Ten populations of the model plant Arabidopsis thaliana were collected along a north-south gradient in Norway and screened for microsatellite polymorphisms in 25 loci and variability in quantitative traits. Overall, the average levels of genetic diversity were found to be relatively high in these populations, compared to previously published surveys of within population variability. Six of the populations were polymorphic at microsatellite loci, resulting in an overall proportion of polymorphic loci of 18%, and a relatively high gene diversity for a selfing species (HE = 0.06). Of the overall variability, 12% was found within populations. Two of six polymorphic populations contained heterozygous individuals. Both FST and phylogenetic analyses showed no correlation between geographical and genetic distances. Haplotypic diversity patterns suggested postglacial colonization of Scandinavia from a number of different sources. Heritable variation was observed for many of the studied quantitative traits, with all populations showing variability in at least some traits, even populations with no microsatellite variability. There was a positive association between variability in quantitative traits and microsatellites within populations. Several quantitative traits exhibited QST values significantly less than FST, suggesting that selection may be acting to retard differentiation for these traits.

Biallelic markers such as single nucleotide polymorphisms (SNPs) and insertion/deletion polymorphisms have become increasingly popular markers for various population genetics applications. However, the effort required to develop biallelic markers in nonmodel organisms is still substantial. In this study, we compared the estimation of various population genetic parameters (genetic divergence and structuring, isolation-by-distance, genetic diversity) using a limited number of biallelic markers (in total 7 loci) to those estimated with 14 microsatellite loci in 21 Atlantic salmon (Salmo salar) populations from northern Europe. Pairwise F ST values were significantly correlated between biallelic loci and microsatellite datasets, as was overall heterozygosity when both anadromous and nonanadromous populations were analyzed together. However, when the anadromous and nonanadromous samples were analyzed separately, only genetic divergence correlations remained significant. Biallelic markers alone were not sufficient for reliable neighbor-joining clustering of populations but gave highly similar isolation-by-distance signals when compared with microsatellites. Finally, although several population prioritization measures for conservation exhibited significant correlation between different marker types, the specific populations highlighted as being most valuable for conservation purposes varied depending on the marker type and conservation criteria applied. This study demonstrates that a relatively small set of biallelic markers can be sufficient for obtaining concordant results in most of the analyses compared with microsatellites, although estimates of genetic distance are generally more concordant than estimates of genetic diversity. This suggests that a relatively small number of biallelic markers can provide useful information for various population genetic applications. However, we emphasize that the use of much higher number of loci is preferable, especially when the genetic differences between populations are subtle or individual multilocus genotype-based analyses are to be performed.

Fourteen microsatellite loci were employed to study the genetic structure of 34 Atlantic salmon (Salmo salar) populations from the White and Barents seas area, the last major European region where the species has remained in its natural state. The populations were separated into four distinct clusters (Atlantic Ocean and western Barents Sea, Kola Peninsula, western White Sea, and eastern Barents Sea) within which genetic divergence varied between 0.02 and 0.10 as estimated with FST. When this structuring was contrasted with previously identified mtDNA-based groupings, a remarkable similarity was observed, implying that these four groups can be considered as a good starting point for defining management units in the region. Indeed, several approaches for assessing every population's conservation value suggested that conservation of populations from each observed cluster would maximize preservation of the region's genetic diversity. Furthermore, each unit may require differing management strategies, as distinct patterns of genetic diversity and divergence characteristics were detected. In addition, individual assignment success within a region was high (87%-96%), indicating that the data can be used as a baseline to differentiate individuals caught in offshore fisheries on a regional level with a relatively high degree of accuracy.Résumé : Quatorze locus microsatellites nous ont servi à étudier la structure génétique de 34 populations de saumons atlantiques (Salmo salar) des environs de la mer Blanche et de la mer de Barents, la dernière grande région d'Europe où l'espèce est demeurée dans son état naturel. Les populations se divisent en quatre regroupements distincts (Atlantique et mer de Barents occidentale, péninsule de Kola, mer Blanche occidentale et mer de Barents orientale) au sein desquels la divergence génétique, estimée par F ST , varie de 0,02 à 0,10. Une comparaison de cette structure avec des groupements basés sur l'ADNmt identifiés précédemment montre une remarquable similarité, ce qui indique que ces quatre groupes forment un bon point de départ pour l'identification des unités de gestion dans la région. En effet, plusieurs méthodes utilisées pour évaluer la valeur de conservation de chaque population indiquent que la conservation de populations de chaque groupement observé permettrait de maximiser la conservation de la diversité génétique dans la région. De plus, il se peut que chaque unité nécessite des stratégies de gestion différentes puisqu'on détecte des patrons distincts de diversité généti-que et des caractéristiques de divergence particulières. Enfin, le succès de l'attribution des individus à un groupement particulier est élevé (87 % -96 %) dans une même région, ce qui indique que nos données peuvent servir de base pour l'identification des individus récoltés dans les pêches du large avec un degré relativement élevé d'exactitude à l'échelle ré-gionale.[Traduit par la Rédaction]