Mining genomes to understand the evolution of Australian eucalypts
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 subgroups such as the ghost gums, red bloodwoods, spotted gums and yellow bloodwoods pictured on the right.
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).
Tanja Schuster (Royal Botanic Gardens Victoria)
This project is funded by the Hermon Slade Foundation (2014–2017).
TM Schuster, SD Setaro, JFG Tibbits, EL Batty, RM Fowler, TGB Mclay, S Wilcox, PK Ades and MJ Bayly (2018) Chloroplast variation is incongruent with classification of the Australian bloodwood eucalypts (genus Corymbia, family Myrtaceae). PLoS ONE 13(4): e0195034. https://doi.org/10.1371/journal.pone.0195034