title: A lack of crowding? Body size does not decrease with density for two behavior-manipulating parasites.
abstract: For trophically transmitted parasites that manipulate the phenotype of their hosts, whether the parasites do or do not experience resource competition depends on such factors as the size of the parasites relative to their hosts, the intensity of infection, the extent to which parasites share the cost of defending against the host's immune system or manipulating their host, and the extent to which parasites share transmission goals. Despite theoretical expectations for situations in which either no, or positive, or negative density-dependence should be observed, most studies document only negative density-dependence for trophically transmitted parasites. However, this trend may be an artifact of most studies having focused on systems in which parasites are large relative to their hosts. Yet, systems are common where parasites are small relative to their hosts, and these trophically transmitted parasites may be less likely to experience resource limitation. We looked for signs of density-dependence in Euhaplorchis californiensis (EUHA) and Renicola buchanani (RENB), two manipulative trematode parasites infecting wild-caught California killifish (Fundulus parvipinnis). These parasites are small relative to killifish (suggesting resources are not limiting), and are associated with changes in killifish behavior that are dependent on parasite-intensity and that increase predation rates by the parasites' shared final host (indicating the possibility for cost sharing). We did not observe negative density-dependence in either species, indicating that resources are not limiting. In fact, observed patterns indicate possible mild positive density-dependence for EUHA. Although experimental confirmation is required, our findings suggest that some behavior-manipulating parasites suffer no reduction in size, and may even benefit when "crowded" by conspecifics.
authors.affiliation: *Graduate Group in Ecology, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Dos Pueblos High School, Goleta, CA 93117, USA; Harvard College, Cambridge, MA 02138, USA; Irvington High School, Fremont, CA 94538, USA; University of Chicago, Chicago, IL 60637, USA; Population Biology Graduate Group, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Department of Biology, University of California, Riverside, CA 92507, USA; **Department of Ecology, Evolution, and Marine Biology and Marine Science Institute, University of California, Santa Barbara, CA 93106, USA; Western Ecological Research Center, US Geological Survey, Santa Barbara, CA 93106, USA KLSmit@UCDavis.edu.
authors.forename: Kelly L
authors.initials: KL
authors.lastname: Weinersmith
authors.affiliation: *Graduate Group in Ecology, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Dos Pueblos High School, Goleta, CA 93117, USA; Harvard College, Cambridge, MA 02138, USA; Irvington High School, Fremont, CA 94538, USA; University of Chicago, Chicago, IL 60637, USA; Population Biology Graduate Group, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Department of Biology, University of California, Riverside, CA 92507, USA; **Department of Ecology, Evolution, and Marine Biology and Marine Science Institute, University of California, Santa Barbara, CA 93106, USA; Western Ecological Research Center, US Geological Survey, Santa Barbara, CA 93106, USA*Graduate Group in Ecology, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Dos Pueblos High School, Goleta, CA 93117, USA; Harvard College, Cambridge, MA 02138, USA; Irvington High School, Fremont, CA 94538, USA; University of Chicago, Chicago, IL 60637, USA; Population Biology Graduate Group, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Department of Biology, University of California, Riverside, CA 92507, USA; **Department of Ecology, Evolution, and Marine Biology and Marine Science Institute, University of California, Santa Barbara, CA 93106, USA; Western Ecological Research Center, US Geological Survey, Santa Barbara, CA 93106, USA.
authors.forename: Chloe B
authors.initials: CB
authors.lastname: Warinner
authors.affiliation: *Graduate Group in Ecology, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Dos Pueblos High School, Goleta, CA 93117, USA; Harvard College, Cambridge, MA 02138, USA; Irvington High School, Fremont, CA 94538, USA; University of Chicago, Chicago, IL 60637, USA; Population Biology Graduate Group, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Department of Biology, University of California, Riverside, CA 92507, USA; **Department of Ecology, Evolution, and Marine Biology and Marine Science Institute, University of California, Santa Barbara, CA 93106, USA; Western Ecological Research Center, US Geological Survey, Santa Barbara, CA 93106, USA*Graduate Group in Ecology, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Dos Pueblos High School, Goleta, CA 93117, USA; Harvard College, Cambridge, MA 02138, USA; Irvington High School, Fremont, CA 94538, USA; University of Chicago, Chicago, IL 60637, USA; Population Biology Graduate Group, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Department of Biology, University of California, Riverside, CA 92507, USA; **Department of Ecology, Evolution, and Marine Biology and Marine Science Institute, University of California, Santa Barbara, CA 93106, USA; Western Ecological Research Center, US Geological Survey, Santa Barbara, CA 93106, USA.
