title: Population size, habitat fragmentation, and the nature of adaptive variation in a stream fish.
abstract: Whether and how habitat fragmentation and population size jointly affect adaptive genetic variation and adaptive population differentiation are largely unexplored. Owing to pronounced genetic drift, small, fragmented populations are thought to exhibit reduced adaptive genetic variation relative to large populations. Yet fragmentation is known to increase variability within and among habitats as population size decreases. Such variability might instead favour the maintenance of adaptive polymorphisms and/or generate more variability in adaptive differentiation at smaller population size. We investigated these alternative hypotheses by analysing coding-gene, single-nucleotide polymorphisms associated with different biological functions in fragmented brook trout populations of variable sizes. Putative adaptive differentiation was greater between small and large populations or among small populations than among large populations. These trends were stronger for genetic population size measures than demographic ones and were present despite pronounced drift in small populations. Our results suggest that fragmentation affects natural selection and that the changes elicited in the adaptive genetic composition and differentiation of fragmented populations vary with population size. By generating more variable evolutionary responses, the alteration of selective pressures during habitat fragmentation may affect future population persistence independently of, and perhaps long before, the effects of demographic and genetic stochasticity are manifest.
authors: Department of Biology, Concordia University, Montreal, Quebec, Canada H4B 1R6 dylan.fraser@concordia.ca.
authors: Dylan J
authors: DJ
authors: Fraser
authors: Thünen-Institute of Fisheries Ecology, Palmaille 9, Hamburg 22765, Germany.
authors: Paul V
authors: PV
authors: Debes
authors: Departement de Biologie, Institut de Biologie Integrative et des Systemes (IBIS), Université Laval, Pavillon Charles-Eugene-Marchand 1030, Avenue de la Medecine Local 1145, Quebec, QC, Canada G1V 0A6.
authors: Louis
authors: L
authors: Bernatchez
authors: Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4R2 Centre for Ecological and Evolutionary Synthesis, Department of Biosciences, University of Oslo, Oslo, Norway.
authors: Jeffrey A
authors: JA
authors: Hutchings
mesh_terms: D000220:Adaptation, Biological; D000818:Animals; D005075:Biological Evolution; D017753:Ecosystem; D040961:Genetic Drift; D005828:Genetics, Population; D009523:Newfoundland and Labrador; D011110:Polymorphism, Genetic; D011156:Population Density; D045483:Rivers; D014337:Trout / Q000235:genetics*
keywords: adaptive variation; fish; genetic variation; habitat fragmentation; population size