UBC Theses and Dissertations
The genetics of contemporary evolution in an invasive perennial sunflower Bock, Dan Gabriel
While it is now widely accepted that contemporary evolution is common, we have limited information on the genetic underpinnings of these transitions. Here, I investigate this topic in invasive perennial sunflowers. First, I review the plant evolutionary biology literature to assess the validity of a common assumption, that plant organelle genome variation is selectively neutral. I show that organelle-encoded adaptations are likely, and supported both theoretically and empirically. I then rely on genome skimming to clarify the origin of Helianthus tuberosus, a hexaploid perennial sunflower and the study system I used for the rest of this thesis. Based on phylogenomic evidence, I show that H. tuberosus is an auto-allopolyploid that formed by hybridization between diploid and auto-tetraploid perennial sunflowers. This study provides an early example of the use of genome skimming for the identification of the progenitors of polyploid taxa, and facilitates studies on genome reorganization following polyploid speciation. Finally, I investigate the genetic architecture of invasiveness in H. tuberosus. I use genomic data to show that invasive genotypes originated repeatedly, and that most derive from hybridization between native and cultivated material. I then combine information from the greenhouse and from a replicated common garden, and show that increased clonal propagation is a major invasiveness trait in this system. I present evidence that high invasiveness in H. tuberosus can be achieved by hybridization and heterosis, or independent of hybridization, through the action of two major additive effect loci. Moreover, I find that these different genetic mechanisms can act synergistically, and that both have been exploited by widespread invasive clones. Collectively, these results show that invasiveness can be achieved via multiple genetic routes in the same system and during the same biological invasion event. These findings contribute to our understanding of the diverse genetic basis of contemporary evolutionary transitions.
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