title: RAD genotyping reveals fine-scale genetic structuring and provides powerful population assignment in a widely distributed marine species, the American lobster (Homarus americanus).
abstract: Deciphering genetic structure and inferring connectivity in marine species have been challenging due to weak genetic differentiation and limited resolution offered by traditional genotypic methods. The main goal of this study was to assess how a population genomics framework could help delineate the genetic structure of the American lobster (Homarus americanus) throughout much of the species' range and increase the assignment success of individuals to their location of origin. We genotyped 10 156 filtered SNPs using RAD sequencing to delineate genetic structure and perform population assignment for 586 American lobsters collected in 17 locations distributed across a large portion of the species' natural distribution range. Our results revealed the existence of a hierarchical genetic structure, first separating lobsters from the northern and southern part of the range (FCT  = 0.0011; P-value = 0.0002) and then revealing a total of 11 genetically distinguishable populations (mean FST  = 0.00185; CI: 0.0007-0.0021, P-value < 0.0002), providing strong evidence for weak, albeit fine-scale population structuring within each region. A resampling procedure showed that assignment success was highest with a subset of 3000 SNPs having the highest FST . Applying Anderson's (Molecular Ecology Resources, 2010, 10, 701) method to avoid 'high-grading bias', 94.2% and 80.8% of individuals were correctly assigned to their region and location of origin, respectively. Lastly, we showed that assignment success was positively associated with sample size. These results demonstrate that using a large number of SNPs improves fine-scale population structure delineation and population assignment success in a context of weak genetic structure. We discuss the implications of these findings for the conservation and management of highly connected marine species, particularly regarding the geographic scale of demographic independence.
authors.affiliation: Institut de Biologie Intégrative des Systèmes (IBIS), Université Laval, Québec, Quebec, Canada, G1V0A6.
authors.forename: Laura
authors.initials: L
authors.lastname: Benestan
authors.affiliation: Institut de Biologie Intégrative des Systèmes (IBIS), Université Laval, Québec, Quebec, Canada, G1V0A6.
authors.forename: Thierry
authors.initials: T
authors.lastname: Gosselin
authors.affiliation: Institut de Biologie Intégrative des Systèmes (IBIS), Université Laval, Québec, Quebec, Canada, G1V0A6.
authors.forename: Charles
authors.initials: C
authors.lastname: Perrier
authors.affiliation: Pêches et Océans Canada, Institut Maurice-Lamontagne, CP 1000, Mont-Joli, Quebec, Canada, G5H 3Z4.
authors.forename: Bernard
authors.initials: B
authors.lastname: Sainte-Marie
authors.affiliation: Department of Biology, University of New Brunswick, PO Box 5050, Saint John, New Brunswick, Canada, E2L 4L5.
authors.forename: Rémy
authors.initials: R
authors.lastname: Rochette
authors.affiliation: Institut de Biologie Intégrative des Systèmes (IBIS), Université Laval, Québec, Quebec, Canada, G1V0A6.
authors.forename: Louis
authors.initials: L
authors.lastname: Bernatchez
mesh_terms: D000818:Animals; D005828:Genetics, Population; D060005:Genotyping Techniques; D008121:Nephropidae / Q000235:genetics*; D009656:North America; D020641:Polymorphism, Single Nucleotide; D018401:Sample Size; D012641:Selection, Genetic
keywords: American lobster; assignment test; fishery management; population genomics; single-nucleotide polymorphism marker