Trait-mediated biological control of schistosomiasis by a facultative molluscivore

Schistosomiasis is a parasitic disease caused by aquatic trematode worms, resulting in considerable human morbidity in the tropics.  Molluscivorous fish are potential biological control agents of Schistosomiasis through their ability to reduce the abundance of vector snail species.  The common haplochromine cichlid Astatoreochromis alluaudi, a widespread East African fish, once was widely touted for its potential to serve this function, but has proved ineffective.  It has been hypothesized that competition with other fish species in the wild drives young A. alluaudi to consume snails, a less preferred food source, while in the absence of competition they select more soft-bodied prey items.  We tested the hypothesis that young A. alluaudi raised in the absence of competitors will select a diet dominated by soft-bodied prey and thus will not develop the necessary jaw apparatus for easily crushing and consuming snails as adults. Young A. alluaudi reared in a replicated tank experiment actually showed a preference for snails over soft-bodied prey during development.  However, A. alluaudi reared entirely on soft-bodied prey develop a jaw morphology poorly suited for the consumption of snails as adults.  We conclude that prey availability during a relatively narrow window of development canalizes jaw morphology in A. alluaudi.