Reproductive assurance and the evolution of self -fertilization in Aquilegia canadensis

The evolution of self-fertilization is among the most common evolutionary transitions in flowering plants. However, the widespread occurrence of self-fertilization seems at odds with the observation that self-fertilized offspring often suffer reduced fitness through inbreeding depression. I examine mating system evolution in Aquilegia canadensis, a species with unexpectedly high self-fertilization given its large investment in pollinator attraction and reward, and apparently strong inbreeding depression.;The fitness consequences of self-fertilization likely depend on whether self-fertilization occurs within flowers (autogamy), or between flowers on the same plant (geitonogamy), because autogamy, when it occurs automatically in the absence of pollinator visitation, may provide reproductive assurance by ensuring seed set when pollinators or mates are scarce. In a broad sample of natural populations, I combined experimental manipulation of flowers with marker-gene analysis to partition the mating system into its within- and between-flower components, and show that most self-fertilization occurs through autogamy. Although autogamy does provide a modest degree of reproductive assurance, this fertility benefit is greatly outweighed by reduced production of high quality outcross seed.;Because self-fertilization appears to be very costly in A. canadensis , I examine phenotypic and quantitative genetic variation in herkogamy (the spatial separation of male and female organs) in the field, and demonstrate that plants with larger herkogamy experience reduced self-fertilization. I then examine the potential for natural selection to act on herkogamy by growing naturally pollinated progeny from plants differing in herkogamy in the greenhouse to examine the heritability of herkogamy, and to test whether parental herkogamy influences progeny fitness. Although herkogamy reduced self-fertilization in the field, and appears to be heritable, plants with larger herkogamy did not produce higher quality offspring. Taken together, the results of this thesis provide a comprehensive analysis of mating system variation in A. canadensis, by examining the evolutionary costs and benefits of self-fertilization, and the fitness consequences of variation in floral traits that influence the mating system.