Multilocus Bayesian Estimates of Intra-Oceanic Genetic Differentiation, Connectivity, and Admixture in Atlantic Swordfish (Xiphias gladius L.)

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Trophic Ecology of Atlantic Bluefin Tuna (Thunnus thynnus) Larvae from the Gulf of Mexico and NW Mediterranean Spawning Grounds: A Comparative Stable Isotope Study

The present study uses stable isotopes of nitrogen and carbon (δ15Nandδ13C) as trophic indicators for Atlantic bluefin tuna larvae (BFT) (6–10mm standard length) in the highly contrasting environmental conditions of the Gulf of Mexico (GOM) and the Balearic Sea (MED). These regions are differentiated by their temperature regime and relative productivity, with the GOM being significantly warmer and more productive. MED BFT larvae showed the highest δ15N signatures, implying an elevated trophic position above the underlyingmicrozooplankton baseline. Ontogenetic dietary shifts were observed in the BFT larvae from the GOM and MED which indicates early life trophodynamics differences between these spawning habitats. Significant trophic differences between the GOM and MED larvae were observed in relation to δ15N signatures in favour of the MED larvae, which may have important implications in their growth during their early life stages. These low δ15N levels in the zooplankton from the GOM may be an indication of a shifting isotopic baseline in pelagic food webs due to diatrophic inputs by cyanobacteria. Lack of enrichment for δ15N in BFT larvae compared to zooplankton implies an alternative grazing pathway from the traditional food chain of phytoplankton— zooplankton—larval fish. Results provide insight for a comparative characterization of the trophic pathways variability of the two main spawning grounds for BFT larvaeVersión del editor4,411

SNP identification and validation in two invasive species: zebra mussel (Dreissena polymorpha) and Asian clam (Corbicula fluminea)

Identificación y validación de PNU en dos especies invasoras: el mejillón cebra (Dreissena polymorpha) y la almeja asiática (Corbicula fluminea) El desarrollo de las plataformas asequibles de secuenciación masiva en paralelo (SMP) ha reducido el coste y el tiempo en la identificación de marcadores de polimorfismos de nucleótido único (PNU) para su uso en estudios de genética de poblaciones y de conservación. Tras la SMP, suele ser necesaria una segunda validación. El análisis de las curvas de fusión a alta resolución (HRMA en su sigla en inglés) es un método rápido y sencillo para escanear mutaciones y, por tanto, es un protocolo adecuado de validación de dichos marcadores, especialmente en especies no modelo. En este trabajo se presenta un juego de nueve marcadores polimórficos de PNU nuevos identificados mediante SMP y validados con el HRMA en dos especies invasoras (el mejillón cebra Dreissena polymorpha y la almeja asiática Corbicula fluminea), que pueden utilizarse en estudios de genética de poblaciones para evaluar y entender correctamente los episodios de invasión pasados y los que podrían ocurrir en el futuro.The development of affordable massive parallel sequencing (MPS) has reduced both time and costs of SNP identification for use in conservation and population genetic studies. After MPS, a second validation is usually required. High resolution melting analysis (HRMA) is a fast and simple method for mutation scanning, and thus a suitable validation protocol, particularly in non–model species. We present a set of nine novel polymorphic SNPs identified by MPS and validated with HRMA in two invasive species (the zebra mussel Dreissena polymorpha and the Asian clam Corbicula fluminea). These SNPs can be used in genetic studies to accurately assess and understand past and future invasion events.Identificación y validación de PNU en dos especies invasoras: el mejillón cebra (Dreissena polymorpha) y la almeja asiática (Corbicula fluminea) El desarrollo de las plataformas asequibles de secuenciación masiva en paralelo (SMP) ha reducido el coste y el tiempo en la identificación de marcadores de polimorfismos de nucleótido único (PNU) para su uso en estudios de genética de poblaciones y de conservación. Tras la SMP, suele ser necesaria una segunda validación. El análisis de las curvas de fusión a alta resolución (HRMA en su sigla en inglés) es un método rápido y sencillo para escanear mutaciones y, por tanto, es un protocolo adecuado de validación de dichos marcadores, especialmente en especies no modelo. En este trabajo se presenta un juego de nueve marcadores polimórficos de PNU nuevos identificados mediante SMP y validados con el HRMA en dos especies invasoras (el mejillón cebra Dreissena polymorpha y la almeja asiática Corbicula fluminea), que pueden utilizarse en estudios de genética de poblaciones para evaluar y entender correctamente los episodios de invasión pasados y los que podrían ocurrir en el futuro

Hierarchical analyses of genetic variation of samples from breeding and feeding grounds confirm the genetic partitioning of northwest Atlantic and South Atlantic populations of swordfish (Xiphias gladius L.)

