Esterases in natural populations of normal and Echinostoma revolutum-infected Helisoma trivolvis (Gastropoda)

Esterases of the digestive gland-gonad (DGG) complex of individual snails from a wild population of Helisoma trivolvis infected with the trematode Echinostoma revolutum were analyzed by vertical slab PAGE and compared to similar DGG homogenates of uninfected conspecifics from the same population. Our analysis indicated that: 1. Four classes of esterases, some atypical, could be resolved using diagnostic inhibitors. 2. Uninfected snails demonstrated polymorphism for two of these four esterase groups, including cholinesterases (CHE), in the 34 individual DGGs analyzed. 3. The rarer of the two ChE phenotypes in the uninfected sample (29.4%) was present in 100% of the 17 infected snails examined. However, no changes in esterase zymograms of infected DGGs due to the parasite were noted. 4. The possibility that the 'rare' ChE phenotype is somehow related to host susceptibility to Echinostoma revolutum is discussed in view of similar apparent linkages in other snail-trematode systems.