The effects of pollinators and sex ratios on the evolution of life-history traits in Aralia nudicaulis

Aralia nudicaulis is a clonal dioecious herb common to forested ecosystems in eastern North America. In this study, I had two main objectives: (1) to understand the factors responsible for variation in female frequencies, and (2) to investigate interactions between A. nudicaulis and its pollinators. I investigated variation in female frequencies at 15 sites in Algonquin Park, Ontario. At each site I recorded the age and sex of each flowering ramet. I found striking variation in the frequency of females vs. males across the study sites, with the percentage of females ranging from 5 to 95%. Because fruit production involves greater resource costs than pollen production, I predicted that females should be less common where resources such as light are limiting. However, the data were not fully consistent with this expectation and I did not find a significant association between canopy closure and female frequencies. Because of the higher cost of reproduction in females, I further predicted females would have lower rates of survival, and therefore that the oldest plants within populations would be male. Contrary to this expectation, I found that the age distribution was skewed towards older ages for females than for males. Because males provide more rewards for pollinators than females, I predicted that variation in the ratio of females:males across sites would be associated with variation in pollinator abundance. However, in complete contrast to this expectation, I found that pollinators were more abundant in sites with more females, not more males Finally, I conducted an experiment to explore the function of infertile staminodes in the pollination of female A. nudicaulis , with the expectation that staminodes, which are superficially similar to the pollen-producing stamens produced by males, would be important in pollinator attraction. As expected, pollen receipt by females that had their staminodes removed was substantially lower than for plants with intact staminodes.;Keywords: life history, sex ratio, trade-off, clonal, sexual, reproduction, dioecy, staminode, age, survival, pollinators.