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      Evaluación de la estructura genética poblacional de Sphyrna lewini para la identificación de unidades de conservación en el Pacífico mexicano Translated title: Assessment of the population genetic structure of Sphyrna lewini to identify conservation units in the Mexican Pacific

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          Abstract

          Debido a la situación actual del tiburón martillo (Sphyrna lewini) como especie amenazada, la evaluación de los niveles de diversidad y divergencia genética, así como de los parámetros demográficos de las poblaciones en el océano Pacifico Oriental, puede ayudar a contribuir a delinear estrategias adecuadas para la pesca sostenible y la conservación de la especie. Se analizaron muestras del periodo 2001-2003 obtenidas de siete localidades en el océano Pacífico mexicano y dos en el sur del golfo de México, mediante la metodología de conformación polimórfica de cadena sencilla de un fragmento de la región control del ADN mitocondrial y el análisis de cinco loci de microsatélites. Los datos mitocondriales no presentaron divergencia entre las localidades del Pacífico mexicano; sin embargo, los datos de microsatélites mostraron una notable divergencia genética de la población de Baja California (BC) con respecto al resto de las localidades analizadas. Similarmente, se encontraron diferencias significativas entre las localidades del norte y centro del Pacifico mexicano. El análisis de la demografía histórica reveló la incidencia de eventos de expansión espacial de las poblaciones, posiblemente relacionados con los ciclos glaciales-interglaciales ocurridos hace aproximadamente 450,000 años. La divergencia encontrada debe ser considerada en la formulación de políticas de gestión de pesca y de conservación de la especie en la región.

          Translated abstract

          Due to the current status of the scalloped hammerhead shark (Sphyrna lewini) as a threatened species, the asseS SMent of genetic diversity, divergence, and demographic parameters of populations in the eastern Pacific Ocean may assist in developing appropriate strategies for sustainable fisheries and species conservation. We analyzed samples collected from 2001 to 2003 from seven locations in the Mexican Pacific Ocean and two in the southwestern Gulf of Mexico, using single-stranded conformation polymorphism of a mitochondrial control region fragment and five microsatellite loci. The mitochondrial data did not show population divergence among locations from the Mexican Pacific Ocean; however, the microsatellite data showed a divergent population in Baja California. Additional differences were also observed between the northern and central locations of the Mexican Pacific. The historical demography analysis revealed spatial expansion events, possibly related to glacial-interglacial cycles that occurred approximately 450,000 years ago. The divergence found should be considered in the formulation of fisheries management and conservation policies of the species in the region.

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          Global phylogeography of the scalloped hammerhead shark (Sphyrna lewini).

          Large marine fishes typically have little population genetic structure. The exceptions are associated with sedentary behaviour, disjunct distributions, or reproductive philopatry. Scalloped hammerhead sharks (Sphyrna lewini) incorporate the contrasting traits of oceanic habitat (usually associated with high dispersal) and possible fidelity to nursery grounds (for reproductive females). To evaluate the expectations of these contrasting behaviours, we examined the global genetic structure of S. lewini based on collections (n = 271 individuals) from 20 nursery areas. A 548-bp fragment of mitochondrial DNA control region revealed 22 polymorphic sites, 24 haplotypes, and three lineages distinguished by 2.56-3.77% sequence divergence. Coalescence analyses based on a provisional molecular clock indicate an origin in the Indo-West Pacific with late Pleistocene radiations into the central Pacific (Hawaii) and eastern Pacific (Central America), as well as recent interchange between oceans via southern Africa. Population subdivisions are strong (overall Phi(ST) = 0.749, P 10). We conclude that nursery populations linked by continuous coastline have high connectivity, but that oceanic dispersal by females is rare. Although we cannot rule out philopatry to natal nurseries, oceanic barriers appear to have a much stronger influence on the genetic architecture of this species and may indicate a mechanism for recent evolutionary radiations in the genus Sphyrna.
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            Comparative phylogeography of Atlantic bluefin tuna and swordfish: the combined effects of vicariance, secondary contact, introgression, and population expansion on the regional phylogenies of two highly migratory pelagic fishes.

            Comparative phylogeography has revealed remarkable patterns of concordance in the maternal phylogenies of many species. The phylogeography and historical demography of the mitochondrial control region I for 607 Atlantic bluefin tuna (Thunnus thynnus) and 275 swordfish (Xiphias gladius) were analyzed to clarify the complex phylogenetic signals in the North Atlantic-Mediterranean region where they are sympatric. Atlantic bluefin tuna mtDNA is polyphyletic, and includes rare sequences sister to Pacific bluefin tuna (Thunnus orientalis) and introgressed albacore (Thunnus alalunga) sequences. There is no geographic partitioning between Atlantic and Mediterranean samples of Atlantic bluefin tuna (Phi(ST)=0.002). In contrast, Atlantic and Mediterranean swordfish are differentiated (Phi(ST)=0.091) due to the combined effects of vicariance, secondary contact, and dissimilar regional demographic histories. Mediterranean swordfish has substantially less variation, and a more recent history (tau=2.42) than that of Atlantic swordfish (tau=7.02). In spite of the discordant phylogenetic and phylogeographic signals, the demographic history of Atlantic swordfish and Atlantic bluefin tuna (tau=7.51) suggests concordance in the timeline of population expansion. Possible scenarios of cladogenesis, expansion, and contraction, influenced by glacial cycles during the Pleistocene, are formulated.
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              Pliocene-Pleistocene evolution of eastern tropical Pacific surface water circulation and thermocline depth

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                Author and article information

                Contributors
                Role: ND
                Role: ND
                Role: ND
                Journal
                ciemar
                Ciencias marinas
                Cienc. mar
                Universidad Autónoma de Baja California, Instituto de Investigaciones Oceanológicas (Ensenada )
                0185-3880
                December 2012
                : 38
                : 4
                : 635-652
                Affiliations
                [1 ] Universidad Nacional Autónoma de México Mexico
                Article
                S0185-38802012000500005
                10.7773/cm.v38i4.2110
                edc4ac24-b077-4d10-8db1-9fbba8efac03

                http://creativecommons.org/licenses/by/4.0/

                Product
                Product Information: website
                Self URI (journal page): http://www.scielo.org.mx/scielo.php?script=sci_serial&pid=0185-3880&lng=en
                Categories
                Marine & Freshwater Biology

                Ecology
                Sphyrna lewini,genetic structure,mtDNA,microsatellites,estructura genética,ADNmt,microsatélites
                Ecology
                Sphyrna lewini, genetic structure, mtDNA, microsatellites, estructura genética, ADNmt, microsatélites

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