UNIVERSITY OF CALGARY Correlates and Consequences of Repeated Nectar Evolution in the Ancestrally Rewardless Orchid Genus Disa by Nina Hobbhahn A THESIS SUBMITTED TO THE FACULTY OF GRADUATE STUDIES IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF BIOLOGICAL SCIENCES CALGARY, ALBERTA JANUARY, 2012 © NINA HOBBHAHN 2012 Library and Archives Bibliothèque et Canada Archives Canada Published Heritage Direction du Branch Patrimoine de l'édition 395 Wellington Street 395, rue Wellington Ottawa ON K1A 0N4 Ottawa ON K1A 0N4 Canada Canada Your file Votre référence ISBN: 978-0-494-83529-6 Our file Notre référence ISBN: 978-0-494-83529-6 NOTICE: AVIS: The author has granted a non- L'auteur a accordé une licence non exclusive exclusive license allowing Library and permettant à la Bibliothèque et Archives Archives Canada to reproduce, Canada de reproduire, publier, archiver, publish, archive, preserve, conserve, sauvegarder, conserver, transmettre au public communicate to the public by par télécommunication ou par l'Internet, prêter, telecommunication or on the Internet, distribuer et vendre des thèses partout dans le loan, distrbute and sell theses monde, à des fins commerciales ou autres, sur worldwide, for commercial or non- support microforme, papier, électronique et/ou commercial purposes, in microform, autres formats. paper, electronic and/or any other formats. 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UNIVERSITY OF CALGARY FACULTY OF GRADUATE STUDIES The undersigned certify that they have read, and recommend to the Faculty of Graduate Studies for acceptance, a thesis entitled "Correlates and Consequences of Repeated Nectar Evolution in the Ancestrally Rewardless Orchid Genus Disa" submitted by Nina Hobbhahn in partial fulfilment of the requirements of the degree of Doctor of Philosophy. Supervisor, Dr. LAWRENCE D. HARDER DEPARTMENT OF BIOLOGICAL SCIENCES Dr. RALPH V. CARTAR DEPARTMENT OF BIOLOGICAL SCIENCES Dr. C. C. CHINNAPPA DEPARTMENT OF BIOLOGICAL SCIENCES Dr. LEONARD V. HILLS DEPARTMENT OF GEOSCIENCE External Examiner Dr. JAMES D. ACKERMAN UNIVERSITY OF PUERTO RICO, PUERTO RICO Date ii UNIVERSITY OF CALGARY FACULTY OF GRADUATE STUDIES The undersigned certify that they have read, and recommend to the Faculty of Graduate Studies for acceptance, a thesis entitled "Correlates and Consequences of Repeated Nectar Evolution in the Ancestrally Rewardless Orchid Genus Disa" submitted by Nina Hobbhahn in partial fulfilment of the requirements of the degree of Doctor of Philosophy. Co-Supervisor, Dr. STEVEN D. JOHNSON UNIVERSITY OF KWAZULU-NATAL, SOUTH AFRICA Date iii Abstract Floral rewards promote regular visitation, flower fidelity, and pollination. Despite these advantages, some species produce no floral rewards and are pollinated by deceit. According to the resource-limitation hypothesis (RLH), rewardlessness evolves when it frees resources for other floral functions in rewardless species. In contrast, the cross- promotion hypothesis (CPH) proposes that rewardlessness alters pollinator behaviour, reducing self-pollination and enhancing outcrossing. I assess these hypotheses based on the co-occurrence of rewarding and rewardless species in the orchid genus Disa and examined whether higher self-pollination in rewarding species reduces pre-dispersal inbreeding depression (IBD) by purging of deleterious alleles. A survey of nectaries revealed seven independent origins of nectar production, including three origins of stomatal nectaries and five of secretory epidermis in different flower parts. Comparison of energy investment in flower and nectar production, and floral maintenance in rewardless and rewarding species found little support for the RLH. Daily nectar production required 1.8% of floral construction energy and costs accrue only briefly, owing to early pollination, discontinuous production, and pollination-induced wilting. Daily floral maintenance required 2.8% of floral construction energy and may accrue considerably in rewardless species, due to infrequent visitation. Rewarding species invested more energy in reproduction, suggesting alternative resolutions of life-history tradeoffs between reproduction and longevity in rewarding and rewardless species. The CPH received limited quantitative support by studies of pollinator behaviour and pollen dispersal in rewarding and