We want to establish experimental evolution in the context of the P. pacificus mouth-form polyphenism. To provide sufficient genetic variation for selection, these experiments start with a newly generated multi-parent population. Eight wild isolates are selected from across the phylogeny of more than 400 sequenced P. pacificus strains to maximize genetic divergence while spanning the natural range of mouth-form bias, environmental sensitivity, and transgenerational memory. We combine these ‘founder’ isolates through successive rounds of crossing and then inbreed them to produce a large panel of recombinant inbred lines. Because each line is a unique mosaic of the eight founder genomes and the founders' genomes are fully sequenced, evolutionary changes can be traced back to the founder that contributed them and ultimately to specific genes. Beyond this project, these recombinant inbred lines will serve as a genetic mapping resource for the broader Pristionchus community and will be used first in the project described below.
Evolutionary theory predicts that plasticity should be favored when environmental cues reliably forecast the conditions an organism will later encounter; when cues are unreliable, a fixed phenotype or a bet-hedging strategy is expected instead. To test this, juveniles are exposed to a neutral chemical cue during the developmental window when mouth form is determined, and as adults they are given either nematode prey, which favors the predatory morph, or bacteria, which favors the bacterivorous morph. By controlling how reliably the cue predicts which food follows – through concordant, discordant, and unreliable regimes – and by fluctuating the environment across generations, we can ask whether populations evolve to use the cue to anticipate their future environment, and which step of the well-characterized mouth-form switch is restored when they do.
