Ecological effects of clonal interference in a changing environment

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This research will advance our understanding of how evolution proceeds and what the maximum rate of evolutionary change might be, which is relevant to understanding whether populations will be able to adapt fast enough to avoid extinction in today's rapidly and globally changing environment. Recent evidence suggests that the fact that many genes reside on the same stretches of DNA makes it difficult for natural selection to act effectively on each one, in a phenomenon known as clonal interference. This limits the maximum speed of evolution, and in a changing environment, populations that evolve too slowly go extinct. This study will address these questions through mathematical models that will calculate the impact of clonal interference on extinction and analyze the nature of competition. This research project also will provide training for undergraduate students, including individuals from groups underrepresented in the sciences, and education for the general public through public lectures, a popular science book, and Wikipedia articles.Recent evidence suggests that high levels of linkage disequilibrium imply that recombination is slow to bring adaptive mutations together on the same genetic background. Different adaptive genotypes compete, causing many adaptations to be lost instead of fixed. To address this topic of slow adaptation due to clonal interference leading to extinction in a changing environment, the researcher will develop mathematical models of evolutionary rescue (adaptive escape from extinction). The researcher proposes a new three dimensional fitness scheme: r-selection for absolute growth speed at low population density, K-selection for absolute efficiency of resource use, and c-selection for relative competitive ability at high population density. This 3D scheme has significant advantages over past 2D schemes, e.g., r vs. K, relative vs. absolute, hard vs. soft, groups vs. individuals. This novel 3D (and extensible) model will be developed and applied to existing model systems and data. Each adaptive mutation affects one or more fitness dimensions, with both tradeoffs and synergies possible. Common combinations indicate natural axes of mutation and adaptation. Preliminary data suggest a natural axis of density-independent fitness, along which environmental change lowers both r and K in equal proportions, while subsequent adaptation (evolutionary rescue) increases both. Adaptation in the presence of clonal interference will be modeled in this dimension alone, and also in the presence of a second dimension. The latter will show how mutations fuelling the relative arms race of c-selection might contribute to extinction via clonal interference with evolutionary rescue along an absolute fitness axis.