Flowers Through Insect Eyes: the Contribution Of
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FLOWERS THROUGH INSECT EYES : THE CONTRIBUTION OF POLLINATOR VISION TO THE EVOLUTION OF FLOWER COLOUR SARAH ELIZABETH JOAN ARNOLD THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY QUEEN MARY , UNIVERSITY OF LONDON 2010 1 ABSTRACT Flowers’ colours are an essential element of their ability to attract visits from pollinators. However, the colours as they appear to human observers can differ substantially from their appearance to insect pollinators, and so it is essential to consider pollinator vision in any study of the ecology of flower colour. In this thesis I describe how I have overseen the development of an online database to provide accurate information on floral spectral reflectance measured without human observational bias. This resource allows a more accurate consideration of flower colours in future studies, and permits investigations of flower colours within and across habitats. Using the records in this database, I analysed flowers from two European habitats for spatial or temporal changes, modelling the colours according to insect visual perception. I discovered that the insect-colour composition of the plant communities does not change either along an altitudinal gradient or throughout the year. These novel and ecologically-relevant analyses contradict previous observational studies, but support the theory of a pollination “market” in which flowers compete for pollinator visitation. I then describe my experimental investigations into the visual capabilities of two pollinators and how this may relate to what colours of flowers they visit. Firstly I study the foraging behaviour of bees under spatially inconsistent illumination and how this impacts on their choice behaviour. I revealed patchy light can have measurable effects on bee foraging behaviour: they intentionally choose familiar over unfamiliar illumination, which may impact on the flowers they visit in complex natural environments. Secondly, I detail the new evidence for a red-sensitive photoreceptor in South African monkey beetles, a major pollinator in a habitat containing many long- wavelength-reflecting flowers, which are not classically “attractive” to bees. Throughout this thesis, I explore how pollinator vision has shaped the evolution of flower colours in different contexts. 2 This thesis is dedicated with love to a remarkable and generous woman who overcame her own fear of insects in order to teach me just how fascinating they truly are. For my mother Petula Arnold (24 th November 1954 – 19 th October 2009) 3 ACKNOWLEDGEMENTS It is a pleasure to thank, first and foremost, my supervisors, Professors Lars Chittka and Vincent Savolainen, for their support, advice and input throughout my thesis. Their enormous expertise and occasional tough love has been invaluable. I am also deeply grateful to the members of the Chittka lab, past and present, who have always been available for advice and troubleshooting: Drs Nigel Raine, Tom Ings, Elli Leadbeater, Nehal Saleh, Mathieu Molet and Mathieu Lihoreau, and Oscar Ramos- Rodriguez, Ralph Stelzer, Helene Muller, Kate Hunt and Mu-Yun Wang. In addition, I thank the administrative and technical staff of Queen Mary who have supported me during my time here. Several people’s programming expertise laid the groundwork for the development of FReD; in particular, I thank Chris Ingram and Beth Hellen, and Samia Faruq for providing further coding when the FReD project continued under my direction. Additionally, I would like to thank the Positive Internet Company for their technical support when launching FReD online. The electrophysiology work would not have been possible without the support, apparatus and guidance of Dr Peter Skorupski, and I am also endebted to Dr Thomas Döring for his suggestions and guidance. I also thank Dr Jonathan Colville and Dr John Manning for taking care of so much paperwork and organisation in order to provide me with monkey beetles for these experiments. Several organisations and companies have supported my project in many different ways: the BBSRC and the Royal Botanic Gardens, Kew have provided funding (BBS/S/L/2005/12155A). Koppert Biological Systems and Syngenta Ltd. have supplied bees for the behavioural experiments. I would also like to thank the editors and referees whose detailed and patient comments improved a number of manuscripts arising from my PhD work, including Dr Neal Williams and Dr Tamar Keasar, who provided very useful constructive criticism of my 4 early publications. Likewise, I thank the friends who offered to proofread chapters of this thesis: Caitlin, Matthew, Lyra, Helen C, Jenny, Helen S, Linda and Stuart. Lastly, but certainly not least, I owe a huge debt of gratitude to my family and friends for their loyal support through the ups and downs inevitable in any PhD. In particular I thank Katie, Ulrica, my flatmates Elizabeth, Anu and Felicia, and my parents, Mike and Petula Arnold. Petula will unfortunately never see the conclusion of this thesis, but I hope she would have approved. Sarah Arnold March 2010 5 SUMMARY OF INPUT I wrote the papers for Chapters III and IV. My contributions to the data chapters are as follows: II. I finalised the development of FReD version 1.0 (initiated by E. Hellen), and supervised development of FReD version 2.0 by S. Faruq, who performed the programming and coding according to a specification which I developed in collaboration with L. Chittka and V. Savolainen. I tested the completed application and oversaw development of new features, bug fixes and fine- tuning. I screened the database manually for problems with records and updated many records according to revised nomenclature for plant species. I set up the current webhosting and oversaw implementation of the database as a live website. III. The data for the alpine study was collected by L. Chittka in 1992. I conducted the data analysis and interpretation for the study. IV. The data for the phenology study was collected by L. Chittka in 1993-4. In the phenology study, the randomisation analysis was performed by S.C. Le Comber according to a specification I developed in consultation with L. Chittka. I performed the other statistical analyses for that study. V. I designed and conducted all behavioural experiments in parts 1 and 2 and performed all statistical analysis on the results. Some of the data collection in part 3 was performed by H.W.H. Mak under my supervision and according to a protocol I designed. I designed the experiment in part 4 in collaboration with H.W.H. Mak; he collected all the data, but I performed all the analysis. VI. The flower readings were taken by V. Savolainen and M.P. Powell. The test animals were collected by J. Colville in collaboration with J. Manning. I conducted all the electrophysiological experiments with mentoring from P. Skorupski and performed all analysis and interpretation of results. 6 DECLARATION I declare that that the work in this thesis is all my own, with the exception of the contributions from others mentioned in the “Summary of input” section above. Sarah Arnold March 2010 7 TABLE OF CONTENTS ABSTRACT................................................................................................................................................ 2 ACKNOWLEDGEMENTS....................................................................................................................... 4 SUMMARY OF INPUT............................................................................................................................. 6 DECLARATION........................................................................................................................................ 7 TABLE OF CONTENTS........................................................................................................................... 8 TABLE OF FIGURES............................................................................................................................. 12 TABLES.................................................................................................................................................... 15 PUBLICATIONS ARISING FROM THESIS....................................................................................... 16 OTHER OUTPUTS .................................................................................................................................... 16 CHAPTER I: INTRODUCTION............................................................................................................ 17 FLOWER COLOUR DEVELOPMENT : PIGMENTS ......................................................................................... 17 FLOWER COLOUR DEVELOPMENT : STRUCTURAL COLOUR ....................................................................... 18 ANCESTRAL FLOWER COLOURS .............................................................................................................. 19 FLOWER COLOUR IN THE CONTEXT OF POLLINATION .............................................................................. 20 OVERVIEW OF THE COLOUR VISION OF INSECT POLLINATORS ................................................................. 21 POLLINATION SYNDROMES ..................................................................................................................... 33 MEASURING FLOWER COLOUR ACCURATELY ......................................................................................... 34 MODELLING COLOUR VISION SYSTEMS ..................................................................................................