Heritability of Floral Characteristics in Wild Radish Raphanus raphanistrum
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For wild radish Raphanus raphanistrum, a plant that depends on insect pollination, floral appearance (which attracts the pollinators) and the relative arrangement of the floral characteristics (which compound to affect pollinator efficiency) both contribute to the ultimate success of the plant. Because flowers play such an important role in the overall fitness of this self-incompatible organism, selective pressures are expected to be acting quite strongly upon these traits. However, before evolutionary change can be predicted, we must investigate to what extent these traits are heritable. To answer this question, we conducted a field study to calculate heritabilities among seven floral traits. The field experiment was conducted in a randomized array of 1188 full- and half-siblings. These plants were grown in natural conditions, including considerable environmental and climactic stresses. Seven floral characteristics (petal width, petal length, corolla tube length, short filament length, long filament length, pistil length, and ovule count) were measured and analyzed in order to determine whether they were significantly heritable. In addition, this experiment provides important insight as to the effectiveness of greenhouse studies in predicting field results that represent natural populations. This same experimental design has already been completed in the greenhouse (Conner and Via, 1993). Because the only differences in these two projects were those intrinsic to these distinct environments, we have the rare and exciting opportunity to compare the greenhouse and field studies directly. The field population revealed significant heritability for four traits (petal length, petal width, pistil length, and ovule number). Comparing greenhouse and field study results, environmental variance (V E) and phenotypic variance (V p) were much greater in the field, while additive genetic variance (V A) was much lower in the field than in the greenhouse. Heritability, which is determined by these variances, was lower in the field for each of the six traits that were investigated in both the field and the greenhouse (ovule count was not included in the greenhouse study).With honors.