Effects of whole genome duplication on adaptation, plasticity and niche variation in the Claytonia perfoliata (Portulacaceae) polyploid complex.

摘要

Genome duplication is a central process in plant evolution. The evolutionary history of all angiosperm lineages is characterized by multiple rounds of polyploidy, or genome duplication, typically followed by genome downsizing and a return to diploidy. With the advent of modern genomics there has been intense interest in why genome duplication is so common in certain groups and whether it provides evolutionary or ecological advantages through processes or factors such as subfunctionalization of duplicate genes, changes in heterozygosity, flexible expression of multiple parental genomes, and stabilization of the hybrid state. This dissertation examines the ecology of diploid and polyploid cytotypes of the Claytonia perfoliata complex.;In the first chapter I use pre-existing and newly collected locality records for cytotypes of C. perfoliata in species distribution models to estimate the ecological distribution of cytotypes. I compared these distributions using randomization approaches to hypothesis testing and found that diploid and polyploid cytotypes possess distinct niches, and that polyploid cytotypes possess broader ecological niches than diploid cytotypes.;In the second chapter I investigate the roles of adaptation and plasticity (both within and across generations) in the distribution of linear and broad leaved populations of hexaploid C. perfoliata. These two forms predominate in adjacent habitats- broad leaved plants form nearly pure stands underneath the canopy of oak trees in the Sierra Nevada foothills, while linear leaved plants often form nearly pure populations in adjacent grassland habitat. Plants exhibited strong local adaptation, with broad- and linear-leaved plants producing over 50% more seeds within the light environment where they typically occur. Maternal planting environment also influenced offspring fitness across generations, with offspring from plants reared in open environments producing more seed than offspring from plants reared in shaded environments when planted in open environments.;In the third chapter I use experimental field transplants across elevation to ask whether cytotypes exhibit niche differentiation and local adaptation and whether polyploids perform better across a range of ecological variation. Cytotypes emerged better and had higher relative fitness within than beyond their naturally occurring elevational ranges. This is consistent with ecological differences among cytotypes contributing to differences in geographic distribution. Polyploid populations did not have a general advantage in performance, but they exhibited greater variation in the relationship between fitness and environmental distance than did diploid populations, suggesting that polyploid cytotypes may have greater ecological variation than diploid cytotypes.;Chapter four summarizes variation in genome size within and across cytotypes. Increased variation in genome size both within and among populations was present at higher ploidy levels, potentially associated with differential contributions of parental genomes, variation in rates of genome loss or undetected hybridization. Plants of the same ploidy level varied by as much as 30% in their genome size, suggesting cryptic diversity within ploidy levels.