Chameleon Color Change Communicates Conquest And
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Chameleon Color Change Communicates Conquest and Capitulation by Russell Ligon A Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Approved July 2015 by the Graduate Supervisory Committee: Kevin McGraw, Chair Dale DeNardo Kristopher Karsten Ronald Rutowski Pierre Deviche ARIZONA STATE UNIVERSITY August 2015 ABSTRACT Sexual and social signals have long been thought to play an important role in speciation and diversity; hence, investigations of intraspecific communication may lead to important insights regarding key processes of evolution. Though we have learned much about the control, function, and evolution of animal communication by studying several very common signal types, investigating rare classes of signals may provide new information about how and why animals communicate. My dissertation research focused on rapid physiological color change, a rare signal-type used by relatively few taxa. To answer longstanding questions about this rare class of signals, I employed novel methods to measure rapid color change signals of male veiled chameleons Chamaeleo calyptratus in real-time as seen by the intended conspecific receivers, as well as the associated behaviors of signalers and receivers. In the context of agonistic male-male interactions, I found that the brightness achieved by individual males and the speed of color change were the best predictors of aggression and fighting ability. Conversely, I found that rapid skin darkening serves as a signal of submission for male chameleons, reducing aggression from winners when displayed by losers. Additionally, my research revealed that the timing of maximum skin brightness and speed of brightening were the best predictors of maximum bite force and circulating testosterone levels, respectively. Together, these results indicated that different aspects of color change can communicate information about contest strategy, physiology, and performance ability. Lastly, when I experimentally manipulated the external appearance of chameleons, I found that "dishonestly" signaling individuals (i.e. those whose behavior did not match their manipulated color) received higher aggression from unpainted opponents. The increased aggression received by dishonest signalers i suggests that social costs play an important role in maintaining the honesty of rapid color change signals in veiled chameleons. Though the color change abilities of chameleons have interested humans since the time of Aristotle, little was previously known about the signal content of such changes. Documenting the behavioral contexts and information content of these signals has provided an important first step in understanding the current function, underlying control mechanisms, and evolutionary origins of this rare signal type. ii DEDICATION To Veronica, your love and support make me feel like I can do anything. You are everything. To Theodore, you have enriched my life in ways you cannot yet understand, though I trust you will someday. To Mom & Dad, thank you for showing me the world. iii ACKNOWLEDGMENTS I would like to thank my dissertation committee, Drs. Kris Karsten, Pierre Deviche, Ron Rutowski, Dale DeNardo, and Kevin McGraw, for the invaluable guidance they have provided me over the last 6 years. Their input, probing questions, and general skepticism have been instrumental in my scientific development. In particular, I would like to thank Dale DeNardo, whose steadfast and vocal support was integral to the process of initiating my independent, unfunded research program at ASU and whose intellectual contributions have greatly improved my research and writing. Additionally, I would like to thank Kevin McGraw for his committed mentorship and friendship during my time at ASU. Kevin gave me the freedom to develop intellectually but was always there to provide key insights and guidance when I needed them. I would also like to thank the community of ASU graduate students that I had the privilege of working with and learning from. In particular, I thank Dr. Mike Butler, Dr. Matt Toomey, Brett Seymoure, Scott Davies, Karla Moeller, Melinda Weaver, and Rick Simpson for their numerous and varied contributions to my dissertation research and continued development as a scientist. Whether by providing training in new techniques, collaborating on side projects, or discussing new ideas, these individuals broadened my thinking and my knowledge. Additionally, I owe so very much to the dedicated undergraduate researchers who worked with me during my time at ASU. Specifically, I would like to thank Kristen McCartney, Sarah Bruemmer, Megan Best, and Brianna Bero- Buell for their patience, hard work, dedication, attention to detail, and friendship. iv This work would not have been possible without the financial support of ASU’s Graduate and Professional Student Association, the School of Life Science’s Research and Training Initiatives Committee, David and Sandy Ligon, crowdfunding from users of the Rockethub website, the Animal Behavior Society, the American Society for Ichthyologists and Herpetologists, Sigma-Xi (ASU chapter), the American Society of Naturalists, the Graduate College at ASU, and the National Science Foundation. Additionally, this work would not have been technically possible without early assistance from Ellis Loew, Jim Bowmaker, Martin Stevens, and Thomas Pike. Thank you all for taking the time to help an unknown student understand and use the data, techniques, and methods you employ masterfully in your own research. Lastly, I would like to thank my family for their love and support. Mom and Dad, thank you for showing me the wonder of nature and the wonder of wondering. Dan and Dave, thank you for always being able to make me laugh. Ronnie, thank you for your encouragement, compassion, and love. You make me feel like I can do anything. Teddy, thank you for bringing new focus to my life. Spending much of the last year with you was one of the best things I've ever done. I love you all. v TABLE OF CONTENTS Page LIST OF TABLES ................................................................................................................ viii LIST OF FIGURES ................................................................................................................. ix PREFACE........... ...................................................................................................................... x CHAPTER 1 THE TIMING OF RAPID COLOR CHANGE SIGNALS DURING AGGRESSIVE INTERACTIONS COMMUNICATES INFORMATION ABOUT PHYSICAL PERFORMANCE .................................................................. 1 Abstract ....................................................................................................... 1 Introduction ................................................................................................ 2 Methods ...................................................................................................... 6 Results ...................................................................................................... 18 Discussion ................................................................................................ 22 Literature Cited ........................................................................................ 30 2 SOCIAL COSTS OF DYNAMIC COLOR SIGNALS ............................................. 40 Abstract ..................................................................................................... 40 Introduction .............................................................................................. 41 Methods .................................................................................................... 44 Results ...................................................................................................... 50 Discussion ................................................................................................ 53 Literature Cited ........................................................................................ 56 vi CHAPTER Page 3 CONCLUDING REMARKS ....................................................................................... 62 REFERENCES ........................................................................................................................ 69 APPENDIX A CHAPTER 1 TABLES AND FIGURES ................................................................. 87 B CHAPTER 2 TABLES AND FIGURES................................................................ 101 C CHAPTER 3 FIGURE ............................................................................................ 112 D CHAMELEONS COMMUNICATE WITH COMPLEX COLOUR CHANGES DURING CONTESTS: DIFFERENT BODY REGIONS CONVEY DIFFERENT INFORMATION .............................................................. 114 E DEFEATED CHAMELEONS DARKEN DYNAMICALLY DURING DYADIC DISPUTES TO DECREASE DANGER FROM DOMINANTS .......... 134 F COAUTHOR PERMISSIONS FOR INCLUSION OF PUBLISHED WORKS 146 vii LIST OF TABLES Table Page 1. Supplemental: Quantified Aggressive Behaviors ........................................................ 93 2. Supplemental: Morphological Correlations ................................................................. 93 3. Supplemental: Morphology & Testosterone Models ................................................. 94 4. Supplemental: Morphology & Bite Force Models ..................................................... 95 5. Supplemental: Phenotype & Approach Behavior Model ..........................................