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Genetic diversity and differentiation in a wide ranging anadromous fish, American shad (Alosa sapidissima), is correlated with latitude

Authors

  • Daniel J. Hasselman,

    Corresponding author
    1. Marine Gene Probe Laboratory, Biology Department, Dalhousie University, Halifax, Nova Scotia, Canada
    • Correspondence: Daniel J. Hasselman, Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA 95060, USA, Fax: (831) 459 3383; E-mail: dhasselm@ucsc.edu

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  • Daniel Ricard,

    1. Biology Department, Dalhousie University, Halifax, Nova Scotia, Canada
    2. Institute of Hydrobiology, Fish Ecology Unit, Biology Centre of the Academy of Sciences of the Czech Republic, České Budějovice, Czech Republic
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  • Paul Bentzen

    1. Marine Gene Probe Laboratory, Biology Department, Dalhousie University, Halifax, Nova Scotia, Canada
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Abstract

Studies that span entire species ranges can provide insight into the relative roles of historical contingency and contemporary factors that influence population structure and can reveal patterns of genetic variation that might otherwise go undetected. American shad is a wide ranging anadromous clupeid fish that exhibits variation in demographic histories and reproductive strategies (both semelparity and iteroparity) and provides a unique perspective on the evolutionary processes that govern the genetic architecture of anadromous fishes. Using 13 microsatellite loci, we examined the magnitude and spatial distribution of genetic variation among 33 populations across the species' range to (i) determine whether signals of historical demography persist among contemporary populations and (ii) assess the effect of different reproductive strategies on population structure. Patterns of genetic diversity and differentiation among populations varied widely and reflect the differential influences of historical demography, microevolutionary processes and anthropogenic factors across the species' range. Sequential reductions of diversity with latitude among formerly glaciated rivers are consistent with stepwise postglacial colonization and successive population founder events. Weak differentiation among U.S. iteroparous populations may be a consequence of human-mediated gene flow, while weak differentiation among semelparous populations probably reflects natural gene flow. Evidence for an effect of reproductive strategy on population structure suggests an important role for environmental variation and suggests that the factors that are responsible for shaping American shad life history patterns may also influence population genetic structure.

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