Master of Science (MSc)
Faculty of Science
Cuscuta (Convolvulaceae), the dodders, is a genus of ca. 200 species of obligate stem parasites distributed across a great diversity of habitats worldwide. The existence of a handful of species that are dangerous crop weeds has led researchers to historically focus on their growth and control. Consequently, there is a dearth of information about their biodiversity, ecology, and in particular their reproductive biology. This thesis surveys aspects of sex allocation, floral evolution, floral rewards for pollinators, and mechanisms of reproductive assurance across the genus. I demonstrate that Cuscuta has evolved a broad spectrum of breeding systems, from obligate selfing to obligate outcrossing. Predictions made by sex allocation theory of negative correlations between pollen number and pollen grain size, and between male investment and female investment are shown to be false in Cuscuta. Histological examination of the floral nectary demonstrates that it is typical in structure, and I predict that it is functional in most facultatively and obligately xenogamous species. Cuscuta pollen is variable in the proportions of lipid and starch reserves, and has a sticky external pollenkitt. The role of the infrastaminal scales is narrowed to 1) defense against seed predators, and 2) a shield against early self-pollination in some strongly protandrous species. Lastlly, I demonstrate that the evolution of two styles, followed by unequal styles in Cuscuta, were critical for the radiation of the genus. The more flexible floral design enabled Cuscuta to evolve different mechanisms of reproductive assurance in coordination with their exploitation of novel host species and new pollination environments.
Wright, Michael, "The Evolution of Sexual Reproduction in Cuscuta (Convolvulaceae)" (2011). Theses and Dissertations (Comprehensive). 1039.