Figure 1.

Outline of the genetic cross experimental design. (a-b) We performed two independent reciprocal genetic crosses (crosses A and B, to account for potential sex specific effect(s)) between single genotypes of SmLE-H and SmBRE-L Schistosoma mansoni parasite populations. These two populations exhibit striking differences in terms of transmission stage production (number of cercariae produced). (c) For each parasite generation (F0 parental populations, F1 and F2 progeny), we exposed individual Biomphalaria glabrata Bg26 inbred snail to single miracidium from either the SmLE-H or SmBRE-L populations for F0 (N = 192/population), or the F1 progeny (N = 288/cross), or the F2 progeny (N = 1000/cross). For each infected snail and each generation of S. mansoni parasites, we measured transmission stage production during 4 weeks of the patent period (week 4 to 7 post-infection). We also evaluated the virulence of these generations of crossed parasites by measuring the total laccase-like activity as well as the hemoglobin rate in infected snail hemolymph samples