The Pennsylvania State University The Graduate School The Huck Institute of the Life Sciences PLANT VOLATILES FROM AN ECOLOGICAL PERSPECTIVE: INTERACTIONS WITH HERBIVORES AND POLLINATORS IN SOLANUM AND NICOTIANA A Dissertation in Ecology by Thomas Granville Bentley 2014 Thomas Granville Bentley Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy December 2014 The dissertation of Thomas Granville Bentley was reviewed and approved* by the following: Mark C. Mescher Associate Professor of Entomology Dissertation Advisor Chair of Committee Consuelo M. De Moraes Professor of Entomology Andrew G. Stephenson Distinguished Professor of Biology David A. Mortensen Professor of Weed and Applied Plant Ecology David Eissenstat Professor of Woody Plant Ecology Chair of the Intercollegiate Graduate Degree Program in Ecology *Signatures are on file in the Graduate School iii ABSTRACT Plant volatiles mediate many important interactions, including plant-predator interactions, plant-herbivore interactions, plant-pollinator interactions, and plant-plant interactions. Plant volatiles can attract predators to prey, repel ovipositing herbivores, attract pollinators, coordinate a plant’s defenses, communicate with other plants, and act as foraging cues. As our knowledge of the diversity and complexity of plant volatile signaling grows, we should view plant volatiles from an ecological perspective informed by signaling theory. This theoretical framework will provide insight into the evolutionary pressures involved in plant volatile communications. This approach will also generate predictions about features that may be found in plant volatile signaling, including mimicry, costly signaling, aposematic signaling, and kin selection. This dissertation investigates three plant communication systems with this approach. In one study, I studied the effects of inbreeding on floral volatile signaling and pollinator interactions in horsenettle. I found that inbreeding negatively affects plant-pollinator signaling through floral volatiles and affects pollinator behavior. This is an example of ecologically mediated inbreeding depression caused by a breakdown of volatile communication. In another study, I investigated the possibility of plant-plant communication in horsenettle in preparation for studying kin selection in plants, though the evidence for plant-plant volatile communication in this study was not straightforward. Lastly, I investigated honest versus dishonest signaling in three species of tobacco and found evidence for a plant that honestly signals its defensive status, providing evidence for aposematic signaling through volatile emissions. This dissertation explores the consequences of diversity on volatile communication, on both the interspecific and intraspecific level, as well as the utility of evolutionary and ecologically motivated study of plant volatile communication. iv TABLE OF CONTENTS List of Figures ................................................................................................................................. vi List of Tables ................................................................................................................................. vii Acknowledgements ......................................................................................................................... ix Chapter 1 –Plant Volatiles As Communication: A Theoretical Foundation For A Complex Phenomenon. .............................................................................................................. 1 Abstract .................................................................................................................. 1 Introduction ............................................................................................................ 2 Costly signaling and honesty ................................................................................. 3 The ecological costs of plant volatiles ................................................................... 5 References .............................................................................................................. 8 Chapter 2 – Inbreeding Depression, Floral Volatiles, And Pollinator Attraction In Horsenettle . 16 Abstract ................................................................................................................ 16 Introduction .......................................................................................................... 17 Materials and Methods ......................................................................................... 20 Results .................................................................................................................. 26 Discussion ............................................................................................................ 29 Tables ................................................................................................................... 32 Figures ................................................................................................................. 35 References ............................................................................................................ 44 Chapter 3 – Plant-Plant Communication: Do Hornsettle Plants Warn Each Other Of Herbivore Attack? ...................................................................................................................... 46 Abstract ................................................................................................................ 46 Introduction .......................................................................................................... 47 Materials and Methods ......................................................................................... 52 Results .................................................................................................................. 58 Discussion ............................................................................................................ 60 Tables ................................................................................................................... 65 Figures ................................................................................................................. 70 References ............................................................................................................ 75 Chapter 4 – Crying Wolf Or Honest Threats? Volatile Emissions And Plant-Herbivore Interactions In Three Nicotiana Species ................................................................... 80 Abstract ................................................................................................................ 80 Introduction .......................................................................................................... 81 Materials and Methods ......................................................................................... 86 Results .................................................................................................................. 92 Discussion ............................................................................................................ 97 Tables ................................................................................................................. 101 v Figures ............................................................................................................... 107 References .......................................................................................................... 119 Chapter 5 – Conclusions............................................................................................................. 125 Inbreeding affects floral volatiles and pollinator behavior in horsenettle.......... 125 Plant-plant signliang decreases volatile emissions in horsenettle ...................... 125 Evidence for honest signaling in Nicotiana species........................................... 126 Future directions ................................................................................................ 127 References .......................................................................................................... 129 vi LIST OF FIGURES Chapter 2: Figure 2-1: Total floral volatile production of inbred and outbred plants .............................. 35 Figure 2-2: Floral volatile production of 9-z-octodecenal by inbred and outbred plants ....... 36 Figure 2-3: Floral volatile production of tetradecyl oxirane by inbred and outbred plants .... 37 Figure 2-4: Total pollinator visits to inbred and outbred patches in the field ........................ 38 Figure 2-5: Flowers first visited by pollinators to inbred and outbred plants ........................ 38 Figure 2-6: Time spent visiting inbred and outbred flowers by pollinators in the field ......... 39 Figure 2-7: Total pollen production by family and breeding ................................................. 40 Figure 2-8: Volatile production versus average pollen per flower ......................................... 41 Figure 2-9: Volatile production versus average pollen per flower for inbred and outbred plants .................................................................................................................. 42 Figure 2-10: Corolla diameter by breeding ............................................................................ 43 Chapter 3: Figure 3-1: Total volatile emissions for primed and