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A hybrid zone between hydrothermal vent mussels (Bivalvia: Mytilidae) from the Mid-Atlantic Ridge

Authors

  • G. D. O’Mullan,

    1. Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ 08901, USA,
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    • Present address: Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA.

  • P. A. Y. Maas,

    1. Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ 08901, USA,
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  • R. A. Lutz,

    1. Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ 08901, USA,
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  • R. C. Vrijenhoek

    Corresponding author
    1. Monterey Bay Aquarium Research Institute, Moss Landing, USA
      R. C. Vrijenhoek. Fax: +831 775 1620; E-mail: vrijen@mbari.org
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R. C. Vrijenhoek. Fax: +831 775 1620; E-mail: vrijen@mbari.org

Abstract

This study provides the first example of a hybrid zone between animal taxa distributed along the mid-ocean ridge system. We examined the distribution and genetic structure of deep-sea hydrothermal vent mussels (Bivalvia: Mytilidae) along a 2888-km portion of the Mid-Atlantic Ridge between 37°50′ N and 14°45′ N latitude. Mitochondrial DNA (mtDNA), allozymes and multivariate–morphometric evidence discriminated between individuals of a northern species, Bathymodiolus azoricus, and a southern species, B. puteoserpentis, that were separated by an intermediate ridge segment almost devoid of mussels. A small sample of mussels from Broken Spur, a vent locality along this intermediate zone, revealed a mixed population with gene frequencies and morphology that were broadly intermediate to those of the northern and southern species. Multilocus clines in mtDNA and allozyme frequencies were centred over the intermediate zone. We consider intrinsic and extrinsic processes that might limit genetic exchange across this hybrid zone.

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