Genetic architecture of transmission stage production and virulence in schistosome parasites

In the blood fluke Schistosoma mansoni, parasite genotypes differ 7-fold in numbers of cercariae larvae shed from infected snails. Furthermore, high shedding parasites cause high mortality to snails while low shedding parasites cause low mortality, consistent with expected trade-offs between parasite transmission and virulence. This project was designed to understand the genetic basis of transmission stage production/virulence. We conducted reciprocal genetic crosses between schistosomes from two laboratory populations that show striking differences in cercarial shedding. Each parasite generation, we determined cercarial shedding profiles in inbred Biomphalaria glabrata snail hosts infected with single miracidia larvae. We sequenced the whole genome of the F0 parents and the ~15Mb exome of the F1 progeny and 188 F2 progeny from each crosses, and used linkage mapping to reveal quantitative trait loci (QTLs) underlying transmission stage production.