Figure 1.
Proportion of Hosts Surviving over Time Depending on Treatment
Solid, dashed, and dotted lines represent infected, exposed but uninfected, and unexposed control daphniids, respectively. Survival analysis showed a highly significant difference in survival between the infected as compared to unexposed control hosts ( p < 0.001), while there was no difference between the two groups of uninfected daphniids ( p = 0.719). The + symbols at the two curves representing uninfected daphniids indicate points where censoring was performed. For more details about the statistics, see Materials and Methods. Mean age at castration is the mean age at which infected animals became castrated. Age at castration is defined as the first day after a host's last reproduction. All infected daphniids had become castrated at an age of 19 d (17 d after infection + 2 d).
Figure 2.
Longevity of D. magna Depending on Spore Production of P. ramosa
The total number of infected females is 39 ( n = 39 data points in the figure). The solid curve represents predicted values from a generalised linear model with best fit (lowest residual deviance). The dashed curves represent 95% confidence interval for the fitted model curve. For more details about the statistics, see Materials and Methods.
Figure 3.
The Genetic Basis of Virulence in P. ramosa
The solid and dashed lines show survival of daphniids infected with secondary spores from early and late killing P. ramosa, respectively. The secondary spores were produced in a previous experiment and were extracted from hosts killed by the parasite at 25 to 37 d and 55 to 67 d of age, respectively. There is a significant difference in survival between daphniids infected with early or late killing spores ( p < 0.001). For more details about the statistics, see Materials and Methods.
Figure 4.
Growth of Genetically Identical D. magna Females Depending on Infection with the Castrating Bacterium P. ramosa
Solid, dashed, and dotted lines represent mean size of infected, exposed but not infected, and unexposed control daphniids at the given ages, respectively. The error bars represent ±1 standard deviation of mean size at the given ages. The number of replicates in each treatment is infected ( n = 39), exposed but not infected ( n = 102), and unexposed control ( n = 71). Nonlinear generalised least-squares models for the growth curves showed that the asymptotic size of infected daphniids were significantly larger than both the unexposed controls and exposed but not infecteds, while the asymptotic size of two latter groups did not differ. This shows that only infections can induce host gigantism while parasite exposure alone is insufficient in doing so. For more details about the statistics, see Materials and Methods. Mean age at castration is explained in Figure 1.