Wilfrid Laurier University Scholars Commons @ Laurier Theses and Dissertations (Comprehensive) 2011 The Evolution of Sexual Reproduction in Cuscuta (Convolvulaceae) Michael Wright Wilfrid Laurier University Follow this and additional works at: https://scholars.wlu.ca/etd Part of the Plant Breeding and Genetics Commons Recommended Citation Wright, Michael, "The Evolution of Sexual Reproduction in Cuscuta (Convolvulaceae)" (2011). Theses and Dissertations (Comprehensive). 1039. https://scholars.wlu.ca/etd/1039 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]. NOTE TO USERS This reproduction is the best copy available. 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While these forms may be included Bien que ces formulaires aient inclus dans in the document page count, their la pagination, il n'y aura aucun contenu removal does not represent any loss manquant. of content from the thesis. 1+1 Canada \ The Evolution of Sexual Reproduction in Cuscuta (Convolvulaceae) By Michael Wright (BMus 2005, BSc 2008, Wilfrid Laurier University) THESIS Submitted to the Department of Biology, Faculty of Science in partial fulfillment of the requirements forthe degree of Master of Science in Integrative Biology Wilfrid Laurier University 2011 Michael Wright ©2011 The Evolution of Reproduction in Cuscuta Michael A. R. Wright Abstract Cuscuta (Convolvulaceae), the dodders, is a genus of ca. 200 species of obligate stem parasites distributed across a great diversity of habitats worldwide. The existence of a handful of species that are dangerous crop weeds has led researchers to historically focus on their growth and control. Consequently, there is a dearth of information about their biodiversity, ecology, and in particular their reproductive biology. This thesis sur­ veys aspects of sex allocation, floral evolution, floral rewards for pollinators, and mechanisms of reproductive assurance across the genus. I demonstrate that Cuscuta has evolved a broad spectrum of breeding systems, from obligate selfing to obligate outcrossing. Predictions made by sex allocation theory of negative correlations be­ tween pollen number and pollen grain size, and between male investment and female investment are shown to be false in Cuscuta. Histological examination of the floral nec­ tary demonstrates that it is typical in structure, and I predict that it is functional in most facultatively and obligately xenogamous species. Cuscuta pollen is variable in the pro­ portions of lipid and starch reserves, and has a sticky external pollenkitt. The role of the infrastaminal scales is narrowed to 1) defense against seed predators, and 2) a shield against early self-pollination in some strongly protandrous species. Lastlly, I demon­ strate that the evolution of two styles, followed by unequal styles in Cuscuta, were criti­ cal for the radiation of the genus. The more flexible floral design enabled Cuscuta to evolve different mechanisms of reproductive assurance in coordination with their exploi­ tation of novel host species and new pollination environments. Page ii The Evolution of Reproduction in Cuscuta Michael A. R. Wright Acknowledgements The work of this thesis would not have been possible without the help of a number of indi­ viduals and institutions. First, I'd like to thank the curators of the following herbaria for pro­ viding the copious breadth of material examined in this study: AAU, ARIZ, ASU, B, BOL, BRIT, CAN, CANB, CAS, CHICO, CHR, CHSC, CIMI, CTES, DS, ENCB, F, G, GAA, GH, GRA, IBUG, IEB, KEW, MERL, MEXU, MICH, MO, NBG, NML, NMS, NU, NY, OAC, QFA, QUE, RB, RSA, S, SD, SI, SMU, UB, UC, UCR, UN, UNM, US, WLU, WTL, and XAL. I'd like to thank Ignacio Garcia Ruiz (CIIDR-IPN, Jiquilpan, Michoacan) for his hospitality and aid during my field research in Michoacan, Jalisco and Nayarit states, Mexico. Dr. Sasa Ste- fanovic kindly gave me an unpublished phylogeny of the genus to use in my analyses cre­ ated from work by himself, Dr. Maria Kuzmina and Dr. Mihai Costea. Atlee Bols was a great help at my two field sites in Ontario, while Mark Welsh accompanied me to Northern