The association between polyploidy and clonal reproduction in the angiosperms.

Abstract

Polyploidy, the presence of 3 or more chromosome sets, is widespread throughout the flowering plants (angiosperms). Asexuality through clonal reproduction is predicted to promote polyploid evolution and establishment in natural populations, but there is little rigorous research on this subject. I explore the relationship between polyploidy and clonal reproduction in the angiosperms, utilizing both analyses of broad-scale trends and species-specific experiments. Phylogenetic comparative analyses in Chapter 1 suggest that polyploidy and clonal reproduction are positively associated at the whole angiosperm level, but polyploidy-clonality interactions appear to be different between major clades. The association between polyploidy and clonality is weakened in perennial species, indicating that correlations with life history may underlie some of the relationship. Transition rate estimates do not support the oft-cited hypothesis that clonal reproduction facilitates polyploid evolution, instead revealing that the overall trend is for clonal reproduction to follow polyploidy. In the next two chapters I generate colchicine-synthesized polyploids (neopolyploids) in the first studies to determine how whole-genome duplication (WGD) directly affects clonal reproduction. In Chapter 2, I find that WGD immediately decreases stolon and plantlet production in neotetraploid vs. diploid Fragaria vesca. This study also demonstrates that the effects of WGD are not uniform, revealing significant differences in clonal investment between independent neopolyploid lines. In contrast, Chapter 3 shows that clonal root bud production is significantly increased in neotetraploid vs. diploid Chamerion angustifolium, but is similar between naturally-occurring tetraploids and diploids, suggesting that strong selection in natural populations acts to reverse the immediate effects of WGD on clonality in this species. Notably, the differences in clonal reproduction between diploids and polyploids in Chapter 3 would have been overlooked without the use of neotetraploids, the use of which remains rare in ecological and evolutionary studies of polyploidy. The studies presented in this thesis are some of the first to explore the relationship between polyploidy and clonality in-depth, providing a novel perspective on old ideas. My research provides evidence for an evolutionary relationship between polyploidy and clonal reproduction, but also emphasizes that the effects of polyploidy on clonal reproduction, and vice-versa, can vary significantly between individuals, species, and angiosperm groups.