Masters Degrees (Botany and Zoology)

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Browsing Masters Degrees (Botany and Zoology) by Author "Becker, Frederik Willem"

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    The gigas effect: A reliable predictor of ploidy? Case studies in Oxalis
    (Stellenbosch : Stellenbosch University, 2021-03) Becker, Frederik Willem; Dreyer, L. L.; Oberlander, Kenneth C.; Travnicek, Pavel; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: Whole Genome Duplication (WGD), or polyploidy is an important evolutionary process, but literature is divided over its long-term evolutionary potential to generate diversity and lead to lineage divergence. WGD often causes major phenotypic changes in polyploids, of which the most prominent is the Gigas effect. The Gigas effect refers to the enlargement of plant cells due to their increased amount of DNA, causing plant organs to enlarge as well. This enlargement has been associated with fitness advantages in polyploids, enabling them to successfully establish and persist, eventually causing speciation. Using Oxalis as a study system, I examine whether Oxalis polyploids exhibit the Gigas effect using 24 species across the genus from the Oxalis living research collection at the Stellenbosch University Botanical Gardens, Stellenbosch. Given that the Gigas effect also holds great potential to increase a polyploid’s competitive ability, and as a result, invasiveness, I also tested for the Gigas effect in 15 traits and WGD-associated increased self-fertilization and bulbil production in the weedy species O. purpurea. Using known correlates of the Gigas effect (stomata length, epidermal cell area and pollen grain diameter) I show that Oxalis polyploids display a very inconsistent and small Gigas effect – contrary to that predicted from the literature. With extensive sampling across 20 populations of O. purpurea in its native range, I show a similar pattern for stomata length, pollen grain diameter and epidermal cell area in this species. In addition, I found a large decrease in effect size of polyploidy and substantial variation across traits in 12 further leaf and flower traits studied. O. purpurea showed very high levels of self-incompatibility among both diploids and polyploids, but polyploids produced significantly more and heavier bulbils than diploids. Overall, these results revealed a very small and inconsistent Gigas effect among Oxalis polyploids. There is, however, an association between polyploidy and invasive potential, using bulbil production as a proxy for invasiveness. Polyploid success and persistence in Oxalis could be as a result of a temporary initial Gigas effect upon formation, which later becomes diluted through local adaptation.