| In plants, widespread seedling mortality and early establishment of competitive hierarchies make an understanding of the factors that contribute to seedling success critical to predicting plant fitness. Many of the characteristics that determine seedling success, including dispersal, dormancy and seed size, are largely under the control of the maternal plant, however, and thus maternal effects may contribute strongly to plant population dynamics. In this dissertation, I explored the effects of environmental variation on patterns of seed dispersal and seed provisioning in Amphicarpaea bracteata, an annual legume that produces two different seed types, and the influence of light availability on the fitness of resulting seedlings. A broad survey of four naturally-occurring populations of A. bracteata revealed that moisture and light availability were significantly autocorrelated over the dispersal distance of the subterranean seed type but less or not predictable over the dispersal distance of the aerial seed type. The environment experienced by individual plants differed within a single population as well as among the populations studied. Variation in environment among maternal individuals coupled with predictability of subterranean seedling environment will select for adaptive plasticity of subterranean seed provisioning such that subterranean seedlings are supplied with resources appropriate for survival in an environment similar to that of its mother. Using patch choice experiments, I found that the subterranean-seed-bearing runners of A. bracteata forage between microsites, and that subterranean seeds are preferentially placed in moist, dark locations. The foraging behavior of runners and non-random placement of subterranean seeds suggests that selection on provisioning of subterranean seeds may favor local adaptation over plasticity. In glasshouse experiments, I showed that selection for increased seed size was stronger in deeper shade. Plants grown under shaded conditions produced a much higher ratio of the massive subterranean seeds compared to the smaller aerial seeds, and the aerial seeds that were produced in shade were larger. Taken together, these results suggest that maternal individuals of A. bracteata can regulate progeny fitness by altering the provisioning of each seed type as well as by manipulating the ratio of subterranean to aerial seeds. |
