Variation in Tropical Tree Seedling Survival, Growth, and Colonization by Arbuscular Mycorrhizal Fungi near Conspecific Adults: Field and Shadehouse Experiments in Panama DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Jenalle Laree Eck, B.S. Graduate Program in Evolution, Ecology and Organismal Biology The Ohio State University 2017 Dissertation Committee: Allison A. Snow, Advisor Liza S. Comita, Co-advisor P. Enrico Bonello Simon A. Queenborough Copyrighted by Jenalle Laree Eck 2017 Abstract The Janzen-Connell hypothesis highlights the important role of species-specific natural enemies like pathogens and herbivores in maintaining species diversity within plant communities by limiting the survival and growth of seedlings near conspecific adult plants. The extent to which natural enemies reduce conspecific seedling performance is thought to influence species richness and relative abundance within plant communities, but within-species variation in this process could also affect plant diversity at the species or population level. Variation in the strength of natural enemy effects among conspecific seedlings could occur due to factors such as the degree of relatedness between conspecific seedlings and adults (i.e., their level of shared susceptibility), or due to the characteristics of the adult that determine natural enemy accumulation (e.g., reproduction), but the causes of such variation and its consequences for patterns of plant diversity have seldom been explored. I conducted experiments with tropical tree species on Barro Colorado Island, Panama, to test new hypotheses about the causes of variation in survival and growth of conspecific seedlings near adult plants, and to examine how this variation could structure patterns of plant diversity. In Chapter 1, I conducted a shadehouse experiment with the tropical tree species Virola surinamensis to test the hypothesis that highly specialized soil microbial communities accumulate around adults within species and reduce the ii performance of offspring seedlings relative to non-offspring conspecifics. In Chapter 2, I conducted a field experiment with four tropical tree species to test the hypothesis that seedling performance is reduced beneath the canopies of their own parent trees than beneath those of different conspecific adults. In Chapter 3, I conducted shadehouse and field experiments with V. surinamensis to test the hypothesis that seed production reduces the performance of conspecific seedlings near female trees relative to males by increasing the density of natural enemies beneath females. I found evidence that the soil microbial communities beneath female trees of V. surinamensis reduce the growth and colonization by mutualistic arbuscular mycorrhizal fungi (AMF) of their own offspring seedlings relative to non-offspring conspecifics. This suggests that the genetic relationship between conspecific seedlings and adults determines the outcome of seedling interactions with soil microbes. I did not find evidence that this relationship determined the survival or growth of seedlings of four species beneath conspecific adults in the field. Thus, while highly specialized interactions between soil microbes and tropical trees can occur, when seedlings are exposed to all potential natural enemies and variable environmental conditions, such effects may not be the most important determinants of seedling survival or growth. Lastly, I did not find evidence that seed production by female trees reduces conspecific seedling survival, growth, or colonization by AMF near females relative to males, suggesting that seed production does not alter natural enemy densities or interactions with seedlings in a meaningful way. These findings improve our understanding of the Janzen-Connell hypothesis by providing evidence that interactions between tropical trees and soil iii microbes can be highly specialized and could help to maintain genetic diversity within tropical tree populations. iv People, plants, animals, places, moments, traces, you lit a way. v Acknowledgments I am humbled to acknowledge my gratitude to a great many people that lit a way here. You have created an astonishing experience of time, place, and life. This journey began with family and place. My mother, Evelyn Dee Evans-Eck, and father, James Edward Eck, Jr., have been wonderfully multifaceted role models of love and hard work, and an endless source of strength, support, and fun. My loving grandparents, the late Richard Edwin Evans, Sr., of Ellensboro, WV and Shirley Jean Evans (York) of Cheboygan, MI, and James Edward Eck, Sr. and Lydia Helen Eck (Bahls) of Toledo, OH, each cared for me and taught me in their own best way. My dear aunts, Marcia Eck and Liz