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Genetic differentiation in relation to marine landscape in a broadcast-spawning bivalve mollusc (Placopecten magellanicus)

Authors

  • E. L. KENCHINGTON,

    Corresponding author
    1. Benthic Fisheries and Aquaculture Division, Halifax Fisheries Research Laboratory, Department of Fisheries and Oceans, Halifax, NS, Canada B3J 2S7,
    2. Biology Department, Dalhousie University, Halifax, NS, Canada B3H 4J1,
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  • M. U. PATWARY,

    1. Biology Department, Dalhousie University, Halifax, NS, Canada B3H 4J1,
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    • Present address: Department of Biology, Medgar Evers College of the City University of New York, Brooklyn, New York 11225, USA.

  • E. ZOUROS,

    1. Biology Department, Dalhousie University, Halifax, NS, Canada B3H 4J1,
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    • **

      Present address: Department of Biology, University of Crete, Iraklion, Crete, Greece.

  • C. J. BIRD

    1. Institute for Marine Biosciences, National Research Council of Canada, Halifax, NS, Canada B3H 3Z1
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    • ††

      Present address: Nova Scotia Museum of Natural History, Halifax, NS, Canada B3H 3A6.


Ellen L. Kenchington, Present address: Fisheries and Oceans, Canada, Bedford Institute of Oceanography, Dartmouth, NS, Canada B2Y 4A2. Fax: 1 902 426 1862; E-mail: kenchingtone@mar.dfo-mpo.gc.ca

Abstract

Marine bivalves are sessile or sedentary as adults but have planktonic larvae which can potentially disperse over large distances. Consequently larval transport is expected to play a prominent role in facilitating gene flow and determining population structure. The sea scallop (Placopecten magellanicus) is a dioecious species with high fecundity, broadcast spawning and a c. 30-day planktonic larval stage, yet it forms discrete populations or ‘beds’ which have significantly different dynamics and characteristics. We analysed variation at six microsatellite loci in 12 locations throughout the geographic range of the species from Newfoundland, Canada, to New Jersey, USA. Significant differentiation was present and the maximum pairwise θ value, between one of the Newfoundland samples in the north and a sample from the southern portion of the range, was high at 0.061. Other proximate pairs of samples had no detectable genetic differentiation. Mantel tests indicated a significant isolation by distance, but only when one of the populations was excluded. A landscape genetic approach was used to detect areas of low gene flow using a joint analysis of spatial and genetic information. The two major putative barriers inferred by Monmonier's algorithm were then used to define regions for an analysis of molecular variance (amova). That analysis showed a significant but low percentage (1.2%) of the variation to be partitioned among regions, negligible variation among populations within regions, and the majority of the variance distributed between individuals within populations. Prominent currents were concordant with the demarcation of the regions, while a novel approach of using particle tracking software to mimic scallop larval dispersal was employed to interpret within-region genetic patterns.

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