title: Secondary contact and asymmetrical gene flow in a cosmopolitan marine fish across the Benguela upwelling zone.
abstract: The combination of oceanographic barriers and habitat heterogeneity are known to reduce connectivity and leave specific genetic signatures in the demographic history of marine species. However, barriers to gene flow in the marine environment are almost never impermeable which inevitably allows secondary contact to occur. In this study, eight sampling sites (five along the South African coastline, one each in Angola, Senegal and Portugal) were chosen to examine the population genetic structure and phylogeographic history of the cosmopolitan bluefish (Pomatomus saltatrix), distributed across a large South-east Atlantic upwelling zone. Molecular analyses were applied to mtDNA cytochrome b, intron AM2B1 and 15 microsatellite loci. We detected uncharacteristically high genetic differentiation (FST0.15-0.20; P<0.001) between the fish sampled from South Africa and the other sites, strongly influenced by five outlier microsatellite loci located in conserved intergenic regions. In addition, differentiation among the remaining East Atlantic sites was detected, although mtDNA indicated past isolation with subsequent secondary contact between these East Atlantic populations. We further identified secondary contact, with unidirectional gene flow from South Africa to Angola. The directional contact is likely explained by a combination of the northward flowing offshore current and endogenous incompatibilities restricting integration of certain regions of the genome and limiting gene flow to the south. The results confirm that the dynamic system associated with the Benguela current upwelling zone influences species distributions and population processes in the South-east Atlantic.
authors.affiliation: Molecular Ecology and Evolution Programme, Department of Genetics, University of Pretoria, Pretoria, South Africa.
authors.forename: K
authors.initials: K
authors.lastname: Reid
authors.affiliation: Molecular Ecology and Evolution Programme, Department of Genetics, University of Pretoria, Pretoria, South Africa.
authors.forename: T B
authors.initials: TB
authors.lastname: Hoareau
authors.affiliation: Department of Fisheries Science, Virginia Institute of Marine Science, College of William & Mary, Williamsburg, VA, USA.
authors.forename: J E
authors.initials: JE
authors.lastname: Graves
authors.affiliation: Department of Ichthyology and Fisheries Science, Rhodes University, Grahamstown, South Africa.
authors.forename: W M
authors.initials: WM
authors.lastname: Potts
authors.affiliation: Molecular Ecology and Evolution Programme, Department of Genetics, University of Pretoria, Pretoria, South Africa.
authors.forename: S M R
authors.initials: SM
authors.lastname: Dos Santos
authors.affiliation: Molecular Ecology and Evolution Programme, Department of Genetics, University of Pretoria, Pretoria, South Africa.
authors.forename: A W
authors.initials: AW
authors.lastname: Klopper
authors.affiliation: Molecular Ecology and Evolution Programme, Department of Genetics, University of Pretoria, Pretoria, South Africa.
authors.forename: P
authors.initials: P
authors.lastname: Bloomer
mesh_terms: D000810:Angola; D000818:Animals; D001267:Atlantic Ocean; D004272:DNA, Mitochondrial / Q000235:genetics; D017753:Ecosystem; D051456:Gene Flow; D014644:Genetic Variation; D005828:Genetics, Population; D006239:Haplotypes; D018895:Microsatellite Repeats; D010473:Perciformes / Q000235:genetics*; D058974:Phylogeography; D011174:Portugal; D012675:Senegal; D017422:Sequence Analysis, DNA; D013019:South Africa
chemical_list: D004272:DNA, Mitochondrial