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Beyond Aggression and Dominance: The Effects of Social and Environmental Factors on Fecal Testosterone and Fecal Glucocorticoid Levels in Wild Female Verreaux's Sifaka (Propithecus verreauxi)

Littlefield, Brandie L. (2010)
Dissertation (218 pages)
Committee Chair / Thesis Adviser: Whitten, Pat
Committee Members: Kingston, John ; Gouzoules, Sarah ; Brockman, Diane (University of North Carolina Charlotte);
Research Fields: Anthropology, Physical
Keywords: lemur; endocrinology; aggression; androgens; stress
Program: Laney Graduate School, Anthropology
Permanent url: http://pid.emory.edu/ark:/25593/7s7tv

Abstract

The study of female competition in non-human primates has generated more attention over recent years and placed an increased focus on the proximate and ultimate causes of female competitive behavior. When contest competition for available resources is high, females form linear dominance hierarchies, which may result in rank-related differences in feeding efficiency, nutrient intake, and reproductive success. The field of socioendocrinology provides the opportunity to examine inter-individual differences in hormonal responses to social factors that may reflect the relative costs of social rank. Research across species of primates has investigated the extent to which dominance and competitive behavior are mediated by hormones associated with aggression (androgens) and stress (glucocorticoids). Despite these advances, relatively few of these studies have examined the relationships among dominance, aggression, and hormonal measures in wild female primates.

The goal of this study was to examine female competitive behavior within an endocrinological framework by assessing the extent to which dominance rank and aggression are mediated by androgens and glucocorticoids in wild female Verreaux's sifaka (Propithecus verreauxi), a lemuroid primate living in southwest Madagascar. Behavioral and hormonal data were collected on eight adult female sifaka with infants from July through December 2007 at Beza Mahafaly Special Reserve, Madagascar.

The results showed that neither dominance rank nor rates of aggression were significant predictors of fecal testosterone (fT) or fecal glucocorticoid (fGC) levels. However, male immigration and infanticide events had a profound effect on both hormonal measures. Females in groups that experienced male takeover events had significantly higher fT and fGC levels compared to females in stable groups. There was a strong seasonal effect on aggressive behavior, suggesting that contest competition increases during the period of resource abundance for female sifaka and that dominance relationships may be seasonally dependent. Fecal glucocorticoid levels dropped significantly after the first rainfall of the season, demonstrating that the endocrine response is particularly sensitive to exogenous cues for this species. These results highlight the need for longitudinal studies with repeated hormonal measures in order to assess the complex interactions of social and ecological factors on the endocrine response in female primates.

Table of Contents

Table of Contents

I. Introduction: Female Competition in Non-human Primates and the
Hormonal Correlates of Aggression and Dominance

Introduction ………………………………………………………………… 1
Research Goals and Organizing Questions …………………… 6
Overview of Female Resource Competition in Primates.. 8
Lemur Behavior, Ecology, and Social Structure …………. 11
The Case of Verreaux's Sifaka ……………………………………. 15
The Endocrinology of Competition ………………………………. 19
Androgens, Aggression, and Dominance ……………………… 20
Competition and the Stress Response ………………………… 29
General Research Aims ………………………………………………… 38
Conclusions …………………………………………………………………. 41
Table …………………………………………………………………………... 43
References …………………………………………………………………. 45
II. Seasonal Changes in Behavior and Competition: Implications for Female
Dominance Relationships in Verreaux's Sifaka (Propithecus verreauxi )

Introduction ……………………………………………………………… 62
Methods ……………………………………………………………………. 65
Results ……………………………………………………………………… 71
Discussion ………………………………………………………………… 78
Conclusions ………………………………………………………………. 87
Tables ………………………………………………………………………. 91
Figures ……………………………………………………………………… 95
References ……………………………………………………………… 106
III. The Effects of Dominance, Aggression, and Male Immigration Events on
Fecal Testosterone Levels in Female Verreaux's Sifaka (Propithecus
verreauxi
)

Introduction …………………………………………………………… 111
Methods …………………………………………………………………. 115
Results …………………………………………………………………… 123
Discussion ……………………………………………………………… 125
Conclusions ……………………………………………………………… 131
Tables ……………………………………………………………………… 134
Figures ……………………………………………………………………. 137
References ……………………………………………………………… 140

IV. The Interaction of Ecological and Social Factors on the Stress Response:

The Effects of Rainfall and Male Immigration Events on Fecal Glucocorticoid

Levels in Female Verreaux's Sifaka (Propithecus verreauxi)

Introduction.................................................... 148

Methods......................................................... 155

Results........................................................... 163

Discussion....................................................... 164

Conclusions..................................................... 170

Tables........................................................... 173

Figures.......................................................... 175

References..................................................... 180

V. Summary and Conclusions 187

References.................................................... 202

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