Figure 1.

(a,b) Mean change in host mortality rate relative to the ancestral parasites in C. elegans host strains CB4856 (a) and ewIR 68 (b). All experimental populations shared a common ancestor, and thus, any change from the ancestral data is indicative of relative virulence. Parasites were evolved in heterogeneous host populations, homogeneous host populations or in vitro (no hosts), and then tested for changes in virulence. The heterogeneous populations, from left to right, are 75–25, 50–50 and 25–75. Circles represent the mean change within each technical replicate (18–36 each). Bars represent ± s.e.m. (Online version in colour.)