Evolution and maintenance of Batesian mimicry, with particular reference to hover flies (Diptera: Syrphidae) By Arash Rashed A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfilment of the requirements for the degree of Doctor of Philosophy Department of Biology Carleton University Ottawa, Ontario August 2006 © 2006, Arash Rashed Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 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ABSTRACT In this project I tackled some of the unanswered questions regarding morphological and behavioural mimicry in hoverflies (Diptera: Syrphidae), using novel approaches. First, I tested the possible role of invertebrate predators, specifically dragonflies, in the evolution of mimicry in hover flies. While dragonflies showed a significant tendency to attack small-sized prey compared to large-sized prey types, they did not seem to avoid the wasp-like colours and patterns of mimetic hover flies and attacked both mimics and non-mimetic prey types, of the same size, at a similar rate. Second, a test of the ‘competitive mimicry’ hypothesis is performed. The basic tenet of this hypothesis is that mimetic hover flies benefit from their similarity to predatory yellow-jackets by an improved access to resources since other pollinators avoid visiting flowers that they occupy. Pollinators were more likely to visit unoccupied flowers compared to flowers occupied with either natural or artificial specimens. However, pollinators did not show reduced visits to flowers pinned with specimens bearing wasp­ like colours compared to flowers occupied by same-sized specimens that were non- mimetic. Third, we used neural network to objectively assess the degree of similarity between hover fly images and their wasp models. Furthermore, using available data on pigeon’s classification of hover fly images and also genetic algorithms along with neural network, we identified a reduced set of characteristics that birds may have used to rank the similarity hover fly images to wasps and flies. Finally, in a behavioural study, I quantitatively compared the sounds produced by species of hymenopteran models and mimetic hover flies, when they were artificially iii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. attacked. Although I found some similarity in the buzzing sounds produced by bumble bees and their hover fly mimic, E. flavipes, I did not observe this similarity between the other two hymenoptera models (wasps and honeybees) and their presumed mimics. Moreover, all of the tested mimetic hover flies buzzed similarly to one another, independent of the model they resemble. The “buzzing behaviour” was not observed in the tested yellow-jacket wasps. However, all of the tested hoverflies, bumblebees and honeybees emitted a distinctive and quantifiable “buzz” when probed. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENT This thesis project would have been a formidable challenge with out the help of as many as people I am about to name and thank. I appreciate all their support, encouragement, and friendship. Dr. Tom Sherratt, my supervisor, deserves special thanks for his attention to his graduate students and providing an enjoyable working environment above his many other commitments. I was lucky to have the chance to work with a knowledgeable scientist like Tom and to learn from him. He provided me with immeasurable support during my academic program. I thank Tom for his patience and understanding. I thank Dr. Mark Forbes, my advisor, for all his support and help over past few years. Mark, I acknowledge that I have been a troublesome student! You believed in my capabilities more than I did myself and took me as a graduate student when I first arrived despite the fact that English was my second language and also I was new to the Canadian lab environment. I first started to volunteer in Dr. John Amason’s lab at the University of Ottawa. I would like to thank John for accepting me in his lab and letting me to help with one of his ongoing projects. It was a great opportunity for me to experience working in a new environment with a great team and to learn about the other projects that his graduate students were working on. I also wish to thank Dr. Jeff Skevington from Canadian National Collection of Arthropods who patiently supervised, while I learned molecular techniques. Jeff also V Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. helped me with a lot of insect identifications for this research and I consider myself lucky to have had him here in Ottawa. I would like to thank Dr. Jayne Yack for letting me to use the sound recording equipment in her lab. Also many thank to Dr. Jeff Dawson for teaching me to use acoustic equipment. At Queen’s University Biological Station, Frank Phelan and Floyd Connor provided me with a valuable research environment, without which various aspects of the study could not have happened. Special thanks to Dr. Rod Bain who patiently answered my questions regarding Neural Networks, an area that I knew absolutely nothing about before the project, and tried to make the system even easier to use for us. I also have to acknowledge that I have learned a lot form my lab-mate Chris Beatty. I would like to thank Chris for all his help. Finally, I wish to specially thank my parents and also my wife Tirazheh Eslami, who have provided support through out my education, and also my friends and colleagues Yemisi Dare, Hume Douglas, Nahideh Haghighi, Shuyou Han, Imran Khan, Stacey Lee-Jankins, David Lowe, Justin Mahoney, Hannah Mir-Rashed, Tonia Robb, Bin Xang and all others who helped me at different stages and in various forms. vi Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table of Contents Page Abstract............................................................................................................................. iii Acknowledgements ........................................................................................................... v Table of Contents ............................................................................................................ vii List of Tables .....................................................................................................................xi List of Figures ..................................................................................................................xiii List of Appendices .......................................................................................................... xix Chapter 1. General Introduction 1.1 Animal Defence ........................................................................................1 1.2 Hover Flies ................................................................................................4 1.2.1 Morphology .............................................................. 5 1.3 Imperfect Mimicry ................................................................................... 6 Chapter 2. Prey selection by dragonflies in relation to prey-size and wasp-like colours and patterns 2.1 Preface................................................................................................... 13 2.2 Introduction ...........................................................................................14