ECOLOGY AND EVOLUTION OF BREEDING ADAPTATIONS IN THE VILLAGE WEAVER PLOCEUS CUCULLATUS by David C. Lahti A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Ecology and Evolutionary Biology) in The University of Michigan 2003 Doctoral Committee: Professor Robert B. Payne, Chair Emeritus Professor Richard D. Alexander Professor Brian A. Hazlett Professor Peter Railton Associate Professor Beverly J. Rathcke David C. Lahti © 2003 All Rights Reserved "One egg is like another." -Cervantes, Don Quixote, part II (1615), bk.III, ch.14. "'Tis good to keep a nest egg." -Cervantes, Don Quixote, part II (1615), bk.III, ch.7. (Sometimes the first point raises problems for the second.) DEDICATION To four individuals who, through their knowledge and their willingness to share it with me generously and enthusastically, encouraged my love for nature and showed me that I could make a career out of exploring and seeking to understand it: (the memory of) Thomas C. Dent, Botanist David C. Mahan, Aquatic Biologist Joseph K. Sheldon, Entomologist Richard T. Wright, Ecologist ii ACKNOWLEDGMENTS To offer thanks to my wife April seems out of place in a way because the empirical research described here was in fact a cooperative effort. She found and quit jobs as necessary to accompany me on all expeditions, and during those periods worked on our project as much as I did. Her intellectual contribution is reflected in her coauthorship of the published versions of most of the chapters in this dissertation. She is the reason for any use of the first person plural in the text. She is due a huge amount of thanks, of course, for handling this whole dissertation thing with love and understanding, especially during the last year. I thank Bob Payne for making birds my taxon of choice. His near unearthly command of the subject led me to my dissertation topic and is directly or indirectly responsible for whatever ornithology I have acquired. I am also grateful to him for introducing me to the art of getting papers published, through example and shrewd advice, and for aiding my research in various other ways. His and Laura's work and travel together have shown April and me how a personal partnership can also be a research partnership. I am grateful to Dick Alexander, especially for encouraging me to think carefully and hard about evolution, which has cultivated in me a deep appreciation of its explanatory power. Beverly Rathcke introduced me to biology graduate work and helped me to develop ideas and focus when I knew too little even to have a particular area of interest. I thank Brian Hazlett for providing me with a background in animal iii behavior, particularly while a GSI for his courses. Long discussions with Arnold Kluge have developed my understanding of phylogenetics and an appreciation of the importance of rigor in evolutionary and phylogenetic hypotheses. Fruitful conversations with colleagues in the Department on various aspects of our fields are too numerous to acknowledge with justice but I do not underestimate their continuing influence on me. I especially thank Miro Kummel, Alec Lindsay, Andrew Richards, Luis Schiesari, and Bret Weinstein in this regard. I am also grateful to Sal Cerchio, Heather Heying, Nate Nowak, Anna Bess Sorin, Lindsay Whitlow, and Matthew Wund. Of course I cannot forget my colleagues in the Bird Division, especially the three now senior graduate students: Anne Fowler, Heather Lerner, and Jill Flachskam. I thank Janet Hinshaw for her consistent help, and education about museum techniques and history. For making our success in the field possible I thank those acknowledged in the publication versions of these chapters, especially Mansa Dampha, Michael Lawes and Harriet Eeley, and Clive Barlow. I am grateful for the generous funding provided by the Department of Ecology and Evolutionary Biology (and before that, Biology), the Museum of Zoology, and Rackham Graduate School. Outside of the University of Michigan, I thank the National Science Foundation, American Philosophical Society, Wilson Ornithological Society, American Museum of Natural History, and the National Academy of Sciences in association with Sigma Xi. iv TABLE OF CONTENTS Dedication ii Acknowledgments iii List of Tables viii List of Figures ix Chapter 1. Introduction 1 Species Introductions and Natural Selection 1 Introductions of the Village Weaver Ploceus cucullatus 4 Brood Parasite – Host Interactions as a Model System for the Study of Natural Selection 4 Case Study: Defenses Against Brood Parasitism in the Village Weaver 5 Structure of the Dissertation 10 References 14 PART I. A CONTRIBUTION TO VARIOUS ASPECTS OF THE BREEDING ECOLOGY OF THE VILLAGE WEAVER 20 Chapter 2. Associations between Nesting Village Weavers Ploceus cucullatus and Other Animal Species in The Gambia 21 References 27 Chapter 3. Cactus Fruits May Facilitate Village Weaver (Ploceus cucullatus) Breeding in Atypical Habitat on Hispaniola 29 References 36 v Chapter 4. A Case Study of Species Assessment in Invasion Biology: The Village Weaverbird Ploceus cucullatus 39 Regions of Past and Possible Future Naturalization 41 Factors Influencing Introduction and Invasion Success 45 Agricultural Pest Status 51 Smallwood-Salmon Rating System 53 Suggestions for Prevention and Control 54 References 60 PART II. THE EVOLUTION OF DEFENSES AGAINST BROOD PARASITISM IN THE VILLAGE WEAVER 69 Chapter 5. How Precise is Egg Discrimination in Weaverbirds? 