Using Manipulated Phenotypes to Evaluate the Contribution of Maternal Effects to Life History Evolution in an Herbaceous Plant

One of the primary goals of the main grant is to test the hypothesis that maternal flowering time determines the timing of offspring germination in the herbaceous plant Campanula americana. Because fall germinating seeds are annuals while spring germinating individuals are biennials, effects of maternal flowering time may influence the evolution of life history schedule. The experiments assume that C. americana seeds begin to germinate in the fall shortly after being produced, remain dormant over the winter, and resume germination after snow melt in the spring, thus creating two distinct cohorts of seedlings. Previous surveys have found almost no germination occurs in the summer. Seeds remain viable for several years in the soil suggesting that lack of summer germination is due to the depletion of seeds from the seed bank. The goal of this REU supplement is to determine whether in fact limited summer germination is due to depletion of the seed bank or whether it may be due to lack of appropriate germination cues. This distinction is important when evaluating the potential for evolution of germination timing as addressed in the main grant.

The REU project will test whether lack of appropriate environmental cues restricts germination using controlled environment and field studies.

1. Soil samples from four populations will be collected monthly during the growing season and placed under near-optimal germination conditions. Germination of seeds out of this soil would suggest that seeds are present but natural germination cues (e.g. day length or moisture) are missing. A survey of fruit ripening and seed dispersal conducted as part of the main grant will provide information on the addition of new seeds to the seed bank. If germination occurs in summer samples, follow-up studies will focus on the role of specific environmental cues.
2. Field plots in two populations will be watered daily throughout summer and early fall. Fall germination typically follows precipitation and most germination occurs in the spring when the soil is moist. Greater germination in watered plots relative to control plots would suggest that seeds are present but limited soil moisture during the summer restricts germination to the fall and the spring. If neither of these experiments yields germination it supports the hypothesis that seasonal germination is in large part due to the depletion of seeds from the seed bank.