authors.forename: Virginia
authors.initials: V
authors.lastname: Tan
authors.affiliation: *Graduate Group in Ecology, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Dos Pueblos High School, Goleta, CA 93117, USA; Harvard College, Cambridge, MA 02138, USA; Irvington High School, Fremont, CA 94538, USA; University of Chicago, Chicago, IL 60637, USA; Population Biology Graduate Group, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Department of Biology, University of California, Riverside, CA 92507, USA; **Department of Ecology, Evolution, and Marine Biology and Marine Science Institute, University of California, Santa Barbara, CA 93106, USA; Western Ecological Research Center, US Geological Survey, Santa Barbara, CA 93106, USA.
authors.forename: David J
authors.initials: DJ
authors.lastname: Harris
authors.affiliation: *Graduate Group in Ecology, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Dos Pueblos High School, Goleta, CA 93117, USA; Harvard College, Cambridge, MA 02138, USA; Irvington High School, Fremont, CA 94538, USA; University of Chicago, Chicago, IL 60637, USA; Population Biology Graduate Group, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Department of Biology, University of California, Riverside, CA 92507, USA; **Department of Ecology, Evolution, and Marine Biology and Marine Science Institute, University of California, Santa Barbara, CA 93106, USA; Western Ecological Research Center, US Geological Survey, Santa Barbara, CA 93106, USA.
authors.forename: Adrienne B
authors.initials: AB
authors.lastname: Mora
authors.affiliation: *Graduate Group in Ecology, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Dos Pueblos High School, Goleta, CA 93117, USA; Harvard College, Cambridge, MA 02138, USA; Irvington High School, Fremont, CA 94538, USA; University of Chicago, Chicago, IL 60637, USA; Population Biology Graduate Group, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Department of Biology, University of California, Riverside, CA 92507, USA; **Department of Ecology, Evolution, and Marine Biology and Marine Science Institute, University of California, Santa Barbara, CA 93106, USA; Western Ecological Research Center, US Geological Survey, Santa Barbara, CA 93106, USA.
authors.forename: Armand M
authors.initials: AM
authors.lastname: Kuris
authors.affiliation: *Graduate Group in Ecology, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Dos Pueblos High School, Goleta, CA 93117, USA; Harvard College, Cambridge, MA 02138, USA; Irvington High School, Fremont, CA 94538, USA; University of Chicago, Chicago, IL 60637, USA; Population Biology Graduate Group, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Department of Biology, University of California, Riverside, CA 92507, USA; **Department of Ecology, Evolution, and Marine Biology and Marine Science Institute, University of California, Santa Barbara, CA 93106, USA; Western Ecological Research Center, US Geological Survey, Santa Barbara, CA 93106, USA*Graduate Group in Ecology, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Dos Pueblos High School, Goleta, CA 93117, USA; Harvard College, Cambridge, MA 02138, USA; Irvington High School, Fremont, CA 94538, USA; University of Chicago, Chicago, IL 60637, USA; Population Biology Graduate Group, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Department of Biology, University of California, Riverside, CA 92507, USA; **Department of Ecology, Evolution, and Marine Biology and Marine Science Institute, University of California, Santa Barbara, CA 93106, USA; Western Ecological Research Center, US Geological Survey, Santa Barbara, CA 93106, USA.
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Lafferty
authors.affiliation: *Graduate Group in Ecology, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Dos Pueblos High School, Goleta, CA 93117, USA; Harvard College, Cambridge, MA 02138, USA; Irvington High School, Fremont, CA 94538, USA; University of Chicago, Chicago, IL 60637, USA; Population Biology Graduate Group, Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Department of Biology, University of California, Riverside, CA 92507, USA; **Department of Ecology, Evolution, and Marine Biology and Marine Science Institute, University of California, Santa Barbara, CA 93106, USA; Western Ecological Research Center, US Geological Survey, Santa Barbara, CA 93106, USA.
authors.forename: Ryan F
authors.initials: RF
authors.lastname: Hechinger
mesh_terms: D000818:Animals; D049628:Body Size / Q000502:physiology*; D002140:California; D023781:Fundulidae / Q000469:parasitology*; D006578:Heterophyidae / Q000033:anatomy & histology* / Q000502:physiology; D011156:Population Density; D014200:Trematoda / Q000033:anatomy & histology* / Q000502:physiology*