Exploring the Genomic Landscape of Local Adaptation in Serpentine Mimulus guttatus
A. H. LAWRENCE ,  J. H. WILLIS
Department of Biology, Duke University French Family Science Center, Science Dr. Durham, NC 27708

Local adaptation arises when spatially divergent selection outpaces migration rates between habitats. Population-genomic scans often reveal candidate genes for local adaptation but struggle to quantify selection strength. Serpentine outcrops are ideal for studying local adaptation because their patchy distribution results in landscapes with abrupt changes from “normal soils” to serpentine. Serpentine soils are unconducive to most plant life due to low Ca:Mg ratios, limited macronutrients, and elevated heavy metals.

Reciprocal transplant experiments in model system Mimulus guttatus reveal extreme local adaptation to serpentine. Population genomic scans of pairs of adjacent serpentine and non-serpentine populations have identified dozens of candidate genes under divergent selection. What are the relative fitness contributions of these genes? I marry a classic mapping experiment with an Evolve & Resequence approach to estimate fitness effects of each loci. I crossed two inbred lines, from adjacent serpentine and non-serpentine habitats, to form F2 progeny. I planted thousands of progeny on serpentine and control soils in the greenhouse, using captive bumblebees to ensure outcrossing. Survivor seeds, planted on parental soils, enable multi-generational adaptation. Pool-sequencing of each population detects loci responding to divergent selection, revealing key loci driving local adaptation to serpentine soil.