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Taking stock: defining populations of American shad (Alosa sapidissima) in Canada using neutral genetic markers

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Abstract:

Knowledge of the scale of population structure is a prerequisite for designating conservation units. American shad (Alosa sapidissima) are of increasing conservation concern, but the scale of population structure within the Canadian portion of the species range is unknown. Using 13 microsatellite loci, we examined the partitioning of genetic variation within four and among 12 Canadian drainages. We detected significant (p< 0.05) and temporally stable genetic differentiation among all drainages, supporting the hypothesis that rivers support genetically distinct populations. However, Bayesian methods identified seven clusters and provided evidence for shad metapopulation structure. We observed a significant (p< 0.01) pattern of isolation by distance (IBD) among all drainages. A strong linear IBD (r = 0.98) was observed among rivers that were outside the Bay of Fundy (BoF). A hypothesized counterclockwise migration route explained a greater proportion of genetic variation (r = 0.87) among BoF rivers than direct route based distances (r = 0.14). Although IBD patterns did not differ regionally (analysis of covariance; p> 0.05), the degree of differentiation among BoF rivers was greater than that among non-BoF rivers, regardless of the geographic scale of comparison. Our results suggest that fisheries managers need to be concerned with the loss of shad genetic diversity on both river and regional scales.

Il faut une connaissance préalable de l’échelle de la structure de la population avant d’établir des unités de conservation. La conservation de l’alose délicieuse (Alosa sapidissima) devient un sujet de plus en plus préoccupant, mais l’échelle de la structure de la population dans la portion canadienne de l’aire de répartition de l’espèce reste inconnue. Par l’étude de 13 locus microsatellites, nous avons examiné le partitionnement de la variation génétique au sein de quatre et entre 12 bassins hydrographiques canadiens. Nous avons décelé une différenciation génétique significative (p< 0,05) et stable dans le temps entre tous les bassins, ce qui appuie l’hypothèse qui veut que les rivières possèdent des populations génétiquement distinctes. Cependant, des méthodes bayésiennes identifient sept groupes et appuient l’existence d’une structure de métapopulation chez les aloses. Il existe un patron significatif (p< 0,01) d’isolement par la distance (IBD) entre tous les bassins. Un fort IBD linéaire (r = 0,98) s’observe parmi les rivières qui ne se jettent pas dans la baie de Fundy. Une route hypothétique de migration dans le sens inverse des aiguilles d’une montre explique une plus grande partie de la variation génétique (r = 0,87) parmi les rivières de la baie de Fundy que ne le font les distances basées sur une route directe (r = 0,14). Bien que les patrons d’IBD ne diffèrent pas à l’échelle régionale (analyse de covariance; p> 0,05), le degré de différenciation est plus grand parmi les rivières de la baie de Fundy qu’entre les rivières qui ne s’y jettent pas, quelle que soit l’échelle géographique de la comparaison. Nos résultats indiquent que les gestionnaires de la pêche doivent se préoccuper de la perte de diversité génétique des aloses, tant à l’échelle des rivières qu’à l’échelle régionale.

Document Type: Research Article

Publication date: 2010-06-01

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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