Meeting Abstract

S4-1.2  Jan. 5  Parasites as consumers of resources: models for disease based on dynamic energy budgets HALL, S.R.*; NISBET, R.M.; SIMONIS, J.; CACERES, C.E.; Indiana University; University of California, Santa Barbara; Florida State University; University of Illinois

In some senses, parasites act as competitors for resources ingested by hosts. Furthermore, virulent effects of parasites frequently depend upon quantity and quality of resources ingested by their host. We illustrate this phenomenon with a Daphnia-fungus-phytoplankton system. Daphnia are pivotal zooplankton grazers in freshwater lakes and ponds, and they become infected inadvertently by spores of a fungal parasite (Metschnikowia) released from dead, infected hosts while eating phytoplankton. Once a host becomes infected, the parasite causes larger reduction in fecundity, kills its host more quickly, and produces increased number of spores per dead host as food levels increase. To explain these phenomena, we turned to a dynamic energy budget (DEB) model for the host. This DEB model tracks energy flow as it is ingested and stored; stored energy is then allocated to growth, maintenance, reproduction, and production of parasites within the body of the infected host. Parasites kill the host by starving it. Using this simple model, we readily captured the signature of resource-enhanced virulence in our laboratory experiments. This model can also produce opposite patterns if hosts pay an energetic cost to kill parasites (through an “immune” response). A similar model structure built on the variable-stores (Droop) model can also capture resource-dependent effects of parasites on plants. Further modification of the DEB model shows how virulent effects of the parasite change if the parasite’s stoichiometric composition differs from that of the host and the food ingested by the host. Thus, simple models that treat parasites as competitors for resources consumed by the host can capture key aspects of host-parasite interactions.