The effects of genetics, mutation and selection on Evolutionary Rescue in complex environments

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The past 150 years of modern evolutionary biology have provided us with a good understanding of how natural populations adapt to the constant changes that they experience in their environment. One important case that remains poorly understood, however, is that of evolutionary rescue (ER), where populations rely on adaptation to escape decline and extinction due to large, abrupt environmental shifts. Understanding the factors that allow or limit ER is fundamental and urgent in both basic and applied contexts. Human interventions such as antibiotic or pesticide treatments aim to impose unsurmountable adaptive challenges on the targeted species, and understanding the limits of ER is essential for maximising the efficacy of these interventions. Conversely, understanding the factors that favour ER is crucial when managing species threatened by rapid climate change.Given its importance, it is crucial to gain a better understanding of what determines a population's capacity for ER. Previous work has demonstrated that the capacity for ER is limited by the supply in advantageous genetic variants and increases with the amount of standing variation, the input of new variants (via mutation and immigration) and pre-adaptation from previous exposure to similar selection pressures. One significant limitation, however, is that previous work on ER has largely focussed on simple environments and changes in the mean of a single environmental variable. This is not realistic, because organisms live and evolve in complex environments, and using univariate environments fails to capture the complexity of multivariate evolution, where adaptive responses can be significantly affected (positively or negatively) by genetic correlations between responses to different variables.The aim of this project is to gain a detailed understanding of ER in multivariate environments. In order to do so, we investigate how the capacity of a population to show ER relates to the different forces that shape the genetic (co)variation for responses to different environmental variables, namely the size and topology of the genetic pathways underlying environmental responses, random genetic mutation, and past selective pressures that shape the amount and orientation of mutational variation.Our project uses the highly malleable fission yeast system and exploits a combination of powerful phenotypic and genetic high-throughput approaches. Using highly replicated growth assays across gradients of three environmental variables, the concentrations of potassium and magnesium chloride and temperature, we will determine the genes and pathways underlying responses to these variables and the degree to which they overlap. Using mutation accumulation, we will then study how random mutations interact with the size, structure and overlap of these pathways to generate covariation in environmental responses. Further, using experimental evolution under different regimes of multivariate environmental fluctuations, we will generate populations with different selective histories. Finally, we will assess ER in these evolved populations, alongside others assembled from selected wild strains, when subjected to changes in the means, variances and covariances of environmental variables.The data collected during the course of our project will allow us to generate a much better understanding of ER in complex environments, thus filling a major gap in our understanding of adaptive evolution. At the same time, we will have created a uniquely complete case study of multivariate evolution that ranges from the genetics underlying the genotype-phenotype map over mutation and selection to evolutionary change in multivariate trait space.Importantly, these insights into the factors determining ER will also be immediately exploitable in several areas of applied science, including the management of endangered species and the design of drug and pesticide treatments (see Impact).