title: Host group formation decreases exposure to vector-borne disease: a field experiment in a 'hotspot' of West Nile virus transmission.
abstract: Animals can decrease their individual risk of predation by forming groups. The encounter-dilution hypothesis extends the potential benefits of gregariousness to biting insects and vector-borne disease by predicting that the per capita number of insect bites should decrease within larger host groups. Although vector-borne diseases are common and can exert strong selective pressures on hosts, there have been few tests of the encounter-dilution effect in natural systems. We conducted an experimental test of the encounter-dilution hypothesis using the American robin (Turdus migratorius), a common host species for the West Nile virus (WNV), a mosquito-borne pathogen. By using sentinel hosts (house sparrows, Passer domesticus) caged in naturally occurring communal roosts in the suburbs of Chicago, we assessed sentinel host risk of WNV exposure inside and outside of roosts. We also estimated per capita host exposure to infected vectors inside roosts and outside of roosts. Sentinel birds caged inside roosts seroconverted to WNV more slowly than those outside of roosts, suggesting that social groups decrease per capita exposure to infected mosquitoes. These results therefore support the encounter-dilution hypothesis in a vector-borne disease system. Our results suggest that disease-related selective pressures on sociality may depend on the mode of disease transmission.
authors.affiliation: School of Integrative Biology, University of Illinois, Urbana, IL 61801, USA bethanylkrebs@gmail.com.
authors.forename: Bethany L
authors.initials: BL
authors.lastname: Krebs
authors.affiliation: Department of Biology, Georgia Southern University, Statesboro, GA 30460, USA.
authors.forename: Tavis K
authors.initials: TK
authors.lastname: Anderson
authors.affiliation: Department of Pathobiological Sciences, University of Wisconsin-Madison, Madison, WI 53706, USA.
authors.forename: Tony L
authors.initials: TL
authors.lastname: Goldberg
authors.affiliation: Department of Entomology, Texas A&M University, College Station, TX 77843-2475, USA.
authors.forename: Gabriel L
authors.initials: GL
authors.lastname: Hamer
authors.affiliation: Department of Environmental Studies, Emory University, Atlanta, GA 30322, USA.
authors.forename: Uriel D
authors.initials: UD
authors.lastname: Kitron
authors.affiliation: Department of Pathobiological Sciences, University of Wisconsin-Madison, Madison, WI 53706, USA.
authors.forename: Christina M
authors.initials: CM
authors.lastname: Newman
authors.affiliation: Department of Pathobiology, University of Illinois, Urbana, IL 61801, USA.
authors.forename: Marilyn O
authors.initials: MO
authors.lastname: Ruiz
authors.affiliation: Department of Microbiology and Molecular Genetics, Michigan State University, Lansing, MI 48824-4320, USA.
authors.forename: Edward D
authors.initials: ED
authors.lastname: Walker
authors.affiliation: Department of Natural Resources and Environmental Sciences, University of Illinois, Urbana, IL 61801, USA.
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Brawn
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D003465:Culex / Q000821:virology*; D009033:Culicidae / Q000821:virology; D054884:Host-Pathogen Interactions; D007303:Insect Vectors / Q000821:virology*; D011156:Population Density; D018570:Risk Assessment; D020308:Songbirds / Q000502:physiology* / Q000821:virology; D014901:West Nile Fever / Q000635:transmission*
keywords: American robin; West Nile virus; disease ecology; encounter-dilution effect; social behaviour; vector-borne disease