Parasites can exert significant influence on their host organisms. Confronted by numerous selection pressures, hosts are faced with the dilemma of which to react to, and with what effort. A host must try to avoid being dinner to its predators, a nursery for its parasite and being out-competed by other species, while simultaneously dealing with an environment that fluctuates in many different ways. We manipulated multitrophic aquatic microcosm communities experimentally to explore how community complexity moderates the capacity of the bacterium Bacillus subtilis to evolve resistance to parasites (SPP1 bacteriophage), predators (Paramecium caudatum) and the presence of competitors (Serratia marcescens).
Results/Conclusions
We show that the evolution of resistance to multiple enemies varies substantially with biotic context, even when the densities and dynamics of the host organism remain unaltered. We found contrasting and indirect effects of competition and predation on bacteriophage resistance evolution and growth strategies in B. subtilis. Furthermore, the presence of the bacteriophage decreased competitive ability, while simultaneously increasing predation defense in hosts. This trade-off in host defense evolution to multiple antagonists highlights the importance of indirect effects of parasites in ecological networks and demonstrates that understanding the effects of parasitism in ecosystems requires assessment of species beyond the host organism. Given the ubiquity of parasites in nature, these findings have profound implications for our understanding of and ability to predict the impacts of biodiversity and environmental change on ecosystems.