title: Morphological clines and weak drift along an urbanization gradient in the butterfly, Pieris rapae.
abstract: Urban areas are increasing globally, providing opportunities for biodiversity researchers to study the process in which species become established in novel, highly disturbed habitats. This ecological process can be understood through analyses of morphological and genetic variation, which can shed light on patterns of neutral and adaptive evolution. Previous studies have shown that urban populations often diverge genetically from non-urban source populations. This could occur due to neutral genetic drift, but an alternative is that selection could lead to allele frequency changes in urban populations. The development of genome scan methods provides an opportunity to investigate these outcomes from samples of genetic variation taken along an urbanization gradient. Here we examine morphological variation in wing size and diversity at neutral amplified fragment length polymorphisms in the butterfly Pieris rapae L. (Lepidoptera, Pieridae) sampled from the center to the periphery of Marseille. We utilize established and novel environmental correlation approaches to scan genetic variation for evidence of selection. We find significant morphological differences in urban populations, as well as weak genetic structure and decreased genetic diversity in urban versus non-urban sites. However, environmental correlation tests provide little support for selection in our dataset. Our comparison of different methods and allele frequency clines suggests that loci identified as significant are false positives. Although there is some indication that selection may be acting on wing size in urban butterflies, genetic analyses suggest P. rapae are undergoing neutral drift.
authors.affiliation: UMR 5525- Laboratoire Techniques de l'Ingénierie Médicale et de la Complexité - Informatique, Mathématiques et Applications, Grenoble, France.
authors.forename: Sean D
authors.initials: SD
authors.lastname: Schoville
authors.affiliation: UMR 151 - Laboratoire Population Environnement et Développement, Institut de Recherche pour le Développement - Université Aix-Marseille, Marseille, France.
authors.forename: Ivo
authors.initials: I
authors.lastname: Widmer
authors.affiliation: UMR 151 - Laboratoire Population Environnement et Développement, Institut de Recherche pour le Développement - Université Aix-Marseille, Marseille, France.
authors.forename: Magali
authors.initials: M
authors.lastname: Deschamps-Cottin
authors.affiliation: UMR 151 - Laboratoire Population Environnement et Développement, Institut de Recherche pour le Développement - Université Aix-Marseille, Marseille, France ; UMR 5120- Laboratoire Botanique et BioinforMatique de l'Architecture des Plantes, Montpellier, France.
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Manel
mesh_terms: D000220:Adaptation, Biological; D054458:Amplified Fragment Length Polymorphism Analysis; D000818:Animals; D044822:Biodiversity; D049628:Body Size; D002080:Butterflies / Q000033:anatomy & histology / Q000235:genetics / Q000502:physiology*; D002947:Cities; D017753:Ecosystem; D040961:Genetic Drift; D016015:Logistic Models; D014921:Wings, Animal / Q000033:anatomy & histology