9410086 Jones Whether a plant is able to persist in a particular natural environment is determined by its reproductive success, or fitness, through evolutionary time. Among the determinants of reproductive success are the schedule of reproduction, i.e. the life history, and the resources available for reproduction. Because a plant's reproductive success is directly influenced by the number of reproductive structures (flowers), plants face a tradeoff between producing flowers that increase reproductive output immediately, versus producing new vegetative structures (leaves and roots) that enhance resource uptake and may lead to higher reproductive success over the life of the plant. This tradeoff is complicated by the interaction between (1) a plant's inherent developmental program, which influences when and what type of new structure will be made, and (2) the efficiency of that structure in resource accumulation, which in turn influences the plant's subsequent developmental program. The influence of this interaction between a plant's developmental program and resource accumulation on the proportion of reproductive individuals in the population, i.e. the population's demography, is poorly understood. Interactions between developmental program, resource uptake and use, and demography in an herbaceous perennial clonal plant, mayapple (Podophyllum peltatum) will be examined. Mayapple is an ideal plant for such a study because each year each rhizome faces a simple developmental decision--to produce either a single foliage leaf, or a simple reproductive shoot bearing a single flower and two foliage leaves. Long-term studies of naturally occurring populations will be used to (1) construct a timetable of developmental decisions for mayapple, emphasizing how and when the type of new aerial "shoot" is determined, (2) examine the interaction between resources acquired in the past and those acquired in the current year on current and future determination of shoot type and (3) determine whether dif ferences in the timing of developmental events among different clones affects their reproductive output over the long term. The results of this study will reveal how variation in developmental timing and resource uptake affect demography. Moreover, this study will reveal at what points selection may act to alter the timing of the expressed developmental program, thus contributing to our understanding of how different life histories evolve, a critical issue for plants facing a rapidly changing environment. These results will contribute to understanding how variation in developmental timing affects vegetative and reproductive productivity in economically important plants as well.
