Previous genetic studies using neutral markers such as allozymes, mtDNA and minisatellite loci have demonstrated varying amounts of population structure in cod Gadus morhua throughout the Atlantic. Microsatellite loci, which are potentially the most informative of presently available neutral genetic markers, have been applied extensively within western and eastern Atlantic areas but not on a range-wide basis. In the present study, six microsatellite DNA loci were used to screen cod samples from nine locations throughout the geographic range from the Scotian Shelf in the West Atlantic to the Barents and Baltic Seas in the east. Overall F ST value was 0Á03 (P ¼ < 0Á001) across all samples. Statistically significant population differences over all loci combined were evident between more geographically distant samples, using either heterogeneity tests or F ST analysis, with at least one locus showing significant differences between all samples (prior to Bonferroni correction). A significant correlation was observed between genetic and geographical distance, suggesting a higher level of historical and contemporary gene flow between adjacent populations than more distant populations. Samples from either end of the geographic range (Scotian Shelf and Baltic Sea) were particularly distinct when analysed using the STRUCTURE programme and also showed a high level of selfassignment when individuals of either the Scotian Shelf or Baltic Sea were tested against the entire data set. The present microsatellite study demonstrates a high level of geographic population structure between the western Atlantic, middle and eastern Atlantic and Baltic Sea, and thus, the findings should be useful in devising overall management and conservation strategies for the species.

The present study examined the contemporary genetic composition of the Eurasian badger, Meles meles, in Ireland, Britain and Western Europe, using six nuclear microsatellite loci and a 215‐bp fragment of the mitochondrial DNA control region. Significant population structure was evident within Europe (global multilocus microsatellite FST = 0.205, P < 0.001; global mitochondrial control region ΦST = 0.399, P < 0.001). Microsatellite‐based cluster analyses detected one population in Ireland, whereas badgers from Britain could be subdivided into several populations. Excluding the island populations of Ireland and Britain, badgers from Western Europe showed further structuring, with evidence of discrete Scandinavian, Central European, and Spanish populations. Mitochondrial DNA cluster analysis grouped the Irish population with Scandinavia and Spain, whereas the majority of British haplotypes grouped with those from Central Europe. The findings of the present study suggest that British and Irish badger populations colonized from different refugial areas, or that there were different waves of colonization from the source population. There are indications for the presence of an Atlantic fringe element, which has been seen in other Irish species. We discuss the results in light of the controversy about natural versus human‐mediated introductions. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ••, ••–••.

A novel method of single nucleotide polymorphism (SNP) analysis in fishes [glycosylase mediated polymorphism detection (GMPD)] was applied, for the first time in any fish species, to polymorphisms present in the Atlantic cod Gadus morhua mtDNA D-loop and nuclear transferrin genes. The utility of the GMPD technique for population genetics of Atlantic cod is highlighted, since significant haplotype frequency differences were observed between Baltic and Atlantic samples of cod at a D-loop SNP and allele frequencies differences between west and east Atlantic samples at an SNP located in the transferrin gene.

Microsatellite DNA loci, when used in population genetic studies, are usually assumed to be neutral (unaffected by natural selection, either directly or as a result of tight linkage), but this assumption is rarely tested. Here, the assumption of neutrality is examined using established methods, principally that based on the expected relationship between F ST and heterozygosity, at 12 putative neutral microsatellite loci utilised in a study of Atlantic herring Clupea harengus in the north east Atlantic (west of Great Britain and around Ireland) and in the Baltic Sea. All but two of these loci demonstrate relationships that suggest that they may be regarded as neutral genetic markers. Of the other two loci, however, one shows a relationship suggestive of the action of directional selection and the other of balancing natural selection, though other locusspecific effects may operate. Thus, the latter two loci may provide inaccurate inference if used in phylogeographic studies and also demonstrate the danger of assuming neutrality at all microsatellite loci without explicit testing. However, such loci, particularly those affected by directional as opposed to balancing selection, may be of great use in stock discrimination studies, and selected loci in general, have considerably potential in studies of adaptation.