Duffy Lab Research

Community Ecology of Parasitism

We have looked at interactions between predators, parasites, and prey in a series of observational, theoretical, and experimental studies. Generally, Daphnia dentifera (formerly Daphnia galeata mendotae and Daphnia rosea) has been the focal host/prey species, with bluegill sunfish (Lepomis macrochirus) as predator and either the yeast Metschnikowia bicuspidata or the bacterium Spirobacillus cienkowskii as parasite. We have found that, in many cases, selective predation can reduce parasitism (see Duffy et al., 2005, Limnology and Oceanography, Hall et al., 2005, American Naturalist, Hall et al., 2006, Ecology, Duffy and Hall, 2008, American Naturalist). However, we have also found that predation can not necessarily be counted upon to reduce parasitism (Duffy, 2007, Oecologia) and some of our theoretical results suggest that, under some conditions, selective predation may actually increase the severity of epidemics (Duffy and Hall, 2008, American Naturalist). Interestingly, we have found parasite-driven trophic cascades (Duffy, 2007, Oecologia), suggesting that parasites can have food web-level effects.

Duffy Lab Research Research in the Duffy Lab lies at the interface of evolutionary, community and disease ecology, and utilizes a combination of field, lab and theoretical studies. Most research focuses on the evolutionary and community ecology of infectious diseases, particularly in natural populations of Daphnia. Some specific areas of research are described below. An overview of some recent work can be found here. Also, pictures of some of our field sites can be found here.
Community Ecology of Parasitism We have looked at interactions between predators, parasites, and prey in a series of observational, theoretical, and experimental studies. Generally, Daphnia dentifera (formerly Daphnia galeata mendotae and Daphnia rosea) has been the focal host/prey species, with bluegill sunfish (Lepomis macrochirus) as predator and either the yeast Metschnikowia bicuspidata or the bacterium Spirobacillus cienkowskii as parasite. We have found that, in many cases, selective predation can reduce parasitism (see Duffy et al., 2005, Limnology and Oceanography, Hall et al., 2005, American Naturalist, Hall et al., 2006, Ecology, Duffy and Hall, 2008, American Naturalist). However, we have also found that predation can not necessarily be counted upon to reduce parasitism (Duffy, 2007, Oecologia) and some of our theoretical results suggest that, under some conditions, selective predation may actually increase the severity of epidemics (Duffy and Hall, 2008, American Naturalist). Interestingly, we have found parasite-driven trophic cascades (Duffy, 2007, Oecologia), suggesting that parasites can have food web-level effects.	Whole-water-column enclosures in Wintergreen Lake, MI
Eco-Evolutionary Host-Parasite Dynamics We are also looking at feedbacks between ecological and evolutionary processes in host-parasite interactions. This includes studies on how host populations evolve in response to parasitism, and, particularly, how rapid evolution of host resistance can affect "ecological" dynamics. We have found that Daphnia dentifera populations evolve quite rapidly in response to Metschnikowia epidemics (Duffy and Sivars-Becker, 2007, Ecology Letters), and have argued that this can drive the termination of epidemics, as well as minimize the effects of these epidemics on host population density and growth rate (Duffy and Sivars-Becker, 2007, Ecology Letters; Duffy and Hall, 2008, American Naturalist, Duffy et al., 2009, Ecology).
Joint influences of genetic diversity and predation on host-parasite dynamics The Duffy Lab was recently awarded funding from the National Science Foundation to look study the joint influences of host genetics and community context on eco-evolutionary host-parasite dynamics. This work is in collaboration with Spencer Hall of Indiana University. We are interested in seeing how host genetic diversity and the presence of natural predators (especially ones who prey selectively on infected hosts) jointly determine the severity of epidemics. More information on this project can be found here.
Effects of Parasitism on Host Diversity Ecologists and evolutionary biologists are intensely interested in the drivers of diversity in nature, and parasites are often invoked as causal agents. We have found that Metschnikowia epidemics can decrease host diversity (via directional selection; Duffy and Sivars-Becker, 2007, Ecology Letters), but that they can also increase host diversity (via disruptive selection; Duffy et al., 2008, BMC Evolutionary Biology). We are working to understand what determines the type of selection that occurs during epidemics, and how that feeds back on subsequent ecological dynamics. Analyzing the data from the population that experienced disruptive selection required developing a novel method for measuring selection in natural populations. Code for this method (and data from our study) are available here.
This research has been supported by funding from the National Science Foundation.
Collaborators Chad Brassil (University of Nebraska), Claes Becker (unaffiliated), Carla Cáceres (University of Illinois), Jeff Conner (Kellogg Biological Station/Michigan State), Jeff Dudycha (University of South Carolina), Dieter Ebert (Universitat Basel), Samantha Forde (University of California-Santa Cruz), Nicole Gerardo (Emory University), Spencer Hall (Indiana University), Marianne Huebner (Michigan State University), Tony Ives (University of Wisconsin-Madison), Chris Klausmeier (Kellogg Biological Station/Michigan State), Jorge Rodrigues (University of Texas-Arlington), Tom Schmidt (Michigan State University), Lena Sivars-Becker (unaffiliated), Alan Tessier (National Science Foundation)