Streisfeld, Matthew,,McLean, Jack2022-07-122022-07-122022https://hdl.handle.net/1794/27376Unlike animals, plants possess the unique ability to pass on mutations to progeny that arise both through meiotic (germline) and mitotic (somatic) division. In spite of these two sources of genetic variation, mutation rates per generation appear to be similar between plants and animals. One explanation for this discrepancy is cell lineage selection (CLS), which claims that cell lineages with deleterious somatic mutations are sieved out of the population of cells in a plant’s shoot apical meristem through natural selection. On the other hand, beneficial mutations may become fixed within the population. To investigate the plausibility of CLS, I performed multiple experiments to determine the fitness effects of somatic mutations by comparing the progeny of Mimulus aurantiacus plants generated via self-pollination made within the same flower (autogamy) to progeny from self-pollinations made between stems on the same plant (geitonogamy). Importantly, autogamy leads to homozygosity of a proportion of somatic mutations, but progeny from geitonogamy remain heterozygous for mutations unique to each stem. Significant differences in fitness were observed among some autogamous and geitonogamous progeny. Surprisingly, autogamous progeny from several genets displayed significantly increased fitness, which challenges the assumption that differences in fitness between autogamous and geitonogamous progeny are caused solely by deleterious mutations. These results support the hypothesis that somatic mutation accumulation during vegetative growth can result in non-negligible—and possibly beneficial—changes in fitness among progeny due to CLS.en-USCC BY-NC-ND 4.0cell lineage selectionsomatic mutationsMimulus aurantiacusterminal drought experimentplant evolutionThesis/Dissertation0000-0003-3206-8811