A tension hybrid zone between the North Atlantic eels of the genus Anguilla
Maes, G.E.; Pujolar, J.M.; Jonsson, B.; Volckaert, F.A.M.J. (2005). A tension hybrid zone between the North Atlantic eels of the genus Anguilla, in: Maes, G.E. Evolutionary consequences of a catadromous life-strategy on the genetic structure of European eel (Anguilla anguilla L.). pp. 61-82
In: Maes, G.E. (2005). Evolutionary consequences of a catadromous life-strategy on the genetic structure of European eel (Anguilla anguilla L.). PhD Thesis. Katholieke Universiteit Leuven. Faculteit Wetenschappen: Leuven. 223 pp., meer
We reassessed the hypothesis of hybridisation between the partly sympatric European eel (Anguilla anguilla L.) and American eel (A. rostrata) by testing the joint distribution of microsatellite markers and vertebral numbers. We first characterized genetic variability and differentiation between both species in populations throughout Europe and America using 8 microsatellite polymorphic loci. Using classical population genetic techniques, we screened several populations of Anguilla on Iceland, where both species have been reported to co- occur, for indications of introgressive hybridisation with the American eel. Icelandic allelic richness, heterozygosity values and allele frequencies were intermediate between both species. Microsatellite loci, selected as moderately variable to avoid homoplasy, yielded a high genetic differentiation between both species (FST = 0.14, RST = 0.11; p < 0.001), congruent with earlier mitochondrial DNA studies. Subsequent multivariate and individual based assignment tests separated both species with a high level of confidence (> 95% assignment score). Global admixture proportions in Icelandic eel populations attributed 8% of the genomic material to American eel. Classical as well as model-based Bayesian individual assignment tests detected a total admixture within Iceland of 11-15 %, mainly composed of F1 hybrids (6.3%) and pure A. rostrata (3.8%) individuals. The Total Number of Vertebrae was lower in Iceland and co- varied strongly with the admixture coefficient. Our results suggest a narrow tension zone, with asymmetric introgressive hybridisation towards the European eel. The incomplete/imperfect genetic isolation of eels spawning sympatrically affects additional locations in Europe with cryptic American like genomes. Differential oceanic migration of both species is thought to be safeguarded through reinforcement and selection against hybrids.
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