Floral Evolution in Wild Radish: The Roles of Pollinators, Natural Selection, and Genetic Correlations Among Traits

Abstract

I review my research on the evolution of floral morphology in wild radish, Raphanus raphanistrum. A comparative study of patterns of phenotypic correlations among floral traits in five species indicated that selection may have acted to increase the correlation between filament and corolla tube lengths in wild radish and two other species. This high correlation maintains a similar position of the anthers relative to the opening of the corolla tube, regardless of flower size, which may be important for effective pollination. Quantitative genetic analysis shows that the high phenotypic correlation between these two traits is caused by a high genetic correlation. Preliminary results from a long-term random mating study suggest that this genetic correlation is a result of pleiotropy, not linkage disequilibrium. Measurements of the effects of anther position on pollen removal by pollinators and estimates of natural selection on floral morphology failed to produce evidence for selection to increase the correlation between filament and corolla tube lengths. In fact, there was little selection on floral morphology overall, and the only strong selection on morphology that occurred was through differences in female fitness, not male fitness, contrary to theoretical expectations.