摘要：

Most flagship species or commonly recognized plants and animals proliferate via sexual reproduction, however, there are a curious number of plants and animals that are asexual. Both modes of reproduction have advantages and disadvantages. Sex, and in particular biparental inheritance, generates the haplotype diversity and standing genetic variation required for effective natural selection, while asexual reproduction offers guaranteed reproduction and a 2-fold increase in genetic transmission. Similarly, sex generates costly phenotypes that hinder survival, and asexual species run the risk of extinction due to the accumulation of deleterious mutations. Numerous plants and animals have converged on self-fertilization as, an alternate mode of sexual reproduction that offers reproductive assurance, increases in genetic transmission, and fosters local adaptation. Self-fertilization is also associated with reductions in heterozygosity and effective recombination which ultimately reduce the efficacy of natural selection. The exact genetic and genomic consequences of self-fertilization are largely unknown. The super model organism Caenorhabditis elegans is uniquely suited to study the evolutionary dynamics that influence breeding shifts and selective pressure placed on genes and genomes of self-fertile organisms. C. elegans offer an exhaustive set of genetic and genomic resources derived from decades of experimentation, a large world-wide sample of biodiversity, and advances in high throughput data collection. Moreover, there were several key observations drawn from this dissertation. Firstly, the selective constrains placed on male-specific mating genes have been relaxed. Genes required for male-specific mating functions contained an excess of slightly deleterious alleles that would likely complicate but not suppress mating. Secondly, variation on the X chromosome (the sex determining chromosome) was not equal to that of the bilaterally inherited autosomes. The factors contributing to variation on the X chromosome and the autosomes varied. Lastly, the hybridization of divergent lineages within the same species yields large genomic blocks of heterosis and genetic incompatibilities. Pockets of the genome are hypothesized to either hinder or support outbreeding. All together these observations provide evidence that C. elegans has a history of outcrossing and that males play an important (but small) role in the upkeep of the species. C. elegans toe a fine line of eventual extinction and the absolute freedom to reproduce at will.

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