Interactions of pollinators and nectar-occupying yeast communities Inaugural-Dissertation to obtain the academic degree Doctor rerum naturalium (Dr. rer. nat.) submitted to the Department of Biology, Chemistry, Pharmacy of Freie Universität Berlin by SEBASTIAN LARS HAUSMANN 2018 This thesis was conducted between October 2015 and October 2018, under the supervision of Prof. Dr. Matthias C. Rillig (Freie Universität Berlin) and Prof. Dr. Britta Tietjen (Freie Universität Berlin). The work was carried out at Freie Universität Berlin. 1st Reviewer: Prof. Dr. Matthias C. Rillig 2nd Reviewer: Prof. Dr. Britta Tietjen Date of defense: 25th January 2019 ACKNOWLEDGEMENTS First of all, I want to thank my supervisor Prof. Dr. Matthias C. Rillig for making this thesis possible and for having always an open ear and an inspiring advice. I also thank my second supervisor Prof. Dr. Britta Tietjen and her excellent guidance in ecological modelling and statistics. I express my gratitude to Prof. Dr. Jens Rolff for mentoring me during the PhD student time and his encouragement already during my master thesis. This work would not be possible without all the support, discussions and humor, I experienced in the Rillig Lab at Freie Universität, especially from my colleagues Dr. Jeannine Wehner, Dr. Moritz Mittelbach, Dr. Stefan Hempel, Dr. Daniel Lammel, Dr. India Mansour, Dr. Masahiro Ryo, Dr. Julien Roy and Dorothea Mayland. I am grateful to Sabine Buchert and Gabriele Erzigkeit who advised me with their technical expertise. Especially during the analyzing and writing process I learned a lot from my co-authors, of which only Florian Jeltsch was not yet named, who is the driving force behind the Biomove Research Training Group (RTG). I am thankful for the whole BioMove RTG, including all supervisors. Especially my PhD student colleagues Larissa Schaub, Carolin Scholz, Pierluigi Colangeli and Gabriele Schiro made the time in the research station Dedelow to a memory I will always smile about. I am very grateful for the encouragement and support of my parents Bernd Hausmann and Kristiane Cullman, my sister Kathleen Hausmann and my girlfriend Lea Z’graggen. I thank Prof. Dr. Randolf Menzel for providing a honeybee flight room at Freie Universität Berlin and the beekeepers Detlef Krause, Erika Mayer, Heinz Risse, Antje Schulz, Andreas Hartmann and Carl Wendt who provided bee hives for sampling. The permission to collect protected insect groups for this research was granted by the Regional Department for Environment Brandenburg. I thank the DFG for funding my position and research within the framework of the Biomove RTG (DFG-GRK 2118/1). 1 TABLE OF CONTENTS ACKNOWLEDGEMENTS ........................................................................................................ 1 TABLE OF CONTENTS ............................................................................................................ 2 SUMMARY .................................................................................................................................... 4 THESIS OUTLINE ................................................................................................................... 10 PUBLICATION LIST ............................................................................................................... 11 LIST OF FIGURES ................................................................................................................... 12 LIST OF TABLES ..................................................................................................................... 13 GENERAL INTRODUCTION ............................................................................................... 14 1 CHAPTER 1: SOLVING THE PUZZLE OF YEAST SURVIVAL IN EPHEMERAL NECTAR SYSTEMS: EXPONENTIAL GROWTH IS NOT ENOUGH ................................................................................................................................ 21 1.1 Abstract .......................................................................................................................... 21 1.2 Introduction ................................................................................................................. 21 1.3 Materials and Methods ............................................................................................ 24 1.4 Results ............................................................................................................................ 30 1.5 Discussion ..................................................................................................................... 36 1.6 Acknowledgements ................................................................................................... 41 1.7 References ..................................................................................................................... 42 2 CHAPTER 2: DISPERSING SPECIES POOLS REVEAL HOW MOBILE LINKS SHAPE METACOMMUNITIES OF NECTAR YEASTS .............................. 46 2.1 Abstract .......................................................................................................................... 46 2.2 Introduction ................................................................................................................. 46 2.3 Materials and Methods ............................................................................................ 48 2.4 Results ............................................................................................................................ 53 2.5 Discussion ..................................................................................................................... 60 2.6 Acknowledgements ................................................................................................... 65 2.7 References ..................................................................................................................... 66 3 CHAPTER 3: NECTAR YEAST COMPETITORS, BUT NOT NECTAR YEASTS, OVERWINTER WITH BEES ......................................................................... 70 3.1 Abstract .......................................................................................................................... 70 3.2 Introduction ................................................................................................................. 70 2 3.3 Materials and Methods ............................................................................................ 74 3.4 Results ............................................................................................................................ 78 3.5 Discussion ..................................................................................................................... 79 3.6 Acknowledgements ................................................................................................... 83 3.7 References ..................................................................................................................... 84 GENERAL DISCUSSION ....................................................................................................... 89 CURRICULUM VITAE............................................................................................................ 96 REFERENCES (Introduction and Discussion) ........................................................... 97 DECLARATION OF AUTHORSHIP ................................................................................ 101 APPENDICES................................................................................................................................ I APPENDIX 1: SUPPLEMENTARY MATERIAL CHAPTER 1 ....................................... I A: Model description ............................................................................................................ i B: Detailed materials and methods of lab experiments .................................... xii C: Plots and tables for results of experiments ........................................................ xv References (Appendix 1) .............................................................................................. xvii APPENDIX 2: SUPPLEMENTARY MATERIAL CHAPTER 2 ................................... XX A: Additional tables and figures ................................................................................... xx B: Molecular yeast identification (Method) ........................................................ xxxi C: Drivers of flower visits ........................................................................................... xxxii References (Appendix 2) ......................................................................................... xxxvii 3 SUMMARY Floral nectar offers a unique niche as habitat for microorganisms. The fluid nectar environment is characterized by a high sugar-concentration, a short flower lifetime and regular nectar depletion and replenishment caused by nectar-foraging pollinators. Microorganisms that live in floral nectar must resist high osmotic pressure, adapt quickly to new environmental conditions, have fast growth rates and manage frequent dispersal to new habitats. Besides generalist bacterial and fungal species that are also known from other sources, there are three yeast species that are almost exclusively found in floral nectar and which are called nectar yeasts: Metschnikowia reukaufii, M. gruessii and Candida rancensis. They can affect their environment by changing nectar chemistry, scent, flower temperature and, as a result,