A multigenerational population-growth assay to capture subtle fitness phenotypes in <i>C. elegans</i> and other nematodes

Heritable fitness differences between individuals are the currency of evolution but can be challenging to quantify with precision. A slight probabilistic fitness advantage to one relatively healthy individual over another is often too subtle to detect in a single generation. For this reason, we have developed an assay to quantify and compare heritable fitness traits in nematodes by allowing their differences to amplify during unrestricted exponential population growth over multiple generations. This method employs continuous imaging as populations expand, and an automated program to detect the time of resource exhaustion. Expanding on our earlier applications, we here describe, motivate, and validate the method's experimental parameters and introduce a new R package to facilitate image processing and statistical analyses. We demonstrate the utility of this method by using it to identify natural differences in mutagen sensitivity between wild isolates of Caenorhabditis elegans. This tool is immediately adaptable to any strain of C. elegans or similar nematode and can be used to quantify fitness differences in the face of any experimental condition that can be created on a petri dish.