Geographic structure of European anchovy: A nuclear-DNA study

Atlantic-Mediterranean anchovies were genetically characterized at two polymorphic nuclear loci (intron 6 of two creatine-kinase genes) and compared to reference Engraulis albidus and E. encrasicolus samples from the northern Western Mediterranean to provide new insights into their geographic structure. Northeastern Atlantic anchovy, represented by one sample from the Canary archipelago and one sample from the Alboran Sea, were genetically distinct from Mediterranean E. encrasicolus (Weir and Cockerham's ^θ = 0.027-0.311), indicating geographic isolation from either side of the Almería-Oran oceanographic front. Generally smaller genetic differences were evident among anchovy populations from different sub-basins in the Mediterranean (^θ = − 0.019-0.116), the genetic differences between Black Sea and Ionian Sea/Aegean Sea anchovies being the strongest (^θ = 0.002-0.116). There was no evidence of the presence of E. albidus in our samples outside Camargue (northern shore of the Western Mediterranean). However, a sample from the southern Western Mediterranean appeared to be genetically intermediate between E. albidus and Mediterranean E. encrasicolus, indicating possible hybridization. Anchovy from the Benguela current system off southern Africa possessed allele frequencies characteristic of E. albidus at one locus and Northeastern Atlantic anchovy at the other locus, suggesting past introgression.