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Evaluating the demographic significance of genetic homogeneity using a coalescent-based simulation: a case study with gag (Mycteroperca microlepis)

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Abstract:

Gag (Mycteroperca microlepis) from the eastern Gulf of Mexico and northwestern Atlantic are managed as separate stocks, although evidence for their demographic isolation remains equivocal. Several hundred individuals were genotyped at 11 microsatellite loci and it was found that gag across these regions were genetically indistinguishable (FST< 0.001). A coalescent-based computer simulation was employed to quantitatively assess the relative importance of dispersal rate, population size, and time since divergence on gag genetic homogeneity. Using empirical estimates of long-term effective population size (16500), a range of dispersal rates and divergence times (500 to 500000 generations) was modeled, and it was concluded that present-day genetic homogeneity must be maintained by dispersal rates of at least 20–30 migrants per generation and up to hundreds or thousands per generation. This study also documents the absence of significant temporal genetic structure and inbreeding in the Atlantic when comparing cohorts separated in time from weeks to 20years. This suggests that the long-standing practice of overfishing gag has yet to manifest as an inbreeding effect. Overall, gag dispersal rates remain uncertain, and consequently, this study can neither support nor refute management schemes that independently regulate gag in the eastern Gulf of Mexico and northwestern Atlantic.

Les badèches baillou (Mycteroperca microlepis) de l’est du golfe du Mexique et du nord-ouest de l’Atlantique sont gérées comme des stocks distincts, bien que les données sur leur isolement démographique restent équivoques. Nous avons déterminé le génotype à 11 locus microsatellites de plusieurs centaines d’individus et nous n’arrivons pas à distinguer génétiquement les badèches baillou dans l’ensemble de ces régions (FST < 0,001). Une simulation sur ordinateur basée sur la coalescence nous à servi à évaluer quantitativement l’importance relative du taux de dispersion, de la taille de la population et du temps depuis la divergence pour l’homogénéité génétique de la badèche. En utilisant des estimations empiriques de la taille effective de la population à long terme (16500), nous avons modélisé une gamme de taux de dispersion et de temps depuis la divergence (500 à 500000 générations); il en ressort que l’homogénéité génétique actuelle doit être maintenue par des taux de dispersion d’au moins 20–30 migrants par génération jusqu’à des centaines ou des milliers de migrants par génération. Notre étude note aussi l’absence de structure génétique temporelle significative et de consanguinité dans l’Atlantique dans des comparaisons de cohortes séparées dans le temps par des périodes allant de semaines à 20 années. Cela indique que la pratique de longue date de surpêche de la badèche baillou ne s’est pas encore manifestée comme un effet de consanguinité. Globalement, les taux de dispersion de la badèche demeurent incertains et, en conséquence, notre étude ne peut ni appuyer, ni rejeter les propositions de gestion qui contrôlent de façon indépendante les badèches baillou de l’est du golfe du Mexique et du nord-ouest de l’Atlantique.

Document Type: Research Article

Publication date: October 1, 2009

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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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