Mining genomes to understand evolution of the iconic Australian eucalypts

A collaborative project undertaken at the Royal Botanic Gardens Melbourne and supervised by Tanja Schuster

Project Team

Tanja Schuster, Royal Botanic Gardens Melbourne & Josquin Tibbits,  Victorian Department of Environment and Primary Industries

Summary

Eucalypts dominate a large proportion of the Australian landscape and knowledge of their diversification gives insight into the history of the continent as shaped by geologic and climatic events. The ecologically important eucalypts include a small group of rainforest genera (Arillastrum, Allosyncarpia, Eucalyptopsis and Stockwellia) that comprise only five species plus three large sclerophyll genera including ca. 950 species of Eucalyptus, Corymbia and Angophora. Corymbia was split from Eucalyptus relatively recently and includes the red and yellow bloodwods, spotted and ghost gums.

The evolutionary relationships among eucalypts remain controversial. For example, it is unclear what the basal relationships within this group are and whether Angophora should be included in Corymbia. This is because of inconsistent results from morphological studies, molecular datasets using only a few gene markers, some chloroplast genes not tracking speciation, and hybridisation between species. Uncertainty of evolutionary relationships undermines our understanding of biogeographic history e.g., the timing of links between the Gondwanan fragments New Caledonia and Australia are contentious.

New molecular tools such as next-generation DNA sequencing (NGS) allow us to reveal patterns and timing of evolution across the tree of life at an unprecedented scale. These data enable us to compare the composition, size, structure and interactions of chloroplast, mitochondrial and nuclear genomes. A preliminary study of whole chloroplast genomes by Bayly et al. (2013) established the potential of NGS for studies of Australian eucalypts by providing many more variable characters for analysis, but had limited sampling for the red bloodwoods (Corymbia. subg. Corymbia) and Angophora.

The goal of this study is to produce a well-resolved, well-supported and dated phylogenetic tree for eucalypts using NGS data and to address questions about the monophyly and evolutionary relationships of Angophora and Corymbia. Combination of novel genomic and fossil data positions us to understand Australia‘s biogeographic history (e.g., divergence and diversification in monsoonal savannah, rainforest and temperate biomes), promote coevolutionary studies (e.g., insects exclusively occurring on Eucalyptus) and inform conservation management (e.g., identifying regions of phylogenetic diversity and significance).


Figure 1. Angophora leiocarpa (NSW Nov 2014)

Figure 2. Angophora euryphylla (NSW Nov 2014)

Figure 3. Angophora bakeri leaf oil glands (NSW Nov 2014)

Figure 4. Corymbia torelliana fallen calyptra and capsules (NSW Nov 2014)