Habitat-Specific Fitness Benefits of Sociality in Octodon Degus

HABITAT-SPECIFIC FITNESS BENEFITS OF SOCIALITY IN OCTODON DEGUS BY MADELINE KLEES STROM Loren Hayes Hope Klug Associate Professor Associate Professor Biology, Geology, and Environmental Science Biology, Geology, and Environmental Science (Advisor) (Committee Member) Mark Schorr Professor Biology, Geology, and Environmental Science (Committee Member) HABITAT-SPECIFIC FITNESS BENEFITS OF SOCIALITY IN OCTODON DEGUS BY MADELINE KLEES STROM A Thesis Submitted to the Faculty of the University of Tennessee at Chattanooga in Partial Fulfillment of the Requirements of the Degree of Master of Science: Environmental Science The University of Tennessee at Chattanooga Chattanooga, Tennessee August 2017 iii Copyright © 2017 By Madeline Klees Strom All Rights Reserved iv ABSTRACT Recent debate has focused on how ecology shapes the evolution of group-living and cooperation in social vertebrates. Evidence suggests that group-living and cooperation enhance reproductive success under harsh local conditions in some species. Across two years, I studied two populations of Octodon degus, a plurally breeding rodent, to answer three questions: (1) Does living in large groups and having strong social network strength improve access to resources in harsh environments? (2) Does increased access to resources improve the reproductive success of group-living females? (3) Does living in large groups and having strong social network strength improve reproductive success of females in harsh environments? I quantified group sizes and social network strength, ecological conditions at burrow systems, and per capita offspring weaned of social groups to answer these questions. I found site- and year-specific relationships in partial support of predictions, demonstrating habitat-specific costs and benefits of social group-living and cooperation. v DEDICATION To Mary K. Harris, for always lifting me up when I doubted myself. vi ACKNOWLEDGMENTS I would like to thank my dedicated advisor, Dr. Loren Hayes, for his continued guidance, wisdom and support during my many years in the Hayes lab. I also thank my thesis committee members, Dr. Hope Klug and Dr. Mark Schorr, for their advice in statistical analyses and the writing process. I am extremely thankful for, and indebted to my collaborators in Chile. Firstly, I thank Dr. Luis Ebensperger and his lab members at Pontificia Universidad Católica de Chile, without whom this project would not exist. Secondly, I thank Dr. Rodrigo Vasquez and his lab members at Universidad de Chile for providing me with essential and hardworking field assistants. I thank the graduate students at UTC for always giving me emotional support (especially fellow Hayes students who accompanied me to remote field stations in Chile), and my friends who encouraged me to pursue a graduate degree. Finally, I thank my loving family, for always cheering me on, teaching me to say yes to every inspiring opportunity that comes my way, and without whom none of my dreams would be possible. vii TABLE OF CONTENTS ABSTRACT ............................................................................................................................. v DEDICATION ........................................................................................................................ vi ACKNOWLEDGEMENTS ...................................................................................................... vii LIST OF TABLES .................................................................................................................... xi LIST OF FIGURES ................................................................................................................. xii LIST OF TERMS .................................................................................................................. xiv LIST OF ABBREVIATIONS ................................................................................................... xvi CHAPTER I. INTRODUCTION .................................................................................................... 1 Hypotheses for the formation of social groups and cooperation ........................ 3 Costs and benefits of group-living and cooperation ............................................ 7 Direct fitness consequences of social group-living ............................................ 13 Challenges .......................................................................................................... 14 Ecology and social variation ............................................................................... 15 Social structure and social network analysis ..................................................... 16 Thesis objectives ................................................................................................ 18 Study sites .......................................................................................................... 21 II. HABITAT-SPECIFIC FITNESS BENEFITS OF SOCIALITY IN OCTODON DEGUS ..... 25 Introduction ....................................................................................................... 25 Habitat-specific fitness consequences .............................................................. 28 Social networks ................................................................................................. 29 Study organism and objectives ......................................................................... 31 Methods ............................................................................................................ 34 Study populations ..................................................................................... 34 Social group identification ........................................................................ 35 viii Social network analysis ............................................................................. 37 Ecological sampling ................................................................................... 38 Fitness estimates ...................................................................................... 39 Statistical analysis ..................................................................................... 39 Hypothesis Tests About Means .................................................... 39 Hypothesis Tests about Regression Relationships ........................ 40 Question 1 ......................................................................... 40 Question 2 ......................................................................... 41 Question 3 ......................................................................... 41 Results ............................................................................................................... 42 Descriptive statistics ................................................................................. 42 Question 1: Does living in large groups and having strong network strength improve access to resources in harsh environments? ............... 44 Rinconada ..................................................................................... 44 Fray Jorge ...................................................................................... 45 Per capita offspring weaned ......................................................... 49 Question 2: Does increased access to resources improve the direct fitness of group-living females? ................................................................ 50 Rinconada ..................................................................................... 50 Fray Jorge ...................................................................................... 52 Question 3: Does living in large groups and having strong network strength improve direct fitness of females in harsh environments? ....... 52 Rinconada ..................................................................................... 52 Fray Jorge ...................................................................................... 53 Discussion .......................................................................................................... 55 Question 1: Benefits of social group-living and cooperation ................... 57 Question 2: Access to resources and fitness benefits .............................. 61 Question 3: Direct fitness benefits of social group-living and cooperation ............................................................................................... 63 Why live in groups? ................................................................................... 64 Evolutionary history .................................................................................. 65 Stress physiology ....................................................................................... 65 III. CONSERVATION IMPLICATIONS ....................................................................... 68 APPENDIX A. SOCIAL GROUPS ................................................................................................ 72 B. ECOLOGICAL DATA ............................................................................................ 75 C. SOCPROG PROCEDURE ..................................................................................... 80 ix D. SOCPROG OUTPUTS/NETWORK DATA ............................................................. 84 REFERENCES ...................................................................................................................... 87 VITA ................................................................................................................................

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