Analysis of the genetic structure of European eel (Anguilla anguilla) using microsatellite DNA and mtDNA markers

The spawning population of European eel (Anguilla anguilla L.) has been con sidered panmictic on the basis of genetic markers and morphometric studies. This hypothesis was tested by screening glass eel from five locations (Ire land, Italy, Morocco, Sweden and U.K.), belonging to two cohorts at the cyt ochrome b (cyt b) locus (392 bp) of the mitochondrion and at five nuclear m icrosatellite loci. Seventeen cyt b haplotypes were detected, of which ten were singletons; the most common haplotype occurred in 47% of all fish. Hap lotype number increased significantly with latitude. Phylogeographical stru cture based on the cytoplasmic marker was weak (F-ST = 0.014) and non-signi ficant. Close similarity was revealed between British and Irish glass eel p opulations, and weak differentiation among the British/lrish, Atlantic Moro ccan, Italian and Swedish Baltic populations, respectively. No hierarchical genetic structure was obvious. Levels of genetic variation detected with f ive microsatellites were much higher levels than found with allozymes in pr evious studies (mean number of alleles per locus = 11.1; mean expected hete rozygosity = 0.68). Overall among-population microsatellite variance was lo w but significant (F-ST = 0.004), and caused by the linked microsatellite l oci Aan03 and Aan04. The Hardy-Weinberg-Castle equilibrium and the absence of gametic disequilibria at these loci in the Moroccan population might poi nt to its genetic isolation, although the impact of just two out of five lo ci is puzzling. Given the weak differentiation typical for marine species a nd the limitations of our data, the results should be interpreted with caut ion. However, combined with recent evidence from a related study, the parad igm that the European eel constitutes a panmictic population becomes diffic ult to maintain.