Figure 3
Reproductive effort versus differential extrinsic mortality for the eight parasitic castrator trematode species (operating stolen host bodies) and both genders of uninfected horn snails. Relative reproductive allocation increases with mortality using (A) raw data (r = 0.88, P = 0.0008, n = 10) and when using (B) phylogenetically independent contrasts (r = 0.87, P = 0.0026, n = 9; regression through the origin: t8 = 5.0, P = 0.0011). Relative reproductive allocation here is a modified gonadosomatic index that accounts for variation in allocation to growth by using total mass growth increment in the denominator instead of total mass. (C) and (D) show that there is no association when the raw gonadosomatic index is used to represent reproductive effort in parallel analyses (r = -0.24, P = 0.49, n = 10 and r = -0.03, P = 0.942, n = 9; regression through the origin: t8 = 0.34, P = 0.74). A two-stage randomization test ensured that these positive relationships were not statistical artifacts driven by the strong negative correlation of growth with mortality (see Additional file 1). Lines, symbols, and differential mortality are as in Figure 2.