Nematomorph parasites indirectly alter the food web and ecosystem function of streams through behavioral manipulation of their cricket hosts

Background/Question/Methods

Due to their small size, parasites have not traditionally been thought to be important parts of food webs and ecosystem processes. Nematomorph parasites manipulate crickets to enter streams where the parasites reproduce. These manipulated crickets become a substantial food subsidy for stream fishes. Here, we used a large-scale field experiment to investigate how this subsidy affects the stream food web and ecosystem functions.

Results/Conclusions

When crickets were available, predatory fish ate fewer benthic invertebrates. The resulting release of the benthic invertebrate community from fish predation indirectly decreased the biomass of benthic algae and slightly increased leaf break-down rate. This is the first experimental demonstration that host manipulation by a parasite can reorganise a food web and alter ecosystem function. Nematomorphs are common, and many other parasites have dramatic effects on host phenotypes, suggesting that similar effects of parasites on ecosystems might be widespread.