Evolution

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Fig. 1.  Clone differences in virulence and parasite densities in single-clone infections. Parasite density in the acute phase of infection is the summed total of all parasites present during this period. Plotted points are the means of the number of mice surviving through to the end of the infection period (day 35). Error bars are ±1 SEM. Open circles represent data from experiment 1 and closed circles data from experiment 2. Error bars are missing for AJ in experiment 1 because only a single mouse survived the entire acute phase of infection in this treatment group. Vertical error bars for AT in experiment 2 are smaller than the symbol; horizontal error bars for CB in experiment 1 are based on just two animals

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Fig. 2.  Densities of individual parasite clones through time (mean ± 1 SEM), showing the four clones in single-clone infections (left columns), and then comparing their performance alone and in competition with each of the other clones in experiment 1 (a, above) and experiment 2 (b, next page). Means are based on the number of mice alive at that point (maximum n = 5). The days postinfection of mouse deaths are indicated as open circles (individual infections) or closed circles (in competition)

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Fig. 2.  Continued.

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Fig. 3.  Parasite density of the four clones individually and in pairwise competition during the acute (a, above) and chronic (b, next page) phases of infection in each experiment. For the acute phase of infection (a), experiment 1 panels (E1: panels A, C, E, G, I) show peak parasite densities, whereas experiment 2 panels (E2: B, D, F, H, J) show total parasite densities. Bars represent mean (±1 SEM) of the number of mice surviving up to the end of each phase (maximum n = 5). A single asterisk indicates a single mouse in a treatment group and two asterisks a treatment group in which all mice died

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Fig. 3.  Continued

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Fig. 4.  Relationship between the relative virulence of clones and the extent of competitive suppression (A, B) and competitiveness (C, D) in competition. Data are pooled across both experiments during the acute (A, C) and chronic (B, D) phases of infections. Relative virulence is the anemia induced by the two competing clones when on their own, expressed as the anemia induced by least virulent competitor as a fraction of that induced by the more virulent. Thus, a value of 1.0 means the competing clones induce equal levels of anemia; a value of 0.5 that the less virulent clone induces half the anemia of the more virulent. Competitive suppression is the proportional reduction in clone density due to the presence of a competitor (1, competitive exclusion; 0, no suppression; <0, facilitation); competitiveness is clone frequency in mixed infections (see text). Dotted lines are least squares regression lines for plotted data. In (A) open circles indicate datapoints from experiment 1 and closed circles datapoints from experiment 2. Solid lines in panels (C) and (D) indicate the null expectation if there was no competition present between the two coinfecting clones (see Materials and Methods). There are a total of 11, not 12, pairwise competitions because there were no surviving mice in the CB + AJ coinfection group in experiment 1

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Fig. 5.  Densities of individual parasite clones through time in mixed intections (mean ± 1 SEM). Panels (A–F) experiment 1 (E1), panels (G–L) experiment 2 (E2). Means are based on the number of mice alive at that point (maximum n = 5). Traces terminate at the time point of the last mouse death if all mice in a treatment group died