The role of pollinator-mediated selection in the maintenance of a flower color polymorphism in an Antirrhinum majus hybrid zone

Ellis, Thomas James (2016) The role of pollinator-mediated selection in the maintenance of a flower color polymorphism in an Antirrhinum majus hybrid zone. PhD thesis, IST Austria.

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Abstract

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 mo- lecular 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 Pyren- ees 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, match- ing 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 pat- tern. 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 Antirrhineae, and found that selection has acted repeatedly to promote the spread of pigment alleles. These results demon- strate that pollinators are a major determinant of reproductive success and mating patterns in wild Antirrhinum.

Item Type: Thesis (PhD)
DOI: 10.15479/AT:ISTA:TH_526
Subjects: 500 Science > 570 Life sciences; biology > 576 Genetics and evolution
Research Group: Barton Group
Depositing User: Patrick Danowski
Date Deposited: 13 Apr 2016 07:57
Last Modified: 30 Aug 2017 07:47
URI: https://repository.ist.ac.at/id/eprint/526

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