title: Signatures of selection in the three-spined stickleback along a small-scale brackish water - freshwater transition zone.
abstract: Local adaptation is often obvious when gene flow is impeded, such as observed at large spatial scales and across strong ecological contrasts. However, it becomes less certain at small scales such as between adjacent populations or across weak ecological contrasts, when gene flow is strong. While studies on genomic adaptation tend to focus on the former, less is known about the genomic targets of natural selection in the latter situation. In this study, we investigate genomic adaptation in populations of the three-spined stickleback Gasterosteus aculeatus L. across a small-scale ecological transition with salinities ranging from brackish to fresh. Adaptation to salinity has been repeatedly demonstrated in this species. A genome scan based on 87 microsatellite markers revealed only few signatures of selection, likely owing to the constraints that homogenizing gene flow puts on adaptive divergence. However, the detected loci appear repeatedly as targets of selection in similar studies of genomic adaptation in the three-spined stickleback. We conclude that the signature of genomic selection in the face of strong gene flow is weak, yet detectable. We argue that the range of studies of genomic divergence should be extended to include more systems characterized by limited geographical and ecological isolation, which is often a realistic setting in nature.
authors.affiliation: Laboratory of Biodiversity and Evolutionary Genomics University of Leuven Ch. Deberiotstraat 32, B-3000 Leuven Belgium.
authors.forename: Nellie
authors.initials: N
authors.lastname: Konijnendijk
authors.affiliation: Ecological Genetics Research Unit Department of Biosciences University of Helsinki P.O. Box 65 FI-000 14 Helsinki Finland.
authors.forename: Takahito
authors.initials: T
authors.lastname: Shikano
authors.affiliation: Laboratory of Biodiversity and Evolutionary Genomics University of Leuven Ch. Deberiotstraat 32, B-3000 Leuven Belgium.
authors.forename: Dorien
authors.initials: D
authors.lastname: Daneels
authors.affiliation: Laboratory of Biodiversity and Evolutionary Genomics University of Leuven Ch. Deberiotstraat 32, B-3000 Leuven Belgium.
authors.forename: Filip A M
authors.initials: FA
authors.lastname: Volckaert
authors.affiliation: Laboratory of Biodiversity and Evolutionary Genomics University of Leuven Ch. Deberiotstraat 32, B-3000 Leuven Belgium.
authors.forename: Joost A M
authors.initials: JA
authors.lastname: Raeymaekers
keywords: Adaptation; candidate gene; evolution; fish; genome scan; population genomics; selection