Date of Award:

2016

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Ecology

Advisor/Chair:

Paul G. Wolf

Abstract

In the history of life, we can observe an astounding diversity of life forms. However, we still lack a thorough understanding of how different species form and even what constitutes a species. In some groups of organisms, especially in plants, hybridization between species is very common. Hybridization has the potential to create new combinations of traits, which can lead to speciation, but hybridization can also lead to extinction or demographic decline of natural populations. Within and between species, genetic variation is ubiquitous in natural populations, which can be observed on various levels. Here, I present several ways to assess such variation in the plant genus Boechera (Brassicaceae). First, I present the evolutionary history and patterns of admixture within a subgroup in the genus, the B. puberula clade. I further show through admixture analyses, that that there is variation in the extent of admixture within the group, but especially when it comes to admixture with two widespread congeners, not part of the B. puberula clade. In a second study, I assessed levels of genetic diversity and patterns of population genetic structure within a member of the B. puberula clade, the montane endemic diploid B. lasiocarpa from Utah. After excluding all hybrids based on estimated admixture proportions, I show that levels of genetic diversity based on genomic data from this rare species are higher than in the widespread B. stricta. Additionally, I assessed common and rare SNVs and show that populations of B. lasiocarpa exhibit variation in genetic diversity and population genetic structure, which seem to be consistent with assumed population sizes. Further, I investigated patterns of gene expression in an experiment under drought-stress in four Boechera species, which exhibit differences in reproductive mode and ploidy level. Across all four species, I did not find a uniform response to drought-stress, and I present evidence for apomixis-specific gene expression, for differential expression associated with ploidy as well as differentially-expressed genes under a model of potential reversal from apomixis to sexual reproduction in B. lignifera.

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