The ability of some plants to self-fertilize has its advantages, especially in areas where there aren't many pollinating insects. But research by Susan Mazer from U.C. Santa Barbara and colleagues suggests that self-fertilization may not always be an evolutionary advantage in and of itself. Rather, it sometimes may evolve because it is linked to physiological traits that help plants deal with seasonal drought.
The researchers studied four closely related species of Clarkia, which belong to the Evening Primrose family. Two of the species are predominantly self-fertilizing (selfers); the other two are predominantly outcrossing, meaning they fertilize via pollen transfer from plant to plant. The research has found that the selfers have physiological traits (faster photosynthetic rates per area of leaf, for example) that appear to promote a more rapid life cycle. As a result, selfers produce flowers and begin the reproductive process weeks before their outcrossing counterparts, and before the onset of the late spring drought in the plants' native habitat.
In addition to avoiding the periods of most intense drought, the faster life cycle is associated with more rapid floral development and the production of smaller flowers. In those smaller flowers, the male and female sex parts are closer together, increasing the chance that pollen will be transferred to the flower's own stigma -- self-fertilization. These results suggest that in the case of Clarkia, self-fertilization may have evolved partly as a "side-effect" of natural selection for a drought-avoiding life cycle.
The research is published in the November/December issue of the International Journal of Plant Sciences.
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