Diversity and Evolution of Seeds in Cuscuta (Dodders, Convolvulaceae): Morphology and Structure
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Wilfrid Laurier University Scholars Commons @ Laurier Theses and Dissertations (Comprehensive) 2019 Diversity and Evolution of Seeds in Cuscuta (dodders, Convolvulaceae): Morphology and structure Magdalena Olszewski [email protected] Follow this and additional works at: https://scholars.wlu.ca/etd Part of the Botany Commons, Integrative Biology Commons, and the Plant Biology Commons Recommended Citation Olszewski, Magdalena, "Diversity and Evolution of Seeds in Cuscuta (dodders, Convolvulaceae): Morphology and structure" (2019). Theses and Dissertations (Comprehensive). 2186. https://scholars.wlu.ca/etd/2186 This Thesis is brought to you for free and open access by Scholars Commons @ Laurier. It has been accepted for inclusion in Theses and Dissertations (Comprehensive) by an authorized administrator of Scholars Commons @ Laurier. For more information, please contact [email protected]. DIVERSITY AND EVOLUTION OF SEEDS IN CUSCUTA (DODDERS, CONVOLVULACEAE): MORPHOLOGY AND STRUCTURE by Magdalena Olszewski (BSc Biology, Wilfrid Laurier University, 2016) THESIS Submitted to the Department of Biology Faculty of Science In partial fulfilment of the requirements for the Master of Science in Integrative Biology Wilfrid Laurier University 2019 Magdalena Olszewski © Diversity and Evolution of Cuscuta Seeds Magdalena Olszewski ABSTRACT Cuscuta is a genus of nearly 200 obligate stem parasites with a nearly cosmopolitan distribution and considerable agricultural and ecological significance. Dodder seeds are considered “unspecialized”, with no morphological adaptations towards particular dispersal vectors; however, the seed coat anatomy has recently suggested an adaptation to endozoochory. This is the first attempt to provide a genus-wide overview of the diversity in morphology and anatomy of Cuscuta seeds, together with an assessment of the water gap and exploration of various form-function relationships. I surveyed 104 species belonging to all four Cuscuta subgenera. Seeds of the species of the first infrageneric dodder lineage diverged, subg. Monogynella, exhibit epidermal cells that are elongated and puzzle-like, morphologically uninfluenced by dryness/wetness (Type I) and possess a seed coat with an incomplete outer palisade layer. In contrast, epidermal cells of the other subgenera, Cuscuta, Pachystigma and Grammica, are more or less isodiametric and have evolved the ability to alternate their morphology and physiology between two states: deeply pitted when dry, and papillose through hydration (Type II). With the exception of four species, taxa of these three subgenera have a complete outer palisade layer throughout the entire seed. An embryo with a globose radicular end has evolved in sect. Denticulatae and sect. Subulatae of subg. Grammica, likely in connection with a storage function. In this thesis, I also examined the route of water entry — the water gap, in seven species and suggested two possible mechanisms for initial physical dormancy break. I investigated the relationship between seed size and geographical distribution as well as between the average number of seeds per capsule and the breeding systems. Finally, using other characters, such as the seed size, hilar region morphology, seed coat micromorphology and the number of palisade layers, I prepared an identification key for 16 species present and of concern in Canada. 2 Diversity and Evolution of Cuscuta Seeds Magdalena Olszewski ACKNOWEDGEMENTS I would first like to thank my thesis supervisor Dr. Mihai Costea. After 7 years of research and this masters” degree, I have so much to be appreciative for. I am grateful for his continued support in making my project my own but steering me back in the right direction whenever I would diverge. This was critical to the completion of my work. I am thankful for his guidance, unlimited patience and invaluable constructive criticism. I will always look back fondly on mornings working in the lab and listening to ABBA. I am grateful for my committee members, Dr. Frédérique Guinel and Dr. Kevin Stevens, and thank them for their expert advice and feedback throughout various stages of my thesis. Additionally, I express my gratitude towards Drs. Tristan Long and Derek Gray of Wilfrid Laurier University for their willingness to guide me through the statistical analyses. I would like to thank Caroline Culshaw for her readiness in helping me with protocols and Dr. Saša Stefanović for agreeing to be my external examiner. And of course, my work would not be possible without the many herbaria curators who provided the specimens required for this study, along with Drs. Stefanović and Ádám Lovas-Kiss for additional seed samples. I would like to recognize all the additional help I have received from other members of the Costea lab. Undergraduates Hiba Adel ElMiari for her help in initial seed sampling, Jazmen Tourangeau for a summer of SEM imaging and Meghan Dilliott for her related research. Finally, MSc graduate Anna Ho for her capacity to answer questions and for familiarizing me with the microscopes and protocols in the lab. I must express my profound gratitude and appreciation to my family. My parents and my sisters for their sustained suffering when I was stressed and overtired. Finally, to Tillo, for giving me unwavering encouragement and still willing to marry me after two years of graduate school. 