Mechanics, Diversity, and Ecology of Gecko Adhesion
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MECHANICS, DIVERSITY, AND ECOLOGY OF GECKO ADHESION A Dissertation Presented in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy with a Major in Biology in the College of Graduate Studies University of Idaho by Travis Jay Hagey August 2013 Major Professor: Luke. J. Harmon, Ph.D. ii AUTHORIZATION TO SUBMIT DISSERTATION This dissertation of Travis J. Hagey, submitted for the degree of Doctor of Philosophy with a major in Biology and titled “Mechanics, Diversity, and Ecology of Gecko Adhesion,” has been reviewed in final form. Permission, as indicated by the signatures and dates given below, is now granted to submit final copies to the College of Graduate Studies for approval. Major Professor ______________________________ Date _______________ Luke J. Harmon Committee ______________________________ Date _______________ Members Craig P. McGowan ______________________________ Date _______________ Jack M. Sullivan ______________________________ Date _______________ Kellar Autumn Department ______________________________ Date _______________ Administrator James J. Nagler College of Science ______________________________ Date _______________ Dean Paul Joyce Final Approval and Acceptance by the College of Graduate Studies ______________________________ Date _______________ Jie Chen iii Abstract The question of why animals are shaped the way they are has intrigued scientists for hundreds of years. Studies of ecological morphology (the relationship between an organism’s form, function, and environment) often bridge multiple disciplines including biomechanics, ecology, phylogenetics, and comparative methods. In this dissertation, I gathered data and tested hypotheses that considered the link between morphology and performance and the relationship between performance and ecology. I focused my research on the adhesive abilities of geckos. Geckos are an understudied, diverse group of lizards, well known for their adhesive toe pads. I propose that geckos are an excellent group to consider ecological morphology due to the breadth of morphological, performance, and ecological variation across species, the presence of many recent phylogenetic hypotheses detailing evolutionary relationships among gecko species, and the fascinating characteristics inherent in the gecko adhesive system. My first research chapter (Chapter 2) focused on the relationship between gecko setal morphology and performance. In this chapter I found that previously described mechanical models of setal performance can likely be applied to a broad range of gecko species, but these models may also be improved for better accuracy. My next chapter (Chapter 3) considered the diversity of adhesive performance across padded lizards. I found that anole lizards, Gekkonidae and Phyllodactylidae geckos, and Diplodactylidae geckos, representing three previously proposed independent origins of adhesive pads, likely exhibit different adhesive performance capabilities and different setal mechanics. In my last research chapter (Chapter 4), I evaluated correlations between gecko adhesive performance, limb morphology, and microhabitat use and found correlations that suggest unique ecomorphological iv relationships may be present in geckos. Overall, my results suggest geckos represent an excellent ecological morphology study system and highlight the need for broader studies considering gecko locomotion kinematics, setal mechanics, and habitat use in the context of ecological adaptation. v Acknowledgments I would like to first thank my current and previous advisors Luke Harmon and Roger Anderson. I cannot stress enough how instrumental they have been in my academic success thus far. Roger’s field course was responsible for setting me on my current professional trajectory and introduced me to fieldwork and herpetology. I am also thankful for Luke’s optimism and vision in giving a starry eyed undergrad such an amazing opportunity. More recently, Craig McGowan has been vital in helping me become a better biomechanist. The other members of my committee, past and present, also offered valuable constructive criticism along the way. I would also like to thank everyone that has given me assistance, whether it be emotional support, a couch to crash on, or stimulating conversations over drinks. My family and friends, especially Shaunte, have helped me through the trials of graduate school. I would like to thank all my coauthors, multiple anonymous reviewers, and all the folks who helped me formulate my ideas and projects, specifically the past and present members of the Harmon, Autumn, McGowan, Rosenblum, Schwarzkopf, Bauer, Jackman, and Losos labs. Matt Big-Canada Pennell, Jon Eastman, Josef Uyeda, Brice DJ B-Plugg Sarver, Katie Shine, Alyssa Stark, Mitch Day, Tony Russell, Tony Gamble, Dan Beck, Matt Vucko, Aaron Bauer, and Todd Jackman all provided valuable conversations and constructive criticisms. Matt Wilkinson assisted immensely with laboratory and field equipment. Chloe Stenkamp-Strahm taught me about histology. Bobby Espinoza, Alissa Luken, JR Wood, Jesse Grismer, Lee Grismer, Mat Vickers, Andrew Schnell, Luke Mayfowleri Mahler, Bryan Falk, Yoel Stuart, Scott Harte, Dan Scantlebury, Rich Eliot Glor, Meghan Wagner, Andrew Gygli, Katie Pond, Christine Van Tubbe, Michael Cota, Miguel Landestoy, Missy Thompson, Alan Odenborg, vi BJ Schenck, Russ Porter, Terry Soule, Eric Wolbrecht, Richard Duffy, Emily Kay, Rose Carlson, and Neely’s Travel all helped me build equipment, plan trip logistics, collect data in the laboratory and field, or graciously lent me a couch to sleep on. Many of my projects would not have been possible without the assistance of staff members and other personnel at the University of Idaho and other facilities, specifically the MCZ and AMNH museum staff, Jon Boone for access to his animals, and the James Cook University Biology staff and motor pool. The Australian Wildlife Conservancy and the Queensland landowners allowed me access to their properties. The University of Idaho, James Cook University, and Lewis and Clark animal care and ethics committees, and the Queensland Government provided vital project approvals and collection permits. I received funding from multiple sources to attend meetings and conduct research, both of which have been invaluable to my growth as a scientist. Funding sources included the BEACON Center for the Study of Evolution in Action, National Geographic/Waitt Institute, Idaho Graduate and Professional Student Association, Society for the Study of Amphibians and Reptiles, American Society of Naturalists, the Idea Network of Biomedical Research Excellence (IDAHO INBRE), the National Science Foundation, University of Idaho Student Grant Program, and the Western Washington University Undergraduate Research Grant Program. I also received logistical support from the University of Idaho’s Institute for Bioinformatics and Evolutionary Studies (IBEST). vii Table of Contents Authorization to Submit Dissertation ....................................................................................... ii Abstract....................................................................................................................................iii Acknowledgments..................................................................................................................... v Table of Contents.................................................................................................................... vii List of Figures........................................................................................................................viii List of Tables ............................................................................................................................ x Chapter 1. Introduction ............................................................................................................. 1 Chapter 1. Bibliography............................................................................................................ 7 Chapter 2. Variation in Setal Micromechanics and Performance of Two Gecko Species ....... 9 Chapter 2. Bibliography.......................................................................................................... 48 Chapter 3. Modeling the Evolution of Adhesive Performance across Padded Lizards.......... 51 Chapter 3. Bibliography.......................................................................................................... 73 Chapter 3. Appendix ............................................................................................................... 77 Chapter 3. Appendix Bibliography......................................................................................... 92 Chapter 4. How Geckos Stick in Nature: Ecology and Biomechanics of Gecko Feet ........... 93 Chapter 4. Bibliography........................................................................................................ 124 Chapter 5. Conclusions ......................................................................................................... 129 Chapter 5. Bibliography........................................................................................................ 139 viii List of Figures Figure 1.1. Linkage Between an Organism’s Morphology, Performance, and Ecology.......... 6 Figure 2.1. Biomechanical Models of Interest........................................................................ 35 Figure 2.2. Measuring Toe Detachment Angle......................................................................