Graduate Thesis Or Dissertation


Genetic Structure, Diversity, and Mating System of Leptasterias: Potential for Local Adaptation? Public Deposited

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  • Understanding of gene flow, connectivity, and diversity is critical to predict the stability of key marine species. The Oregon coast of the U.S.A. shows fine-scale levels of geographic variation in environmental stressors such as temperature, pH, and oxygen levels, prompting questions about the potential for local adaptation. In this thesis, I unite population genetics with ecology, oceanography, and life history to investigate the resilience of Leptasterias sp., a six-rayed brooding sea star and important intertidal predator along the Oregon coast. In Chapter 2, I use nine neutral microsatellite markers to establish the genetic structure and diversity of Leptasterias populations across three capes and six sites. I find evidence of strong population structure at the level of capes, and further divergence between two sites (CB and RP) within Cape Blanco. Though this genetic structure is broadly consistent with an isolation-by-distance pattern, the scale and strength of divergence may be partially driven by differing magnitudes and directions of oceanographic currents and patchy between-site habitat composition. In Chapter 3, I investigate mixed paternity as a mechanism by which this brooding species may maintain high genetic diversity in the face of limited gene flow. I use five microsatellite markers to quantify the level of multiple paternity (sires per brood, sire evenness, and paternity skew) at six sites, and I compare these measures across the Oregon range of Leptasterias. I find consistently high levels of multiple paternity (frequency 100%, mean 11.6 sires per brood, range 2-20) across all capes, consistent with predictions of obligate/convenience polyandry experienced by sperm-casting species in dynamic marine environments. Despite differences in population density and inbreeding coefficients, I find no differences in paternity levels between capes or sites, suggesting that fine-scale gradients in environment or ecology may exert more influence on sperm dispersal and fertilization than geographic differences. Overall, my thesis illustrates the way in which multiple factors—life history, ecology, oceanography, habitat composition, and more—can influence the connectivity, structure, and genetic diversity of a brooding marine species. I contribute to ongoing efforts by the PISCO and OMEGAS research consortiums to investigate the physiological, ecological, and genetic performance of key species in the mosaic environment of the California Current Large Marine Ecosystem.
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