Understanding the evolutionary repercussions of adaptation to new threats

This project will analyse the wider evolutionary repercussions of genetic adaptation to novel threats, by analysing genomic and trait data from tree populations suffering from a fungal pathogen epidemic. In common with many organisms, forest trees face increasing threats to their survival. When exposed to an entirely new threat - such as a pest or pathogen - most individuals are unable to fully defend themselves and may die. Genetic variants already present within natural populations can provide the basis for successful adaptation in response to such threats. Yet, during natural selection, species may lose overall genetic diversity, leaving them at greater risk from subsequent threats. Furthermore, selection on one trait – such as disease resistance – can lead to change in others, with possible consequences for the ecology and survival of the species. The ash dieback epidemic provides the opportunity to further understand how these processes operate in natural populations, and their implications for ecologically important species such as forest trees. We have recently demonstrated that selection for reduced susceptibility to the ash dieback pathogen is happening in Fraxinus excelsior (the ash tree; 10.1126/science.adp2990). Using a large genomic dataset, you will analyse the wider impact of this selection within multiple natural populations of ash trees, also collecting new trait data from woodlands. You will use these data to address key questions such as: - Is selection for reduced susceptibility to ash dieback accompanied by loss of genetic diversity? - Are other adaptive traits also evolving as the epidemic progresses?