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Title: Host resistance reverses the outcome of competition between microparasites
Authors: Gruner, Daniel
Kolekar, Arunima
McLaughlin, John
Strong, Donald
Type: Article
Keywords: Bodega Marine Laboratory, California
entomopathogenic nematodes
Galleria mellonella
Hepialus californicus
Heterorhabditis and Steinernema
intraspecific and interspecific competition
predator–prey interactions
trophic cascade
Issue Date: 2009
Publisher: Ecological Society of America
Citation: Gruner, D. S., A. Kolekar, J. P. McLaughlin, and D. R. Strong. 2009. Host resistance reverses the outcome of competition between microparasites. Ecology 90:1721-1728
Abstract: Predators and parasites can control the abundance or biomass of herbivores with indirect effects on producer communities and ecosystems, but the interplay of multiple natural enemies may yield unexpected dynamics. We experimentally examined interactions between two microparasites (entomopathogenic nematodes) isolated from sandy grassland soils of coastal California: Heterorhabditis marelatus (Heterorhabditidae) and Steinernema feltiae (Steinernematidae). Heterorhabditis marelatus drives trophic cascades by attacking root- and stem-boring ghost moth caterpillars (Hepialus californicus, Hepialidae), thereby indirectly protecting bush lupine shrubs (Lupinus arboreus, Fabaceae). Extensive field surveys demonstrated sympatric overlap in microhabitat use under lupine canopies and similar mean prevalence of the two nematode species. Using a response-surface design in the laboratory, we varied relative and absolute microparasite densities to test for competitive outcomes within an evolutionary naı¨ve host, larvae of the greater wax moth Galleria mellonella (Pyralidae), and within the native host Hepialus californicus. Independent of conspecific or interspecific density, S. feltiae dominated as expected over H. marelatus within the naı¨ve Galleria, but S. feltiae infected hosts at low frequency and showed lower reproductive fitness than H. marelatus within native Hepialus hosts. Contrary to studies that demonstrate the pairwise dominance of steinernematid over heterorhabditid species in laboratory hosts, host resistance to S. feltiae may provide a mechanism for coexistence of multiple microparasite species. We hypothesize that the ubiquitous field prevalence and rapid life history of S. feltiae imply its use of widespread, abundant but small-bodied hosts and indicate the lack of direct competition with H. marelatus in the Hepialus–Lupinus trophic cascade.
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