Abstract:
Adaptation to new environments is a driver of biodiversity, and often involves the coordinated action of many genomic loci that contribute to the fitness of an organism. Although adaptation has been extensively studied, an unanswered question is whether the rate or extent of adaptation depends not only upon what genes are involved but on their organization in the genome. To address this question we use the threespine stickleback (Gasterosteus aculeatus) as an evolutionary model system. This small fish inhabits coastal habitats in the northern hemisphere. Oceanic stickleback have repeatedly colonized new freshwater environments, resulting in rapid bouts of adaptive evolution involving parallel changes at the phenotypic and genomic levels. By investigating the structure of the stickleback genome in relation to adaptive evolution, we aim to determine factors that allow this quick and sustained adaptation to novel environments. Gene flow between divergent populations breaks up associations between loci involved in adaptation due to the homogenizing action of meiotic recombination. Therefore, genomic architecture that isolates adaptive genomic regions may evolve. I characterized the recombination landscape of three distinct stickleback lineages by creating genome-wide genetic maps of divergently evolved and hybrid stickleback. We compared these genetic maps with molecular and population genetic statistics to determine whether genomic patterns of divergence might be influenced by recombination rate variation. We find that recombination rate varies extensively across the stickleback genome, and importantly that a hybrid ocean-freshwater stickleback displays strikingly unique patterns of recombination and that genomic islands of divergence are inherited as compact genetic units, indicating that adaptive loci maintain their associations. Our results give insight into how non-random genomic organization can encourage rapid adaptation to novel environments.
Description:
72 pages. A thesis presented to the Department of Biology and the Clark Honors College of the University of Oregon in partial fulfillment of the requirements for degree of Bachelor of Science, Spring 2017