While the potential for sexual selection as an important factor in plant evolution is now becoming recognized, there is surprisingly little direct knowledge about how often conditions required for its actions occur. One indication of the opportunity for sexual selection in plants is the occurrence of multiply sired fruits. Such fruits are unambiguous evidence that pollen from more than one mate was available to fertilize seeds, and therefore indicate that female choice of male competition (forms of sexual selection) may act. However, there is detailed knowledge about the frequency of multiply sired fruits for only a single, introduced species. The P.I. will study the occurrence of and mechanisms causing multiply sired fruits for a native plant of South Western deserts, Lesquerella fendleri. To determine frequency, the P.I. will ascertain paternity for seeds from plants in 3 separate populations at the Sevilleta Long-Term Ecological Research Site. Preliminary studies indicate that Lesquerella fruits are commonly multiply sired. To determine the mechanisms causing multiply sired fruits two approaches will be taken. First, paternity resulting from single and multiple pollinator visits in nature will be compared. Second, observed pollinator visitation rates will be used to construct a realistic schedule of hand pollinations to investigate the effects of single and multiple visits under more controlled conditions. Knowledge of the responsible mechanisms will not only help to predict which species are likely to produce multiply sired fruits, but can help delimit their possible evolutionary consequences.
