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The effects of isolation and colonization history on the genetic structure of marine-relict populations of Atlantic cod (Gadus morhua) in the Canadian Arctic

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Abstract:

The genetic consequences of extended periods at low population size are fundamental to the conservation of depleted species such as the Atlantic cod (Gadus morhua). We compared microsatellite genetic variability among cod populations in Canadian Arctic lakes with that of Gilbert Bay resident and inshore cod from eastern Canada. The Arctic populations had the lowest genetic diversity and were the most strongly genetically structured and distinct. By contrast, eastern Canadian samples expressed high allelic diversity and were not significantly genetically structured or distinct relative to each other, whereas Gilbert Bay resident cod were intermediate to the Arctic and eastern Canadian groups. Our results are consistent with the hypothesis that the Arctic populations were colonized between 8000 and 5000 years ago and have experienced little or no gene flow since that time. Despite isolation at the extreme of the species' range, the Arctic populations have retained relatively high heterozygosities and high genetic effective population sizes relative to census sizes (NeNc ratios). Potential explanations for this include the absence of fishing pressure, allowing for the persistence of large, highly fecund individuals, as well as biotic (e.g., absence of planktivores) and abiotic (e.g., low environmental stochasticity) factors in the Arctic lakes that minimize individual variance in reproductive success.

La connaissance des conséquences génétiques de longues périodes de faible densité de population est essentielle pour la conservation des espèces surexploitées, telles que la morue franche (Gadus morhua). Nous avons comparé la variabilité génétique des microsatellites de populations de lacs de l'arctique canadien avec celles de morues habitant la baie de Gilbert et les côtes de l'Est canadien. Les populations arctiques possèdent la diversité génétique la plus faible et elles sont celles qui sont les plus structurées et distinctes du point de vue génétique. En revanche, les échantillons de l'Est canadien montrent une forte diversité allélique, ne sont pas significativement structurées génétiquement et ne se distinguent pas l'une de l'autre; les morues vivant dans la baie de Gilbert sont intermédiaires entre les groupes de l'arctique et de l'Est canadien. Nos résultats sont compatibles avec l'hypothèse selon laquelle les populations arctiques ont été établies il y entre 8000 et 5000 ans et qu'elles n'ont connu que peu ou pas de flux génétique depuis cette époque. Malgré leur isolement à l'extrême marge de la répartition de l'espèce, les populations arctiques ont conservé une forte hétérozygotie et des tailles de population génétique effective élevées par rapport aux tailles d'inventaire (rapports NeNc). Les explications possibles de cette situation comprennent l'absence de pression de pêche qui permet la persistance de gros individus à forte fécondité, mais aussi des facteurs biotiques (par ex., l'absence de planctonophages) et abiotiques (par ex., la stochasticité environnementale faible) dans les lacs arctiques, ce qui minimise la variance individuelle du succès reproductif.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: August 1, 2006

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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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