title: Constitutive innate immunity is a component of the pace-of-life syndrome in tropical birds.
abstract: We studied the relationship between one component of immune function and basal metabolic rate (BMR), an indicator of the 'pace-of-life syndrome', among 12 tropical bird species and among individuals of the tropical house wren (Troglodytes aedon), to gain insights into functional connections between life history and physiology. To assess constitutive innate immunity we introduced a new technique in the field of ecological and evolutionary immunology that quantifies the bactericidal activity of whole blood. This in vitro assay utilises a single blood sample to provide a functional, integrated measure of constitutive innate immunity. We found that the bactericidal activity of whole blood varied considerably among species and among individuals within a species. This variation was not correlated with body mass or whole-organism BMR. However, among species, bacteria killing activity was negatively correlated with mass-adjusted BMR, suggesting that species with a slower pace-of-life have evolved a more robust constitutive innate immune capability. Among individuals of a single species, the house wren, bacteria killing activity was positively correlated with mass-adjusted BMR, pointing to physiological differences in individual quality on which natural selection potentially could act.
authors.affiliation: Department of Biology, University of Missouri-St Louis, 8001 Natural Bridge Road, St Louis, MO 63121, USA. b.i.tieleman@rug.nl
authors.forename: B
authors.initials: B
authors.lastname: Irene Tieleman
authors.forename: Joseph B
authors.initials: JB
authors.lastname: Williams
authors.forename: Robert E
authors.initials: RE
authors.lastname: Ricklefs
authors.forename: Kirk C
authors.initials: KC
authors.lastname: Klasing
mesh_terms: D000818:Animals; D001481:Basal Metabolism / Q000502:physiology*; D001715:Bird Diseases / Q000276:immunology* / Q000382:microbiology*; D001717:Birds / Q000276:immunology / Q000502:physiology*; D001770:Blood Bactericidal Activity / Q000276:immunology*; D049628:Body Size; D015169:Colony Count, Microbial; D004926:Escherichia coli; D004927:Escherichia coli Infections / Q000097:blood / Q000276:immunology*; D010176:Panama; D013045:Species Specificity; D014329:Tropical Climate