Deadly decomposers: distinguishing life history strategies on the parasitism-saprotrophy spectrum

The ability to parasitize living hosts as well as decompose dead organic matter is both common and widespread across prokaryotic and eukaryotic taxa. These parasitic decomposers have long been considered merely accidental or facultative parasites. However, this is often untrue: in many cases, parasitism is integral to the ecology and evolution of these organisms. Combining life cycle information from the literature with a generalized eco-evolutionary model, we define four distinct life history strategies followed by parasitic decomposers. Each strategy has a unique fitness expression, life cycle, ecological context, and set of evolutionary constraints. Correctly classifying parasitic decomposers is essential for understanding their ecology and epidemiology and directly impacts efforts to manage important medical and agricultural pathogens.