title: Genetic and morphometric divergence in threespine stickleback in the Chignik catchment, Alaska.
abstract: Divergent selection pressures induced by different environmental conditions typically lead to variation in life history, behavior, and morphology. When populations are locally adapted to their current environment, selection may limit movement into novel sites, leading to neutral and adaptive genetic divergence in allopatric populations. Subsequently, divergence can be reinforced by development of pre-or postzygotic barriers to gene flow. The threespine stickleback, Gasterosteus aculeatus, is a primarily marine fish that has invaded freshwater repeatedly in postglacial times. After invasion, the established freshwater populations typically show rapid diversification of several traits as they become reproductively isolated from their ancestral marine population. In this study, we examine the genetic and morphometric differentiation between sticklebacks living in an open system comprising a brackish water lagoon, two freshwater lakes, and connecting rivers. By applying a set of microsatellite markers, we disentangled the genetic relationship of the individuals across the diverse environments and identified two genetic populations: one associated with brackish and the other with the freshwater environments. The "brackish" sticklebacks were larger and had a different body shape than those in freshwater. However, we found evidence for upstream migration from the brackish lagoon into the freshwater environments, as fish that were genetically and morphometrically similar to the lagoon fish were found in all freshwater sampling sites. Regardless, few F1-hybrids were identified, and it therefore appears that some pre-and/or postzygotic barriers to gene flow rather than geographic distance are causing the divergence in this system.
authors.affiliation: Centre for Ecological and Evolutionary Synthesis (CEES)Department of Biosciences, University of Oslo P.O.Box 1066, Blindern, NO-0316, Norway.
authors.forename: Annette
authors.initials: A
authors.lastname: Taugbøl
authors.affiliation: Centre for Ecological and Evolutionary Synthesis (CEES)Department of Biosciences, University of Oslo P.O.Box 1066, Blindern, NO-0316, Norway.
authors.forename: Claudia
authors.initials: C
authors.lastname: Junge
authors.affiliation: School of Aquatic and Fishery Sciences, University of Washington Box 355020, Seattle, Washington, 98195-5020.
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Quinn
authors.affiliation: Centre for Ecological and Evolutionary Synthesis (CEES)Department of Biosciences, University of Oslo P.O.Box 1066, Blindern, NO-0316, Norway.
authors.forename: Anders
authors.initials: A
authors.lastname: Herland
authors.affiliation: Centre for Ecological and Evolutionary Synthesis (CEES)Department of Biosciences, University of Oslo P.O.Box 1066, Blindern, NO-0316, Norway.
authors.forename: Leif Asbjørn
authors.initials: LA
authors.lastname: Vøllestad
keywords: Adaptation; hybridization; life-history polymorphism; microsatellites; phenotypic differentiation; population differentiation