Fig 1. Day-by-day depiction of the experimental evolution design shown at the population level and at the sperm level.

On day 1 sterility is induced by transferring worms to auxin-containing media. Auxin activates TIR1 to target the degron tag on SPE-44. The depletion of SPE-44 stops the production of sperm thereby inducing sterility. Females start laying eggs on day 1, using sperm from experimental males. On day 2, competitor males are added to the population at a ratio of 1 competitor male to 2.5 experimental males. Progeny are collected on day 3 from eggs laid on day 2 and then heat-shocked on day 4 to induce ectopic expression of the toxic protein PEEL-1. This expression kills competitor cross-progeny, leaving only the progeny from sperm transferred during the day 1 mating phase. Each selective event is followed by a recovery generation.