70 Introduction 71 Methods 75 Results 80 Discussion 83 References 92 Chapter 6. Evolution of Egg Appearance Following a Change in Selective Regime 98 Introduction 98 Methods 104 Results 109 Discussion 114 References 152 vi Chapter 7. Does Egg Recognition Decay in the Absence of Cuckoo Brood Parasitism? 162 Introduction 162 Methods 167 Results 172 Discussion 178 References 202 Appendix. Eigenvectors for Principal Component Analysis of Differences Between Host and Experimental Eggs 209 vii LIST OF TABLES Table 1.1 Necessary Criteria for Effective Evolutionary Analysis of Change in a Heritable Trait by Comparison of Source and Introduced Populations 3 1.2 Hypotheses Tested in Part II of This Dissertation 7 4.1 Factors Correlated with Introduction Success and Invasiveness in Birds, and Relation to the Village Weaver Ploceus cucullatus (VW) 56 4.2 Expected Ratings of Concern for Invasion, According to the Smallwood-Salmon Rating System (Smallwood & Salmon 1992) 59 5.1 Quantification of Egg Speckling Variables by Indexing 88 5.2 Parameters of Multiple Logistic Regression Model, Predicting Egg Rejection on the Basis of Egg Colour and Speckling Differences Between Host and Foreign Eggs 89 6.1 Sources of Variation in Egg Appearance in the Village Weaver 133 6.2 Comparison of Within-Clutch Variation in Egg Spotting Among Populations of the Village Weaver 134 7.1 Foreign Egg Rejection on the Basis of Egg and Clutch Characteristics: Four-Population Combined Logistic Regression Model 191 7.2 Foreign Egg Rejection on the Basis of Egg and Clutch Characteristics: Single-Population Logistic Regression Models 192 7.3 Egg Rejection by Village Weavers in the Dominican Republic: Replication of Cruz & Wiley (1989) 193 7.4 Egg Rejection by Village Weavers in the Dominican Republic: Replication of Robert & Sorci (1999) 194 viii LIST OF FIGURES Figure 3.1 Ripe Fruit of Stenocereus hystrix in the Dominican Republic, Having Been Fed Upon by Village Weavers 35 5.1 Weaver Rejection of Experimental Eggs by the Difference in Colour Between Host and Experimental Eggs 90 5.2 Weaver Rejection of Experimental Eggs by the Difference in Spot Density Between Host and Experimental Eggs 91 6.1 Geographic Range of the Village Weaver (Ploceus cucullatus). 135 6.2 Fourteen Complete Clutches (a-n) of Village Weaver (Ploceus cucullatus) Eggs, from Janjangbureh Island, The Gambia (Actual Size) 136 6.3 Spectra of 18 Eggs in Different Clutches of the Village Weaver, Dominican Republic (all eggs scored as E 12/6, a medium blue-green, on Villalobos Color Atlas (Villalobos 1947)) 137 6.4 Spectra of a 4-Egg Clutch of a Village Weaver, South Africa (all eggs scored as E 19/0, white, on Villalobos Color Atlas (Villalobos 1947)) 138 6.5 Spot Size in Village Weaver Eggs: Relation of Quantitative Measurements to Index Categories (means above each column) 139 6.6 Spot Density in Village Weaver Eggs: Relation of Quantitative Measurements to Index Categories (means above each column) 140 6.7 Spot Color in Village Weaver Eggs: Relation of Quantitative Measurements to Index Categories 141 6.8 Spot Aggregation in Village Weaver Eggs: Relation of Quantitative Measurements to Index Categories (means above each column) 142 ix 6.9 ANOVAs of Within-Clutch Disparity in (A) Egg Shape and (B) Egg Mass Between Village Weaver Populations 143 6.10 ANOVAs of Between-Individual Disparity in (A) Egg Shape and (B) Egg Mass Between Village Weaver Populations 144 6.11 ANOVAs of Within-Clutch Disparity in (A) Egg Brightness and (B) Egg Chroma Between Village Weaver Populations 145 6.12 ANOVAs of Between-Individual Disparity in Egg Brightness Between Village Weaver Populations, by (A) Color Charts, and (B) Spectrophotometry 146 6.13 ANOVAs of Between-Individual Disparity in Eggshell Chroma Between Village Weaver Populations, by (A) Color Charts, and (B, C) Spectrophotometry 147 6.14 Population-Level Egg Color Variability in Village Weavers: South Africa vs. Mauritius 148 6.15 Population-Level Egg Color Variability in Village Weavers: The Gambia vs. Dominican Republic 149 6.16 Variation