All roads lead to home: panmixia of European eel in the Sargasso Sea

Authors

  • THOMAS D. ALS,

    1. National Institute of Aquatic Resources, Technical University of Denmark, Vejlsøvej 39, DK-8600 Silkeborg, Denmark
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    • These authors contributed equally to this work.

  • MICHAEL M. HANSEN,

    1. Department of Biological Sciences, Aarhus University, Ny Munkegade 114, DK-8000 Aarhus C, Denmark
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    • These authors contributed equally to this work.

  • GREGORY E. MAES,

    1. Laboratory of Animal Diversity and Systematics, Katholieke Universiteit Leuven, B-3000, Leuven, Belgium
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  • MARTIN CASTONGUAY,

    1. Institut Maurice-Lamontagne, Fisheries and Oceans Canada, PO Box 1000 Mont-Joli, QC G5H 3Z4, Canada
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  • LASSE RIEMANN,

    1. Department of Natural Sciences, Linnaeus University, SE-39182 Kalmar, Sweden
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    • Present address: Section for Marine Biology, University of Copenhagen, Strandpromenaden 5, DK-3000 Helsingør, Denmark.

  • KIM AARESTRUP,

    1. National Institute of Aquatic Resources, Technical University of Denmark, Vejlsøvej 39, DK-8600 Silkeborg, Denmark
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  • PETER MUNK,

    1. National Institute of Aquatic Resources, Technical University of Denmark, DK-2920 Charlottenlund, Denmark
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  • HENRIK SPARHOLT,

    1. International Council for Exploration of the Sea, DK-1553 Copenhagen, Denmark
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  • REINHOLD HANEL,

    1. Institute of Fisheries Ecology, Johann Heinrich von Thünen-Institut (vTI), Federal Research Institute for Rural Areas, Forestry and Fisheries, Palmaille 9, 22767 Hamburg, Germany
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  • LOUIS BERNATCHEZ

    1. Département de Biologie, Institut de Biologie Intégrative et des Systèmes (IBIS), Pavillon Charles-Eugène-Marchand, 1030, Avenue de la Médecine, Université Laval, QC G1V 0A6, Canada
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Michael M. Hansen, Fax: +45 89422722; E-mail: michael.m.hansen@biology.au.dk

Abstract

European eels (Anguilla anguilla) spawn in the remote Sargasso Sea in partial sympatry with American eels (Anguilla rostrata), and juveniles are transported more than 5000 km back to the European and North African coasts. The two species have been regarded as classic textbook examples of panmixia, each comprising a single, randomly mating population. However, several recent studies based on continental samples have found subtle, but significant, genetic differentiation, interpreted as geographical or temporal heterogeneity between samples. Moreover, European and American eels can hybridize, but hybrids have been observed almost exclusively in Iceland, suggesting hybridization in a specific region of the Sargasso Sea and subsequent nonrandom dispersal of larvae. Here, we report the first molecular population genetics study based on analysis of 21 microsatellite loci in larvae of both Atlantic eel species sampled directly in the spawning area, supplemented by analysis of European glass eel samples. Despite a clear East–West gradient in the overlapping distribution of the two species in the Sargasso Sea, we only observed a single putative hybrid, providing evidence against the hypothesis of a wide marine hybrid zone. Analyses of genetic differentiation, isolation by distance, isolation by time and assignment tests provided strong evidence for panmixia in both the Sargasso Sea and across all continental samples of European eel after accounting for the presence of sibs among newly hatched larvae. European eel has declined catastrophically, and our findings call for management of the species as a single unit, necessitating coordinated international conservation efforts.

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