Microsatellite analyses of spatial genetic structure in darkblotched rockfish (Sebastes crameri): Is pooling samples safe?

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By pooling or removing samples of small size, we investigated how results from microsatellite analyses of spatial genetic structure in darkblotched rockfish (Sebastes crameri) were affected. Genotypes from six and seven microsatellite loci from 1206 specimens collected offshore from Washington to California were employed in the analyses. Sample sizes varied greatly among locations (n = 11–114). When adjacent samples of n < 25 were pooled using an absolute genetic distance (FST ≤ 0), the correlation between genetic and geographic distance found in the original data set increased nearly twofold, and overall FST (95% confidence interval) increased from 0.001 (0.000–0.002) to 0.002 (0.001–0.003). Removing samples where n < 25 gave a similar result, yet the correlation increase was smaller. Another pooling strategy based on similarity tests allowed larger sizes in composite samples (n > 100) and further increased the correlation, although this strategy did not raise overall FST. These results indicate that under genetic isolation by distance, excessive pooling might not enhance the overall genetic differentiation among populations. The regression slope in isolation by distance plots was robust throughout all treatments, and its value suggests limited dispersal distance on this species.

Nous avons étudié comment les résultats d'analyses des microsatellites sur la structure génétique spatiale chez le sébaste tacheté (Sebastes crameri) sont affectés par la fusion et le retrait d'échantillons de petite taille. Des génotypes de six et sept locus microsatellites chez 1206 spécimens récoltés du Washington à la Californie ont servi aux analyses. Les tailles des échantillons varient considérablement selon les sites (n = 11–114). Lorsque des échantillons adjacents de n < 25 sont fusionnés à l'aide d'une distance génétique absolue (FST ≤ 0), la corrélation entre les distances génétique et géographique calculées dans les données originales double presque et le FST (intervalle de confiance de 95 %) global augmente de 0,001 (0,000–0,002) à 0,002 (0,001–0,003). Le retrait des échantillons de n < 25 mène à des résultats semblables, bien que l'augmentation de la corrélation soit moins grande. Une autre stratégie de fusion basée sur des tests de similarité produit des échantillons combinés de taille plus grande (n > 100) et augmente encore plus la corrélation, mais sans accroître le FST global. Ces résultats indiquent que, lorsque l'isolement génétique est dû à la distance, la fusion excessive des échantillons peut ne pas augmenter la différentiation génétique globale entre les populations. La pente de la régression dans les graphiques de l'isolement en fonction de la distance est robuste, quel que soit le traitement imposé, et sa valeur laisse croire que l'espèce se disperse sur de courtes distances.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: August 1, 2005

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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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