title: The genetic consequences of spatially varying selection in the panmictic American eel (Anguilla rostrata).
abstract: Our understanding of the genetic basis of local adaptation has recently benefited from the increased power to identify functional variants associated with environmental variables at the genome scale. However, it often remains challenging to determine whether locally adaptive alleles are actively maintained at intermediate frequencies by spatially varying selection. Here, we evaluate the extent to which this particular type of balancing selection explains the retention of adaptive genetic variation in the extreme situation of perfect panmixia, using the American eel (Anguilla rostrata) as a model. We first conducted a genome scan between two samples from opposite ends of a latitudinal environmental gradient using 454 sequencing of individually tagged cDNA libraries. Candidate SNPs were then genotyped in 992 individuals from 16 sampling sites at different life stages of the same cohort (including larvae from the Sargasso Sea, glass eels, and 1-year-old individuals) as well as in glass eels of the following cohort. Evidence for spatially varying selection was found at 13 loci showing correlations between allele frequencies and environmental variables across the entire species range. Simulations under a multiple-niche Levene's model using estimated relative fitness values among genotypes rarely predicted a stable polymorphic equilibrium at these loci. Our results suggest that some genetic-by-environment interactions detected in our study arise during the progress toward fixation of a globally advantageous allele with spatially variable effects on fitness.
authors.affiliation: Institut de Biologie Intégrative et des Systèmes, Département de Biologie, Université Laval, Quebec City, Quebec G1V 0A6, Canada.
authors.forename: Pierre-Alexandre
authors.initials: PA
authors.lastname: Gagnaire
authors.forename: Eric
authors.initials: E
authors.lastname: Normandeau
authors.forename: Caroline
authors.initials: C
authors.lastname: Côté
authors.forename: Michael
authors.initials: M
authors.lastname: Møller Hansen
authors.forename: Louis
authors.initials: L
authors.lastname: Bernatchez
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics; D000483:Alleles; D000811:Anguilla / Q000235:genetics*; D000818:Animals; D019143:Evolution, Molecular; D005787:Gene Frequency; D059647:Gene-Environment Interaction; D056426:Genetic Loci; D014644:Genetic Variation; D005838:Genotype; D008957:Models, Genetic; D009792:Oceans and Seas; D011110:Polymorphism, Genetic; D020641:Polymorphism, Single Nucleotide; D012641:Selection, Genetic; D013696:Temperature