Towards a phylogenetic ecology of plant pests and pathogens: using evolutionary history to model species interactions

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Plant pests and pathogens play an important role in structuring ecological communities; yet both native and introduced pests impose significant pressure on wild and managed systems, and pose a threat to food security. A warming climate is likely to further increase the range, frequency and severity of pest and disease outbreaks in the future. There is a critical need, therefore, to expand on current theory to address these challenges. Here, I propose to develop a novel phylogenetic framework for the study of plant and pest interactions. In plants, a growing body of work has suggested that host evolutionary relatedness-phylogeny-strongly structures pathogen host range. The consequences of such phylogenetic structuring are profound. For example, rates of pathogen spread will be mediated by the taxonomic composition of the host species in a community, and the likelihood of non-native pest establishment may be estimated from the phylogenetic relatedness between the plant species in its introduced range and those in its native range. In addition, we would predict that disease pressure on agricultural crops from native pests will covary negatively with the evolutionary distinctiveness of the crop species from the native plant community, while the spread of invasive plants will covary positively with their evolutionary distinctiveness. A major goal of this research is to improve on our current understanding of host-pest associations in plants, better predict disease impacts of new and emerging plant pests, and guide proactive pest surveillance. First, I aim to characterise the phylogenetic structure of plant-pest interactions using existing plant-pest databases and a mega-phylogeny for plants to describe the phylogenetic distribution of pests across the plant tree-of-life. I will then use these data to model the likelihood of pest sharing among plant hosts, and to redefine the host breadth of pests based on the evolutionary distances separating host species. Second, I will use the vast historical record housed in herbarium collections to model shifting pest and disease pressures through time, and use this model to generate predictions of pest host-expansion which can then be validated in the field. Third, I will evaluate the relationship between phylogenetic host-breadth and virulence using experimental cross infections of the wine-grape fungal pathogen Botryosphaeriaceae as a model system. The proposed framework I outline above holds promise to inform models of disease and pest risk in crops, improve prediction of invasive species spread and emerging pathogen outbreaks in native species, and contribute to our fundamental understanding of species coexistence and the importance of pests and pathogens in regulating diversity in natural communities.