ABR: Natural Selection in Radish Raphanus spp.

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The striking diversity of size, color, and form seen in flowers is thought to have arisen by natural selection for greater pollinator attractiveness as well as enhanced pollination efficiency. Until quite recently, however, estimates of pollination success were based solely upon one component of a flower's reproductive success, i.e. the seeds produced. Flower colors or forms that set more seeds than other variants seen within a species have been presumed to enjoy an overall evolutionary advantage. Most flowers, however, reproduce through both seeds (female function) and pollen (male function). One- half of the genes transmitted to future generations are contributed by pollen, but we know almost nothing about the impact of flower features on pollen, but we know almost nothing about the impact of flower features on pollen donating (male) function. Because of this gap in our knowledge, our understanding of flowers and the evolutionary forces that have shaped them is in need of major re-examination. The research program for which this grant is a one-year renewal is designed to understand how floral features influence both male and female reproduction by flowering plants. The principal investigator has shown, for two species of wild radish (abundant weeds of agricultural land on both coasts of North America), that variation for petal color, petal size, and pollen production can influence reproduction. Most importantly, male reproduction seems to be more strongly influenced by floral variation than seed production. To understand how these weedy species proliferate and evolve, the factors influencing male, pollen-donating function must be understood. During the renewal period, the principal investigator will study the effects of pollen grain number and size upon evolutionary fitness. The results have implications for weed control, as well as for crop breeding.