3 Diversity and Evolution of Cuscuta Seeds Magdalena Olszewski TABLE OF CONTENTS ABSTRACT ACKNOWLEDGEMENTS TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES AND ILLUSTRATIONS 1. INTRODUCTION 1.1 GENERAL OVERVIEW OF CUSCUTA 1.2 NATURAL HISTORY AND REPRODUCTIVE BIOLOGY OF CUSCUTA 1.3 SYSTEMATICS AND EVOLUTION OF CUSCUTA 1.4 SIGNIFICANCE OF CUSCUTA 2. BACKGROUND 2.1 DEVELOPMENT (EMBRYOLOGY) 2.2 MORPHOLOGY AND ANATOMY 2.3 SEED DISPERSAL AND GEOGRAPHY 2.4 GERMINATION BIOLOGY 3. OBJECTIVES AND HYPOTHESES 4. MATERIALS AND METHODS 4.1 MORPHOLOGY AND MICROMORPHOLOGY 4.2 ANATOMY 4.3 WATER GAP ANATOMY 4 Diversity and Evolution of Cuscuta Seeds Magdalena Olszewski 4.4 CHARACTERS AND ANALYSES 4.5 STATISTICAL ANALYSES 4.6 FUNCTIONAL RELATIONSHIPS 5. RESULTS 5.1 MORPHOLOGY AND MICROMORPHOLOGY 5.2 ANATOMY 5.3 SYSTEMATIC AND TAXONOMIC SIGNIFICANCE 5.4 QUANTITATIVE ANALYSIS AND RELATIONSHIPS 5.5 WATER GAP ANATOMY AND DYE TRACKING 5.6 FUNCTIONAL RELATIONSHIPS 6. DISCUSSION 6.1 DIVERSITY OF MORPHOLOGY AND ANATOMY IN SEEDS 6.2 WATER GAP ANATOMY 6.3 FUNCTIONAL RELATIONSHIPS 6.4 FUTURE DIRECTIONS 7. SUMMARY 8. INTEGRATIVE NATURE OF THIS THESIS 9. LITERATURE CITED 10. APPENDICES 11. GLOSSARY 5 Diversity and Evolution of Cuscuta Seeds Magdalena Olszewski LIST OF TABLES Table 1. Seed characters surveyed and their representative codes and states Table 2. Ratio of epidermal cell diameter to seed size in the three subgenera of Cuscuta Table 3. Key to Canadian Cuscuta species Table 4. Pearson’s r correlation statistic of seed characters of Cuscuta Table 5. Summary statistics for quantitative seed characters Table 6. Kendall’s Tau correlation statistic () Table 7. ANOVA results LIST OF FIGURES AND ILLUSTRATIONS Figure 1. Illustration of seed characters surveyed based on Table 1 Figure 2. Scanning electron microscopy of morphology of Cuscuta seeds Figure 3. Light microscopy of anatomy of seeds Figure 4. Scanning electron microscopy of anatomy of seeds Figure 5. Cuscuta phylogeny displaying epidermal cell diameter and seed size ratio Figure 6. Overview phylogeny of Cuscuta Figure 7. Principal coordinate analysis of seed characters and seed character data Figure 8. Transposed PCoA of seed characters 6 Diversity and Evolution of Cuscuta Seeds Magdalena Olszewski Figure 9. Water gap morphology and anatomy and dye tracking Figure 10. Schematic representation of water gap in Cuscuta Figure 11. XY graph of pollen/ovule ratio and average number of seeds per capsule Figure 12. Bipartite network graph of breeding system categories, and average number of seeds per capsule Figure 13. Boxplot of breeding system ANOVA results Figure 14. Regression tree of the breeding system 7 Diversity and Evolution of Cuscuta Seeds Magdalena Olszewski 1. INTRODUCTION 1.1 GENERAL OVERVIEW OF CUSCUTA Cuscuta (Convolvulaceae), otherwise known as dodders, is a group of obligate parasitic plants consisting of nearly 200 species that is sub-cosmopolitan in distribution and thriving in a great variety of habitats (Yuncker 1932; Good 1947; García et al. 2014). Parasitic plants, in general, have an immense influence on their natural ecosystems as well as in agricultural environments (Dawson et al. 1994; Pennings and Callaway 2002; Costea and Tardif 2006). Once successfully attached to the host via haustoria, Cuscuta becomes a powerful sink for water and assimilates, dramatically reducing growth and fitness of the host (e.g., Dawson et al. 1994; Kim and Westwood 2015). When it attacks crops, it decreases both the quantity and the quality of the yield (e.g., amount of sugars and other nutrients in edible organs), thus causing significant economic losses (Knepper et al. 1990; Sandler et al. 1997). In an effort to eliminate the potential threat of dodders, legislation has been enforced worldwide, often with the entire genus being placed on quarantine lists (Costea and Tardif 2006). Commercial seed lots are screened at the border and quarantined if containing seeds of Cuscuta (McDonald and Copeland 2012; Canadian Food Inspection Agency 2018). However, within the genus, only a relatively small number of Cuscuta species (~15) have been documented as noxious weeds of crops globally (Dawson et al. 1994; Knepper