The evolution of reproductive strategies in clonal plants: Investment in sexual vs. asexual reproduction and its implications for the evolution of clonal plant life-histories.

摘要

Plants are modular and autotrophic. These two basic features of the land plants complicate the measurement and interpretation of life history trade-offs. This thesis presents a new way in which to interpret and measure the effect of these trade-offs. First, I provide a novel interpretation of the effect of a particular form of plant modularity, clonality, on fitness gains through male and female sex functions. Previous discussions of this topic focus on the negative impacts of clonality to sexual reproduction, but the results of this conceptually-driven chapter suggest that clonality can serve to increase fitness through the male function. I then show how clonality influences patterns of pollen dispersal and seed fitness in natural populations of an invasive clonal plant (Cirsium arvense). When clones are patchily distributed in the landscape, fitness through the female function can become strongly limited by inadequate pollen receipt. Finally, I present the results of an experimental investigation of trade-offs between clonal growth and sexual reproduction. The use of inappropriate scales (i.e., at a sub-organismal level of biological organization) and units of measurement have limited previous research in this area. My data provide clear evidence for a strong trade-off between sexual and clonal propagation, but only for reproduction through female function. I was unable to detect a cost for reproduction through male function. Overall, my thesis provides new perspectives on several aspects of fitness in clonal plants.;Keywords: Clonal plants, sex allocation, trade-offs, cost of reproduction, Sagittaria latifolia, sex ratios, nearest mate distances, pollination success, Cirsium arvense , seed fertility