Studying Evolutionary Constraints on an Invariant Floral Trait in Wild Radish Raphanus raphanistrum
Fergus, C. Emi
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Traits that appear to be fixed either in a population or across taxa must be maintained by some mechanism. In the plant Raphanus raphanistrum, the trait of zero anther exsertion, which is a high correlation between filament and corolla tube lengths, is relatively fixed across populations and believed to be critical to plant fitness. Traits linked to zero anther exsertion that affect plant fitness, would be developmental constraints and would restrict phenotypic variability. The experiment utilized artificial selection, to create phenotypic variability, and field observations of natural pressures to test for evolutionary influences on anther exsertion. Female fitness (number of seeds produced) was measured to determine if plant fitness was affected by female traits linked with anther exsertion. Viable pollen counts were made twice through the season to observe possible developmental constraints acting through the male fitness side. The results found no significant relationship between the different degrees of anther exsertion and female fitness, indicating that traits correlated with anther exsertion do not affect female fitness. The pollen viability results for the early season count found a significant relationship between amount of viable pollen and plant treatment. However, in the late season count there were no statistically significant relationships. The data suggests that viable pollen may be linked to zero anther exsertion for younger plants, but as the plants age the relationship diminishes.