Fig. 4.

Virulence of parasites against contemporary host clones did not significantly differ across the three time points, nor did the impact of parasites from two different time points on time 3 hosts; however, time 3 parasites yielded fewer spores and had a slower within host growth rate in time 3 hosts, as compared to time 1 parasites. Left panels: virulence of parasites against hosts from the same time point (e.g., when hosts from time 2 were exposed to parasites from time 2). Right panels: virulence of parasites from time 1 and time 3 in hosts from time 3; this allows for isolation of the effects of parasite evolution. There were no significant differences in lifespan (a&b) or reproduction (c&d). The number of spores produced per infected host, and the parasite growth rate within infected hosts, did not differ significantly for hosts from the three time points exposed to their contemporary parasites (e&g). However, when time 3 hosts were exposed to parasites from time 1 vs. time 3, hosts infected with time 1 parasites produced significantly more spores (f) and had a significantly faster growth rate (h); this suggests that the parasite evolved to grow slower and produce fewer spores, which was contrary to our expectations. Statistical analyses used individual-level data; in order to more clearly visualize the data, averages for each host clone x parasite exposure combination are plotted