title: Introgressive hybridization and latitudinal admixture clines in North Atlantic eels.
abstract: BACKGROUND
  Hybridization, the interbreeding of diagnosably divergent species, is a major focus in evolutionary studies. Eels, both from North America and Europe migrate through the Atlantic to mate in a vast, overlapping area in the Sargasso Sea. Due to the lack of direct observation, it is unknown how these species remain reproductively isolated. The detection of inter-species hybrids in Iceland suggests on-going gene flow, but few studies to date have addressed the influence of introgression on genetic differentiation in North Atlantic eels.
  
  
  RESULTS
  Here, we show that while mitochondrial lineages remain completely distinct on both sides of the Atlantic, limited hybridization is detectable with nuclear DNA markers. The nuclear hybridization signal peaks in the northern areas and decreases towards the southern range limits on both continents according to Bayesian assignment analyses. By simulating increasing proportions of both F1 hybrids and admixed individuals from the southern to the northern-most locations, we were able to generate highly significant isolation-by-distance patterns in both cases, reminiscent of previously published data for the European eel. Finally, fitting an isolation-with-migration model to our data supports the hypothesis of recent asymmetric introgression and refutes the alternative hypothesis of ancient polymorphism.
  
  
  CONCLUSIONS
  Fluctuating degrees of introgressive hybridization between Atlantic eel species are sufficient to explain temporally varying correlations of geographic and genetic distances reported for populations of the European eel.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Wielgoss
authors.forename: Aude
authors.initials: A
authors.lastname: Gilabert
authors.forename: Axel
authors.initials: A
authors.lastname: Meyer
authors.affiliation: Lehrstuhl für Zoologie und Evolutionsbiologie, Universität Konstanz, 78457 Konstanz, Germany. wirth@mnhn.fr.
authors.forename: Thierry
authors.initials: T
authors.lastname: Wirth
mesh_terms: D000811:Anguilla / Q000145:classification / Q000235:genetics* / Q000502:physiology; D025041:Animal Migration; D000818:Animals; D001499:Bayes Theorem; D004272:DNA, Mitochondrial / Q000235:genetics; D005060:Europe; D005828:Genetics, Population; D006824:Hybridization, Genetic; D018895:Microsatellite Repeats; D009656:North America; D009792:Oceans and Seas; D011110:Polymorphism, Genetic; D012098:Reproduction
chemical_list: D004272:DNA, Mitochondrial