Heterotrophic Protists As Useful Models for Studying Microbial Food Webs in a Model Soil Ecosystem and the Universality of Complex Unicellular Life
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Brigham Young University BYU ScholarsArchive Theses and Dissertations 2019-07-01 Heterotrophic Protists as Useful Models for Studying Microbial Food Webs in a Model Soil Ecosystem and the Universality of Complex Unicellular Life Andrew Robert Thompson Brigham Young University Follow this and additional works at: https://scholarsarchive.byu.edu/etd BYU ScholarsArchive Citation Thompson, Andrew Robert, "Heterotrophic Protists as Useful Models for Studying Microbial Food Webs in a Model Soil Ecosystem and the Universality of Complex Unicellular Life" (2019). Theses and Dissertations. 8575. https://scholarsarchive.byu.edu/etd/8575 This Dissertation is brought to you for free and open access by BYU ScholarsArchive. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. Heterotrophic Protists as Useful Models for Studying Microbial Food Webs in a Model Soil Ecosystem and the Universality of Complex Unicellular Life Andrew Robert Thompson A dissertation submitted to the faculty of Brigham Young University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Byron James Adams, Chair Zachary Thomas Aanderud Christopher P. McKay Seth Mikaya Bybee Perry Gene Ridge Department of Biology Brigham Young University Copyright © 2019 Andrew Robert Thompson All Rights Reserved ABSTRACT Heterotrophic Protists as Useful Models for Studying Microbial Food Webs in a Model Soil Ecosystem and the Universality of Complex Unicellular Life Andrew Robert Thompson Department of Biology, BYU Doctor of Philosophy Heterotrophic protists, consisting largely of the Cercozoa, Amoebozoa, Ciliophora, Discoba and some Stramenopiles, are a poorly characterized component of life on Earth. They play an important ecological role in soil communities and provide key insights into the nature of one of life’s most enigmatic evolutionary transitions: the development of the complex unicell. Soil ecosystems are crucial to the functioning of global biogeochemical cycles (e.g. carbon and nitrogen) but are at risk of drastic change from anthropogenic climate change. Heterotrophic protists are the primary regulators of bacterial diversity in soils and as such play integral roles in biogeochemical cycling, nutrient mobilization, and trophic cascades in food webs under stress. Understanding the nature of these changes requires examining the rates, diversity, and resiliency of interactions that occur between soil organisms. However, soils are the most taxonomically diverse ecosystems on Earth and disentangling the complexities of dynamic and varied biotic interactions in them requires a unique model system. The McMurdo Dry Valleys of Antarctica, one of the harshest terrestrial environments on Earth, serve as a model soil ecosystem owing to their highly reduced biological diversity. Exploring the functioning of heterotrophic protists in these valleys provides a way to test the applicability of this model system to other soil food webs. However, very little is known about their taxonomic diversity, which is a strong predictor of function. Therefore, I reviewed the Antarctic literature to compile a checklist of all known terrestrial heterotrophic protists in Antarctica. I found significant geographical, methodological, and taxonomic biases and outlined how to address these in future research programs. I also conducted a molecular survey of whole soil communities using 18 shotgun metagenomes representing major landscape features of the McMurdo Dry Valleys. The results revealed the dominance of Cercozoa and point to an Antarctic heterotrophic protist soil community that is taxonomically diverse and reflects the structure and composition of communities at lower latitudes. To investigate whether biotic interactions or abiotic factors were a larger driver for Antarctic heterotrophic protists, I conducted variation partitioning using environmental data (e.g. moisture, pH and electrical conductivity). Biotic variables were more significant and accounted for more of the variation than environmental variables. Taken together, it is clear that heterotrophic protists play key ecological roles in this ecosystem. Deeper insights into the ecology of these organisms in the McMurdo Dry Valleys also have implications for the search for complex unicellular life in our universe. I discuss the theoretical underpinnings of searching for these forms of life outside of Earth, conclude that they are likely to occur, and postulate how future missions could practically search for complex unicells. Keywords: heterotrophic soil protists, McMurdo Dry Valleys, shotgun metagenomics, network analysis, life on Mars, key evolutionary innovations, universal complex unicellular life ACKNOWLEDGEMENTS I would like to thank my advisor, Byron Adams, for his continual support of my research and personal aspirations. Byron believed in my potential from the very beginning and has made it a priority that I believe in that potential myself, as he does with all his students. I am grateful for his willingness to discuss a myriad of scientific topics with me over the years, his earnest interest in my ideas and in pushing the boundaries of scientific inquiry, and his insightful wisdom about life in general. Byron is a passionate scientist and a great disciple of the human spirit and Christian values. I am grateful to him for his example in these regards. I would also like to thank the members of my committee—Zach Aanderud, Chris McKay, Seth Bybee, and Perry Ridge—who have been helpful in realizing a greater level of scientific quality in my research than I could have hoped to have done on my own. I would like to thank them for their time, their zeal for scientific discovery, and for their keen interest in my professional and personal future. I would like to thank the MCM LTER for allowing me the opportunity to participate in their science initiatives and to be part of the team. Working in the Antarctic was an eye-opening experience from both a personal and professional perspective. Seeing how engaging and effective interdisciplinary science is has impressed upon me the importance of collaboration and maintaining a big picture perspective even when tackling specialized problems. I would like to thank Taylor Thompson, my wife, who has been a huge support. I would not have and could not have completed this achievement without her. She has encouraged me constantly to keep pushing forward, to always do the best that I can. She has also been a steady, grounding force, helping me to see the value of taking breaks to rest and recharge, and being upbeat and positive when I was feeling down and overwhelmed. She has done all of this while sacrificing so many of her own personal goals and ambitions, and I hope to be able to one day return the favor. I would also like to thank Asher, my son, for being a relatively easygoing kid this last year and always making time for his Dad when he needed to smile. I am grateful to my parents and siblings who have been extremely supportive of this endeavor and have continually been cheering me on. I would also like to thank my wife’s family for their support and encouragement. I am grateful for each of the many friends I’ve made here in this department and in institutions around the world over the years as I’ve pursued this degree. Without all the conversations, laughs, and stimulating intellectual conversations, I doubt I would have made it through. TABLE OF CONTENTS TITLE PAGE ................................................................................................................................... i ABSTRACT .................................................................................................................................... ii ACKNOWLEDGEMENTS ........................................................................................................... iii TABLE OF CONTENTS ................................................................................................................ v LIST OF TABLES ......................................................................................................................... ix LIST OF FIGURES ........................................................................................................................ x Chapter 1: Checklist of terrestrial protists from continental and peninsular Antarctica, including the South Shetland Islands .............................................................................................................. 1 Abstract ........................................................................................................................................ 2 Introduction ................................................................................................................................. 3 Methods ....................................................................................................................................... 4 Results ......................................................................................................................................... 5 Discussion .................................................................................................................................. 36 Acknowledgements ................................................................................................................... 39 References ................................................................................................................................