title: The phenotypic variance gradient - a novel concept.
abstract: Evolutionary ecologists commonly use reaction norms, which show the range of phenotypes produced by a set of genotypes exposed to different environments, to quantify the degree of phenotypic variance and the magnitude of plasticity of morphometric and life-history traits. Significant differences among the values of the slopes of the reaction norms are interpreted as significant differences in phenotypic plasticity, whereas significant differences among phenotypic variances (variance or coefficient of variation) are interpreted as differences in the degree of developmental instability or canalization. We highlight some potential problems with this approach to quantifying phenotypic variance and suggest a novel and more informative way to plot reaction norms: namely "a plot of log (variance) on the y-axis versus log (mean) on the x-axis, with a reference line added". This approach gives an immediate impression of how the degree of phenotypic variance varies across an environmental gradient, taking into account the consequences of the scaling effect of the variance with the mean. The evolutionary implications of the variation in the degree of phenotypic variance, which we call a "phenotypic variance gradient", are discussed together with its potential interactions with variation in the degree of phenotypic plasticity and canalization.
authors.affiliation: Department 18/Section of Environmental Engineering, Aalborg University Aalborg, Denmark ; Aalborg Zoo Aalborg, Denmark.
authors.forename: Cino
authors.initials: C
authors.lastname: Pertoldi
authors.affiliation: Department of Bioscience, Aarhus University Aarhus C, Denmark.
authors.forename: Jørgen
authors.initials: J
authors.lastname: Bundgaard
authors.affiliation: Department of Bioscience, Aarhus University Aarhus C, Denmark.
authors.forename: Volker
authors.initials: V
authors.lastname: Loeschcke
authors.affiliation: School of Environmental and Rural Science, University of New England Armidale, NSW, 2351, Australia.
authors.forename: James Stuart Flinton
authors.initials: JS
authors.lastname: Barker
keywords: Canalization; Drosophila aldrichi; Taylor's power law; environmental variability; phenotypic plasticity; wing traits