Determining the evolutionary causes of sexual reproduction remains one of the biggest open questions in biology. Investigations of facultative sexuals can shed substantial insight on this subject due to the span of mating systems exhibited, ranging from outcrossing to asexual reproduction. Due to the widespread availability and reduced cost of sequencing technologies, it is now feasible to perform detailed genomic analysis of many individuals, and combine these data with mathematical models to determine how the underlying form of natural selection differs between asexual and sexual individuals. This genomic analysis is essential for providing insight into the evolutionary transitions between different mating systems. We propose to investigate the genetic basis of selection in asexual and sexual organisms, primarily with species of duckweeds (Lemna minor and Landoltia punctata). The initial plan will be to determine the effect of balancing selection on the evolution of recombination and outcrossing rates. Balancing selection is believed to be a widespread force in various eukaryotic genomes, and since loci exhibiting balancing selection tend to be extremely polymorphic, they should strongly influence the evolution of mating systems. After investigating this question using a multi-locus mathematical model, we will create comparative genomic methods by comparing allele and species trees to determine the extent of balancing selection in asexual and sexual organisms. We will then adapt recent mathematical theory on adaptation in selfers and outcrossers to create computational tools for detecting the extent of adaptation from novel and standing mutations, and whether the form of adaptation differs depending on the mating type.
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