PARENT SESSION
Contributed Oral Session 151: Mutualism / Parasitism: Disease; Pathogens
Friday, August 12, 8:00 AM - 11:30 AM, Meeting Room 513 C, Level 5, Palais des congrès de Montréal
Eating yourself sick: linking host-parasite and producer-grazer interactions in a Daphnia- parasite-algal system.
Hall, Spencer *,1, Sivars Becker, Lena2, Becker, Claes 2, Duffy, Meghan 2, Tessier, Alan3, Caceres, Carla1, 1 University of Illinois, Urbana-Champaign, IL2 Kellogg Biological Station/MSU, Hickory Corners, MI3 National Science Foundation, Arlington, VA
ABSTRACT- Just what are hosts doing when they contract disease? Often we assume that parasites are transmitted to susceptible hosts at some constant rate. However, in many systems hosts likely contact parasites inadvertently while pursuing their various other ecological roles. Consider the freshwater zooplankton Daphnia; it serves simultaneously as host to several parasites and as a pivotal herbivore in the open waters of lakes. It consumes free-floating spores of the fungal parasite Metschnikowia unintentionally while grazing. We study this mechanism of disease transmission using laboratory experiments and several models. In the lab, infection prevalence of Daphnia depended sensitively upon both algal food quality and quantity (where low food quantity and quality promoted higher infection rates). These results were readily captured by simple models which assumed that host-grazers consume spores proportional to the rate at which they clear habitat while eating algae. Furthermore, since body size of host-grazers and clearance rates are closely interrelated, models predict and experimental and field data show that larger animals are more readily infected than smaller animals. However, consumption of too many spores (superinfection) can kill hosts before they produce new spores. Thus, factors promoting high infection prevalence could also undermine fitness of the parasite. We consider the interplay between all of these factors in a fully-dynamical model which considers direct and indirect feedbacks between host-parasite and grazer-producer interactions. While specifically designed around zooplankton-fungal parasite biology, these mechanisms should broadly apply to other systems in which hosts contract disease while interacting with their habitat and/or resources.
Key words: host-parasite, plant-herbivore, clearance, transmission