Figure 2. Infection trajectory of pure and mixed Gyrodactylus turnbulli populations on individual guppies (Poecilia reticulata).

(A) Mean parasite intensity in pure (blue) and mixed parasite populations (green) (± Standard error of the mean; Experiment 2) in the initial phases of infection showing increased fitness in the mixed parasite population. Increased variation after day 7 is due to the onset of the host’s immune response and is not displayed in this graph. (B) Predicted mean parasite burden over time (controlled for fish standard length, ±95% Confidence Intervals) showing that increased parasite fitness in mixed parasite populations leads to faster population growth and higher maximum parasite burdens.