Flowering plant species exhibit a great deal of variation in their mating systems. One of the dominant paradigms currently used to describe plant mating systems is the mixed-mating model. Perfect flowered plants are understood to reproduce through some combination of self and outcross pollinations. The proportion of seeds produced by outcrossing events, or outcrossing rate, can vary between 0 and 1. While empirical investigations have identified natural plant populations representing the full range of potential outcrossing rates, theoretical predictions suggest that natural selection should act on intermediate outcrossing rates to produce either extreme of complete outcrossing or complete selfing. There is currently no empirical evidence of the forces of natural selection acting upon intermediate outcrossing rates with which to test these theoretical predictions. The proposed research will address the evolutionary dynamics of intermediate outcrossing rates in a natural population of the annual California lupine, Lupinus nanus. Estimates of outcrossing rates have been made for populations throughout the species' range, and demonstrate a great deal of variation between populations, with most of the populations outcrossing at intermediate rates. Morphological variation between populations has been suggested as an important determinant of the variable outcrossing rates. Outcrossing rate variation had also been reported for the same population between years, and for individuals within a population. The proposed research will focus on mating system variation within a population. Individual plants will be measured for morphological, phenological and ecological characters. Naturally pollinated seed will be collected from these plants, and the outcrossing rate for individuals will be determined using genetic information gathered from the use of starch-gel electrophorsis. In addition, artificial self and outcross pollinations will be performed and the seed will be used to assess the relative success of selfed and outcrossed offspring. With this information, the effect of selection on the outcrossing rate can be determined. In addition to providing empirical evidence for testing the theoretical expectations concerning mating system evolution, this study will also provide information of general value of plant breeders.
