The role of local adaptation in natural populations of Arabidopsis thaliana

In the face of climate change, habitat loss and invasive competitors, populations that are particularly well adapted to their specific environment may actually be at a disadvantage. Adaptation is a process that increases the frequency of a trait by conferring a fitness advantage to individuals expressing that trait when compared to individuals without it. Local adaptation is a more specific process where individuals with the trait are more successful in their native conditions when compared to those from foreign conditions. With the recent availability of large amounts of genomic data for a select set of model organisms, the genome-wide causes of being adapted to a specific habitat can be better understood.;I explored the potential for local adaptation to edaphic conditions in Midwestern US collections of the model plant Arabidopsis thaliana . Though I found variability in fitness-related traits among maternal lines from different sites, differences between soil treatments played a large role in plant performance. I used a computational approach with genetic data for worldwide A. thaliana accessions to determine an appropriate geographical in which to perform reciprocal transplant experiments: the gold standard for testing local adaptation. Results from these analyses suggested that natural selection may have affected genetic differentiation in wild Swedish populations of A. thaliana; a potential consequence is that these populations may be locally adapted. To further investigate, I used a bottom-up approach, beginning with known genetic differences and aimed to understand how they manifest at the phenotypic level. In the field component of this research, I planted natural accessions and F3 offspring from these crossed accessions reciprocally in different habitats (northern and southern Sweden) and looked at relative survival and fecundity rates. At southern Swedish sites, I found that experimental populations were consistently enriched for individuals carrying southern alleles in both the parental and F3 populations. Given the coarse genetic mapping of fitness-related traits from the experiments in Sweden, further exploration of these questions is necessary to find causal genomic regions. I gave specific attention in the discussion to improvements in experimental design and methodology. Finally, I investigated native populations of A. thaliana in Sweden, made new collections, and described and photographed field conditions.