(A) Image of a young adult C. elegans and schematic depicting the twelve pairs of sensory neurons in the anterior amphid individuals carrying a virus with k deleterious mutations at its endemic equilibrium. class carrying the fewest number of deleterious mutations is defined as mutation class k = 0. Inset: variation in the basic reproductive rate of infected individuals (gray histogram) and variation in the net reproductive rate R of infected individuals (brown histogram) resulting from variation in the number of deleterious mutations carried by circulating viruses.