Thermal preferences of resistant and susceptible strains ofBiomphalaria glabrata(Gastropoda) exposed toschistosoma mansoni(Trematoda)

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Abstract
The thermal preferences of two strains of the snailBiomphalaria glabrata, one resistant to, and one susceptible to, the parasiteSchistosoma mansoniwere determined in an aquatic thermal gradient. Snails were tested without exposure to the parasite, and 2 h and 5 weeks after exposure to trematode miracidia. The mean temperature selected by susceptible strain snails 2 h post-exposure tended to be lower than that of unexposed controls, although this was not statistically significant. In this strain, at 5 weeks post-exposure, the preferred temperature dropped by 1.9±0.5°C. The resistant strain displayed a significant drop of 1.8±0.6°C 2 h post-exposure. These results are consistent with the hypothesis that a drop in mean temperatures selected by snails is due to altered levels of endogenous cytokines such as IL-1 or TNF in association with parasite activation of the snail internal defense system.