SCHISTOSOMA-MANSONI - RELATIONSHIP BETWEEN LOW FECUNDITY AND REDUCED SUSCEPTIBILITY TO PARASITE INFECTION IN THE SNAIL BIOMPHALARIA-GLABRATA

Biomphalaria glabrata snails which were not susceptible as juveniles t o infection by Schistosoma mansoni were selectively bred (by self-fert ilization) from the highly susceptible NMRI laboratory snail stock. Th e susceptibility rate among juvenile snails derived from interbreeding NMRI parents was initially 85-95%, but after several generations of s election, less than 5% of exposed snails became infected by the parasi te. Selection for low susceptibility also resulted in a large proporti on of snails that displayed low fecundity and produced abnormal egg ma sses. Individual adult snails which were isolated from an interbreedin g population of nonselected NMRI snails usually produced well-develope d egg masses each containing 15-30 embryos. However, when juvenile sna ils from this same population were reared in isolation and not allowed to cross-fertilize, many displayed a pattern of low fecundity and abn ormal egg production similar to that observed in the selected low susc eptible line. Furthermore, it was found that many of the isolated snai ls which exhibited low egg production were also not susceptible to par asitic infection. (C) 1994 Academic Press, Inc.