Cali­ fornia and provided some of the gynoecium and pollen data I used in my analyses. I thank Dr. Peter Kevan (University of Guelph) for some helpful advice at the outset of my project. I'd also like to thank undergraduates Michael lanni, Rebecca Borody, Stephanie Riviere, Aldaine Hunt, Ezzat Khalili, Caitlin Shea and Lindsay McGoran for the pollen counts they contributed as part of their lab projects in a directed study course. My committee mem­ bers, Drs. Jane Rutherford, Marianne Fieldes, and Frederique Guinel, and my external ex­ aminer Dr. Maria Kuzmina provided much helpful feedback during the research process and on the final thesis document. Finally, I'd like to thank Dr. Mihai Costea for guiding me throughout the process of completing my Master's research, and for putting up with a city boy out in the field. Hiking through the alpine meadows of the Wasatch Mountains in Utah in full summer bloom, and my field experience in southern Mexico are things I will never forget. Page iii The Evolution of Reproduction in Cuscuta Michael A. R. Wright Table of Contents Abstract ii Acknowledgements iii Table of Contents iv List of Tables vi List of Figures and Illustrations vii 1. Introduction 1 1.1 Problem setting 1 1.2 Outline of the thesis 4 2. Background 6 2.1 Reproduction in the flowering plants 6 2.2 Mating strategies and reproductive assurance 7 2.3 Floral gender, resource allocation, and breeding system 11 2.4 Pollinator fidelity and floral rewards 13 2.5 The study system: sexual reproduction in Cuscuta 17 3. Objectives 25 4. Materials & Methods 26 4.1 Sex allocation & floral morphology 26 4.2 Floral Rewards 30 4.3 Timing of sexual function & patterns of stylar growth 33 4.4 Phylogenetic and evolutionary contextualizations 33 5. Results I: Sex Allocation & Floral Morphology 37 5.1 Male & Female Reproductive Investment 37 5.2 Floral morphology 38 5.3 Correlations between morphology and sex allocation 39 6. Results II: Floral Rewards 60 6.1 Morphology and anatomy of the floral nectary 60 Page iv The Evolution of Reproduction in Cuscuta Michael A. R. Wright 6.2 Pollen histochemistry 61 6.3 Infrastaminal scales 62 7. Results III: Stigma Receptivity & Spatial-Temporal Orientation 76 8. Discussion 87 8.1 Breeding systems in Cuscuta -within expectations? 87 8.2 Breeding system evolution and floral morphology 89 8.3 Do the predictions of sex allocation theory hold up? 91 8.4 Nectary structure & pollen composition 93 8.5 Infrastaminal Scales 94 8.6 Fitting of stigma receptivity and growth patterns to host life-cycle and community structure 96 8.7 The evolution of separate and unequal styles 98 8.8 Limitations of this study 99 8.8 Future Directions 101 9. Summary 107 10. Glossary 109 11. References 114 Appendix A- List of Specimens 131 Appendix B - Data Matrix 138 Page v The Evolution of Reproduction in Cuscuta Michael A. R. Wright List of Tables Table 5.1 - Regression and correlation of sex allocation variables 41 Table 5.2 - Perianth size vs floral features regression & correlation 42 Table 5.3 - Pollen count vs floral features regression & correlation 42 Table 5.4 - Pollen volume vs floral features regression & correlation 43 Table 5.5 - Total pollen volume vs floral features regression & correlation 43 Table 5.6 - Ovary volume vs floral features regression & correlation 44 Table 5.7 - Seed length vs floral features regression & correlation 44 Table 6.1 - Pollen and pollenkitt histochemistry 61 Table 7.1 - Stigma receptivity across floral stages 79 Table 8.1 - P/Os and self-compatibility in other Convolvulaceae 103 Page vi The Evolution of Reproduction in Cuscuta Michael A. R. Wright List of Figures and Illustrations Figure 1.1 -- General habit of Cuscuta 05 Figure 2.1 -- Cuscuta floral ground plan 23 Figure 2.2 -- General style/stigma morphologies 24 Figure 4.1 -- Floral character measurements 35 Figure 4.2 -- Corolla shape categories 36 Figure 5.1 -- Pollen distribution 45 Figure 5.2 -- Distribution of pollen counts across the genus 46-47 Figure 5.3 -- Regression of pollen counts against pollen volumes 48 Figure 5.4 -- Scatter of pollen count vs.