Gomez Quijano, Maria Jose2021-09-242021-09-242021-07https://hdl.handle.net/11299/224517University of Minnesota M.S. thesis. July 2021. Major: Biology. Advisors: Briana Gross, Julie Etterson. 1 computer file (PDF); iv, 56 pages.The massive scale and cold temperature of Lake Superior creates unique microclimates in coastal terrestrial environments resulting in cooler summers, an extended fall season, warmer winters, and a reduced risk of spring frost. This gives rise to a steep climate gradient from coastal to inland regions that could lead to genetic differentiation among populations. To test this hypothesis, we studied Northern red oak (Quercus rubra L.) to examine phenotypic and molecular differentiation among populations ranging from 1–160 km from the lake shore. In a common garden experiment, we found 30% of germination and juvenile traits differed significantly from expectation. We also used restriction site associated DNA sequencing (RAD-seq) to examine population structure and genomic signatures of selection in these populations. Our results suggest that, in contrast to quantitative traits, Q. rubra populations are not differentiated at neutral genetic markers according to their distance from Lake Superior. However, unexpectedly, we also found evidence of increasing levels of introgression from the closely related species Quercus ellipsoidalis E.J. Hill into Q. rubra as species overlap and population distance from the lake increased. Our scan for selection and environmental association analysis identified one outlier locus in common, and this locus is associated with the precipitation of the wettest month. Overall, despite the lack of molecular population structure, the common garden experiment revealed that Q. rubra populations differ for key phenotypic traits. This, in combination with the genomic scans for selection, suggests the influence of natural selection driven by climate heterogeneity with increasing distance from the lake. Moreover, this is the first study that has jointly leveraged quantitative and molecular genetics to dissect signatures of selection in Q. rubra across a fine geographical scale.enGene flowNatural SelectionPopulation GeneticsQuantitative GeneticsQuercus rubraThesis or Dissertation