title: Contemporary population structure and post-glacial genetic demography in a migratory marine species, the blacknose shark, Carcharhinus acronotus.
abstract: Patterns of population structure and historical genetic demography of blacknose sharks in the western North Atlantic Ocean were assessed using variation in nuclear-encoded microsatellites and sequences of mitochondrial (mt)DNA. Significant heterogeneity and/or inferred barriers to gene flow, based on microsatellites and/or mtDNA, revealed the occurrence of five genetic populations localized to five geographic regions: the southeastern U.S Atlantic coast, the eastern Gulf of Mexico, the western Gulf of Mexico, Bay of Campeche in the southern Gulf of Mexico and the Bahamas. Pairwise estimates of genetic divergence between sharks in the Bahamas and those in all other localities were more than an order of magnitude higher than between pairwise comparisons involving the other localities. Demographic modelling indicated that sharks in all five regions diverged after the last glacial maximum and, except for the Bahamas, experienced post-glacial, population expansion. The patterns of genetic variation also suggest that the southern Gulf of Mexico may have served as a glacial refuge and source for the expansion. Results of the study demonstrate that barriers to gene flow and historical genetic demography contributed to contemporary patterns of population structure in a coastal migratory species living in an otherwise continuous marine habitat. The results also indicate that for many marine species, failure to properly characterize barriers in terms of levels of contemporary gene flow could in part be due to inferences based solely on equilibrium assumptions. This could lead to erroneous conclusions regarding levels of connectivity in species of conservation concern.
authors.affiliation: Marine Genomics Laboratory, Department of Life Sciences, Harte Research Institute, Texas A&M University-Corpus Christi, 6300 Ocean Drive, Corpus Christi, TX, 78412, USA.
authors.forename: D S
authors.initials: DS
authors.lastname: Portnoy
authors.forename: C M
authors.initials: CM
authors.lastname: Hollenbeck
authors.forename: C N
authors.initials: CN
authors.lastname: Belcher
authors.forename: W B
authors.initials: WB
authors.lastname: Driggers
authors.forename: B S
authors.initials: BS
authors.lastname: Frazier
authors.forename: J
authors.initials: J
authors.lastname: Gelsleichter
authors.forename: R D
authors.initials: RD
authors.lastname: Grubbs
authors.forename: J R
authors.initials: JR
authors.lastname: Gold
mesh_terms: D025041:Animal Migration; D000818:Animals; D001267:Atlantic Ocean; D001499:Bayes Theorem; D003247:Conservation of Natural Resources; D004272:DNA, Mitochondrial / Q000235:genetics; D005260:Female; D051456:Gene Flow; D014644:Genetic Variation; D005828:Genetics, Population; D005838:Genotype; D005843:Geography; D006239:Haplotypes; D008297:Male; D018895:Microsatellite Repeats; D008969:Molecular Sequence Data; D017422:Sequence Analysis, DNA; D012754:Sharks / Q000235:genetics*
chemical_list: D004272:DNA, Mitochondrial
keywords: conservation genetics; elasmobranchs; glacial refugia; secondary contact