Lack of polymorphism suggests a recent bottleneck of Aloidendron pillansii: Exploration into the population of Aloidendron pillansii from phylogeographical analysis of molecular data

Bachelor Thesis


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University of Cape Town

The Karoo-Namib is a species rich region in which many iconic and keystone species are found, such as Aloe pillansii. The recent population history of A.pillansii is poorly understood. However the suggested climatic shifts that occurred throughout the Holocene era may have affected its distribution, demographics and gene flow. The glacial/interglacial refugia hypothesis predicts that the southernmost population served as a refuge population and that the subsequent expansion of the population was to the north in concert with the northward expansion of the winter rainfall regime. I evaluated this hypothesis by linking the molecular data (cpDNA and nDNA) of 84 individuals from three main populations with phylogeographical techniques. Based on the combination of percentage of mutations percentage per million years range and the chloroplast sequences, it has been estimated that the time of divergences was between 3.45 to 16.67 million years ago. The molecular analysis identified a significant lack of genetic diversity within and among the three dominant populations of A.pillansii. This suggests that the species experienced a severe bottleneck event prior to its recent expansion that has been suggested to have occurred within the time frame of 100 to 1000 years ago. This pattern is compared with its sister taxa Aloe dichtotma, which possesses variation within and among its populations. The lack of genetic variation evident within A. pillansii leaves it vulnerable to future climate shifts as low genetic variation within a species lowers the ability of that species to adapt to both environmental and climatic changes. This thesis has provided a brief insight into the population history of A.pillansii, but further research is needed.

Includes bibliographical references.