rewardless species. Rewardless species iv experienced proportionally equivalent self-pollination to rewarding species and exported less pollen. Equivalent self-pollination was also reflected in equal pre-dispersal inbreeding depression in rewarding and rewardless species (overall = 0.27). Self-pollen had lower fertilization ability than cross-pollen in five of ten species. Reproduction of rewardless species was severely limited by pollinator visitation. In the absence of quantitative reproductive benefits, the incidence and persistence of rewardlessness in Disa suggest that post-dispersal processes, perhaps related to offspring quality, determine the relative merits of reward production. Whether species produce nectar is likely one component of a suite of adaptations to specific mating and/or physical environments, so that consideration of the mating system alone cannot adequately explain the benefits and persistence of rewardlessness. v Acknowledgements This thesis took me to two continents that were not (yet) home and gave me the opportunity to meet countless people that provided invaluable support, both academic and personal, and have made this enjoyable, exciting, and challenging journey possible. In Canada I thank first and foremost my supervisor, Lawrence Harder, for his implicit trust in my abilities, his generosity, patience, thoroughness, and for all the challenges. I have never and will never regret doing my PhD with him. My supervisory committee is thanked for their interest and support, and Dr. James D. Ackerman in particular for undertaking the journey to Calgary in the midst of winter. The combined input from all committee members helped to widen and balance my perspective on my topic and thereby greatly improved this thesis. I am grateful to Dr. E.C. Yeung (Department of Biological Sciences, University of Calgary) for his help and interest in the histology of Disa nectaries. The amazingly dedicated, efficient, and friendly support staff in the Main Office were a great source of help and are much appreciated. Of my fellow graduate students (including post-docs) in the Department of Biological Sciences I particularly want to thank Anna Hargreaves, Andy Wong, Sarah Hechtenthal, Magdalene Leung, Veerle de Wever, Colin Olito, Chandra Venables, and Lisa Hensel for their friendship and support over countless cups of coffee. My time in South Africa began in Cape Town, where I was warmly welcomed by University of Cape Town Administrative Officer Sandy Smuts, who took me under her wings and made sure I had everything I needed. Professors William J Bond and Jeremy J. Midgley generously accepted me into their Department and provided access to all vi facilities. Terry Trinder-Smith, Curator of the Bolus Herbarium, kindly provided access to all the precious Disa specimens and provided wet-collection material for my histological studies. Petra Muller, technician in the Zoology Department, kindly helped with the difficult task of photographing glistening nectar bubbles. The staff at the Electron Microscopy Unit at the University of Cape Town is thanked for access and support, in particular Chief Technical Officers Miranda Waldron and Mohammed A. Jaffer. My time in Cape Town was made particularly enjoyable by Diane Steyn (nee Southey, University of Cape Town), who ensured that I had everything a girl could and should need, introduced me to her friends and family, nursed me when I was ill, joined me on field trips despite gale-force winds, and, together with Tai, provided me with a home numerous times. Cape Town would also have been much less fun without Clelia Sirami (SANBI) and the amazingly hardworking field-assistance team consisting of Michelle Malan and Ruth Cozien (both University of Cape Town), who worked so efficiently that there was always time to explore, eat ice cream, and spend time at Jaqui Daya’s Coffee Shop (now sadly extinct), who served us even when we were covered in soot from head to toe. Ruth Cozien indeed deserves a special mention, for being the world’s best, most dedicated, hard-working, thorough, patient, and enthusiastic field assistant, travel companion, and friend. Without her, I could not have achieved all the field and lab work that went into this thesis, and would definitively not have enjoyed it so much. Together with her invaluable field dog Thami and her