Morrow (Evans), have imparted their unique perspectives and enjoyments of life. The countless hours I spent learning from and being cared for by each of these people, at home and in the outdoors, allowed me to grow in a great many areas. I am eternally grateful to each of these people for their roles in nurturing my development, and for their tolerance and encouragement of a life spent pursuing dreams, even when those dreams have taken me far from home. My advisor, Liza Comita, opened the door for me to conduct graduate research in the tropical forests of Panama six years ago, and since then, has done everything in her power to impart on me the skills and qualities needed to become a scientist. She has been generous with her time and knowledge, patient and constructive in her approach to vi advising, understanding of the trials of graduate school, and an all-around excellent professional role model. Thank you, Liza, for opening the doors to Ohio State, Panama, the Smithsonian Tropical Research Institute, Yale, Penn State, and beyond, and equipping me to step through them confidently; it has been an honor to be your student. My passion for research in plant ecology has been cultivated by inspiration and opportunity granted to me by several other skilled, dedicated mentors and teachers. Allison Snow, and her lab manager, Patty Sweeney, were the first to introduce me to research in plant ecology during my undergraduate degree at Ohio State. In the Snow lab, I learned to apply my love of plants and the outdoors to research in the field, lab, and greenhouse, and I became interested in a career in plant ecology. I was granted another opportunity to develop as a plant scientist by Anne Dorrance, who hired me to study soybean disease resistance in her lab in Wooster, OH. The skills and perspectives I gained while in the Dorrance lab further shaped the direction of my own research. As a graduate student taking courses at Ohio State, I benefitted greatly from the instruction of P. Enrico Bonello, Simon Queenborough, Libby Marschall, Maria Miriti, Peter Curtis, Lisle Gibbs, Charles Goebel, Kristin Mercer, Terry Niblack, and Dan Herms. The members of my candidacy and dissertation committee, Enrico Bonello, Simon Queenborough, and Allison Snow, in addition to Liza Comita, have provided helpful direction and feedback on my research goals and proposals and manuscript drafts. At the Smithsonian Tropical Research Institute in Panama, I was fortunate to receive research support and mentorship from Scott Mangan, E. Allen Herre, S. Joseph Wright, Helene Muller-Landau, and Egbert Giles Leigh, Jr. At Penn State University, I am grateful to be vii embarking on a new genetics project with the expertise, efforts, and support of James Marden, Claude dePamphilis, and Howard Fescemyer. My deepest gratitude is extended to each of these mentors for their role in my professional development. My professional peers, the graduate students and post-docs I have been lucky to meet and learn with along the way, have been an inspiration, as well as a source of help, support, and comradery. Special thanks are extended to the past and present members of the Comita lab, who have been my academic family at Ohio State and Yale: Stephen Murphy, Meghna Krishnadas, Juan Carlos Penagos Zuluaga, Kara Salpeter, Noelle Beckman, Andrew Muehliesen, Dan Johnson, Livia Audino-Dorneles, Yan Zhu, Megan Sullivan, Anna Sugiyama, Harikrishnan Venugopalan Nair Radhamoni, and Madelon Case. The many talented, dedicated students I met at the Smithsonian Tropical Research Institute in Panama have forever shaped my life in the years that I spent working, living, and learning alongside of them on Barro Colorado Island and in Gamboa: Dana Frederick, Carolyn Delevich, Kristen Becklund, Matthew Lutz, Katie Heineman, KC Cushman, Lourdes Hernández, Maria Muriel Garcia, Jerry Schneider, Krystaal McClain, Peter Marting, Victoria Weaver, Merlin Sheldrake, Luis Beltran, Tom Bochynek, Chris Reid, Justin Shaffer, Emily Francis, Natalie Christian, Callum Kingwell, Julian Schmid, Georg Eibner, Eli Rodriguez, Eric Griffin, Camilo Zalamea, Carolina Sarmiento, Laura Walker, Jacquelline Dillard, Meghan Strong, Max Adams, Adriana Corrales Osario, Sara Fern Leitman Neihaus, Margarita Cecilia Prada, Megan Pendred, Tim Alvey, Erin Welsh, Dan Revillini, Emily Borodkin, Ernesto Bonadies, and countless others, thank you for making my time in Panama truly cherished. Of these people, Matthew Lutz deserves viii special mention for his years of unwavering love, support, and companionship, in Panama and beyond. Many other graduate students and post-docs at Ohio State, Yale, STRI and Penn State also improved my graduate experience – thank you all. The projects