Project Description

Dr Catherine Grueber

 University of Sydney

Adaptation and conservation insights from the koala genome include a diversity of diversifying selection on cytochrome P450 monooxygenase sequences

Next generation sequencing & bioinformatics

Monday 1 July 2019

Catherine completed her PhD at the University of Otago (New Zealand), followed by a postdoctoral position at the University of Sydney. She has recently been awarded a prestigious Robinson Fellowship in the School of Life and Environmental Sciences at the University of Sydney, which has allowed her to set up a research group in applied evolutionary genetics. Catherine and her team investigate how animal populations respond to natural and “unnatural” conditions: whether bringing threatened species into captivity to prevent extinction, or securing a more productive food supply through animal breeding. This research uses evolutionary theory, population genetics, computational modelling and meta-analysis to learn how to maximise species resilience for the future. Catherine’s research has been supported by the Australian Research Council, the Save the Tasmanian Devil Program, and San Diego Zoo Global.

Koala (Phascolarctos cinereus), an endemic Australian marsupial, feeds almost entirely on leaves from the Eucalyptus genus, a diet that would be toxic to most mammals. Sequencing the koala genome enables us to better understand the species’ unique adaptations to this diet. The presented work forms part of this larger investigation (by researchers from the Koala Genome Consortium), into the evolutionary and conservation lessons we can learn from the koala genome, including adaptation to diet. The presentation begins with an overview of the koala reference genome construction. I next present a specific analysis of selection on cytochrome P450 monooxygenase (CYP) gene sequences across a multispecies alignment (N = 154 sequences, 33 from koala, as well as sequences from nine other species). We tested for diversifying selection utilising a mixed-effects model of episodic diversifying selection to reveal episodic selection: codons under positive selection in only a part of the tree, while under purifying selection elsewhere. We found conserved regions of the alignment showing a strong tendency towards negative (purifying) selection, as would be expected for a functional protein. Nevertheless, many codons showed evidence of episodic selection, including some with significantly greater evidence for selection in koala-specific lineages than in other species. These effects also varied across gene paralogues. Collectively these results suggest that koala CYPs evolve under diversifying selection: multiple genes are under different types of selection, and different codons appear to be under selection across genes. Together these results from the koala genome have implications for our understanding of the evolution of toxin metabolism in mammals.