title: Multiple aspects of plasticity in clutch size vary among populations of a globally distributed songbird.
abstract: Plasticity in life-history characteristics can influence many ecological and evolutionary phenomena, including how invading organisms cope with novel conditions in new locations or how environmental change affects organisms in native locations. Variation in reaction norm attributes is a critical element to understanding plasticity in life history, yet we know relatively little about the ways in which reaction norms vary within and among populations. We amassed data on clutch size from marked females in eight populations of house sparrows (Passer domesticus) from North America and Europe. We exploited repeated measures of clutch size to assess both the extent of within-individual phenotypic plasticity and among-individual variation and to test alternative hypotheses about the underlying causes of reaction norm shape, particularly the decline in clutch size with date. Across all populations, females of this multibrooded species altered their clutch size with respect to date, attempt order, and the interaction of date and order, producing a reaction norm in multidimensional environmental space. The reaction norm fits that predicted by a model in which optimal clutch size is driven by a decline with date hatched in the ability of offspring to recruit. Our results do not fit those predicted for other proposed causes of a seasonal decline in clutch size. We also found significant differences between populations in response to date and the date by attempt order interaction. We tested the prediction that the relationship with date should be increasingly negative as breeding season becomes shorter but found steeper declines in clutch size with date in populations with longer seasons, contrary to the prediction. Populations also differed in the level of among-individual variation in reaction norm intercept, but we found no evidence of among-individual variation in reaction norm slope. We show that complex reaction norms in life-history characters exhibit within- and among-population variance. The nature of this variance is only partially consistent with current life-history theory and stimulates expansions of such theory to accommodate complexities in adaptive life history.
authors.affiliation: Department of Biology and Center for Ecology, Evolution, and Behavior, University of Kentucky, 101 Morgan Building, Lexington, KY, 40506-0225, USA.
authors.forename: David F
authors.initials: DF
authors.lastname: Westneat
authors.affiliation: Department of Limnology, University of Pannonia, Pf. 158, Veszprém, H-8201, Hungary.
authors.forename: Veronika
authors.initials: V
authors.lastname: Bókony
authors.affiliation: Department of Genetics, University of Nottingham, NG7 2RD, UK.|Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S10 2TN, UK.
authors.forename: Terry
authors.initials: T
authors.lastname: Burke
authors.affiliation: Centre d'Etudes Biologiques de Chizé, Centre Nationale de la Recherche Scientifique, Villiers-en-Bois, Beauvoir sur Niort, F-79360, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Chastel
authors.affiliation: Department of Biology, Centre for Biodiversity Dynamics, Norwegian University of Science and Technology, Trondheim, NO-7491, Norway.
authors.forename: Henrik
authors.initials: H
authors.lastname: Jensen
authors.affiliation: Department of Biology, Centre for Biodiversity Dynamics, Norwegian University of Science and Technology, Trondheim, NO-7491, Norway.
authors.forename: Thomas
authors.initials: T
authors.lastname: Kvalnes
authors.affiliation: Centre d'Etudes Biologiques de Chizé, Centre Nationale de la Recherche Scientifique, Villiers-en-Bois, Beauvoir sur Niort, F-79360, France.|Department of Biology, Virginia Tech, 4102 Derring Hall, Blacksburg, VA, 24060, USA.
authors.forename: Ádám Z
authors.initials: ÁZ
authors.lastname: Lendvai
authors.affiliation: Department of Limnology, University of Pannonia, Pf. 158, Veszprém, H-8201, Hungary.|Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S10 2TN, UK.
authors.forename: András
authors.initials: A
authors.lastname: Liker
authors.affiliation: Department of Biology, 730 Van Vleet Oval, Norman, OK, 73019, USA.
authors.forename: Douglas
authors.initials: D
authors.lastname: Mock
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S10 2TN, UK.
authors.forename: Julia
authors.initials: J
authors.lastname: Schroeder
authors.affiliation: Department of Biology, 730 Van Vleet Oval, Norman, OK, 73019, USA.
authors.forename: P L
authors.initials: PL
authors.lastname: Schwagmeyer
authors.affiliation: Biogéosciences, CNRS UMR 6282, Université de Bourgogne, 6 Boulevard Gabriel, Dijon, F-21000, France.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Sorci
authors.affiliation: Department of Biology and Center for Ecology, Evolution, and Behavior, University of Kentucky, 101 Morgan Building, Lexington, KY, 40506-0225, USA.
authors.forename: Ian R K
authors.initials: IR
authors.lastname: Stewart
mesh_terms: D000818:Animals; D005075:Biological Evolution; D052284:Clutch Size; D005060:Europe; D005260:Female; D005843:Geography; D009656:North America; D012098:Reproduction; D012641:Selection, Genetic; D046370:Sparrows / Q000235:genetics / Q000502:physiology*
keywords: adaptation; clutch size; life history; phenology of breeding; phenotypic plasticity; trade‐offs; within‐individual variance