Fig. 2.

Relationships between parasite replication, virulence, and transmission. Increasing within-host replication (i.e., parasite spore load) resulted in lower proportions of animals surviving to the adult stage (a) and lower mating probabilities (b). Higher parasite loads also led to increased transmission through higher proportions of monarch eggs that acquired spores (c), and higher numbers of parasites per egg and milkweed leaf (d and f); these higher parasite numbers increased the probability of infection (e and g). Data points are average proportions (a, b, e, and g) or individual monarchs (c, d, and f). Lines are least-squares regression lines (see Table S1 for functions).