[
International Worm Meeting,
2017]
Selection can drive sub-populations to become differentiated, both in phenotype and genotype, but gene flow between them can affect the evolutionary trajectories of the phenotypes in question, potentially by mitigating the effects of selection and slowing the rate of adaptation to novel environments. Migration-selection dynamics are one of the fundamental aspects of speciation and population divergence, but they have not been rigorously investigated in an experimental context. Stress resistance is a heritable complex trait involving interactions between numerous genes and pathways. Previous studies in Caenorhabditis elegans have identified correlations between single genes and stress responses, but few have investigated genome-wide, causative relationships. Multiple questions remain in understanding how complex, polygenic traits evolve on the whole-genome scale under the opposing influences of strong selection and gene flow. The goals of this project are to dissect the genetic basis of chronic heat stress, a model complex trait, in C. remanei; to elucidate how gene flow affects rates of adaptation to a novel environment; and to investigate migration-selection dynamics. We utilized an evolve-and-resequence framework, which allowed for selection on standing genetic variation in the ancestral strain of C. remanei that was derived from a wild isolate and lab-adapted for 75 generations. Populations of C. remanei derived from this ancestral population were evolved in pairs to either a control (20 deg C) or heat stress (31 deg C) environment for forty generations. We tested the effect of migration between sub-populations with three migration rates: 0 (no migration), 5, and 20 percent. Female fecundity was measured to estimate the strength of selection in the heat stress environment. We observe a significant effect of selection and a significant interaction between selection and migration. The no-migration 31 deg C-evolved, 5-percent migration 31 deg C-evolved, and ancestor populations were sequenced via whole genome pooled population sequencing. The ancestral and descendant populations were compared on a locus-by-locus basis, allowing us to identify the number and location of putative loci under selection in the heat stress environment. We find that the 5-percent 31 deg C-evolved populations show fewer divergent regions than the no migration 31 deg C-evolved populations, as expected due to the homogenizing effects of migration. Preliminary analysis shows that there are more sites with significant divergence in the no migration populations.