OPUS: MCS: Is self-fertilization an evolutionary dead end? Artificial selection of a key outcrossing trait and its consequences in partially selfing populations

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Understanding the processes that limit evolution and adaptation remains a major question in biology. Many plants and animals evolve traits that allow them to produce offspring through self-fertilization. However, this transition is thought to be a one-way street because self-fertilization limits genetic variation which prevents further evolution. This project will determine whether plants that primarily self-fertilize can re-evolve to be outcrossing. Highly outcrossing and primarily selfing species of monkeyflower will be compared for their genetic variation and artificially selected for flower traits that determine the rate of selfing. The project will involve undergraduates in the conduct of independent experiments and the analysis of genetic data, and new laboratory materials will be developed on artificial selection and genetic evolution for an undergraduate course at Washington State University.Limited heritable variation in predominantly selfing populations is thought to be a primary constraint on the evolution of outcrossing traits. While declines in effective population size and the efficacy of recombination are expected with close inbreeding, there is scant information on their consequences for adaptive trait evolution. Constraints on the re-evolution of outcrossing traits in primarily selfing lineages suggest either that genetic variation is limiting or that such responses are possible but unlikely to occur. Outcrossing populations of Mimulus guttatus and selfing populations of M. laciniatus and M. micranthus will be subject to five generations of artificial selection for increasing the anther-stigma distance, a key outcrossing trait, and the realized heritability will be determined. Pooled whole-genome population sequencing of the control and selection lines before and after the experiments will reveal the comparative effects of selection on their genomes. This whole-genome information has the potential to critically link constraints on adaptation to the genetic consequences of self-fertilization (i.e., low nucleotide diversity and strong linkage disequilibrium).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.