Hybrid zones represent evolutionary laboratories, where recombination brings together alleles in combinations which have not previously been tested by selection. This provides an excellent opportunity to test the effect of molecular variation on fitness, and how this variation is able to spread through populations in a natural context. The snapdragon Antirrhinum majus is polymorphic in the wild for two loci controlling the distribution of yellow and magenta floral pigments. Where the yellow A. m. striatum and the magenta A. m. pseudomajus meet along a valley in the Spanish Pyrenees they form a stable hybrid zone Alleles at these loci recombine to give striking transgressive variation for flower colour. The sharp transition in phenotype over ~1km implies strong selection maintaining the hybrid zone. An indirect assay of pollinator visitation in the field found that pollinators forage in a positive-frequency dependent manner on Antirrhinum, matching previous data on fruit set. Experimental arrays and paternity analysis of wild-pollinated seeds demonstrated assortative mating for pigmentation alleles, and that pollinator behaviour alone is sufficient to explain this pattern. Selection by pollinators should be sufficiently strong to maintain the hybrid zone, although other mechanisms may be at work. At a broader scale I examined evolutionary transitions between yellow and anthocyanin pigmentation in the tribe Antirrhinae, and found that selection has acted strate that pollinators are a major determinant of reproductive success and mating patterns in wild Antirrhinum.
I am indebted to many people for their support during my PhD, but I particularly wish to thank Nick Barton for his guidance and intuition, and for encouraging me to take the time to look beyond the immediate topic of my PhD to understand the broader context. I am also especially grateful to David Field his bottomless patience, invaluable advice on experimental design, analysis and scientific writing, and for tireless work on the population surveys and genomic work without most of my thesis could not have happened. It has been a pleasure to work with the combined strengths of the groups at The John Innes Centre, University of Toulouse and IST Austria. Thanks to Enrico Coen and his group for hosting me in Norwich in 2011 and especially for setting up the tag experiment. I thank David Field, Desmond Bradley and Maria Clara Melo-Hurtado for organising field collections, as well as Monique Burrus and Christophe Andalo and a large number of volunteers for their e ff orts helping with the field work. Furthermore I thank Coline Jaworski for providing seeds and for her input into the design of the experimental arrays, and Matthew Couchman for maintaining the database of. In addition to those mentioned above, I am grateful to Melinda Pickup, Spencer Barrett, and four anonymous reviewers for their insightful comments on sections of this manuscript. I also thank Jana Porsche for her e ff orts in tracking down the more obscure references for chapter 5, and Jon Bollback for his advice about the analysis. I am indebted to Jon Ågren for his patience whilst I finished this thesis, and to Sylvia Cremer and Magnus Nordborg for taking the time to read and evaluate the thesis given a shorter deadline than was fair. A very positive aspect of my PhD has been the supportive atmosphere of IST. In particular, I have come to appreciate the enormous support from our group assistants Nicole Hotzy, Julia Asimakis, Christine Ostermann and Jerneja Beslagic. I also thank Christian Chaloupka and Stefan Hipfinger for their enthusiasm and readiness to help where possible in setting up our greenhouse and experiments.
Ellis T. The role of pollinator-mediated selection in the maintenance of a flower color polymorphism in an Antirrhinum majus hybrid zone. 2016. doi:10.15479/AT:ISTA:TH_526
Ellis, T. (2016). The role of pollinator-mediated selection in the maintenance of a flower color polymorphism in an Antirrhinum majus hybrid zone. Institute of Science and Technology Austria. https://doi.org/10.15479/AT:ISTA:TH_526
Ellis, Thomas. “The Role of Pollinator-Mediated Selection in the Maintenance of a Flower Color Polymorphism in an Antirrhinum Majus Hybrid Zone.” Institute of Science and Technology Austria, 2016. https://doi.org/10.15479/AT:ISTA:TH_526 .
T. Ellis, “The role of pollinator-mediated selection in the maintenance of a flower color polymorphism in an Antirrhinum majus hybrid zone,” Institute of Science and Technology Austria, 2016.
Ellis T. 2016. The role of pollinator-mediated selection in the maintenance of a flower color polymorphism in an Antirrhinum majus hybrid zone. Institute of Science and Technology Austria.
Ellis, Thomas. The Role of Pollinator-Mediated Selection in the Maintenance of a Flower Color Polymorphism in an Antirrhinum Majus Hybrid Zone. Institute of Science and Technology Austria, 2016, doi:10.15479/AT:ISTA:TH_526 .
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