another and linear dominance hierarchies (Sterck et al 1997)

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Results