Graduate Thesis Or Dissertation
 

Cost to Biomphalaria glabrata of Resisting Infection by Schistosoma mansoni

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/44558h58h

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  • Schistosomiasis is a neglected tropical disease caused by parasitic trematodes in the genus Schistosoma. 200 million people are infected with schistosomes. Schistosomiasis causes acute and chronic disease, and may lead to death in chronic infections. Schistosomes have a complex life cycle that requires passage through a snail intermediate host. Understanding the interactions between schistosomes and their snail hosts may lead to methods for breaking schistosome transmission through manipulation of their snail hosts. Biomphalaria glabrata that carry an allele at SOD1 that causes them to produce more H₂O₂ (allele B) have increased resistance to infection by S. mansoni. ROS are thought to be important mediators of life history traits, and so it was hypothesized that there might be a cost to carrying the B allele. However, a recent study showed no constitutive costs in growth, survival or reproduction to carrying the B allele in the absence of challenge by parasites, relative to carrying the more susceptible C allele. We assessed whether inbred lines of B. glabrata having the BB genotype incur greater fitness costs (measured by growth and survival) after successfully resisting a challenge by S. mansoni than lines having the CC genotype. Snails with either genotype did not bear any apparent costs to resisting infection, although we did find greater early mortality in snails with the BB genotype, regardless of exposure status. Furthermore, snail lines with greater percent resistance, regardless of SOD1 genotype, grew less over the course of the study, regardless of parasite exposure status. Percent resistance per se had no effect on early snail mortality. We conclude laboratory populations of B. glabrata carrying the more resistant SOD1 genotypes do not show greater costs in growth or mortality after resisting infection by S. mansoni than do more susceptible SOD1 genotypes. However, in contrast to a previous study, we see some evidence of a slightly higher mortality among BB than CC lines, regardless of exposure, and evidence that resistance per se (regardless of SOD1 genotype) was negatively correlated with growth.
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