We noticed that the mutant strain tended to develop slower. So we hypothesized that selection was acting on development, and we found that the wild type strain would develop much slower in concentrations of ivermectin that were not favored. In contrast, the resistant strain was not impaired.

We found that we could carefully modulate selection by simply changing the ivermectin concentration, and our barcoded lines allowed us to quantify the selection within a genotype with high precision.

We focused on competing strain across a gradient of ivermectin concentrations, and we see a clear trend where ivermectin is low, wild type is favored. However, after around ~2nM of ivermectin, we start to see the mutant strain become favored.

We utilized our TARDIS barcoding system to barcode wildtype worms and a worm strain resistant to ivermectin to quantify the selective strength. We then mixed several several barcoded strains together to compete them.