16 pages, 3 figures, 2 tablesIn species with high migratory potential, the genetic signal revealing population differentiation is often obscured by population admixture. To our knowledge, the explicit comparison of genetic samples from known spawning and feeding areas has not been conducted for any highly migratory pelagic fish species. This study examines the geographic heterogeneity of swordfish mitochondrial DNA (mtDNA) lineages within the Atlantic Ocean using 330 base pairs of sequence of the control region from 480 individuals. Hierarchical analyses of sequence variation were conducted to test whether samples from areas identified as the corresponding spawning and feeding grounds for the northwest (NW) Atlantic (Caribbean and Georges Banks-US northeast) and the South Atlantic (Brazil-Uruguay and Gulf of Guinea), were more closely related to each other than to samples from any other region, including the Mediterranean Sea, the Indian Ocean, and the Pacific Ocean. Phylogeographic analyses reveal that swordfish mtDNA phylogeny is characterized by incomplete lineage sorting and secondary contact of two highly divergent clades. However, despite this complex phylogenetic signature, results from an analysis of nucleotide diversity and from an analysis of molecular variance (AMOVA) were for the most part concordant and indicate that NW Atlantic and South Atlantic swordfish belong to separate populations. The mtDNA distinctiveness of NW Atlantic and South Atlantic swordfish populations is indicative of philopatric behavior in swordfish towards breeding and feeding areas. © 2005 Elsevier B.V. All rights reservedThis study was funded in part by the Texas Institute of Oceanography, and by the Cooperative Institute for Fisheries Molecular Biology (FISHTEC) NOAA-NMFS (RT/F-1) and is listed as FISHTEC contribution number FT 02-05 (number will be provided after final acceptance). Additional support was provided by IEO-4.03 and Economic Union project DGXIV, MED93-013Peer Reviewe

Multilocus Bayesian Estimates Oceanic Genetic Differentiation, Connectivity, and Admixture in Swordfish (Xiphias gladius L.)

Previous genetic studies of Atlantic swordfish (Xiphias gladius L.) revealed significant differentiation among Mediterranean, North Atlantic and South Atlantic populations using both mitochondrial and nuclear DNA data. However, limitations in geographic sampling coverage, and the use of single loci, precluded an accurate placement of boundaries and of estimates of admixture. In this study, we present multilocus analyses of 26 single nucleotide polymorphisms (SNPs) within 10 nuclear genes to estimate population differentiation and admixture based on the characterization of 774 individuals representing North Atlantic, South Atlantic, and Mediterranean swordfish populations. Pairwise FST values, AMOVA, PCoA, and Bayesian individual assignments support the differentiation of swordfish inhabiting these three basins, but not the current placement of the boundaries that separate them. Specifically, the range of the South Atlantic population extends beyond 5°N management boundary to 20°N-25°N from 45°W. Likewise the Mediterranean population extends beyond the current management boundary at the Strait of Gibraltar to approximately 10°W. Further, admixture zones, characterized by asymmetric contributions of adjacent populations within samples, are confined to the Northeast Atlantic. While South Atlantic and Mediterranean migrants were identified within these Northeast Atlantic admixture zones no North Atlantic migrants were identified respectively in these two neighboring basins. Owing to both, the characterization of larger number of loci and a more ample spatial sampling coverage, it was possible to provide a finer resolution of the boundaries separating Atlantic swordfish populations than previous studies. Finally, the patterns of population structure and admixture are discussed in the light of the reproductive biology, the known patterns of dispersal, and oceanographic features that may act as barriers to gene flow to Atlantic swordfish.Postprint4,411