| Popis: |
Systematists study the diversity of life on Earth, aiming to describe its variety of forms and the relationships between them, as well as to understand the processes that influence changes in diversity over time and space. One of the most striking aspects of Earth’s biodiversity is that its distribution is highly heterogeneous, varying enormously not just between geographic regions but also between lineages. One place that exemplifies this is the Cape Floristic Region (CFR), a global biodiversity hotspot that hosts roughly 9,000 vascular plant species, of which nearly 70% are found nowhere else. The CFR flora comprises a taxonomically unusual mixture of lineages whose origins lie in Africa, South America, Australia, and Europe. One of its European-origin components, the heathers (genus Erica), stands out as a remarkable example of floristic diversity globally. Out of a global total of around 850 species, almost 700 are found in the CFR, all of which share a single common ancestor that arrived in the region at the earliest around 15 million years ago. Almost immediately after its arrival in the Cape, Erica began to rapidly diversify, attaining a large variety of novel forms. The reasons for this exceptional diversity, however, remain unclear. In this thesis, I aimed to investigate the diversification of Cape Erica by applying recently developed genomic methods to infer inter- and intraspecific relationships in much finer detail than has previously been achieved. I begin by introducing the study of biological diversification in general, in the context of the CFR, and in the context of Erica. In the next chapter I develop a suite of resources to better enable genome-scale phylogenetics (i.e., phylogenomics) in Erica using a genome sampling approach known as target capture, and show that it provides high quality, informative data. In the third chapter I apply this new resource to an unresolved phylogenetic problem regarding the recent diversification of a charismatic group of Cape Erica, the E. abietina/E. viscaria clade. This results in the resolution of some long-standing taxonomic questions, uncovers evidence of interspecific hybridisation, but also indicates a high degree of uncertainty regarding phylogenetic relationships at deep and shallow phylogenetic levels alike. However, rather than indicating a lack of statistical power this uncertainty is shown to more likely be a direct consequence of historical biological processes such as incomplete lineage sorting and rapid diversification. In the fourth chapter I focus in on E. abietina, a species complex that shows evidence of recent, rapid phenotypic diversification, aiming to explore the dynamics of diversification in its earliest stages at the interface of micro- and macroevolution. To do so I employ genotyping-by-sequencing, another genome sampling method that is, relative to target capture, better suited to investigating genetic relationships at such a shallow scale. This reveals a highly dynamic system that is a product of the interplay between divergent selection on floral traits, adaptation to different environments, geographic isolation, secondary contact, and both recent and ancient introgression. Lastly, I conclude with a discussion of what the results of the thesis imply about the modes and drivers of diversification in Cape Erica. |
