Abstract
Geographic surveys of allozymes, microsatellites, nuclear DNA (nDNA) and mitochondrial DNA (mtDNA) have detected several genetic subdivisions among European anchovy populations. However, these studies have been limited in their power to detect some aspects of population structure by the use of a single or a few molecular markers, or by limited geographic sampling. We use a multi-marker approach, 47 nDNA and 15 mtDNA single nucleotide polymorphisms (SNPs), to analyze 626 European anchovies from the whole range of the species to resolve shallow and deep levels of population structure. Nuclear SNPs define 10 genetic entities within two larger genetically distinctive groups associated with oceanic variables and different life-history traits. MtDNA SNPs define two deep phylogroups that reflect ancient dispersals and colonizations. These markers define two ecological groups. One major group of Iberian-Atlantic populations is associated with upwelling areas on narrow continental shelves and includes populations spawning and overwintering in coastal areas. A second major group includes northern populations in the North East (NE) Atlantic (including the Bay of Biscay) and the Mediterranean and is associated with wide continental shelves with local larval retention currents. This group tends to spawn and overwinter in oceanic areas. These two groups encompass ten populations that differ from previously defined management stocks in the Alboran Sea, Iberian-Atlantic and Bay of Biscay regions. In addition, a new North Sea-English Channel stock is defined. SNPs indicate that some populations in the Bay of Biscay are genetically closer to North Western (NW) Mediterranean populations than to other populations in the NE Atlantic, likely due to colonizations of the Bay of Biscay and NW Mediterranean by migrants from a common ancestral population. Northern NE Atlantic populations were subsequently established by migrants from the Bay of Biscay. Populations along the Iberian-Atlantic coast appear to have been founded by secondary waves of migrants from a southern refuge.
Highlights
European anchovies, Engraulis encrasicolus, are widely distributed in near-shore pelagic waters in the Eastern Atlantic from the North Sea and into the Mediterranean and Black Sea and as far south as southern Africa
A mitochondrial DNA (mtDNA) haplotype frequency shift occurs between Mediterranean and Atlantic populations [9,10], and this shift is echoed by a shift in microsatellite allele frequencies [13]
A similar pattern of population differentiation appeared in genetic distances between populations
Summary
Engraulis encrasicolus, are widely distributed in near-shore pelagic waters in the Eastern Atlantic from the North Sea and into the Mediterranean and Black Sea and as far south as southern Africa. The analysis of mitochondrial (mt) DNA has further resolved two deep matriarchal lineages in European anchovies that appear to reflect ancient isolations, dispersals and colonizations [9,10,18] These lineages, or mtDNA phylogroups, vary greatly in frequency from one location to another, but are not strictly associated with the geographical population groups delimited by nuclear molecular markers [5,6,7,8,9,10,11,12,13]. No morphological or adaptive differences have been detected between individuals in phylogroups A and B [11]
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