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Plants often respond to elevated UV-B by increasing the concentration of UV-B absorbing compounds in their tissues. However, evidence that UV-B absorbing compounds confer an adaptive advantage to plants in elevated UV-B environments has not been produced. Three of four experiments utilized an Arabidopsis mutant deficient in the ability to produce flavonoids (a set of UV-B absorbing compounds) to address this question. Results from a life history experiment showed that the wild type out-performed the mutant plants under both UV-B environments, indicating that flavonoids may confer an adaptive advantage across UV-B environments. Germination results were the exception with UV-B initially delaying germination more in mutant than wild type seeds under high UV-B. An expanded life history study, which included one additional UV-B treatment, showed identical results for the germination portion of the study. Significant UV-B x genotype interactions showed that wild type plants clearly had a growth and reproductive advantage over the flavonoid-deficient mutants as UV-B increased, indicating that flavonoids were serving an advantage as UV-B increased. This effect of UV-B on genotype did not appear to be differentially affected by the nutritional environment of the plant. A multi-generation study confirmed results of the two single-generation studies. Wild type genotypic frequency increased significantly more in treatments containing UV-B, when compared with the zero UV-B treatment. The final experiment utilized a plant native to an environment which is experiencing rapid increases in UV-B radiation. Colobanthus quitensis, a native Antarctic plant, was used to determine whether there is genetic variation in performance, and if this variation is related to UV-B absorbing compound levels. Families varied significantly in response to UV-B levels. As would be expected if UV-B absorbing compounds increased fitness in high UV-B environments, the probability of producing flowers increased with increasing absorbance values in the highest UV-B treatment. Results from these studies indicate that flavonoids do confer a fitness advantage in environments containing UV-B. Furthermore, plants which produce more UV-B absorbing compounds in environments experiencing rapid increases in UV-B appear to have a reproductive advantage. This advantage will permit the evolution of existing and new populations in elevated UV-B environments.