Susan Rutherford
PhD Alumni
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Adaptive variation versus vicariance: What drives speciation in Eucalyptus

This project investigates speciation in a group of closely related eucalypts known as the ‘green-leaved ashes’ and is a joint project between the University of New South Wales and the Royal Botanic Gardens Sydney. The green-leaved ashes are a diverse group including tall trees, medium trees, and mallees (multi-stemmed plants with a lignotuber), which occupy a range of habitats in south-eastern Australia. They include the commercially important timber species, E. regnans, E. obliqua and E. fastigata, as well a number of rare or localised species such as E. burgessiana, E. cunninghamii, E. apiculata, E. laophila and E. langleyi.  During my PhD, I will aim to address the following questions: 1) what are the evolutionary relationships between these taxa and patterns of divergence; 2) what drives speciation and adaptation in this group; and 3) what constitutes a species and how can a better understanding of adaptive evolution in these taxa contribute to theories of speciation?

Evolution and divergence of the green-leaved ashes is being investigated using DArT (Diversity Arrays Technology) markers, a recently developed technique that sequences across the genome. In addition, selected green-leaved ash taxa are currently being grown under varying nutrient and water regimes to test for adaptive traits. This molecular and growth data will be used in combination with distributional, environmental and morphological data in order to study speciation of these taxa across altitudinal gradients (focusing on the Sydney region: from the coast to the upper Blue Mountains). There is still much debate and uncertainty regarding many fundamental aspects of speciation and it is hoped that a better understanding of adaptive evolution in this group will provide insights into theories of speciation.

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