Pathways for diffusion of nutrients in male and female schistosomes.

Confocal images of stained adult male (left) and female (right) schistosome cross sections at the same magnification (yellow, phalloidin for actin; blue, DAPI for nuclei; green, tegument and gut). The parameter values are the mean of 12 females and 11 males in near perfect cross section. Areas and distances were measured using the polygon line and path tools in the Analyzing Digital Images package from the Lawrence Hall of Science, Berkeley, California (http://www.globalsystemsscience.org/software/download). Solid white arrows show diffusion distances from the tegument surface to the midpoint, dotted white arrows those from the gut lumen to the furthest extremity. The gut lumen of the female occupies 9.7% of the cross section, that of the male only 1.9%. Nutrients diffusing from the male gut would have to travel >400 µm to reach the furthest tissues whereas the maximum distance from the female gut is only 85 µm. The distance a nutrient has to diffuse from the tegument surface to the tissue midpoint in both male and female is very similar at ∼40 µm. Central boxes list metabolite classes that are transported across the tegument (upper box, yellow arrows) or via the gastrointestinal tract (lower box, yellow arrows). Metabolites that have been shown experimentally to be transported are listed in the upper group in each box. Those that have been inferred to be transported from proteomic, transcriptomic, or other work are indicated by italics.