A Dual Ecological Genomics Approach Unravels the Genetics Underlying Local Adaptation in Swedish Arabidopsis thaliana Accessions

Understanding the genetic basis of local adaptation has been a long-standing goal of evolutionary genetics. While extensive genomic resources are available in Arabidopsis, field experiments are key to identify variants underlying natural variation and investigate their adaptive value. Here we present results from two sets of complementary experiments carried out in natural environments in order to investigate the extent and genetic basis of local adaptation. The first set of experiments consists of four common garden studies located in realistic Arabidopsis habitats both in the North and the South of Sweden. These experiments include multiple replicates of 200 genome-resequenced Swedish accessions, representing a total of nearly 20,000 plants. By scoring multiple potentially fitness-related traits as well as estimating fitness via survival and seed production, we test for local adaptation, investigate the effect of traits of interest on fitness and identify the underlying genetics using genome wide association mapping. Traits of particular focus are herbivore resistance and composition of the leaf pathogen community. The second set of studies consists of natural selection experiments. Populations composed of the 200 Swedish accessions were established in replicated plots in multiple realistic Arabidopsis habitats. The composition of these populations is being assayed three times per year, allowing us to track allele frequency changes and potentially locate regions of the genome responding to natural selection. Preliminary results from our experiments suggest that herbivory and pathogen resistance both play important fitness effects. Initial association mapping of plant survival detected multiple herbivore and pathogen resistance related genes. Additionally, herbivore damage negatively impacted overwinter survival and the underlying genetics were successfully explored using association mapping analyses. Ongoing investigation will shed light on the variation of pathogen community in rosette leaves between regions of Sweden and among Arabidopsis accessions, with the unique opportunity to test for fitness effects in realistic environments.